Are Satellite-Derived Aerosol Types Useful for Evaluating Global Chemistry Transport Models?

Inter-model diversity in estimates of Radiative Forcing due to aerosol-radiation interactions (RFari) is caused by different methods for estimating aerosol properties in the models (e.g., mass, lifetime, and composition), and to a lesser extent by surface and cloud albedos, water vapor absorption, and radiative transfer schemes [Randles et al., 2013; Myhre et al., 2013; Stier at al., 2013]. In particular, RFari for individual aerosol species are less certain than the total RFari [Boucher et al., 2013]. Global coverage of satellite-derived aerosol chemical speciation would undoubtedly greatly improve Chemical Transport Models (CTMs), but does not currently exist. Instead, we infer qualitative aerosol types (i.e., urban industrial for two different types of economies, pure and polluted dust, dark and white biomass burning smoke and maritime aerosols) from A-Train’s POLDER (Polarization and Directionality of Earth’s Reflectances) passive satellite optical retrievals [Hasekamp et al., 2011]. We use POLDER retrievals of particle size, spectral light absorption and a pre-specified clustering method described in Russell et al. [2014]. In order to use these aerosol types successfully to evaluate CTMs, we need to characterize the chemical speciation of remotely sensed aerosol types. To this end, we translate aerosol type identifications into an averaged distribution of different chemical components (e.g., organic, sulfate, nitrate, ammonium, soot, mineral) by using a suite of airborne instruments on board the DC-8 aircraft (i.e., TSIneph, PSAP, DASH-SP, PI-Neph, PALMS, HR-ToF-AMS, SP2) during the 2013 SEAC4RS (Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys) field experiment over the United States. Finally, we compare POLDER-derived aerosol types, the optical-to-chemical translation defined above, airborne chemical measurements and GEOS-Chem CTM estimates of black and organic carbon, sulfate, sea salt and dust during the 2006 INTEX-B (Intercontinental Chemical Transport Experiment Phase B) field experiment. These observations and model estimates from a detailed multi-sensor, multi-platform case study are used to discuss the usefulness of optically-derived aerosol types from satellite in the evaluation of global CTMs