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

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