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Light absorbing organic carbon from prescribed and laboratory biomass burning and gasoline vehicle emissions
Xie, M., M. Hays, AND A. Holder. Light absorbing organic carbon from prescribed and laboratory biomass burning and gasoline vehicle emissions. Scientific Reports. Nature Publishing Group, London, Uk, , online, (2017).
Carbonaceous aerosols are ubiquitous in the atmosphere and can directly affect public health and the Earth’s climate by absorbing and scattering incoming solar radiation. This study attempts to address limitations in understanding brown carbon (BrC) as it relates to primary source combustion emissions. While biomass burning aerosols are a significant influence on the atmospheric BrC budget, we find that motor vehicles are also a potential BrC source that should not be ignored.
The light absorption of carbonaceous aerosols plays an important role in the atmospheric radiation balance. Light-absorbing organic carbon (OC), also called brown carbon (BrC), from laboratory-based biomass burning (BB) has been studied intensively to understand the contribution of BB aerosol to radiative forcing — a measure of climate change influence. However, very few measurements have been conducted on field burns and even fewer measurements have been done on BrC from other combustion sources like motor vehicle emissions. In this work, we examined the light absorption of methanol-extractable OC from prescribed and laboratory BB and gasoline vehicle emissions based on spectrophotometric measurements. The light absorption by the methanol extracts had a strong wavelength dependence for both BB and gasoline vehicle emissions. The mass absorption coefficients at 365 nm (MAC365, m2 g-1C) – a measure of BrC – were significantly correlated (p < 0.05) with the ratios of elemental carbon (EC) to OC for BB with the identical fuel, while no significant correlation could be observed if we pooled different fuel samples, indicating that both burn conditions and fuel types impact the characteristics of BrC resulting from BB. The average MAC365 of all gasoline vehicle emission samples is 0.61 ± 0.76 m2 g-1C, the same magnitude as all BB samples (1.27 ± 0.76 m2 g-1C). These results suggested that in addition to BB, gasoline vehicle emissions might also be an important BrC source in urban areas.