GMD Publications for 2019

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Alden, Caroline B., Sean C. Coburn, Robert J. Wright, Esther Baumann, Kevin Cossel, Edgar Perez, Eli Hoenig, Kuldeep Prasad, Ian Coddington and Gregory B. Rieker, (2019), Single-Blind Quantification of Natural Gas Leaks from 1 km Distance Using Frequency Combs, Environmental Science & Technology, 53, 5, 2908-2917, 10.1021/acs.est.8b06259

Abstract

A new method is tested in a single-blind study for detection, attribution, and quantification of methane emissions from the natural gas supply chain, which contribute substantially to annual U.S. emissions. The monitoring approach couples atmospheric methane concentration measurements from an open-path dual frequency comb laser spectrometer with meteorological data in an inversion to characterize emissions. During single-blind testing, the spectrometer is placed >1 km from decommissioned natural gas equipment configured with intentional leaks of controllable rate. Single, steady emissions ranging from 0 to 10.7 g min–1 (0–34.7 scfh) are detected, located, and quantified at three gas pads of varying size and complexity. The system detects 100% of leaks, including leaks as small as 0.96 g min–1 (3.1 scfh). It attributes leaks to the correct pad or equipment group (tank battery, separator battery, wellhead battery) 100% of the time and to the correct equipment (specific separator, tank, or wellhead) 67% of the time. All leaks are quantified to within 3.7 g min–1 (12 scfh); 94% are quantified to within 2.8 g min–1 (9 scfh). These tests are an important initial demonstration of the methodology’s viability for continuous monitoring of large regions, with extension to other trace gases and industries.

Andrews, Elisabeth, Patrick J. Sheridan, John A. Ogren, Derek Hageman, Anne Jefferson, Jim Wendell, Andrés Alástuey, Lucas Alados-Arboledas, Michael Bergin, Marina Ealo, A. Gannet Hallar, András Hoffer, Ivo Kalapov, Melita Keywood, Jeongeun Kim, Sang-Woo Kim, Felicia Kolonjari, Casper Labuschagne, Neng-Huei Lin, AnneMarie Macdonald, Olga L. Mayol-Bracero, Ian B. McCubbin, Marco Pandolfi, Fabienne Reisen, Sangeeta Sharma, James P. Sherman, Mar Sorribas and Junying Sun, (2019), Overview of the NOAA/ESRL Federated Aerosol Network, Bulletin of the American Meteorological Society, 100, 1, 123-135, 10.1175/BAMS-D-17-0175.1

Abstract

To estimate global aerosol radiative forcing, measurements of aerosol optical properties are made by the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL)’s Global Monitoring Division (GMD) and their collaborators at 30 monitoring locations around the world. Many of the sites are located in regions influenced by specific aerosol types (Asian and Saharan desert dust, Asian pollution, biomass burning, etc.). This network of monitoring stations is a shared endeavor of NOAA and many collaborating organizations, including the World Meteorological Organization (WMO)’s Global Atmosphere Watch (GAW) program, the U.S. Department of Energy (DOE), several U.S. and foreign universities, and foreign science organizations. The result is a long-term cooperative program making atmospheric measurements that are directly comparable with those from all the other network stations and with shared data access. The protocols and software developed to support the program facilitate participation in GAW’s atmospheric observation strategy, and the sites in the NOAA/ESRL network make up a substantial subset of the GAW aerosol observations. This paper describes the history of the NOAA/ESRL Federated Aerosol Network, details about measurements and operations, and some recent findings from the network measurements.

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Cho, Chaeyoon, Sang-Woo Kim, Meehye Lee, Saehee Lim, Wenzheng Fang, Örjan Gustafsson, August Andersson, Rokjin J. Park and Patrick J. Sheridan, (2019), Observation-based estimates of the mass absorption cross-section of black and brown carbon and their contribution to aerosol light absorption in East Asia, Atmospheric Environment, 212, 65-74, 10.1016/j.atmosenv.2019.05.024

Abstract

In this study, we estimated the contribution of black carbon (BC) and brown carbon (BrC) to aerosol light absorption from surface in-situ and aerosol robotic network (AERONET) columnar observations. The mass absorption cross-section (MAC) of BC () was estimated to be 6.4 ± 1.5 m2 g−1 at 565 nm from in-situ aerosol measurements at Gosan Climate Observatory (GCO), Korea, in January 2014, which was lower than those observed in polluted urban areas. A BrC MAC of 0.62 ± 0.06 m2 g−1 (565 nm) in our estimate is approximately ten times lower than at 565 nm. The contribution of BC and BrC to the carbonaceous aerosol absorption coefficient at 565 nm from the in-situ measurements was estimated at 88.1 ± 7.4% and 11.9 ± 7.4%, respectively at GCO. Similarly, the contribution of BC and BrC to the absorption aerosol optical depth (AAOD) for carbonaceous aerosol (CA), constrained by AERONET observations at 14 sites over East Asia by using different spectral dependences of the absorption (i.e., absorption Ångström exponent) of BC and BrC, was 84.9 ± 2.8% and 15.1 ± 2.8% at 565 nm, respectively. The contribution of BC to CA AAOD was greater in urban sites than in the background areas, whereas the contribution of BrC to CA AAOD was higher in background sites. The overall contribution of BC to CA AAOD decreased by 73%–87% at 365 nm, and increased to 93%–97% at 860 nm. The contribution of BrC to CA AAOD decreased significantly with increasing wavelength from approximately 17% at 365 nm to 4% at 860 nm.

Cox, C.J., R.S. Stone, D.C. Douglas, D. Stanitski and M.R. Gallagher, (2019), The Aleutian Low – Beaufort Sea Anticyclone: A climate index correlated with the timing of springtime melt in the Pacific Arctic cryosphere, Geophysical Research Letters, 10.1029/2019GL083306

Abstract

Early and late extremes in the timing of snowmelt have recently been observed in the Pacific Arctic. Subseasonal‐to‐seasonal forecasts of this timing are important for industry, environmental management and Arctic communities. In northern Alaska, the timing is influenced by the advection of marine air from the north Pacific by the Aleutian Low, modulated by high pressure centered in the Beaufort Sea. A new climate index that integrates their interaction could advance melt predictions. We define this index based on 850 hPa geopotential height at four fixed locations, and refer to it as the Aleutian Low – Beaufort Sea Anticyclone (ALBSA). During positive ALBSA in May, advection of +0.5‐1.5 K/day is observed through the Bering Strait. ALBSA is correlated with both snowmelt in northern Alaska and the onset of sea ice melt over the adjacent seas. ALBSA, therefore, may be suitable for monitoring the relevant circulation patterns and for developing predictive tools.

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Flores, Edgar, Joële Viallon, Tiphaine Choteau, Philippe Moussay, Faraz Idrees, Robert I Wielgosz, Jeongsoon Lee, Ewelina Zalewska, Gerard Nieuwenkamp, Adriaan van der Veen, L A Konopelko, Y A Kustikov, A V Kolobova, Y K Chubchenko, O V Efremova, BI Zhe, Zeyi Zhou, Zeyi Zhou, George C Rhoderick, Joseph T Hodge, Takuya Shimosaka, Nobuyuki Aoki, Brad Hall, Paul Brewer, Dariusz Cieciora, Michela Sega, Tatiana Macé, Judit Fükő, Zsófia Nagyné Szilágyi, Tamás Büki, Mudalo I Jozela, Napo G Ntsasa, Nompumelelo Leshabane, James Tshilongo, Prabha Johri and Tanil Tarhan, (2019), CCQM-K120 (Carbon dioxide at background and urban level), Metrologia, 56, 1A, 08001-08001, 10.1088/0026-1394/56/1A/08001

Abstract

CCQM-K120.a comparison involves preparing standards of carbon dioxide in air which are fit for purpose for the atmospheric monitoring community, with stringent requirements on matrix composition and measurement uncertainty of the CO2 mole fraction. This represents an analytical challenge and is therefore considered as a Track C comparison. The comparison will underpin CMC claims for CO2 in air for standards and calibrations services for the atmospheric monitoring community, matrix matched to real air, over the mole fraction range of 250 μmol/mol to 520 μmol/mol.

CCQM-K120.b comparison tests core skills and competencies required in gravimetric preparation, analytical certification and purity analysis. It is considered as a Track A comparison. It will underpin CO2 in air and nitrogen claims in a mole fraction range starting at the smallest participant's reported expanded uncertainty and ending at 500 mmol/mol. Participants successful in this comparison may use their result in the flexible scheme and underpin claims for all core mixtures

This study has involved a comparison at the BIPM of a suite of 44 gas standards prepared by each of the participating laboratories. Fourteen laboratories took part in both comparisons (CCQM-K120.a, CCQM-K120.b) and just one solely in the CCQM-K120.b comparison.

