An A-train and model perspective on the vertical distribution of aerosols and CO in the Northern Hemisphere

We use A-train satellite observations of aerosols and carbon monoxide (CO) (CALIOP, MODIS, and TES) with GEOS-Chem model simulations to analyze long range transport in the Northern Hemisphere over 3 years (December 2006-November 2009), with a focus on the vertical distribution of pollutants. GEOS-Chem underestimates TES observations of CO in all seasons (<25%) except winter. MODIS and GEOS-Chem aerosol optical depths (AOD) are both generally biased high in comparison with CALIOP (0.042 over land/0.036 over ocean and 0.016 over land/-0.0071 over ocean, respectively; for spring seasons, but similar results for all seasons). Comparisons between GEOS-Chem and CALIOP improve when the CALIOP detection limits are accounted for, and the bias over land in particular is reduced (0.010). However, we find that GEOS-Chem with applied detection limits still overestimates the CALIOP observations of aerosol extinction over sources in Asia and Europe, but underestimates in marine environments and over North America in spring and summer. Vertical cross-sections indicate that GEOS-Chem may be removing aerosol too efficiently in the boundary layer in addition to underestimating marine aerosol sources. We show that mimicking the single aerosol type per layer retrieval of CALIOP with GEOS-Chem could lower simulated AOD by 10-30% at midlatitudes. TES and CALIOP observations confirm that while CO is efficiently transported aloft (only 12% of the CO column is within the planetary boundary layer (PBL) on average), the efficient removal of aerosol limits export and subsequent transport with over 50% of observed aerosol extinction occurring within the PBL.