Diurnal cycle of fossil and nonfossil carbon using radiocarbon analyses during CalNex

Abstract

Radiocarbon ( 14 C) analysis is a unique tool to distinguish fossil/nonfossil sources of carbonaceous aerosols. We present 14 C measurements of organic carbon (OC) and total carbon (TC) on highly time resolved filters (3-4 h, typically 12 h or longer have been reported) from 7 days collected during California Research at the Nexus of Air Quality and Climate Change (CalNex) 2010 in Pasadena. Average nonfossil contributions of 58% ± 15% and 51% ± 15% were found for OC and TC, respectively. Results indicate that nonfossil carbon is a major constituent of the background aerosol, evidenced by its nearly constant concentration (2-3 μgC m À3). Cooking is estimated to contribute at least 25% to nonfossil OC, underlining the importance of urban nonfossil OC sources. In contrast, fossil OC concentrations have prominent and consistent diurnal profiles, with significant afternoon enhancements (~3 μgC m À3 ), following the arrival of the western Los Angeles (LA) basin plume with the sea breeze. A corresponding increase in semivolatile oxygenated OC and organic vehicular emission markers and their photochemical reaction products occurs. This suggests that the increasing OC is mostly from fresh anthropogenic secondary OC (SOC) from mainly fossil precursors formed in the western LA basin plume. We note that in several European cities where the diesel passenger car fraction is higher, SOC is 20% less fossil, despite 2-3 times higher elemental carbon concentrations, suggesting that SOC formation from gasoline emissions most likely dominates over diesel in the LA basin. This would have significant implications for our understanding of the on-road vehicle contribution to ambient aerosols and merits further study.

Evaluating the impact of new observational constraints on P-S/IVOC emissions, multi-generation oxidation, and chamber wall losses on SOA modeling for Los Angeles, CA

“…The OFR exposed ambient air to varying concentrations of OH radicals in order to obtain photochemical ages much higher than the ambient levels observed at the Pasadena site, and the amount of SOA produced was quantified as a function of OH exposure. Moreover, radiocarbon ( 14 C) analysis has been performed on filter samples and results were combined with positive matrix factorization (PMF) data to determine fossil and nonfossil fractions of the SOA components as reported in Zotter et al (2014). The 14 C results are used for subsequent comparison against the box model from which fossil and non-fossil SOA mass can be estimated.…”

Impacts of traffic emissions on atmospheric particulate nitrate and organics at a downwind site on the periphery of Guangzhou, China

“…It is worthwhile to conduct further study on vehicle-related organic emissions to SVOOA formation. For example, combining radiocarbon and ECOC measurements with the AMS and organic marker measurements, Zotter et al (2014) found that the noon-to-afternoon SVOOA peak can be attributed to the large increase in fossil OC in the measurements in Pasadena, California, US. LVOOA showed a relatively flat diurnal pattern, as was found in Shenzhen (He et al, 2011), in contrast to the significant noon-to-afternoon peaks for LVOOA at rural sites in Kaiping (Huang et al, 2011b) and Heshan (Gong et al, 2012).…”

Composition and Sources of Particulate Matter Measured near Houston, TX: Anthropogenic-Biogenic Interactions

“…The contemporary end member used for this study was 67.5 , an average of the 2010 biomass burning end member (∆ 14 C = 107.5 ) corresponding to wood smoke and the 2010 biogenic end member (∆ 14 C = 28 ) corresponding to primary and secondary biogenic emissions, meat cooking and combustion of grass, prunings and agricultural waste [42,43]. The fossil fuel end member waś 1000 [44].…”