The standards were sent to the BIPM where the comparison measurements were performed. Two measurement methods were used to compare the standards, to ensure no measurement method dependant bias: GC-FID and FTIR spectroscopic analysis corrected for isotopic variation in the CO2 gases, measured at the BIPM using absorption laser spectroscopy. Following the advice of the CCQM Gas Analysis Working Group, results from the FTIR method were used to calculate the key comparison reference values.

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Hall, Bradley D., Andrew M. Crotwell, Benjamin R. Miller, Michael Schibig and James W. Elkins, (2019), Gravimetrically prepared carbon dioxide standards in support of atmospheric research, Atmospheric Measurement Techniques, 12, 1, 517-524, 10.5194/amt-12-517-2019

Abstract

Abstract. We have explored a one-step method for gravimetric preparation of CO2-in-air standards in aluminum cylinders. We consider both adsorption to stainless steel surfaces used in the transfer of highly pure CO2 and adsorption of CO2 to cylinder walls. We demonstrate that CO2-in-air standards can be prepared with relatively low uncertainty (∼0.04%, ∼95% confidence level) by introducing aliquots whose masses are known to high precision and by using well-characterized cylinders. Five gravimetric standards, prepared over the nominal range of 350 to 490µmol mol−1 (parts per million,ppm), showed excellent internal consistency, with residuals from a linear fit equal to 0.05ppm. This work compliments efforts to maintain the World Meteorological Organization, Global Atmosphere Watch, mole fraction scale for carbon dioxide in air, widely used for atmospheric monitoring. This gravimetric technique could be extended to other atmospheric trace gases, depending on the vapor pressure of the gas.

Hossaini, Ryan, Elliot Atlas, Sandip S. Dhomse, Martyn P. Chipperfield, Peter F. Bernath, Anton M. Fernando, Jens Mühle, Amber A. Leeson, Stephen A. Montzka, Wuhu Feng, Jeremy J. Harrison, Paul Krummel, Martin K. Vollmer, Stefan Reimann, Simon O'Doherty, Dickon Young, Michela Maione, Jgor Arduini and Chris R. Lunder, (2019), Recent Trends in Stratospheric Chlorine From Very Short‐Lived Substances, Journal of Geophysical Research: Atmospheres, 124, 4, 2318-2335, 10.1029/2018JD029400

Abstract

Very short‐lived substances (VSLS), including dichloromethane (CH2Cl2), chloroform (CHCl3), perchloroethylene (C2Cl4), and 1,2‐dichloroethane (C2H4Cl2), are a stratospheric chlorine source and therefore contribute to ozone depletion. We quantify stratospheric chlorine trends from these VSLS (VSLCltot) using a chemical transport model and atmospheric measurements, including novel high‐altitude aircraft data from the NASA VIRGAS (2015) and POSIDON (2016) missions. We estimate VSLCltot increased from 69 (±14) parts per trillion (ppt) Cl in 2000 to 111 (±22) ppt Cl in 2017, with >80% delivered to the stratosphere through source gas injection, and the remainder from product gases. The modeled evolution of chlorine source gas injection agrees well with historical aircraft data, which corroborate reported surface CH2Cl2 increases since the mid‐2000s. The relative contribution of VSLS to total stratospheric chlorine increased from ~2% in 2000 to ~3.4% in 2017, reflecting both VSLS growth and decreases in long‐lived halocarbons. We derive a mean VSLCltot growth rate of 3.8 (±0.3) ppt Cl/year between 2004 and 2017, though year‐to‐year growth rates are variable and were small or negative in the period 2015–2017. Whether this is a transient effect, or longer‐term stabilization, requires monitoring. In the upper stratosphere, the modeled rate of HCl decline (2004–2017) is −5.2% per decade with VSLS included, in good agreement to ACE satellite data (−4.8% per decade), and 15% slower than a model simulation without VSLS. Thus, VSLS have offset a portion of stratospheric chlorine reductions since the mid‐2000s.

Hu, Lei, Arlyn E. Andrews, Kirk W. Thoning, Colm Sweeney, John B. Miller, Anna M. Michalak, Ed Dlugokencky, Pieter P. Tans, Yoichi P. Shiga, Marikate Mountain, Thomas Nehrkorn, Stephen A. Montzka, Kathryn McKain, Jonathan Kofler, Michael Trudeau, Sylvia E. Michel, Sébastien C. Biraud, Marc L. Fischer, Doug E. J. Worthy, Bruce H. Vaughn, James W. C. White, Vineet Yadav, Sourish Basu and Ivar R. van der Velde, (2019), Enhanced North American carbon uptake associated with El Niño, Science Advances, 5, 6, eaaw0076, 10.1126/sciadv.aaw0076

Abstract

Long-term atmospheric CO mole fraction and δ CO observations over North America document persistent responses to the El Niño–Southern Oscillation. We estimate these responses corresponded to 0.61 (0.45 to 0.79) PgC year more North American carbon uptake during El Niño than during La Niña between 2007 and 2015, partially offsetting increases of net tropical biosphere-to-atmosphere carbon flux around El Niño. Anomalies in derived North American net ecosystem exchange (NEE) display strong but opposite correlations with surface air temperature between seasons, while their correlation with water availability was more constant throughout the year, such that water availability is the dominant control on annual NEE variability over North America. These results suggest that increased water availability and favorable temperature conditions (warmer spring and cooler summer) caused enhanced carbon uptake over North America near and during El Niño.

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Japngie-Green, Crystal M., Elisabeth Andrews, Ian B. McCubbin, John A. Ogren and Anna G. Hallar, (2019), Climatology of Aerosol Optical Properties at Storm Peak Laboratory, Aerosol and Air Quality Research, 19, 6, 1205-1213, 10.4209/aaqr.2018.05.0204

Abstract

Aerosols create large uncertainty in the planetary energy balance due to both direct and indirect radiative forcing. Understanding aerosol seasonal patterns is essential for accurate climate change prediction, but mountain regions are often difficult for climate models to resolve. Therefore, long-term observations collected at high elevations are particularly useful. In-situ surface aerosol optical measurements were analyzed for the years 2011–2016 at a mountain site located in western Colorado and tied to potential sources based on relationships among the aerosol properties.

The peak values for the scattering and absorption coefficients were observed during the summer, suggesting greater aerosol loading (likely due to wildfires), whereas the lowest values were observed during the winter, indicating cleaner conditions (due to less influence from the boundary layer). The scattering Ångström exponent, a property that provides information about size distributions, revealed the predominance of coarse-mode particles during the spring, which is consistent with the presence of dust. The aerosols observed during the summer, however, were mostly composed of fine-mode particles. This increase in the fine fraction points to combustion, likely wildfires during the dry season (Hallar, 2015), as a source, which is further supported by the absorption Ångström exponent dropping to its lowest value (close to 1) during the summer after exhibiting a slightly higher value (~1.3) during the spring. Schmeisser et al. (2017) suggests that, for in-situ aerosol, absorption Angstrom exponents larger than 1.5 may be indicative of dust if they are associated with low (< 1.3) scattering Ångström exponents. The increase in combustion aerosols during the summer accompanied by high values for the single scattering albedo suggests that these aerosols underwent processing in the atmosphere before reaching Storm Peak Laboratory. These results are important for improving visibility and predicting future aerosol concentrations in the western U.S.

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Lan, Xin, Pieter Tans, Colm Sweeney, Arlyn Andrews, Edward Dlugokencky, Stefan Schwietzke, Jonathan Kofler, Kathryn McKain, Kirk Thoning, Molly Crotwell, Stephen Montzka, Benjamin R. Miller and Sébastien C. Biraud, (2019), Long‐Term Measurements Show Little Evidence for Large Increases in Total U.S. Methane Emissions Over the Past Decade, Geophysical Research Letters, 46, 9, 4991-4999, 10.1029/2018GL081731

Abstract

Recent studies show conflicting estimates of trends in methane (CH4) emissions from oil and natural gas (ONG) operations in the United States. We analyze atmospheric CH4 measurements from 20 North American sites in the National Oceanic and Atmospheric Administration Global Greenhouse Gas Reference Network and determined trends for 2006–2015. Using CH4 vertical gradients as an indicator of regional surface emissions, we find no significant increase in emissions at most sites and modest increases at three sites heavily influenced by ONG activities. Our estimated increases in North American ONG CH4 emissions (on average approximately 3.4 ± 1.4 %/year for 2006–2015, ±σ) are much smaller than estimates from some previous studies and below our detection threshold for total emissions increases at the east coast sites that are sensitive to U.S. outflows. We also find an increasing trend in ethane/methane emission ratios, which has resulted in major overestimation of oil and gas emissions trends in some previous studies.

