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Air quality measurements and emissions within the Los Angeles Basin during CalNex-2010 from a regional model perspective

Speaker: Stu McKeen, NOAA ESRL CSD & CU CIRES

When: Wednesday, December 4, 2013, 3:30 p.m. Mountain Time
Location: Room 2A305, DSRC (NOAA Building), 325 Broadway, Boulder
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Emission inventories are a key component of air quality models designed for regulatory and research applications, yet only within the last year have "reliable" emission inventories become available for the summer of 2010. High quality observations of dozens of gas-phase species during CalNex-2010 provide a valuable basis for evaluation of these inventories, but deriving flux estimates from atmospheric measurements is not always practical or possible. Regional-scale photochemical/transport models have proven in the past to be useful tools for relating emissions to expected mixing ratios, and assessing their importance to secondary pollutants such as ozone and particulate matter. In the first half of this talk results from the WRF/Chem community model are compared to CalNex observations to evaluate recent bottom-up emission estimates from the U.S. EPA and California Air Resources Board, as well as top-down estimates based on linear inversion of NOAA P-3 aircraft data. Comparisons with aircraft data are also used to critically evaluate additional features of the model system, including impacts of weekend emission reductions, spatial variability of pollutants, photolysis rates, and basic meteorology. The second part of the talk deals exclusively with comparisons between observations collected aboard the NOAA P-3 aircraft and those collected at the surface super-site located on the CalTech campus. The NOAA aircraft flew within 15 km of the Caltech site twenty-seven times at altitudes from 100 m to ~850 m AGL while the surface site was operational. When correlations of long-lived species (CO, NOy, CO2 and black carbon) between the two platforms are compared, nine of the aircraft overpasses exhibit overlapping correlations, implying that both platforms sampled air originating from the same source region and diluting with a common background. Despite the consistency with long-lived species, constituents with photochemical sources or lifetimes that depend directly on odd-hydrogen chemistry exhibit distinct differences in correlations between the two platforms, with the surface site appearing to have faster photochemical processing and higher oxidation rates. Possible reasons and implications for these discrepancies will be discussed.