Evaluation and Interpretation of AEROCOM Model Absorptive Aerosol Using Satellite Retrievals of AAOD and SSA

Absorbing aerosol has the capacity to warm the climate, but the amount of warming is highly uncertain. AAOD (Absorptive Aeorosl Optical Depth) is an optical measure of the abundance of this absorbing aerosol, comprising mineral dust, black and brown carbon and can be retrieved from satellite measurements providing an almost global view on absorbing aerosol. In this study we evaluate AEROCOM models with satellite observations of AAOD and SSA (Single Scattering Albedo) and interpret the discrepancies. We show that models tend to underestimate global AAOD, in particular over ocean. Over land, the situation is more mixed with known hotspots (e.g. the Amazon) yielding either too small or too large AAOD depending on the model. In addition we show that the AEROCOM ensemble shows strong correlations between emissions (of either black carbon or dust) and AAOD over individual source regions. In combination with the satellite observations of AAOD, this leads to emergent constraints on emissions of absorbing aerosol from e.g. the Amazon, the Savannah and the Sahara. Similar constraints on life-times will also be discussed. This study was conducted using four satellite datasets of AAOD and SSA, based on measurements from OMI on Aura, POLDER on PARASOL or a combination of MODIS (on Aqua), CALIOP (on CALIPSO) and OMI (on Aura). As part of this study we conducted an in-depth evaluation of these satellite datasets using AERONET Inversion data. We show that notwithstanding retrieval biases and limited sampling, these satellite datasets yield consistent results when evaluating models.