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GMD Publications for 2015

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Buller, David B., Marianne Berwick, Kathy Lantz, Mary Klein Buller, James Shane, Ilima Kane and Xia Liu, (2015), Smartphone Mobile Application Delivering Personalized, Real-Time Sun Protection Advice, JAMA Dermatology, , , 10.1001/jamadermatol.2014.3889

Abstract

Importance  Mobile smartphones are rapidly emerging as an effective means of communicating with many Americans. Using mobile applications (apps), they can access remote databases, track time and location, and integrate user input to provide tailored health information.

Objective  A smartphone mobile app providing personalized, real-time sun protection advice was evaluated in a randomized clinical trial.

Design, Setting, and Participants  The trial was conducted in 2012 and had a randomized pretest-posttest controlled design with a 10-week follow-up. Data were collected from a nationwide population-based survey panel. A sample of 604 non-Hispanic and Hispanic adults from the Knowledge Panel 18 years or older who owned an Android smartphone were enrolled.

Interventions  The mobile app provided advice on sun protection (ie, protection practices and risk of sunburn) and alerts (to apply or reapply sunscreen and get out of the sun), hourly UV Index, and vitamin D production based on the forecast UV Index, the phone’s time and location, and user input.

Main Outcomes and Measures  Percentage of days using sun protection and time spent outdoors (days and minutes) in the midday sun and number of sunburns in the past 3 months were collected.

Results  Individuals in the treatment group reported more shade use (mean days staying in the shade, 41.0% vs 33.7%; P = .03) but less sunscreen use (mean days, 28.6% vs 34.5%; P  = .048) than controls. There was no significant difference in number of sunburns in the past 3 months (mean, 0.60 in the treatment group vs 0.62 for controls; P = .87). Those who used the mobile app reported spending less time in the sun (mean days keeping time in the sun to a minimum, 60.4% for app users vs 49.3% for nonusers; P = .04) and using all protection behaviors combined more (mean days, 39.4% vs 33.8%; P = .04).

Conclusions and Relevance  The mobile app improved some sun protection. Use of the mobile app was lower than expected but associated with increased sun protection. Providing personalized advice when and where people are in the sun may help reduce sun exposure.

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Buller, David B., Marianne Berwick, Kathy Lantz, Mary Klein Buller, James Shane, Ilima Kane and Xia Liu, (2015), Evaluation of Immediate and 12-Week Effects of a Smartphone Sun-Safety Mobile Application, JAMA Dermatology, , , 10.1001/jamadermatol.2014.3894

Abstract

Importance  Mobile applications on smartphones can communicate a large amount of personalized, real-time health information, including advice on skin cancer prevention, but their effectiveness may be affected by whether recipients can be convinced to use them.

Objective  To evaluate a smartphone mobile application (Solar Cell) delivering real-time advice about sun protection for a second time in a randomized clinical trial.

Design, Setting, and Participants  A previous trial conducted in 2012 used a randomized pretest-posttest design. For the present trial, we collected data from a volunteer sample of 202 adults 18 years or older who owned a smartphone. Participants were recruited nationwide through online promotions. Screening procedures and a 3-week run-in period were added to increase the use of the mobile application. We conducted follow-ups at 3 and 8 weeks after randomization to examine the immediate and the longer-term effects of the intervention.

Interventions  Use of the mobile application. The application gave feedback on sun protection (ie, sun-safety practices and the risk for sunburn) and alerted users to apply or to reapply sunscreen and to get out of the sun. The application also displayed the hourly UV Index and vitamin D production based on the forecast UV Index, time, and location.

Main Outcomes and Measures  Percentage of days with the use of sun protection, time spent outdoors in the midday sun (days and hours), and the number of sunburns in the last 3 months.

