The Chemical Context of ATom-1: Insights from Satellite Observations and Modeling

The GEOS-5 chemical forecasts performed for the ATom mission show considerable skill in predicting the observed CO distribution and the timing of CO enhancements. We present a comparison of the GEOS-5 CO analyses to the ATom CO measurements from the QCLS instrument. We then use the GEOS-5 tagged CO tracers to assess the source contributions to the ATom flights and how these differ by region and altitude. We find that the largest contribution usually comes from non-biomass burning sources with the exception of the tropical Atlantic, where African biomass burning makes a large contribution to the CO concentration. Biomass burning also leads to plumes of enhanced CO in the Arctic. Since one of the goals of ATom is to provide a chemical climatology of the remote atmosphere, we examine whether August 2016, the month when ATom-1 occurred, is a typical or anomalous August using CO observations from MOPITT and aerosol optical thickness from MODIS. This analysis shows that CO and AOT for August of 2016 were below the multi-year median for many of the regions sampled by the ATom flights, suggesting that August, 2016 concentrations were anomalously low compared to previous years.