US EPA

Organic aerosols (OA) in the atmosphere affect Earth’s energy budget by not only scattering but also absorbing solar radiation due to the presence of the so-called “brown carbon” (BrC) component. However, the absorptivities of OA are not or poorly represented in current climate models. In this study, we provide a method to address the BrC issue at the emission inventory level. We review available measurements of the light-absorbing primary OA (POA), and quantify the wavelength-dependent imaginary refractive indices (kOA, the fundamental optical parameter determining the particle’s absorptivity) and their uncertainties of the bulk POA emitted from biomass/biofuel, lignite, propane, and oil combustion sources. In particular, we parameterize the kOA of biomass/biofuel combustion sources as a function of the black carbon (BC)-to-OA ratio, implying that the absorptive properties of POA depend strongly on burning conditions. The derived fuel-type-based kOA profiles are incorporated into a global carbonaceous aerosol emission inventory and the integrated kOA values of sectoral and total POA emissions are presented. Results of a simple radiative transfer model show that the POA absorptivity warms the atmosphere significantly and leads to ~27% reduction in the amount of the negative global average POA radiative forcing compared to results using the non-absorbing assumption.

Article assimilates available information on the optical properties of organic aerosols and estimates absorption of solar radiation by brown carbon.

Lu, Z., D. Streets, E. Winijkul, F. Yan, Y. Chen, T. Bond, Y. Feng, M. Dubey, S. Liu, J. Pinto, AND G. Carmichael. Light Absorption Properties and Radiative Effects of Primary Organic Aerosol Emissions. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 49(8):4868-4877, (2015).