Results  Participants in the intervention group used wide-brimmed hats more at 7 weeks than control participants (23.8% vs 17.4%; F = 4.07; P = .045). Women who used the mobile application reported using all sun protection combined more than men (46.4% vs 43.3%; F = 1.49; P = .04), whereas men and older individuals reported less use of sunscreen (32.7% vs 35.5%; F = 5.36; P = .02) and hats (15.6% vs 17.9%; F = 4.72; P = .03).

Conclusions and Relevance  The mobile application initially appeared to confer weak improvement of sun protection. Use of the mobile application was greater than in a previous trial and was associated with greater sun protection, especially among women. Strategies to increase the use of the mobile application are needed if the application is to be deployed effectively to the general adult population.

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Burleyson, Casey D., Charles N. Long and Jennifer M. Comstock, (2015), Quantifying Diurnal Cloud Radiative Effects by Cloud Type in the Tropical Western Pacific, Journal of Applied Meteorology and Climatology, , , 10.1175/JAMC-D-14-0288.1

Abstract

Cloud radiative effects are examined using long-term datasets collected at the three Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facilities in the tropical western Pacific. The surface radiation budget, cloud populations, and cloud radiative effects are quantified by partitioning the data by cloud type, time of day, and large scale modes of variability such as El Niño Southern Oscillation (ENSO) phase and wet/dry seasons at Darwin. The novel aspect of this analysis is the breakdown of aggregate cloud radiative effects by cloud type across the diurnal cycle. The Nauru cloud populations and subsequently the surface radiation budget are strongly impacted by ENSO variability whereas the cloud populations over Manus only shift slightly in response to changes in ENSO phase. The Darwin site exhibits large seasonal monsoon related variations. When present, deeper convective clouds have a strong influence on the amount of radiation reaching the surface. However, their limited frequency reduces their aggregate radiative impact. The largest source of shortwave cloud radiative effects at all three sites comes from low clouds. The observations are used to demonstrate that potential model biases in the amplitude of the diurnal cycle and mean cloud frequency would lead to larger errors in the surface energy budget compared to biases in the timing of the diurnal cycle of cloud frequency. These results provide solid benchmarks to evaluate model simulations of cloud radiative effects in the tropics.

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Cambaliza, M. O. L., P. B. Shepson, J. Bogner, D. R. Caulton, B. Stirm, C. Sweeney, S. A. Montzka, K. R. Gurney, K. Spokas, O. E. Salmon, T. N. Lavoie, A. Hendricks, K. Mays, J. Turnbull, B. R. Miller, T. Lauvaux, K. Davis, A. Karion, B. Moser, C. Miller, C. Obermeyer, J. Whetstone, K. Prasad, N. Miles and S. Richardson, (2015), Quantification and source apportionment of the methane emission flux from the city of Indianapolis, Elementa: Science of the Anthropocene, 3, , 10.12952/journal.elementa.000037
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Desai, Ankur R., Ke Xu, Hanqin Tian, Peter Weishampel, Jonathan Thom, Dan Baumann, Arlyn E. Andrews, Bruce D. Cook, Jennifer Y. King and Randall Kolka, (2015), Landscape-level terrestrial methane flux observed from a very tall tower, Agricultural and Forest Meteorology, 201, , 10.1016/j.agrformet.2014.10.017
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Harris, N. R. P., B. Hassler, F. Tummon, G. E. Bodeker, D. Hubert, I. Petropavlovskikh, W. Steinbrecht, J. Anderson, P. K. Bhartia, C. D. Boone, A. Bourassa, S. M. Davis, D. Degenstein, A. Delcloo, S. M. Frith, L. Froidevaux, S. Godin-Beekmann, N. Jones, M. J. Kurylo, E. Kyrölä, M. Laine, S. T. Leblanc, J.-C. Lambert, B. Liley, E. Mahieu, A. Maycock, M. de Mazière, A. Parrish, R. Querel, K. H. Rosenlof, C. Roth, C. Sioris, J. Staehelin, R. S. Stolarski, R. Stübi, J. Tamminen, C. Vigouroux, K. Walker, H. J. Wang, J. Wild and J. M. Zawodny, (2015), Past changes in the vertical distribution of ozone – Part 3: Analysis and interpretation of trends, Atmospheric Chemistry and Physics Discussions, 15, 6, , 10.5194/acpd-15-8565-2015

