3 research outputs found
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Source signatures from combined isotopic analyses of PM2.5 carbonaceous and nitrogen aerosols at the peri-urban Taehwa Research Forest, South Korea in summer and fall.
Isotopes are essential tools to apportion major sources of aerosols. We measured the radiocarbon, stable carbon, and stable nitrogen isotopic composition of PM2.5 at Taehwa Research Forest (TRF) near Seoul Metropolitan Area (SMA) during August-October 2014. PM2.5, TC, and TN concentrations were 19.4 ± 10.1 μg m-3, 2.6 ± 0.8 μg C m-3, and 1.4 ± 1.4 μg N m-3, respectively. The δ13C of TC and the δ15N of TN were - 25.4 ± 0.7‰ and 14.6 ± 3.8‰, respectively. EC was dominated by fossil-fuel sources with Fff (EC) of 78 ± 7%. In contrast, contemporary sources were dominant for TC with Fc (TC) of 76 ± 7%, revealing the significant contribution of contemporary sources to OC during the growing season. The isotopic signature carries more detailed information on sources depending on air mass trajectories. The urban influence was dominant under stagnant condition, which was in reasonable agreement with the estimated δ15N of NH4+. The low δ15N (7.0 ± 0.2‰) with high TN concentration was apparent in air masses from Shandong province, indicating fossil fuel combustion as major emission source. In contrast, the high δ15N (16.1 ± 3.2‰) with enhanced TC/TN ratio reveals the impact of biomass burning in the air transported from the far eastern border region of China and Russia. Our findings highlight that the multi-isotopic composition is a useful tool to identify emission sources and to trace regional sources of carbonaceous and nitrogen aerosols
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A radiocarbon study of black carbon aerosol emissions in the Earth System
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