Research Program Area: Climate Change
Black carbon (BC) absorbs light and gives off heat, and is now recognized as a significant contributor to global warming. More recently, "brown carbon" (BrC-light-absorbing organic carbon) has also attracted interest as a possible cause of climate change. Previous global model simulations suggest that the strongly absorbing BrC could contribute up to +0.25 watt per square meter (W/m 2) or about 19 percent of the absorption by anthropogenic aerosols. Through a multi-institution collaboration, this study identified and characterized the contribution of BrC to climate forcing in California. Areas with significant residential burning in the San Joaquin Valley (Fresno) and with photochemical aerosol formation in the South Coast Air Basin (Fontana) were investigated to characterize their different mixes of emission sources and seasonality. The quantitative analysis of these results separated and characterized BrC, providing important quantification of emissions-specific particle absorption properties for modeling climate forcing. The regional climate modeling result indicates that top of atmosphere radiative forcing increased by ~0.28 watt per square meter (W/m2) due to BrC absorption. The results, averaged over one year (2014-2015), of the global through regional nested simulations indicate that absorption by BrC in aerosol particles and clouds increased domain-averaged near-surface air temperatures by ~0.018 degree Kelvin (K), whereas absorption by organic matter (OM) plus BC increased it by ~0.17 K, suggesting a warming by BC of ~0.15 K. Overall, climate impacts from BC emitted from fossil fuel sources are predicted to dominate over the effects of BrC. The results of this project provide valuable insights regarding the fundamental processes that govern BrC formation and its evolution in the atmosphere, and help us determine the potential climate benefits of mitigating emission sources of BrC in California.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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