Abstract

Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised datasets. The amount of ozone-depleting compounds in the stratosphere (as measured by Equivalent Effective Stratospheric Chlorine – EESC) maximised in the second half of the 1990s. We therefore examine the trends in the periods before and after that peak to see if any change in trend is discernible in the ozone record. Prior to 1998, trends in the upper stratosphere (~ 45 km, 4 hPa) are found to be −5 to −10% per decade at mid-latitudes and closer to −5% per decade in the tropics. No trends are found in the mid-stratosphere (28 km, 30 hPa). Negative trends are seen in the lower stratosphere at mid-latitudes in both hemispheres and in the deep tropics. However it is hard to be categorical about the trends in the lower stratosphere for three reasons: (i) there are fewer measurements, (ii) the data quality is poorer, and (iii) the measurements in the 1990s are perturbed by aerosols from the Mt. Pinatubo eruption in 1991. These findings are similar to those reported previously even though the measurements for the two main satellite instruments (SBUV and SAGE II) and the ground-based Umkehr and ozonesonde stations have been revised.

There is no sign of a continued negative trend in the upper stratosphere since 1998: instead there is a hint of an average positive trend of ~ 2% per decade in mid-latitudes and ~ 3% per decade in the tropics. The significance of these upward trends is investigated using different assumptions of the independence of the trend estimates found from different datasets. The averaged upward trends are significant if the trends derived from various datasets are assumed to be independent, but are generally not significant if the trends are not independent. This arises because many of the underlying measurement records are used in more than one merged dataset. At this point it is not possible to say which assumption is best. Including an estimate of the drift of the overall ozone observing system decreases the significance of the trends. The significance will become clearer as (i) more years are added to the observational record, (ii) further improvements are made to the historic ozone record (e.g. through algorithm development), and (iii) the data merging techniques are refined, particularly through a more rigorous treatment of uncertainties.

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Herman, J., R. Evans, A. Cede, N. Abuhassan, I. Petropavlovskikh and G. McConville, (2015), Comparison of ozone retrievals from the Pandora spectrometer system and Dobson spectrophotometer in Boulder, Colorado, Atmospheric Measurement Techniques Discussions, 8, 3, , 10.5194/amtd-8-3049-2015

Abstract

A comparison of retrieved total column ozone amounts TCO between the Pandora #34 spectrometer system and the Dobson #061 spectrophotometer from direct-sun observations was performed on the roof of the Boulder, Colorado NOAA building. This paper, part of an ongoing study, covers a one-year period starting on 17 December 2013. Both the standard Dobson and Pandora total column ozone TCO retrievals required a correction TCOcorr = TCO (1+C(T)) using the effective climatology derived ozone temperature T to remove a seasonal difference caused by using a fixed temperature in each retrieval algorithm. The respective corrections C(T) are CPandora = 0.00333(T−225) and CDobson = −0.0013 (T−226.7) per K. After the applied corrections removed the seasonal retrieval dependence on ozone temperature, TCO agreement between the instruments was within 1% for clear-sky conditions. For clear-sky observations, both co-located instruments tracked the day-to-day variation in total column ozone amounts with a correlation of r2 = 0.97 and an average offset of 1.1 ± 5.8 DU. In addition, the Pandora data showed 0.3% annual average agreement with satellite overpass data from AURA/OMI (Ozone Monitoring Instrument) and 1% annual average offset with Suomi-NPP/OMPS (Suomi National Polar-orbiting Partnership, the nadir viewing portion of the Ozone Mapper Profiler Suite).

