Vertical Profiles of Aerosol Mass, Number, and Cloud Droplet Number Concentrations: Comparisons of GEOS‐Chem‐APM Simulations With ATom Airborne Measurements and CloudSat Retrievals

Abstract

AbstractA better understanding of vertical distributions of aerosol and cloud droplet number concentrations is important for the study of aerosol‐cloud interaction which is one of the key uncertainties in climate change projection. In this study, we compared the aerosol mass and number concentrations simulated by a size‐resolved advanced particle microphysics (APM) package coupled with a global 3‐D chemical transport model (GEOS‐Chem) with the NASA’s Atmospheric Tomography Mission (ATom) measurements at the Pacific Ocean and the Atlantic Ocean during ATom‐1 and ATom‐2 campaign periods. Generally, the model captured the spatial pattern and seasonal variation of aircraft observed aerosol mass and number concentrations. The model simulated cloud droplet number concentrations (CDNC) were compared with CloudSat retrievals whose orbits were nearby ATom's flight tracks on the same days. Correlation coefficients of simulated and retrieved CDNC at ATom‐1 Pacific Ocean, ATom‐1 Atlantic Ocean, ATom‐2 Pacific Ocean, and ATom‐2 Atlantic Ocean are 0.83, 0.97, 0.87, and 0.73, respectively. Both satellite retrievals and model simulations indicated that the averaged values of CDNC at the Pacific Ocean and the Atlantic Ocean during ATom‐1 and ATom‐2 periods decreased with altitudes. The ratio of CDNC in the lower troposphere (1,000–800 hPa) to those in the middle troposphere (600–400 hPa) was 1.9 (1.6–2.3) based on CloudSat retrievals and 2.2 (1.2–3.0) based on the model simulations. Model analysis indicated that secondary particles dominate CDNC in the atmosphere and primary organic aerosols have important contributions to CDNC, especially at the Atlantic Ocean during ATom‐1.