Research Projects

Project at a Glance

Title: Characterization of ambient aerosol sources and processed during CALNEX 2010 with aerosol mass spectrometry

Principal Investigator / Author(s): Jimenez, Jose-Luis

Contractor: University of Colorado

Contract Number: 08-319


Research Program Area: Atmospheric Processes

Topic Areas: Field Studies


Abstract:

A suite of measurements from the CalNex Pasadena ground site are utilized to characterize aerosols, especially organic aerosols (OA), in the Los Angeles Basin. The concentrations of the species comprising PM2.5 and PM1 are quantified. Sea salt exhibits extensive chloride depletion due to chemical aging leading to substantial supermicron nitrate. Five OA components are identified using positive matrix factorization including hydrocarbon-like organic aerosol (HOA), cooking-influenced organic aerosol (CIOA), and two types of oxygenated organic aerosol (OOA). The correlations with tracers and photochemical age indicate that HOA is a surrogate for primary combustion OA, and OOA is dominated by secondary OA (SOA) mass. A majority of the OA mass is OOA, with lesser contributions from HOA and CIOA. HOA concentrations are lower on Sundays displaying a weekly cycle consistent with reductions in diesel emissions. The OOA to odd-oxygen (ozone + NO2) ratios for Pasadena, Mexico City, and Riverside are nearly equal, suggesting that SOA and odd-oxygen formation rates are proportional at the different sites. Dilution-corrected OA enhancements for Pasadena increase with photochemical age similar to or slightly higher than analogous data for Mexico City and the northeastern United States. The OA elemental composition for Pasadena is described in a Van Krevelen diagram (H/C vs. O/C) and follows a line that is less steep than that observed in Riverside. The difference is attributed to the greater influence of freshly emitted HOA in Riverside, while the OOA factors from the two locations follow a common evolution. Overall the results demonstrate similarities in SOA properties across several urban locations. Within experimental uncertainties, OOA/ΔCO does not display a weekly cycle, which suggests the dominance of gasoline emissions in secondary OA (SOA) formation under the assumption that most urban SOA precursors are from motor vehicles. After propagation of uncertainties, a diesel contribution to SOA of 0 Ė 35% is calculated based on the lack of an observed weekly cycle.


 

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