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Hu, Lei, Stephen A. Montzka, John B. Miller, Aryln E. Andrews, Scott J. Lehman, Benjamin R. Miller, Kirk Thoning, Colm Sweeney, Huilin Chen, David S. Godwin, Kenneth Masarie, Lori Bruhwiler, Marc L. Fischer, Sebastien C. Biraud, Margaret S. Torn, Marikate Mountain, Thomas Nehrkorn, Janusz Eluszkiewicz, Scot Miller, Roland R. Draxler, Ariel F. Stein, Bradley D. Hall, James W. Elkins and Pieter P. Tans, (2015), U.S. emissions of HFC-134a derived for 2008-2012 from an extensive flask-air sampling network, Journal of Geophysical Research: Atmospheres, 120, 2, , 10.1002/2014JD022617

Abstract

U.S. national and regional emissions of HFC-134a are derived for 2008–2012 based on atmospheric observations from ground and aircraft sites across the U.S. and a newly developed regional inverse model. Synthetic data experiments were first conducted to optimize the model assimilation design and to assess model-data mismatch errors and prior flux error covariances computed using a maximum likelihood estimation technique. The synthetic data experiments also tested the sensitivity of derived national and regional emissions to a range of assumed prior emissions, with the goal of designing a system that was minimally reliant on the prior. We then explored the influence of additional sources of error in inversions with actual observations, such as those associated with background mole fractions and transport uncertainties. Estimated emissions of HFC-134a range from 52 to 61 Gg yr−1 for the contiguous U.S. during 2008–2012 for inversions using air transport from Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model driven by the 12 km resolution meteorogical data from North American Mesoscale Forecast System (NAM12) and all tested combinations of prior emissions and background mole fractions. Estimated emissions for 2008–2010 were 20% lower when specifying alternative transport from Stochastic Time-Inverted Lagrangian Transport (STILT) model driven by the Weather Research and Forecasting (WRF) meteorology. Our estimates (for HYSPLIT-NAM12) are consistent with annual emissions reported by U.S. Environmental Protection Agency for the full study interval. The results suggest a 10–20% drop in U.S. national HFC-134a emission in 2009 coincident with a reduction in transportation-related fossil fuel CO2 emissions, perhaps related to the economic recession. All inversions show seasonal variation in national HFC-134a emissions in all years, with summer emissions greater than winter emissions by 20–50%.

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Höpner, F., F. A.-M. Bender, A. M. L. Ekman, P. S. Praveen, C. Bosch, J. A. Ogren, A. Andersson, Ö. Gustafsson and V. Ramanathan, (2015), Vertical profiles of optical and microphysical particle properties above the northern Indian Ocean during CARDEX 2012, Atmospheric Chemistry and Physics Discussions, 15, 3, , 10.5194/acpd-15-3907-2015

Abstract

A detailed analysis of optical and microphysical properties of aerosol particles during the dry winter monsoon season above the northern Indian Ocean is presented. The Cloud Aerosol Radiative Forcing Experiment (CARDEX), conducted in February and March 2012 at the Maldives Climate Observatory on Hanimaadhoo island (MCOH) in the Republic of the Maldives, used autonomous unmanned aerial vehicles (AUAV) to perform vertical in-situ measurements of particle number concentration, particle number size distribution as well as particle absorption. These measurements were used together with surface-based Mini Micro Pulse Lidar (MiniMPL) observations and aerosol in-situ and off-line measurements to investigate the vertical distribution of aerosol particles.

Air masses were mainly advected over the Indian subcontinent and the Arabian Peninsula. Mean surface aerosol number concentration was 1717±604 cm−3 and the highest values were found in air masses from the Bay of Bengal and Indo–Gangetic Plain (2247±370 cm−3). Investigations of the free tropospheric air showed that elevated aerosol layers with up to 3 times higher aerosol number concentrations than at the surface occurred mainly during periods with air masses originating from the Bay of Bengal and the Indo–Gangetic Plain. Compared to the Indian Ocean Experiment (INDOEX) conducted in winter 1999, elevated aerosol layers with increased aerosol number concentration were observed more frequently in 2012. However, lower particle absorption at the surface (σabs(520 nm)=8.5±4.2 Wm−1) was found during CARDEX compared to INDOEX 1999.

