Research Projects

Project at a Glance

Title: Hourly, in-situ quantitation of organic aerosol marker compounds.

Principal Investigator / Author(s): Goldstein, Allen H

Contractor: UC Berkeley

Contract Number: 03-324


Research Program Area: Atmospheric Processes

Topic Areas: Field Studies, Modeling


Abstract:

This study was conducted to determine the contribution from various organic aerosol sources downwind of the Los Angeles Air Basin, a region currently out of compliance with air quality standards. Organic marker compounds were measured with hourly time resolution and analyzed by principal component methods to provide hourly source attribution. Measurements were made using an automated, in-situ thermal desorption aerosol gas chromatograph (TAG) with mass spectrometry analysis. The TAG instrument was deployed in Riverside, California during the summer and late fall, 2005. Measurements were made in as part of the Study of Organic Aerosols in Riverside (SOAR). This multi-investigator study, organized through support from Environmental Protection Agency and the California Air Resources Board, brought together many time-resolved aerosol measurements, including the UC San Diego Aerosol Time of Flight Mass Spectrometer and the Aerodyne Aerosol Mass Spectrometer.

The data set produced consists of hourly measurements of 300 compounds, including alkanes, branched alkanes, alkenes, polycyclic aromatic hydrocarbons, branched PAHs, hopanes, acids, phthalates, furanones, guaiacols, syringols, and other oxygenated compounds. The hourly concentration of organic marker compounds measured by TAG, together with the total organic mass from the AMS, were analyzed using positive matrix factorization (PMF).

Major findings of this study include:

1. There are multiple types of secondary organic aerosol (SOA) at Riverside, together creating an average 47% of summertime total organic aerosol mass. Differences between these SOA types likely include particle age and formation mechanism (i.e. heterogeneous chemistry in primary aerosol verses oxidation of gas phase precursors that creates low volatility products favoring the particle phase).

2. The high time resolution obtained by TAG measurements allowed us to observe diurnal changes in aerosol sources. For the first time it was observed that SOA contributes 75% of the organic aerosol mass during average summertime afternoons in this region downwind of Los Angeles.

3. The PMF results make a distinction between local traffic and regional anthropogenic primary sources. There is an indication that hopanes associated with traffic are not long-lived in the atmosphere.

4. In Riverside, regional primary anthropogenic sources contribute approximately 5 times more organic aerosol mass on average than local traffic emissions during the summer, and 15 times more during fall. Overall, however, total SOA sources contribute 2.5 times more organic aerosol mass than the combination of these two primary aerosol sources in summer. In the fall SOA was not completely separable from primary sources. While primary vehicle emissions (local and regional) account for less than 20% of the total organic aerosol mass during both seasons, a significant amount of vehicle emissions have been processed in the atmosphere contributing to the large amounts of observed SOA.

5. Biogenic sources contribute more organic aerosol mass during the summer than in the fall at Riverside, and conversely biomass burning sources contribute a larger fraction of the total organic aerosol mass during the fall.


 

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