Inter-annual variation in NO2 over the United States

Nitrogen dioxide (NO2) plays a key part in atmospheric photochemical processes, including catalytic production of ozone. Emissions of nitrogen oxides also result in nitric acid deposition and increase radiative forcing effects due to the absorption of downward propagating visible light. Recent studies based on GOME and SCIAMACHY satellites observations have shown that NO2 concentrations over the United States have been decreasing by 1-2% per year [Richter et al., 2005; Ghude et al., 2009]. To overcome the detection and sensitivity limitations of these satellites, an improved satellite (Ozone Monitoring Instrument - OMI) was launched in 2004 on the Aura platform as a part of the A-train constellation of satellites. In this study we are using four years (2005-08) of OMI observations to study short-term trends by assessing the spatial and temporal patterns of variation in NO2 over the United States. The focus of this study is over the subdomain 30N-50N, 70W-125W. Our initial analysis suggests that NO2 over the eastern as well as western United States continues to decrease from 2005 through 2008; however, the rate of decrease is higher over the eastern United States. This analysis of Inter-annual variation in NO2 using OMI observations will be used to compare the existing results from GOME and SCIAMACHY satellites. Detail results will be presented in the AGU meeting. References: Richter et al., Increase in tropospheric nitrogen dioxide over China observed from space, Nature, volume 437, doi:10.1038/nature04092, 2005. Ghude et al., Satellite derived trends in NO2 over the major global hotspot regions during the past decade and their inter-comparison, Environmental Pollution, volume 157 Page 1873-1878, 2009.