By combining vertical in-situ measured particle absorption with scattering calculated with Mie-theory, layers with single-scattering albedo (SSA) values of specific source regions were derived and utilized to calculate vertical particle absorption profiles from MiniMPL profiles. SSA surface values for dry conditions were found to be 0.94±0.02 and 0.91±0.02 for air masses from the Arabian Sea (and Middle East countries) and India (and Bay of Bengal), respectively. Lidar-derived particle absorption profiles showed both a similar magnitude and structure as the in-situ profiles measured with the AUAV. However, primarily due to insufficient accuracy in the SSA estimates, the lidar-derived absorption profiles have large uncertainties and are generally weakly correlated to vertically in-situ measured particle absorption.

Furthermore, the mass absorption efficiency (MAE) for the northern Indian Ocean during the dry monsoon season was calculated to determine equivalent black carbon (EBC) concentrations from particle absorption measurements. A mean MAE of 11.6 and 6.9 m2 g−1 for 520 and 880 nm, respectively, was found, likely representing internally mixed BC containing particles. Lower MAE values for 880 nm were found for air masses originating from dust regions such as the Arabian Peninsula and western Asia (5.6 m2 g−1) or from closer source regions as southern India (4.3m2 g−1).

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Ogle, Stephen M, Kenneth Davis, Thomas Lauvaux, Andrew Schuh, Dan Cooley, Tristram O West, Linda S Heath, Natasha L Miles, Scott Richardson, F Jay Breidt, James E Smith, Jessica L McCarty, Kevin R Gurney, Pieter Tans and A Scott Denning, (2015), An approach for verifying biogenic greenhouse gas emissions inventories with atmospheric CO concentration data , Environmental Research Letters, 10, 3, , 10.1088/1748-9326/10/3/034012

Abstract

Verifying national greenhouse gas (GHG) emissions inventories is a critical step to ensure that reported emissions data to theUnited Nations Framework Convention on ClimateChange (UNFCCC) are accurate and representative of a country’s contribution toGHGconcentrations in the atmosphere. Furthermore, verifying biogenic fluxes provides a check on estimated emissions associated with managing lands for carbon sequestration and other activities, which often have large uncertainties.We report here on the challenges and results associatedwith a case study using atmosphericmeasurements ofCO2 concentrations and inversemodeling to verify nationally-reported biogenicCO2 emissions.The biogenicCO2emissions inventory was compiled for theMid-Continent region ofUnited States based onmethods and data used by theUS government for reporting to theUNFCCC, along with additional sources and sinks to produce a full carbon balance.The biogenicemissions inventory produced an estimated flux of −408 ± 136 TgCO2 for the entire study region, whichwas not statistically different fromthe biogenic flux of−478 ± 146 TgCO2 that was estimated using the atmosphericCO2 concentration data. At sub-regional scales, the spatial density of atmospheric observations did not appear sufficient to verify emissions in general.However, a difference between the inventory and inversion results was found in one isolated area ofWest-centralWisconsin.This part of the region is dominated by forestlands, suggesting that further investigationmay be warranted into the forestCstock or harvestedwood product data fromthis portion of the study area.The results suggest that observations of atmosphericCO2 concentration data and inversemodeling could be used to verify biogenic emissions, and providemore confidence in biogenicGHGemissions reporting to theUNFCCC.

