Observations of July surface ozone from EPA's CASTNET network show negative trends for 1990-2010 over the eastern United States, and some positive trends over the western U.S. (left panel). A GMI model simulation with time-dependent emissions captures this East-West gradient in the ozone trends (center panel). The negative trends are absent in an identical model simulation with emissions held fixed at year 2000 levels (right panel), indicating that decreases in ozone precursor emissions are responsible for the declining summertime surface ozone over the eastern U.S. More information is available in Strode et al., JGR, 2015.
Left panel: Observations of the CO column from the MOPITT instrument (black line) show a negative trend over the eastern United States. The GMI RefC1-SD simulation (red line), conducted as part of the CCMI model intercomparison project, captures this decline in CO concentrations. In contrast, a GMI simulation with fixed emissions (blue line) does not capture the decrease, illustrating the impact of declining regional CO emissions on the CO column. Model simulations are convolved with the MOPITT a priori (gray line) and averaging kernels for comparison to MOPITT data. Right panel: The inclusion of time-dependent emissions improves the ability of the GMI simulation to capture the de-seasonalized monthly anomalies in the MOPITT CO column over the eastern U.S., particularly the peaks between 2002 and 2004, and the dip in 2008-2009. More information is available in Strode et al., ACP, 2016.