Light-absorbing carbonaceous aerosols at Detling in winter 2012: evidence of enhanced absorption
Authors
Shang Liu — Los Alamos National Laboratory
Allison C Aiken — Los Alamos National Laboratory
Kyle Gorkowski — Los Alamos National Laboratory
Manvendra K. Dubey — Los Alamos National Laboratory
Scott C Herndon — Aerodyne Research, Inc.
Leah R Williams — Aerodyne Research Inc
Paola Massoli — Aerodyne Research, Inc.
Ed Fortner — Aerodyne Research, Inc.
Andrew Freedman — Aerodyne Research, Inc.
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Nga Lee Ng — Georgia Institute of Technology
Claudia Mohr — University of Washington
Felipe Lopez-Hilfiker — University of Washington
Joel Thornton — University of Washington
Description
Atmospheric light-absorbing carbonaceous aerosols directly affect the Earth’s radiation balance by absorbing solar radiation. A recent assessment finds the anthropogenic mean radiative forcing by black carbon (BC) to be 1.1 W m-2 (Bond et al. 2013), suggesting that BC is second only to CO2 in warming the atmosphere. However, the magnitude of this forcing is associated with large uncertainties (0.17–2.1 W m-2) due to the complicated interaction between BC, organic carbon, and other atmospheric species and processes. For example, laboratory studies show that organic coatings on BC can enhance light absorption (Cross et al. 2009), but field observations show no enhancement in aged urban emissions (Cappa et al. 2012). Furthermore, carbonaceous aerosols from biomass burning show significant absorption at short wavelengths that was attributed to brown carbon (Lack et al. 2012). In order to elucidate these complex processes that control the variability in carbonaceous aerosols, optical and chemical properties of ambient particles were measured continuously from January 18 to February 15, 2012, at Detling, UK, during 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. The campaign average absorption coefficients were 10.1, 8.3, and 4.4 Mm-1 at 405 nm, 532 nm, and 781 nm wavelengths, respectively. The absorption coefficients correlated to the hydrocarbon-like organic aerosol component and the biomass burning organic aerosol component that were extracted from the aerosol mass spectrometer measurements, suggesting the contribution of primary (likely vehicular exhaust) and biomass burning sources to the light-absorbing carbon particles at Detling. In addition, the BC absorption enhancement was measured by comparing the absorption of ambient particles to the absorption of particles after heating in a thermal denuder (TD). The enhancement factor ranged from 1.1 to 1.5, with higher TD temperatures resulting in greater enhancement factors. By comparing the enhancement factor from this study to other field measurements, the results suggest that the absorption properties of ambient particles may vary greatly. This study reinforces the need for more field measurements to constrain the absorption parameters used in climate models.