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Petropavlovskikh, I., R. Evans, G. McConville, G. L. Manney and H. E. Rieder, (2015), The influence of the North Atlantic Oscillation and El Niño–Southern Oscillation on mean and extreme values of column ozone over the United States, Atmospheric Chemistry and Physics, 15, 3, , 10.5194/acp-15-1585-2015

Abstract

Continuous measurements of total ozone (by Dobson spectrophotometers) across the contiguous United States began in the early 1960s. Here, we analyze temporal and spatial variability and trends in total ozone from the five US sites with long-term records. While similar long-term ozone changes are detected at all five sites, we find differences in the patterns of ozone variability on shorter timescales. In addition to standard evaluation techniques, STL-decomposition methods (Seasonal Trend decomposition of time series based on LOESS (LOcally wEighted Scatterplot Smoothing)) are used to address temporal variability and "fingerprints" of dynamical features in the Dobson data. Methods from statistical extreme value theory (EVT) are used to characterize days with high and low total ozone (termed EHOs and ELOs, respectively) at each station and to analyze temporal changes in the frequency of ozone extremes and their relationship to dynamical features such as the North Atlantic Oscillation (NAO) and El Niño–Southern Oscillation. A comparison of the fingerprints detected in the frequency distribution of the extremes with those for standard metrics (i.e., the mean) shows that more fingerprints are found for the extremes, particularly for the positive phase of the NAO, at all five US monitoring sites. Results from the STL decomposition support the findings of the EVT analysis. Finally, we analyze the relative influence of low- and high-ozone events on seasonal mean column ozone at each station. The results show that the influence of ELOs and EHOs on seasonal mean column ozone can be as much as ±5 %, about as large as the overall long-term decadal ozone trends.

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Turnbull, Jocelyn C., Colm Sweeney, Anna Karion, Timothy Newberger, Scott J. Lehman, Pieter P. Tans, Kenneth J. Davis, Thomas Lauvaux, Natasha L. Miles, Scott J. Richardson, Maria Obiminda Cambaliza, Paul B. Shepson, Kevin Gurney, Risa Patarasuk and Igor Razlivanov, (2015), Toward quantification and source sector identification of fossil fuel CO emissions from an urban area: Results from the INFLUX experiment , Journal of Geophysical Research: Atmospheres, 120, 1, , 10.1002/2014JD022555

Abstract

The Indianapolis Flux Experiment (INFLUX) aims to develop and assess methods for quantifying urban greenhouse gas emissions. Here we use CO2, 14CO2, and CO measurements from tall towers around Indianapolis, USA, to determine urban total CO2, the fossil fuel derived CO2 component (CO2ff), and CO enhancements relative to background measurements. When a local background directly upwind of the urban area is used, the wintertime total CO2 enhancement over Indianapolis can be entirely explained by urban CO2ff emissions. Conversely, when a continental background is used, CO2ff enhancements are larger and account for only half the total CO2 enhancement, effectively representing the combined CO2ff enhancement from Indianapolis and the wider region. In summer, we find that diurnal variability in both background CO2 mole fraction and covarying vertical mixing makes it difficult to use a simple upwind-downwind difference for a reliable determination of total CO2 urban enhancement. We use characteristic CO2ff source sector CO:CO2ff emission ratios to examine the contribution of the CO2ff source sectors to total CO2ff emissions. This method is strongly sensitive to the mobile sector, which produces most CO. We show that the inventory-based emission product (“bottom up”) and atmospheric observations (“top down”) can be directly compared throughout the diurnal cycle using this ratio method. For Indianapolis, the top-down observations are consistent with the bottom-up Hestia data product emission sector patterns for most of the diurnal cycle but disagree during the nighttime hours. Further examination of both the top-down and bottom-up assumptions is needed to assess the exact cause of the discrepancy.