Li, Pingyang, Jens Mühle, Stephen A. Montzka, David E. Oram, Benjamin R. Miller, Ray F. Weiss, Paul J. Fraser and Toste Tanhua, (2019), Atmospheric histories, growth rates and solubilities in seawater and other natural waters of the potential transient tracers HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116, Ocean Science, 15, 1, 33-60, 10.5194/os-15-33-2019

Abstract

Abstract. We present consistent annual mean atmospheric histories and growth rates for the mainly anthropogenic halogenated compounds HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116, which are all potentially useful oceanic transient tracers (tracers of water transport within the ocean), for the Northern and Southern Hemisphere with the aim of providing input histories of these compounds for the equilibrium between the atmosphere and surface ocean. We use observations of these halogenated compounds made by the Advanced Global Atmospheric Gases Experiment (AGAGE), the Scripps Institution of Oceanography (SIO), the Commonwealth Scientific and Industrial Research Organization (CSIRO), the National Oceanic and Atmospheric Administration (NOAA) and the University of East Anglia (UEA). Prior to the direct observational record, we use archived air measurements, firn air measurements and published model calculations to estimate the atmospheric mole fraction histories. The results show that the atmospheric mole fractions for each species, except HCFC-141b and HCFC-142b, have been increasing since they were initially produced. Recently, the atmospheric growth rates have been decreasing for the HCFCs (HCFC-22, HCFC-141b and HCFC-142b), increasing for the HFCs (HFC-134a, HFC-125, HFC-23) and stable with little fluctuation for the PFCs (PFC-14 and PFC-116) investigated here. The atmospheric histories (source functions) and natural background mole fractions show that HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125 and HFC-23 have the potential to be oceanic transient tracers for the next few decades only because of the recently imposed bans on production and consumption. When the atmospheric histories of the compounds are not monotonically changing, the equilibrium atmospheric mole fraction (and ultimately the age associated with that mole fraction) calculated from their concentration in the ocean is not unique, reducing their potential as transient tracers. Moreover, HFCs have potential to be oceanic transient tracers for a longer period in the future than HCFCs as the growth rates of HFCs are increasing and those of HCFCs are decreasing in the background atmosphere. PFC-14 and PFC-116, however, have the potential to be tracers for longer periods into the future due to their extremely long lifetimes, steady atmospheric growth rates and no explicit ban on their emissions. In this work, we also derive solubility functions for HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116 in water and seawater to facilitate their use as oceanic transient tracers. These functions are based on the Clark–Glew–Weiss (CGW) water solubility function fit and salting-out coefficients estimated by the poly-parameter linear free-energy relationships (pp-LFERs). Here we also provide three methods of seawater solubility estimation for more compounds. Even though our intention is for application in oceanic research, the work described in this paper is potentially useful for tracer studies in a wide range of natural waters, including freshwater and saline lakes, and, for the more stable compounds, groundwaters.

Lossow, Stefan, Farahnaz Khosrawi, Michael Kiefer, Kaley A. Walker, Jean-Loup Bertaux, Laurent Blanot, James M. Russell, Ellis E. Remsberg, John C. Gille, Takafumi Sugita, Christopher E. Sioris, Bianca M. Dinelli, Enzo Papandrea, Piera Raspollini, Maya García-Comas, Gabriele P. Stiller, Thomas von Clarmann, Anu Dudhia, William G. Read, Gerald E. Nedoluha, Robert P. Damadeo, Joseph M. Zawodny, Katja Weigel, Alexei Rozanov, Faiza Azam, Klaus Bramstedt, Stefan Noël, John P. Burrows, Hideo Sagawa, Yasuko Kasai, Joachim Urban, Patrick Eriksson, Donal P. Murtagh, Mark E. Hervig, Charlotta Högberg, Dale F. Hurst and Karen H. Rosenlof, (2019), The SPARC water vapour assessment II: profile-to-profile comparisons of stratospheric and lower mesospheric water vapour data sets obtained from satellites, Atmospheric Measurement Techniques, 12, 5, 2693-2732, 10.5194/amt-12-2693-2019

Abstract

Abstract. Within the framework of the second SPARC (Stratosphere-troposphere Processes And their Role in Climate) water vapour assessment (WAVAS-II), profile-to-profile comparisons of stratospheric and lower mesospheric water vapour were performed by considering 33 data sets derived from satellite observations of 15 different instruments. These comparisons aimed to provide a picture of the typical biases and drifts in the observational database and to identify data-set-specific problems. The observational database typically exhibits the largest biases below 70 hPa, both in absolute and relative terms. The smallest biases are often found between 50 and 5 hPa. Typically, they range from 0.25 to 0.5 ppmv (5 % to 10 %) in this altitude region, based on the 50 % percentile over the different comparison results. Higher up, the biases increase with altitude overall but this general behaviour is accompanied by considerable variations. Characteristic values vary between 0.3 and 1 ppmv (4 % to 20 %). Obvious data-set-specific bias issues are found for a number of data sets. In our work we performed a drift analysis for data sets overlapping for a period of at least 36 months. This assessment shows a wide range of drifts among the different data sets that are statistically significant at the 2σ uncertainty level. In general, the smallest drifts are found in the altitude range between about 30 and 10 hPa. Histograms considering results from all altitudes indicate the largest occurrence for drifts between 0.05 and 0.3 ppmv decade−1. Comparisons of our drift estimates to those derived from comparisons of zonal mean time series only exhibit statistically significant differences in slightly more than 3 % of the comparisons. Hence, drift estimates from profile-to-profile and zonal mean time series comparisons are largely interchangeable. As for the biases, a number of data sets exhibit prominent drift issues. In our analyses we found that the large number of MIPAS data sets included in the assessment affects our general results as well as the bias summaries we provide for the individual data sets. This is because these data sets exhibit a relative similarity with respect to the remaining data sets, despite the fact that they are based on different measurement modes and different processors implementing different retrieval choices. Because of that, we have by default considered an aggregation of the comparison results obtained from MIPAS data sets. Results without this aggregation are provided on multiple occasions to characterise the effects due to the numerous MIPAS data sets. Among other effects, they cause a reduction of the typical biases in the observational database.

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Mielke-Maday, Ingrid, Stefan Schwietzke, Tara Yacovitch, Benjamin Miller, Steve Conley, Jonathan Kofler, Philip Handley, Eryka Thorley, Scott C. Herndon, Bradley Hall, Ed Dlugokencky, Patricia Lang, Sonja Wolter, Eric Moglia, Molly Crotwell, Andrew Crotwell, Michael Rhodes, Duane Kitzis, Timothy Vaughn, Clay Bell, Dan Zimmerle, Russ Schnell and Gabrielle Pétron, (2019), Methane source attribution in a U.S. dry gas basin using spatial patterns of ground and airborne ethane and methane measurements, Elem Sci Anth, 7, 1, 13, 10.1525/elementa.351

Abstract

An intensive coordinated airborne and ground-based measurement study was conducted in the Fayetteville Shale in northwestern Arkansas during September and October 2015 to compare and explain potential discrepancies between top-down and bottom-up estimates of regional natural gas (NG) methane (CH4) emissions. In situ mobile downwind measurements are used to document the ethane to methane enhancement ratios (ERs) in emission plumes from NG operations in the region. Enhancement ratios are low (<2% for 87% of NG sources sampled) in this dry gas-producing region and normally distributed around 1.3% in the western half of the study area. A few sampled landfills emitted CH4 but no ethane (C2H6). Sampling drives around large chicken farms, prevalent in the region, did not detect significant downwind CH4 enhancements. In situ airborne measurements of C2H6 and CH4 from area-scale surveys over and downwind of the region documented the resulting ERs from a mix of CH4 sources. Based on these measurements, we show that on average during the measurement windows 85–95% of total CH4 emissions in the western half of the Fayetteville Shale originated from NG sources, which agrees well with bottom-up estimates from the same field study. Lower mixing ratios measured over the eastern half of the region did not support the ER analysis due to the low signal-to-noise on C2H6 measurements.

