UC Irvine

The black carbon (BC) aerosol is a major climate-forcing agent. Its high capacity for light absorption and its role in key atmospheric processes lead to a range of impacts in the Earth System. Black carbon is also a major constituent of fine particulate matter (PM2.5) and is linked to a broad array of adverse health effects. Increased fossil fuel and biomass burning have contributed to a significantly larger input of BC to the atmosphere, but the lack of measurement constraints on BC have limited the development of mitigation strategies. My thesis aims to improve our understanding of BC emission sources by utilizing radiocarbon (14C) to quantify the fossil fuel and biomass combustion contribution to the BC emissions and their spatiotemporal variations.

I developed a method allowing me to efficiently separate and collect BC and organic carbon (OC) from PM2.5 and perform 14C measurements of these ultra-small samples with high accuracy and low carbon blanks. I used this method to measure the isotopic composition of BC and OC emitted from boreal forest wildfires and showed that fires were the dominant contributor to the variability in carbonaceous aerosols in Alaska during the summer. The Δ14C of BC from boreal fires was 131 ± 52‰ in 2013, corresponding to a mean fuel age of 20 years. and consistent with a depth of burning in organic soil horizons of 20 cm (range: 8–47 cm). To explore urban emission of BC, I measured fossil and biomass contributions to BC and OC in Salt Lake City, Utah. Combined with information of endmember 14C composition, my results indicated that fossil fuels were the dominant source during winter, contributing on average 88% (range: 80–98%) of BC and 58% (range: 48–69%) of OC.

Combining innovative techniques, extensive field measurements and detailed laboratory analysis, I explored both the natural and anthropogenic sources of BC. By providing BC aerosol direct measurements and isotopic characterization, this work contributes to a growing body of knowledge on BC source contribution and dynamics necessary for the development of successful strategies for mitigating BC’s effects on the Earth System and human health.