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Turnbull, Jocelyn C., Colm Sweeney, Anna Karion, Timothy Newberger, Scott J. Lehman, Pieter P. Tans, Kenneth J. Davis, Thomas Lauvaux, Natasha L. Miles, Scott J. Richardson, Maria Obiminda Cambaliza, Paul B. Shepson, Kevin Gurney, Risa Patarasuk and Igor Razlivanov, (2015), Toward quantification and source sector identification of fossil fuel C emissions from an urban area: Results from the INFLUX experiment , Journal of Geophysical Research: Atmospheres, 120, 1, , 10.1002/2014jd022555

Abstract

The Indianapolis Flux Experiment (INFLUX) aims to develop and assess methods for quantifying urban greenhouse gas emissions. Here we use CO2, 14CO2, and CO measurements from tall towers around Indianapolis, USA, to determine urban total CO2, the fossil fuel derived CO2 component (CO2ff), and CO enhancements relative to background measurements. When a local background directly upwind of the urban area is used, the wintertime total CO2 enhancement over Indianapolis can be entirely explained by urban CO2ff emissions. Conversely, when a continental background is used, CO2ff enhancements are larger and account for only half the total CO2 enhancement, effectively representing the combined CO2ff enhancement from Indianapolis and the wider region. In summer, we find that diurnal variability in both background CO2 mole fraction and covarying vertical mixing makes it difficult to use a simple upwind-downwind difference for a reliable determination of total CO2 urban enhancement. We use characteristic CO2ff source sector CO:CO2ff emission ratios to examine the contribution of the CO2ff source sectors to total CO2ff emissions. This method is strongly sensitive to the mobile sector, which produces most CO. We show that the inventory-based emission product (“bottom up”) and atmospheric observations (“top down”) can be directly compared throughout the diurnal cycle using this ratio method. For Indianapolis, the top-down observations are consistent with the bottom-up Hestia data product emission sector patterns for most of the diurnal cycle but disagree during the nighttime hours. Further examination of both the top-down and bottom-up assumptions is needed to assess the exact cause of the discrepancy.

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Zhang, L., J. Y. Sun, X. J. Shen, Y. M. Zhang, H. C. Che, Q. L. Ma, Y. W. Zhang, X. Y. Zhang and J. A. Ogren, (2015), Observations of relative humidity effects on aerosol light scattering in the Yangtze River Delta of China, Atmospheric Chemistry and Physics Discussions, 15, 2, , 10.5194/acpd-15-2853-2015

Abstract

Scattering of solar radiation by aerosol particles is highly dependent on relative humidity (RH) as hygroscopic particles take up water with increasing RH. To achieve a better understanding of the effect of aerosol hygroscopic growth on light scattering properties and radiative forcing, a field campaign was carried out in the Yangtze River Delta of China in March 2013. During the observation period, the mean and standard deviation of enhancement factors at RH=85% for the scattering coefficient (f(85%)), backscattering coefficient (fb(85%)) and hemispheric backscatter fraction (fβ(85%)) were 1.58 ± 0.12, 1.25 ± 0.07 and 0.79 ± 0.04, respectively, i.e. aerosol scattering coefficient and backscattering coefficient increased by 58 and 25% as the RH increased from 40 to 85%. Meanwhile, the aerosol hemispheric backscatter fraction decreased by 21%. The relative amount of organic matter (OM) and inorganics in PM1 was found to be a main factor determining the magnitude of f(RH), the highest values of f(RH) corresponded to the aerosols with a small fraction of organic matter (OM), and vice versa. The relative amount of NO3 in fine particles was strongly correlated to f(85%), which suggests NO3 played a vital role in aerosol hygroscopic growth during this study. The mass percentage of nitrate also had a close relation to the curvature of humidograms, namely, the higher the nitrate concentration is, the straighter the humidogram will be. Air masses that arrived at LinAn in March can be classified into northerly-polluted, locally-polluted and dust-influenced types, the scattering enhancement factors at 85% RH were 1.52 ± 0.10, 1.64 ± 0.09 and 1.48 ± 0.05, respectively. The sensitivity of the aerosol radiative forcing to f(RH) at the measured mean ambient RH 67% for various aerosol types was also estimated. The direct radiative forcing increased by 11.8, 19.5, and 10.5%, respectively, for locally-polluted, northerly-polluted and dust-influenced aerosols due to aerosol hygroscopic growth at LinAn in March 2013.

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