Aerosol Composition in Los Angeles During the 2010 CalNex Campaign Studied by High Resolution Aerosol Mass Spectrometry
Abstract
Submicron atmospheric aerosols impact climate and human health, but their sources and composition are poorly understood. To address this knowledge gap, high-resolution time-of-flight aerosol mass spectrometry (AMS) [DeCarlo et al. Anal. Chem. 2006] and other advanced instrumentation were deployed during the CalNex field campaign in May and June 2010 for 4 weeks to characterize the composition of aerosols in the Los Angeles area. Utilizing AMS, the concentrations for both organic and non-refractory inorganic (sulfate, nitrate, ammonium, chloride) submicron aerosols were quantified at the Caltech/Pasadena ground site 15 km NE of downtown Los Angeles. The total submicron mass concentration as well as the species concentrations measured by AMS compare well with other instruments. Nitrate aerosols appear to dominate in the cooler mornings, but their concentration is reduced in the afternoon when organic aerosols (OA) increase and dominate. The diurnal variations in concentration are strongly influenced by vertical dilution from the rising planetary boundary layer in the afternoon. Secondary organic aerosols (SOA) are an important fraction of submicron aerosols. To assess the concentrations of different OA components present at the site, positive matrix factorization (PMF) is used to analyze the field data. The major OA classes are oxygenated OA (OOA, a surrogate for total SOA), and hydrocarbon-like OA (HOA, a surrogate for primary combustion OA). Preliminary PMF analysis finds that OOA is consistently the largest type of OA present (~75% of the total OA concentration). This result suggests that the air mass over the site has undergone substantial chemical aging. The correlations between OOA and Ox (O3 + NO2) concentrations, as well as between HOA, CO and black carbon concentrations are strong and consistent with previous studies. AMS and 14C measurements are combined to determine the fractions of HOA and OOA from non-fossil vs. fossil sources. Using measurements of SOA precursors and oxidants that were carried out during CalNex, we test whether different SOA mechanisms implemented in box models [Dzepina et al. ACP 2009, Jimenez et al. Science 2009] and regional models can reproduce the SOA concentrations observed during CalNex.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.A21C0112H
- Keywords:
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- 0305 ATMOSPHERIC COMPOSITION AND STRUCTURE / Aerosols and particles;
- 0345 ATMOSPHERIC COMPOSITION AND STRUCTURE / Pollution: urban and regional;
- 0394 ATMOSPHERIC COMPOSITION AND STRUCTURE / Instruments and techniques;
- 3355 ATMOSPHERIC PROCESSES / Regional modeling