Minschwaner, Kenneth, Anthony T. Giljum, Gloria L. Manney, Irina Petropavlovskikh, Bryan J. Johnson and Allen F. Jordan, (2019), Detection and classification of laminae in balloon-borne ozonesonde profiles: application to the long-term record from Boulder, Colorado, Atmospheric Chemistry and Physics, 19, 3, 1853-1865, 10.5194/acp-19-1853-2019

Abstract

Abstract. We quantify ozone variability in the upper troposphere and lower stratosphere (UTLS) by investigating lamination features in balloon measurements of ozone mixing ratio and potential temperature. Laminae are defined as stratified variations in ozone that meet or exceed a 10 % threshold for deviations from a basic state vertical profile of ozone. The basic state profiles are derived for each sounding using smoothing methods applied within a vertical coordinate system relative to the World Meteorological Organization (WMO) tropopause. We present results of this analysis for the 25-year record of ozonesonde measurements from Boulder, Colorado. The mean number of ozone laminae identified per sounding is about 9±2 (1σ). The root-mean-square relative amplitude is 20 %, and laminae with much larger amplitudes (&gt;40 %) are seen in ∼ 2 % of the profiles. The vertical scale of detected ozone laminae typically ranges between 0.5 and 1.2 km. The lamina occurrence frequency varies significantly with altitude and is largest within ∼2 km of the tropopause. Overall, ozone laminae identified in our analysis account for more than one-third of the total intra-seasonal variability in ozone. A correlation technique between ozone and potential temperature is used to classify the subset of ozone laminae that are associated with gravity wave (GW) phenomena, which accounts for 28 % of all laminar ozone features. The remaining 72 % of laminae arise from non-gravity wave (NGW) phenomena. There are differences in both the vertical distribution and seasonality of GW versus NGW ozone laminae that are linked to the contrast in main generating mechanisms for each laminae type.

Moeini, Omid, Zahra Vaziri Zanjani, C. Thomas McElroy, David W. Tarasick, Robert D. Evans, Irina Petropavlovskikh and Keh-Harng Feng, (2019), The effect of instrumental stray light on Brewer and Dobson total ozone measurements, Atmospheric Measurement Techniques, 12, 1, 327-343, 10.5194/amt-12-327-2019

Abstract

Abstract. Dobson and Brewer spectrophotometers are the primary, standard instruments for ground-based ozone measurements under the World Meteorological Organization's (WMO) Global Atmosphere Watch program. The accuracy of the data retrieval for both instruments depends on a knowledge of the ozone absorption coefficients and some assumptions underlying the data analysis. Instrumental stray light causes nonlinearity in the response of both the Brewer and Dobson to ozone at large ozone slant paths. In addition, it affects the effective ozone absorption coefficients and extraterrestrial constants that are both instrument-dependent. This effect has not been taken into account in the calculation of ozone absorption coefficients that are currently recommended by WMO for the Dobson network. The ozone absorption coefficients are calculated for each Brewer instrument individually, but in the current procedure the effect of stray light is not considered. This study documents the error caused by the effect of stray light in the Brewer and Dobson total ozone measurements using a physical model for each instrument. For the first time, new ozone absorption coefficients are calculated for the Brewer and Dobson instruments, taking into account the stray light effect. The analyses show that the differences detected between the total ozone amounts deduced from Dobson AD and CD pair wavelengths are related to the level of stray light within the instrument. The discrepancy introduced by the assumption of a fixed height for the ozone layer for ozone measurements at high latitude sites is also evaluated. The ozone data collected by two Dobson instruments during the period of December 2008 to December 2014 are compared with ozone data from a collocated double monochromator Brewer spectrophotometer (Mark III). The results illustrate the dependence of Dobson AD and CD pair measurements on stray light.

Montzka, S.A., G.J.M. Velders, P.B. Krummel, J. Muhle, V.L. Orkin, S. Park, N. Shah and H. Walters-Terrinoni, (2019), Scientific Assessment of Ozone Depletion: 2018, Chapter 2: Hydrofluorocarbons (HFCs), World Meteorological Organization, Report, 58, 144-204,

Abstract

The Montreal Protocol is an international agreement designed to heal the ozone layer. It outlines schedules for the phase-out of ozone-depleting substances (ODSs) such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), chlorinated solvents, halons, and methyl bromide. As a result of this phase-out, alternative chemicals and procedures were developed by industry for use in many applications including refrigeration, air-conditioning, foam-blowing, electronics, medicine, agriculture, and fire protection. Hydrofluorocarbons (HFCs) were used as ODS alternatives in many of these applications because they were suitable substitutes and they do not contain ozone-depleting chlorine or bromine; in addition, most HFCs have smaller climate impacts per molecule than the most widely used ODSs they replaced. Long-lived HFCs, CFCs, and HCFCs, however, are all potent greenhouse gases, and concerns were raised that uncontrolled future use of HFCs would lead to substantial climate warming.  As a result of these concerns, HFCs were included as one group of greenhouse gases for which emissions controls were
adopted by the 1997 Kyoto Protocol under the 1992 United Nations Framework Convention on Climate Change (UNFCCC). Consequently, developed countries (those listed in Annex I to this Convention, or “Annex I” Parties) supply annual emission estimates of HFCs to the UNFCCC. Since the Kyoto Protocol only specified limits on the sum of all controlled greenhouse gases, emissions of HFCs were not explicitly controlled. However, following the Kyoto Protocol, some countries enacted additional controls specifically limiting HFC use based on their global warming potentials (GWPs). Ultimately the Kigali Amendment to the
Montreal Protocol was agreed upon in 2016, and this Amendment supplies schedules for limiting the production and consumption of specific HFCs. Although the radiative forcing supplied by HFCs is currently small, this Amendment was designed to ensure that the radiative forcing from HFCs will not grow uncontrollably in the future. The Kigali Amendment will come into force at the start of 2019. HFC concentrations are currently monitored through atmospheric measurements. All HFCs with large abundances are monitored, as are most with small abundances. Most HFCs that are emitted to the atmosphere are intentionally produced for use in a variety of applications that were once dependent on ODSs. An exception is HFC-23, which is emitted to the atmosphere primarily as a by-product of HCFC-22 production. HFC-23 is also unique in that it has a substantially longer atmospheric lifetime and higher GWP than nearly all other HFCs. As a result, the Kigali Amendment includes different control schedules for HFC-23 production than for other HFCs. To date, HFC-23 emissions have been partially abated in developed countries through regulations or voluntary measures and in developing countries with assistance from the UNFCCC’s Clean Development Mechanism (CDM).

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Naus, Stijn, Stephen A. Montzka, Sudhanshu Pandey, Sourish Basu, Ed J. Dlugokencky and Maarten Krol, (2019), Constraints and biases in a tropospheric two-box model of OH, Atmospheric Chemistry and Physics, 19, 1, 407-424, 10.5194/acp-19-407-2019

Abstract

Abstract. The hydroxyl radical (OH) is the main atmospheric oxidant and the primary sink of the greenhouse gas CH4. In an attempt to constrain atmospheric levels of OH, two recent studies combined a tropospheric two-box model with hemispheric-mean observations of methyl chloroform (MCF) and CH4. These studies reached different conclusions concerning the most likely explanation of the renewed CH4 growth rate, which reflects the uncertain and underdetermined nature of the problem. Here, we investigated how the use of a tropospheric two-box model can affect the derived constraints on OH due to simplifying assumptions inherent to a two-box model. To this end, we derived species- and time-dependent quantities from a full 3-D transport model to drive two-box model simulations. Furthermore, we quantified differences between the 3-D simulated tropospheric burden and the burden seen by the surface measurement network of the National Oceanic and Atmospheric Administration (NOAA). Compared to commonly used parameters in two-box models, we found significant deviations in the magnitude and time-dependence of the interhemispheric exchange rate, exposure to OH, and stratospheric loss rate. For MCF these deviations can be large due to changes in the balance of its sources and sinks over time. We also found that changes in the yearly averaged tropospheric burden of CH4 and MCF can be obtained within 0.96ppbyr−1 and 0.14%yr−1 by the NOAA surface network, but that substantial systematic biases exist in the interhemispheric mixing ratio gradients that are input to two-box model inversions.

