Abstract
Abstract. Black carbon, light-absorbing organic carbon (often called "brown carbon") and mineral dust are the major light-absorbing aerosols. Currently the sources and formation of brown carbon aerosol in particular are not well understood. In this study we estimated the amount of light–absorbing organic carbon and black carbon from AERONET measurements. We find that the columnar absorbing organic carbon (brown carbon) levels in biomass burning regions of South America and Africa are relatively high (about 15–20 mg m−2 during biomass burning season), while the concentrations are significantly lower in urban areas in US and Europe. However, we estimated significant absorbing organic carbon amounts from the data of megacities of newly industrialized countries, particularly in India and China, showing also clear seasonality with peak values up to 30–35 mg m−2 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 the global Oslo CTM for several sites. Model values are higher in biomass burning regions than AERONET-based retrievals, while the opposite is true in urban areas in India and China.
Highlights
Aerosols affect both directly and indirectly the Earth’s climate
We find that the columnar absorbing organic carbon levels in biomass burning regions of South America and Africa are relatively high, while the concentrations are significantly lower in urban areas in US and Europe
In our study reported the approach of Schuster et al (2005) was extended and refined to assess whether relevant information about the relative role of organic carbon (OC) absorption can be inferred from AErosol RObotic NETwork (AERONET) measurements
Summary
Aerosols affect both directly and indirectly the Earth’s climate. Currently, aerosol forcing is the largest uncertainty in assessing the anthropogenic climate change (IPCC, 2007). Russell et al (2010) assessed the usefulness of AERONET-retrieved single scattering albedo (SSA), aerosol absorption optical depth (AAOD), and absorption Angstrom exponent (AAE) as indicators of aerosol composition, including black carbon, organic matter, and mineral dust. Sato et al (2003) focused on OC in addition to BC, but they still constrained the modeling by aerosol absorption optical depth from AERONET, not attempting to retrieve directly OC concentrations from AERONET data. They did not, estimate the composition from AERONET measurements. Significant absorbing OC amounts were estimated from the data of megacities of newly industrialized countries, in India and China during coldest season
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