Evaluation of Nitrogen Oxides Emissions over California in Spring 2010

Nitrogen Dioxide (NO2) belongs to the regulated 'six common air pollutants' by the US Environmental Protection Agency (EPA), due to its adverse impacts on the human respiratory system. It is also often used as the indicator for the highly reactive group of gases nitrogen oxides (NOx), the important ozone precursors. We model California air quality during the NOAA CalNex field campaign period in May 2010 using the STEM chemical transport model on a 12 km horizontal resolution grid. Three different anthropogenic emission inventories were used in the simulations: 1) 2005 National Emission Inventory (NEI 2005); 2) daily-varying emissions recently developed by California Air Resources Board (CARB); and 3) NEI 2008. The model-simulated NO2 were compared with the measurements by aircraft and the Ozone Monitoring Instrument (OMI) on board of the Aura satellite. We further conduct NO2 emission inversion using the four-dimensional variational approach [Chai et al., 2009] and the OMI NO2 column data. The inversion generated grid-based emission scaling factors on the NEI 2005, and the resulting NOx fields were 'cross-validated' by comparing with aircraft NO2 measurements. The adjustment on original emissions was then compared with 1) the CARB-documented NOx emission trends, 2) other 'top-down' estimates of California NOx emissions using aircraft measurements [Brioude et al., 2013], and 3) the space-observed NO2 column trends [Russell et al., 2012]. References Chai, T., Carmichael, G., Tang, Y., and Sandu, A., Regional NO2 emission inversion through four-dimensional variational approach using Sciamachy tropospheric column observations, Atmos. Environ., 43, 5046-5055, 2009. Brioude, J., Angevine, W. M., Ahmadov, R., Kim, S.-W., Evan, S., McKeen, S. A., Hsie, E.-Y., Frost, G. J., Neuman, J. A., Pollack, I. B., Peischl, J., Ryerson, T. B., Holloway, J., Brown, S. S., Nowak, J. B., Roberts, J. M., Wofsy, S. C., Santoni, G. W., Oda, T., and Trainer, M.: Top-down estimate of surface flux in the Los Angeles Basin using a mesoscale inverse modeling technique: assessing anthropogenic emissions of CO, NOx and CO2 and their impacts, Atmos. Chem. Phys., 13, 3661-3677, doi:10.5194/acp-13-3661-2013, 2013. Russell, A. R., Valin, L. C., and Cohen, R. C.: Trends in OMI NO2 observations over the United States: effects of emission control technology and the economic recession, Atmos. Chem. Phys., 12, 12197-12209, doi: 10.5194/acp-12-12197-2012, 2012.