To investigate the impact of the identified biases on constraints on OH, we accounted for these biases in a two-box model inversion of MCF and CH4. We found that the sensitivity of interannual OH anomalies to the biases is modest (1%–2%), relative to the uncertainties on derived OH (3%–4%). However, in an inversion where we implemented all four bias corrections simultaneously, we found a shift to a positive trend in OH concentrations over the 1994–2015 period, compared to the standard inversion. Moreover, the absolute magnitude of derived global mean OH, and by extent, that of global CH4 emissions, was affected much more strongly by the bias corrections than their anomalies (∼10%). Through our analysis, we identified and quantified limitations in the two-box model approach as well as an opportunity for full 3-D simulations to address these limitations. However, we also found that this derivation is an extensive and species-dependent exercise and that the biases were not always entirely resolvable. In future attempts to improve constraints on the atmospheric oxidative capacity through the use of simple models, a crucial first step is to consider and account for biases similar to those we have identified for the two-box model.

O
Oltmans, S. J., L. C. Cheadle, B. J. Johnson, R. C. Schnell, D. Helmig, A. M. Thompson, P. Cullis, E. Hall, A. Jordan, C. Sterling, A. McClure-Begley, J. T. Sullivan, T. J. McGee and D. Wolfe, (2019), Boundary layer ozone in the Northern Colorado Front Range in July–August 2014 during FRAPPE and DISCOVER-AQ from vertical profile measurements, Elem Sci Anth, 7, 1, 6, 10.1525/elementa.345

Abstract

The Northern Colorado Front Range (NCFR) east of the foothills of the Rocky Mountains and north of Denver and its nearby suburbs includes the moderate sized (~100,000) population centers of Boulder, Longmont, Ft. Collins, and Greeley. To the east is the Denver-Julesburg Basin (DJB), a major oil and natural gas production region that also includes significant agricultural and livestock operations. To the west, the Rocky Mountains with a number of 3000 m peaks rise abruptly and contribute to a complex geographical and meteorological regime (Losleben et al., 2000). During summer months, the Front Range and nearby foothills and mountains regularly experience high ozone (O3) episodes that exceed the National Ambient Air Quality Standard (NAAQS). The U.S. EPA classifies the region as an O3 non-attainment area.

During July–August 2014 a multi-institution campaign was carried out to investigate contributors to the high O3 episodes and possible solutions for controlling air pollution in the region. Two major components of the campaign were the Front Range Air Pollution and Photochemistry Experiment (FRAPPE), led by the Colorado Department of Public Health and Environment (CDPHE) and the National Center for Atmospheric Research (NCAR), and a Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) deployment led by NASA. An array of measurement platforms was deployed during the study period that included multiple aircraft, instrumented surface sites, mobile instrumented vans, and profiling capabilities using lidar, tethered balloons, release balloons, and a tall tower. Along with an extensive suite of chemical measurements many of the platforms and sites included meteorological parameters as well.

In this paper several vertical profile observing platforms including tethered and free release ozonesondes, a tall tower, and surface sites along a vertical elevation gradient (Figure 1) are used to relate surface O3 observations that are the basis for O3 regulatory actions to O3 dynamics and synoptic transport within the boundary layer. The focus of this study is primarily the NCFR, stretching approximately from Boulder to Ft. Collins and the area to the east. This region (Figure 1) is subject to several O3 precursor sources including urban emissions, agricultural and landfill emissions, and notably oil and natural gas related emissions (Pétron et al., 2012; Thompson et al., 2014; McDuffie et al., 2016; Halliday et al., 2016; Abeleira et al., 2017; Cheadle et al., 2017). Elevated O3 occurrences in the NCFR have been found to be influenced by both local and synoptic meteorology patterns (Toth and Johnson, 1985; Pfister et al., 2017b; Evans and Helmig, 2016).

 Original | PPT

Figure 1 

Map of the Northern Colorado Front Range. Map of the Northern Colorado Front Range showing monitoring sites (red triangles), population centers (black dots), and oil and natural gas wells (small gray dots). The inset shows sites along the Colorado Front Range in Boulder County that measured O3 during this study. Numbers next to the site name indicate the site elevation in km. DOI: https://doi.org/10.1525/elementa.345.f1

Meteorological conditions during July and August 2014 were generally typical of those seen during the summer in the NCFR (Toth and Johnson, 1985) with prevailing daytime upslope and nighttime downslope flow (Losleben et al, 2000). On selected occasions closed cyclonic circulations NE of Denver developed under conditions when synoptic frontal system passed through the region (Pfister et al., 2017b). Especially in July several periods of high pressure dominated the region leading to the thermally driven circulation systems noted above. Transport pathways computed from back trajectories reflected both these more local circulations patterns and periods when synoptic scale disturbances dominated.

In this paper profiles of O3 and accompanying meteorological variables are used to investigate the contribution of O3 mixed down into the boundary layer, boundary layer O3 dependence on transport, and the production of O3 within the boundary layer including near the surface. Cases with enhanced afternoon O3 levels (≥75 ppb) are contrasted with days with minimal afternoon O3 enhancements (O3 ≤65 ppb).

Ortega, Ivan, Rebecca R. Buchholz, Emrys G. Hall, Dale F. Hurst, Allen F. Jordan and James W. Hannigan, (2019), Tropospheric water vapor profiles obtained with FTIR: comparison with balloon-borne frost point hygrometers and influence on trace gas retrievals, Atmospheric Measurement Techniques, 12, 2, 873-890, 10.5194/amt-12-873-2019

Abstract

Abstract. Retrievals of vertical profiles of key atmospheric gases provide a critical long-term record from ground-based Fourier transform infrared (FTIR) solar absorption measurements. However, the characterization of the retrieved vertical profile structure can be difficult to validate, especially for gases with large vertical gradients and spatial–temporal variability such as water vapor. In this work, we evaluate the accuracy of the most common water vapor isotope (H216O, hereafter WV) FTIR retrievals in the lower and upper troposphere–lower stratosphere. Coincident high-quality vertically resolved WV profile measurements obtained from 2010 to 2016 with balloon-borne NOAA frost point hygrometers (FPHs) are used as reference to evaluate the performance of the retrieved profiles at two sites: Boulder (BLD), Colorado, and at the mountaintop observatory of Mauna Loa (MLO), Hawaii. For a meaningful comparison, the spatial–temporal variability has been investigated. We present results of comparisons among FTIR retrievals with unsmoothed and smoothed FPH profiles to assess WV vertical gradients. Additionally, we evaluate the quantitative impact of different a priori profiles in the retrieval of WV. An orthogonal linear regression analysis shows the best correlation among tropospheric layers using ERA-Interim (ERA-I) a priori profiles and biases are lower for unsmoothed comparisons. In Boulder, we found a negative bias of 0.02±1.9 % (r=0.95) for the 1.5–3 km layer. A larger negative bias of 11.1±3.5 % (r=0.97) was found in the lower free troposphere layer of 3–5 km attributed to rapid vertical change of WV, which is not always captured by the retrievals. The bias improves in the 5–7.5 km layer (1.0±5.3 %, r=0.94). The bias remains at about 13 % for layers above 7.5 km but below 13.5 km. At MLO the spatial mismatch is significantly larger due to the launch of the sonde being farther from the FTIR location. Nevertheless, we estimate a negative bias of 5.9±4.6 % (r=0.93) for the 3.5–5.5 km layer and 9.9±3.7 % (r=0.93) for the 5.5–7.5 km layer, and we measure positive biases of 6.2±3.6 % (r=0.95) for the 7.5–10 km layer and 12.6 % and greater values above 10 km. The agreement for the first layer is significantly better at BLD because the air masses are similar for both FTIR and FPH. Furthermore, for the first time we study the influence of different WV a priori profiles in the retrieval of selected gas profiles. Using NDACC standard retrievals we present results for hydrogen cyanide (HCN), carbon monoxide (CO), and ethane (C2H6) by taking NOAA FPH profiles as the ground truth and evaluating the impact of other WV profiles. We show that the effect is minor for C2H6 (bias <0.5 % for all WV sources) among all vertical layers. However, for HCN we found significant biases between 6 % for layers close to the surface and 2 % for the upper troposphere depending on the WV profile source. The best results (reduced bias and precision and r values closer to unity) are always found for pre-retrieved WV. Therefore, we recommend first retrieving WV to use in subsequent retrieval of gases.

