AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Enhanced Light Absorption by Internally Mixed Atmospheric Black Carbon in Europe
SHANG LIU, Allison Aiken, Kyle Gorkowski, Manvendra Dubey, Scott Herndon, Leah Williams, Paola Massoli, Edward Fortner, Andrew Freedman, Douglas Worsnop, Nga Lee Ng, Claudia Mohr, Felipe Lopez-Hilfiker, Joel Thornton, James Allan, Christopher Cappa, Los Alamos National Lab
Abstract Number: 160 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Solar absorption by black carbon (BC) particles from fossil fuel and biomass combustion could be responsible for the second largest radiative forcing after carbon dioxide. Control of the short-lived BC would slow climate warming immediately and improve air quality. BC’s large radiative forcing results from model formulation that as BC ages it mixes with other species, a process that enhances its specific light absorption significantly consistent with laboratory studies. However, recent field observations show negligible absorption enhancement calling into question the large role of BC in climate forcing. To address this discrepancy, optical and chemical properties of ambient particles were measured continuously during 15 January to 15 February 2012 at Detling, UK as part of the ClearfLo (Clean Air for London) campaign. A three-laser photoacoustic spectrometer (PASS-3) was used to quantify the absorption and scattering coefficients of submicron particles. By evaporating the volatile components using a thermal denuder that operated that 250 Celsius degree, the absorption enhancement was directly measured. We find significant absorption enhancement (40%) due to the internal mixing by BC and other non-absorbing components, which is in contrast to previous measurements. In addition, the enhancement factor increases with photochemical aging and is consistent with theoretical predictions constrained by the in situ measurements. Furthermore, we find for the first time that the non-volatile, light-absorbing organic (brown) carbon (BrC) accounts for 22% of the absorption at 405 nm wavelength. The non-volatile BrC correlates with the oxygenated organic aerosol factor retrieved from the positive matrix factorization analysis, suggesting its secondary formation in the atmosphere. Our field results support parameterizations of enhanced light absorption by BC in climate models and show that diverse regimes need to be sampled to improve quantification.