Environ. Sci. Technol. 2004, 38, 1296-1304
Diurnal Variations of Individual Organic Compound Constituents of Ultrafine and Accumulation Mode Particulate Matter in the Los Angeles Basin P H I L I P M F I N E , * ,† BHABESH CHAKRABARTI,† MEG KRUDYSZ,‡ JAMES J. SCHAUER,§ AND CONSTANTINOS SIOUTAS† Department of Civil and Environmental Engineering, University of Southern California, 3620 South Vermont Avenue, Los Angeles, California 90089, School of Public Health, University of CaliforniasLos Angeles, 650 Young Drive South, Los Angeles, California 90095, and Department of Civil and Environmental Engineering, University of Wisconsins Madison, 660 North Park Street, Madison, Wisconsin 53706
Individual organic compounds can be used as tracers for primary sources of ambient particulate matter (PM) in chemical mass balance receptor models. Previous work has examined PM2.5 only and usually over long sampling periods encompassing entire days or longer. In this study, a high-flow-rate, low-pressure-drop ultrafine particle separator was deployed to collect sufficient mass for organic speciation of ultrafine and accumulation mode aerosol on a diurnal basis. Particles between 0.18 and 2.5 µm in diameter were collected on a quartz-fiber impaction substrate, and ultrafine particles below 0.18 µm were collected downstream on a high-volume filter. Four daily time period samples (morning, midday, evening, and overnight) were sampled over five weekdays to form a weekly average composite for each diurnal period. Sampling was conducted at two sites over two seasons; summer (August) and winter (January) samples were collected at both an urban site near downtown Los Angeles (University of Southern California) and a downwind, inland site in Riverside, CA. Hopanes, used as organic markers for vehicular emissions, were found to exist primarily in the ultrafine mode. Levoglucosan, an indicator of wood combustion, was quantified in both size ranges, but more was present in the accumulation mode particles. An indicator of photochemical secondary organic aerosol formation, 1,2benzenedicarboxylic acid, was found primarily in the accumulation mode and varied with site, season, and time of day as one would expect for a photochemical product. The atmospheric variations of particulate cholesterol and other organic acids were also considered. By examining the diurnal variation, size-fractionation, and intercorrelations of individual organic compounds, the sources and * Corresponding author phone: (213) 740-0560; fax: (213) 7441426; e-mail:
[email protected]. † University of Southern California. ‡ University of CaliforniasLos Angeles. § University of WisconsinsMadison. 1296
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 38, NO. 5, 2004
atmospheric fate of these tracers can be better understood and their utility as molecular markers can be assessed.
Introduction Several studies have measured individual organic compounds in atmospheric particulate matter (PM) samples. Using gas chromatography/mass spectrometry methods, hundreds of particle-phase individual compounds have been identified and quantified in ambient air (1-14). Usually, only between 10% and 20% of the total particulate organic compound mass can be quantified as individual organic species, but many of these compounds have been used to trace primary particle emissions via source apportionment techniques (1-3, 11). Specific organic tracers of primary particle sources include levoglucosan for wood smoke, hopanes and steranes for vehicular emissions, odd-numbered alkanes for vegetative material, and cholesterol for meat cooking. Recent evidence demonstrates that particle size is a major factor in the relative toxicity and health effects of ambient particles. In particular, ultrafine particles (diameters of less than about 100 nm) have been shown to cause more oxidative stress and cell damage than an equivalent mass of fine particles (diameters