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Pani, Shantanu Kumar, Chang-Feng Ou-Yang, Sheng-Hsiang Wang, John A. Ogren, Patrick J. Sheridan, Guey-Rong Sheu and Neng-Huei Lin, (2019), Relationship between long-range transported atmospheric black carbon and carbon monoxide at a high-altitude background station in East Asia, Atmospheric Environment, 210, 86-99, 10.1016/j.atmosenv.2019.04.053

Abstract

Lulin Atmospheric Background Station (LABS, 23.47°N, 120.87°E; 2862 m above sea level) at the summit of Mount Lulin in central Taiwan was established in spring 2006 and is the only high-altitude background station over western Pacific region in East Asia to study the impact of various air pollutants through long-range transport. Continuous in-situ measurements of equivalent black carbon (EBC) and carbon monoxide (CO) concentrations were made at LABS from June 2012 to May 2014 and their association was investigated in this study. The highest monthly concentration of EBC (median; 840 ng m−3) and CO (212 ppbv) in March were primarily attributed to the westerly winds coupled with biomass-burning (BB) emissions from Southeast Asia (SEA) region. The association of EBC and CO was weak at LABS possibly due to the influence of dissimilar air masses from various sources, and scavenging or dilution of EBC during the long-range atmospheric transport to Mt. Lulin. The mean ΔEBC/ΔCO ratio (slope of least-squares regression line of ΔEBC-ΔCO scatterplot; where Δ indicates surplus amounts with respect to the background value) was found the most significant in March (5.3 ng m−3 ppbv−1 or 7.3 × 10−3 g of carbon as EBC per gram of carbon as CO). On the basis of episodic cases, the mean ΔEBC/ΔCO ratios at LABS were estimated to be 6.1, 8.0, and 2.4 ng m−3 ppbv−1 for SEA BB emissions, southern China mixed pollution, and northern China mixed pollution, respectively. A total of 32% loss in EBC aerosols (6.4% of EBC removal per day) was estimated for the atmospheric transport of BB emissions from SEA region to LABS. This study provides needful information to understand the ΔEBC/ΔCO ratios at a remote site and would be used in model simulations to evaluate BC aging and scavenging over western Pacific region in East Asia.

Park, Soojin, Sang-Woo Kim, Neng-Huei Lin, Shantanu Kumar Pani, Patrick J. Sheridan and Elisabeth Andrews, (2019), Variability of Aerosol Optical Properties Observed at Polluted Marine (Gosan, Korea) and High-altitude Mountain (Lulin, Taiwan) Sites in the Asian Continental Outflow, Aerosol and Air Quality Research, 10.4209/aaqr.2018.11.0416

Abstract

We investigated variability of in-situ and columnar aerosol optical properties (AOPs) at two regional background sites in the Asian continental outflow from 2012 to 2014. The monthly variability of AOPs at each site was explained using regional-scale atmospheric circulation patterns and the resulting changes in air mass sources. The median aerosol scattering and absorption coefficient values for sub-10 μm particles (σsp10 μm and σap10 μm) at the polluted marine site, Gosan (GSN; σsp10 μm: 59.94 Mm-1σap10 μm: 4.73 Mm-1), were larger than those of the high-altitude mountain site, Lulin (LLN; σsp10 μm: 17.07 Mm-1, σap10 μm: 1.72 Mm-1). Elevated σsp10 μm and σap10 μm at GSN in May and June can be explained by the accumulation of locally emitted aerosols together with long-range transported aerosols under stagnant synoptic patterns, enhanced particle formation and subsequent growth. The significant peaks of σsp10 μm and σap10 μm, with median values of 50.76 Mm-1 and 5.92 Mm-1, at LLN during March and April can be attributed to biomass burning aerosols transported from Northern Indochina and Southern China. The LLN site was mostly influenced by clean free tropospheric air and maritime air masses during the other months, showing medians of 14.65±19.81 Mm-1 and 1.46±1.86 Mm-1 in σsp10 μm and σap10 μm, respectively. Smaller median values of the sub-micron to sub-10 μm ratio of aerosol scattering (0.60) and absorption (0.81) at GSN, compared to LLN (0.81 and 0.91, respectively), are indicative of the larger proportion of coarse aerosols such as sea salt and dust at GSN. Single scattering albedo for sub-10 μm particles showed similar median values at both sites (GSN: 0.93±0.02, LLN: 0.91±0.03).

Petersen, Ross C., Anna G. Hallar, Ian B. McCubbin, John A. Ogren, Elisabeth Andrews, Douglas Lowenthal, Riley Gorder, Rick Purcell, Darrah Sleeth and Igor Novosselov, (2019), Numerical, wind-tunnel, and atmospheric evaluation of a turbulent ground-based inlet sampling system, Aerosol Science and Technology, 1-15, 10.1080/02786826.2019.1602718
Petropavlovskikh, I., S. Godin-Beekmann, D. Hubert, R. Damadeo, B. Hassler and V. Sofieva, (2019), SPARC/IO3C/GAW Report on Long-term Ozone Trends and Uncertainties in the Stratosphere, SPARC LOTUS Activity, SPARC , i-78, 10.17874/f899e57a20b

Abstract

EXECUTIVE SUMMARY

The assessment of long-term observations by LOTUS confirms the significant decline of ozone concentrations in the upper stratosphere (at altitudes above the 10–5 hPa level) between January 1985 and December 1996. The strongest trends are observed near 2 hPa (~42 km) with values of 5.9–6.2 % per decade at mid-latitudes and 4.8 % per decade in the tropics. Trends are significant at more than 5 standard deviations in this altitude range.
ŸŸ
Trends derived from satellite and ground-based records in the pre-1997 time period agree with climate model simulations within respective uncertainties thus confirming our understanding of ozone loss processes in the upper stratosphere during that period.
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Between January 2000 and December 2016, positive trends are obtained throughout the upper stratosphere for satellite and ground-based records. The combined trends from six merged satellite records are larger in the Northern Hemisphere mid-latitudes (2–3 % per decade between ~5–1 hPa) than in the tropics (1–1.5 % per decade between ~3–1 hPa) and Southern Hemisphere mid-latitudes (~2 % per decade near 2 hPa). Statistical confidence is largest for trends in the Northern Hemisphere mid-latitudes.
ŸŸ
For altitudes below the 4 hPa level, ozone trends in the post-2000 time period are not significant. Though not significant, negative ozone trends of 0.5–1.5 % per decade are consistently detected by multiple satellite combined records in the 50–15 hPa altitude range over the tropics. Trends derived from ground-based data and Chemistry-Climate Model Initiative (CCMI) model simulations are generally consistent but more variable in this region. The mean CCMI model trend is negative at altitudes below 30 hPa, but the range of individual model trends is large; trends in ground-based records tend to be negative at 20 hPa but increase at lower altitudes (except trends from the microwave records). At mid-latitudes, the trends are close to zero down to 50 hPa.
ŸŸ
Larger differences in post-2000 trends from the various records are observed in the lowermost stratosphere (100–50 hPa) in all latitude bands. Non-significant negative trends are derived from merged satellite records over the tropics and the Northern Hemisphere mid-latitudes. Model simulations show positive trends in the mid-latitudes in both hemispheres in this altitude range, although the trends are not statistically significant.
ŸŸ
LOTUS estimates of past and recent ozone trends are in fairly good agreement with results from previous studies. For the post-2000 period, the largest differences are found throughout the middle stratosphere. These differences stem primarily from extensions of and revisions to existing data records, the addition of new data records, and in some cases the use of a different trend model.
ŸŸ
While trend values in recent studies are fairly similar, the uncertainties and hence significances of the combined trends in broad latitude bands differ substantially. The LOTUS approach, based on both error propagation and standard error of the mean, also explicitly accounts for correlation between the data sets, which results in more conservative uncertainties and thus lower, but more realistic, confidence in positive upper stratospheric trend values compared to the most recently published assessment of merged satellite data set trends.

Have ozone concentrations in the stratosphere significantly increased since the end of the 1990s when levels of ozone depleting substances (ODSs) started to decline? Finding an answer to this question is of great societal importance to ensure that the measures taken by the Montreal Protocol and subsequent amendments to reduce ODSs continue to adequately protect the ozone layer. However, the confidence with which we can assess changes in stratospheric ozone since the mid-1990s has been the subject of considerable scientific debate in recent years, as it depends on the data sets and the analysis methods used. Settling this scientific debate is one of the main objectives of the LOTUS activity, short for Long-term Ozone Trends and Uncertainties in the Stratosphere. Below, we summarise the main results obtained during the first phase of LOTUS, which was primarily targeted at providing timely input to the 2018 World Meteorological Organization (WMO) Ozone Assessment (WMO, 2018). During this phase we reevaluated the satellite and ground-based data records as well as the time series analysis methods commonly used to derive long-term trends. Using a single “LOTUS regression” model, we reassessed past and recent trends in the vertical distribution of stratospheric ozone from the updated individual data records. We then developed a new approach for combining the individual trend estimates from satellite-based records into a single best estimate of ozone profile trends with associated uncertainty estimates. Finally, we compared the satellite-based profile trends in broad latitude bands to trends from ground-based data, from the collection of CCMI-1 model simulations, and from past evaluations of satellite-based trends in peer-reviewed literature.  Some regions in the stratosphere have not been considered (e.g., polar) or have not been analysed in full detail (e.g.,
lower stratosphere) because of the timeline for the 2018 WMO Ozone Assessment (WMO, 2018).
 
