Black carbon, light-absorbing organic carbon (often called "brown carbon") and mineral dust arethe major light-absorbing aerosols. Currently the sources and formation of brown carbon aerosolin particular are not well understood. In this study we estimated the amount oflight–absorbing organic carbon and black carbon from AERONET measurements. We find that thecolumnar absorbing organic carbon (brown carbon) levelsin biomass burning regions of South America and Africa are relatively high (about 15–20 mg mduring biomass burning season), while theconcentrations are significantly lower in urban areas in US and Europe. However, we estimated significantabsorbing organic carbon amounts from the data of megacities of newly industrializedcountries, particularly in India and China, showing also clear seasonality with peak valuesup to 30–35 mg m during the coldest season, likely caused by the coal and biofuel burning used for heating.We also compared our retrievals with the modeled organic carbon by theglobal Oslo CTM for several sites. Model values are higher in biomass burning regions thanAERONET-based retrievals, while the opposite is true in urban areas in India and China.
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