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Rigby, M., S. Park, T. Saito, L. M. Western, A. L. Redington, X. Fang, S. Henne, A. J. Manning, R. G. Prinn, G. S. Dutton, P. J. Fraser, A. L. Ganesan, B. D. Hall, C. M. Harth, J. Kim, K.-R. Kim, P. B. Krummel, T. Lee, S. Li, Q. Liang, M. F. Lunt, S. A. Montzka, J. Mühle, S. O’Doherty, M.-K. Park, S. Reimann, P. K. Salameh, P. Simmonds, R. L. Tunnicliffe, R. F. Weiss, Y. Yokouchi and D. Young, (2019), Increase in CFC-11 emissions from eastern China based on atmospheric observations, Nature, 569, 7757, 546-550, 10.1038/s41586-019-1193-4

Abstract

The recovery of the stratospheric ozone layer relies on the continued decline in the atmospheric concentrations of ozone-depleting gases such as chlorofluorocarbons1. The atmospheric concentration of trichlorofluoromethane (CFC-11), the second-most abundant chlorofluorocarbon, has declined substantially since the mid-1990s2. A recently reported slowdown in the decline of the atmospheric concentration of CFC-11 after 2012, however, suggests that global emissions have increased3,4. A concurrent increase in CFC-11 emissions from eastern Asia contributes to the global emission increase, but the location and magnitude of this regional source are unknown3. Here, using high-frequency atmospheric observations from Gosan, South Korea, and Hateruma, Japan, together with global monitoring data and atmospheric chemical transport model simulations, we investigate regional CFC-11 emissions from eastern Asia. We show that emissions from eastern mainland China are 7.0 ± 3.0 (±1 standard deviation) gigagrams per year higher in 2014–2017 than in 2008–2012, and that the increase in emissions arises primarily around the northeastern provinces of Shandong and Hebei. This increase accounts for a substantial fraction (at least 40 to 60 per cent) of the global rise in CFC-11 emissions. We find no evidence for a significant increase in CFC-11 emissions from any other eastern Asian countries or other regions of the world where there are available data for the detection of regional emissions. The attribution of any remaining fraction of the global CFC-11 emission rise to other regions is limited by the sparsity of long-term measurements of sufficient frequency near potentially emissive regions. Several considerations suggest that the increase in CFC-11 emissions from eastern mainland China is likely to be the result of new production and use, which is inconsistent with the Montreal Protocol agreement to phase out global chlorofluorocarbon production by 2010.

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Sorribas, M., E. Andrews, J.A. Ogren, A. del Aguila, R. Fraile, P. Sheridan and M. Yela, (2019), Climatological study for understanding the aerosol radiative effects at southwest Atlantic coast of Europe, Elsevier, 205, 52-66, 10.1016/j.atmosenv.2019.02.017

Abstract

In order to describe the means, variability and trends of the aerosol radiative effects on the southwest Atlantic coast of Europe, 11 years of aerosol light scatteringsp) and 4 years of aerosol light absorptionap) are analyzed. A 2006–2016 trend analysis of σsp for D < 10 μm indicates statistically significant trends for March, May–June and September–November, with a decreasing trend ranging from −1.5 to −2.8 Mm−1/year. In the 2009–2016 period, the decreasing trend is only observed for the months of June and September. For scattering Ångström exponent (SAE) there is an increasing trend during June with a rate of 0.059/year and a decreasing trend during October with −0.060/year. The trends observed may be caused by a reduction of Saharan dust aerosol or a drop in particle loading in anthropogenic influenced air masses. The relationship between SAE and absorption Ångström exponent is used to assess the aerosol typing. Based on this typing, the sub-micron particles are dominated by black carbon, mixed black and brown carbon or marine with anthropogenic influences, while the super-micrometer particles are desert dust and sea spray aerosol. The mean and standard deviation of the dry aerosol direct radiative effect at the top of the atmosphere (DRETOA) are −4.7 ± 4.2 W m−2. DRETOA for marine aerosol shows all observations more negative than −4 W m−2 and for anthropogenic aerosol type, DRETOA ranges from −5.0 to −13.0 W m−2. DRETOA of regional marine aerosol ranges from −3 to −7 W m−2, as it consists of a mixture of sea salt and anthropogenic aerosol. The variability in DRETOA is mainly dependent on AOD, given that variations in backscatter fraction and the single scattering albedo tend to counteract each other in the radiative forcing efficiency equation. The results shown here may help in interpretation of satellite retrieval products and provide context for model evaluation.

Suntharalingam, P., E. Buitenhuis, L. J. Carpenter, J. H. Butler, M. J. Messias, S. J. Andrews and S. C. Hackenberg, (2019), Evaluating Oceanic Uptake of Atmospheric CCl: A Combined Analysis of Model Simulations and Observations , Geophysical Research Letters, 46, 1, 472-482, 10.1029/2018GL080612

Abstract

We provide new estimates of the air‐sea flux of CCl4 using simulations from a global ocean biogeochemistry model (NEMO‐PlankTOM) in combination with depth‐resolved CCl4 observations from global oceanic databases. Estimates of global oceanic CCl4 uptake are derived from a range of model analyses, including prescribed parameterizations using reported values on hydrolysis and degradation, and analyses optimized using the global observational databases. We evaluate the sensitivity of our results to uncertainties in air‐sea gas exchange parameterization, estimation period, and circulation processes. Our best constrained estimate of ocean CCl4 uptake for the period 1996–2000 is 20.1 Gg/year (range 16.6–22.7), corresponding to estimates of the partial atmospheric lifetime with respect to ocean uptake of 124 (110–150) years. This new oceanic lifetime implies higher emissions of CCl4 than currently estimated and therefore a larger missing atmospheric source of CCl4.

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Thompson, Anne M., Herman G. J. Smit, Jacquelyn C. Witte, Ryan M. Stauffer, Bryan J. Johnson, Gary Morris, Peter von der Gathen, Roeland Van Malderen, Jonathan Davies, Ankie Piters, Marc Allaart, Françoise Posny, Rigel Kivi, Patrick Cullis, Nguyen Thi Hoang Anh, Ernesto Corrales, Tshidi Machinini, Francisco R. da Silva, George Paiman, Kennedy Thiong’o, Zamuna Zainal, George B. Brothers, Katherine R. Wolff, Tatsumi Nakano, Rene Stübi, Gonzague Romanens, Gert J. R. Coetzee, Jorge A. Diaz, Sukarni Mitro, Maznorizan Mohamad and Shin-Ya Ogino, (2019), Ozonesonde Quality Assurance: The JOSIE–SHADOZ (2017) Experience, Bulletin of the American Meteorological Society, 100, 1, 155-171, 10.1175/BAMS-D-17-0311.1

Abstract

The ozonesonde is a small balloon-borne instrument that is attached to a standard radiosonde to measure profiles of ozone from the surface to 35 km with ∼100-m vertical resolution. Ozonesonde data constitute a mainstay of satellite calibration and are used for climatologies and analysis of trends, especially in the lower stratosphere where satellites are most uncertain. The electrochemical concentration cell (ECC) ozonesonde has been deployed at ∼100 stations worldwide since the 1960s, with changes over time in manufacture and procedures, including details of the cell chemical solution and data processing. As a consequence, there are biases among different stations and discontinuities in profile time series from individual site records. For 22 years the Jülich (Germany) Ozonesonde Intercomparison Experiment (JOSIE) has periodically tested ozonesondes in a simulation chamber designated the World Calibration Centre for Ozonesondes (WCCOS) by WMO. During October–November 2017 a JOSIE campaign evaluated the sondes and procedures used in Southern Hemisphere Additional Ozonesondes (SHADOZ), a 14-station sonde network operating in the tropics and subtropics. A distinctive feature of the 2017 JOSIE was that the tests were conducted by operators from eight SHADOZ stations. Experimental protocols for the SHADOZ sonde configurations, which represent most of those in use today, are described, along with preliminary results. SHADOZ stations that follow WMO-recommended protocols record total ozone within 3% of the JOSIE reference instrument. These results and prior JOSIEs demonstrate that regular testing is essential to maintain best practices in ozonesonde operations and to ensure high-quality data for the satellite and ozone assessment communities.

V
Vasebi, Yalda, Marco E. Mechan Llontop, Regina Hanlon, David G. Schmale III, Russell Schnell and Boris A. Vinatzer, (2019), Comprehensive characterization of an aspen (Populus tremuloides) leaf litter sample that maintained ice nucleation activity for 48 years, Biogeosciences, 16, 8, 1675-1683, 10.5194/bg-16-1675-2019

Abstract

Abstract. Decaying vegetation was determined to be a potentially important source of atmospheric ice nucleation particles (INPs) in the early 1970s. The bacterium Pseudomonas syringae was the first microorganism with ice nucleation activity (INA) isolated from decaying leaf litter in 1974. However, the ice nucleation characteristics of P. syringae are not compatible with the characteristics of leaf litter-derived INPs since the latter were found to be sub-micron in size, while INA of P. syringae depends on much larger intact bacterial cells. Here we determined the cumulative ice nucleation spectrum and microbial community composition of the historic leaf litter sample 70-S-14 collected in 1970 that conserved INA for 48 years. The majority of the leaf litter-derived INPs were confirmed to be sub-micron in size and to be sensitive to boiling. Culture-independent microbial community analysis only identified Pseudomonas as potential INA. Culture-dependent analysis identified one P. syringae isolate, two isolates of the bacterial species Pantoea ananatis, and one fungal isolate of Mortierella alpina as having INA among 1170 bacterial colonies and 277 fungal isolates, respectively. Both Pa. ananatis and M. alpina are organisms that produce heat-sensitive sub-micron INPs. They are thus both likely sources of the INPs present in sample 70-S-14 and may represent important terrestrial sources of atmospheric INPs, a conclusion that is in line with other recent results obtained in regard to INPs from soil, precipitation, and the atmosphere.

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Wandji Nyamsi, William, Philippe Blanc, John A. Augustine, Antti Arola and Lucien Wald, (2019), A New Clear-Sky Method for Assessing Photosynthetically Active Radiation at the Surface Level, Atmosphere, 10, 4, 219, 10.3390/atmos10040219

Abstract

A clear–sky method to estimate the photosynthetically active radiation (PAR) at the surface level in cloudless atmospheres is presented and validated. It uses a fast and accurate approximation adopted in several radiative transfer models, known as the k-distribution method and the correlated-k approximation, which gives a set of fluxes accumulated over 32 established wavelength intervals. A resampling technique, followed by a summation, are applied over the wavelength range [0.4, 0.7] µm in order to retrieve the PAR fluxes. The method uses as inputs the total column contents of ozone and water vapor, and optical properties of aerosols provided by the Copernicus Atmosphere Monitoring Service. To validate the method, its outcomes were compared to instantaneous global photosynthetic photon flux density (PPFD) measurements acquired at seven experimental sites of the Surface Radiation Budget Network (SURFRAD) located in various climates in the USA. The bias lies in the interval [−12, 61] µmol m−2 s−1 ([−1, 5] % in values relative to the means of the measurements at each station). The root mean square error ranges between 37 µmol m−2 s−1 (3%) and 82 µmol m−2 s−1 (6%). The squared correlation coefficient fluctuates from 0.97 to 0.99. This comparison demonstrates the high level of accuracy of the presented method, which offers an accurate estimate of PAR fluxes in cloudless atmospheres at high spatial and temporal resolutions useful for several bio geophysical models.

Wilczak, James M., Mark Stoelinga, Larry K. Berg, Justin Sharp, Caroline Draxl, Katherine McCaffrey, Robert M. Banta, Laura Bianco, Irina Djalalova, Julie K. Lundquist, Paytsar Muradyan, Aditya Choukulkar, Laura Leo, Timothy Bonin, Yelena Pichugina, Richard Eckman, Charles N. Long, Kathleen Lantz, Rochelle P. Worsnop, Jim Bickford, Nicola Bodini, Duli Chand, Andrew Clifton, Joel Cline, David R. Cook, Harinda J.S. Fernando, Katja Friedrich, Raghavendra Krishnamurthy, Melinda Marquis, Jim McCaa, Joseph B. Olson, Sebastian Otarola-Bustos, George Scott, William J. Shaw, Sonia Wharton and Allen B. White, (2019), The Second Wind Forecast Improvement Project (WFIP2): Observational Field Campaign, Bulletin of the American Meteorological Society, 10.1175/BAMS-D-18-0035.1

Abstract

The science of wind energy forecasting has taken a leap forward with the unique meteorological observations gathered in complex terrain during the Second Wind Forecast Improvement Project (WFIP2)

The Second Wind Forecast Improvement Project (WFIP2) is a U.S. Department of Energy (DOE) and National Oceanic and Atmospheric Administration (NOAA) funded program, with private-sector and university partners, which aims to improve the accuracy of numerical weather prediction (NWP) model forecasts of wind speed in complex terrain for wind energy applications. A core component of WFIP2 was an 18-month field campaign which took place in the U.S. Pacific Northwest between October 2015 and March 2017. A large suite of instrumentation was deployed in a series of telescoping arrays, ranging from 500 km across to a densely instrumented 2 x 2 km area similar in size to a high-resolution NWP model grid cell. Observations from these instruments are being used to improve our understanding of the meteorological phenomena that affect wind energy production in complex terrain, and to evaluate and improve model physical parameterization schemes. We present several brief case studies using these observations to describe phenomena that are routinely difficult to forecast, including wintertime cold pools, diurnally driven gap flows, and mountain waves/wakes. Observing system and data product improvements developed during WFIP2 are also described.

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Yang, Huang, Darryn W. Waugh, Clara Orbe, Prabir K. Patra, Patrick Jöckel, Jean-Francois Lamarque, Simone Tilmes, Douglas Kinnison, James W. Elkins and Edward J. Dlugokencky, (2019), Evaluating Simulations of Interhemispheric Transport: Interhemispheric Exchange Time Versus SF Age , Geophysical Research Letters, 46, 2, 1113-1120, 10.1029/2018GL080960

Abstract

Two recent studies using sulfur hexafluoride (SF6) observations to evaluate interhemispheric transport in two different ensembles of atmospheric chemistry models reached different conclusions on model performance. We show here that the different conclusions are due to the use of different metrics and not differences in the performance of the models. For both model ensembles, the multimodel mean interhemispheric exchange time τex agrees well with observations, but in nearly all models the SF6 age in the southern hemisphere is older than observed. This occurs because transport from the northern extratropics into the tropics is too slow in most models, and the SF6 age is more sensitive to this bias than τex. Thus, simulating τex correctly does not necessarily mean that transport from northern midlatitudes into the southern hemisphere is correct. It also suggests that more attention needs to be paid to evaluating transport from northern midlatitudes into the tropics.

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Zhang, Taiping, Paul W. Stackhouse, Stephen J. Cox, J. Colleen Mikovitz and Charles N. Long, (2019), Clear-sky shortwave downward flux at the Earth's surface: Ground-based data vs. satellite-based data, Journal of Quantitative Spectroscopy and Radiative Transfer, 224, 247-260, 10.1016/j.jqsrt.2018.11.015

Abstract

The radiative flux data and other meteorological data in the BSRN archive start in 1992, but the RadFlux data, the clear-sky radiative fluxes at the BSRN sites empirically inferred through regression analyses of actually observed clear-sky fluxes, did not come into existence until the early 2000s, and at first, they were limited to the 7 NOAA SURFRAD and 4 DOE ARM sites, a subset of the BSRN sites. Recently, the RadFlux algorithm was applied more extensively to the BSRN sites for the production of clear-sky ground-based fluxes. At the time of this writing, there are 7119 site-months of clear-sky fluxes at 42 BSRN sites spanning from 1992 to late 2017. These data provide an unprecedented opportunity to validate the satellite-based clear-sky fluxes. In this paper, the GEWEX SRB GSW(V3.0) clear-sky shortwave downward fluxes spanning 24.5 years from July 1983 to December 2007, the CERES SYN1deg(Ed4A) and EBAF(Ed4.0) clear-sky shortwave fluxes spanning March 2000 to mid-2017 are compared with their RadFlux counterparts on the hourly, 3-hourly, daily and monthly time scales. All the three datasets show reasonable agreement with their ground-based counterparts. Comparison of the satellite-based surface shortwave clear-sky radiative fluxes to the BSRN RadFlux analysis shows negative biases (satellite-based minus RadFlux). Further analysis shows that the satellite-based atmosphere contains greater aerosol loading as well as more precipitable water than RadFlux analysis estimates.