Organic aerosol mass (OM) components were investigated at Fresno in winter and at Fontana in summer by positive matrix factorization of high‐resolution time‐of‐flight aerosol mass spectra and of Fourier Transform infrared spectra, as well as by k‐means clustering of light‐scattering (LS) aerosol single‐particle spectra. The results were comparable for all three methods at both sites, showing different contributions of primary and secondary organic aerosol sources to PM1. At Fresno biomass burning organic aerosol contributed 27% of OM on low‐fog days, and nitrate‐related oxidized OA (NOOA) accounted for 47% of OM on high‐fog days, whereas at Fontana very oxygenated organic aerosol (VOOA) components contributed 58–69% of OM. Amine and organosulfate fragment concentrations were between 2 and 3 times higher on high‐fog days than on low‐fog days at Fresno, indicating increased formation from fog‐related processes. NOOA and biomass burning organic aerosol components were largely on different particles than the VOOA components in Fresno, but in Fontana both NOOA and VOOA components were distributed on most particle types, consistent with a longer time for and a larger contribution from gas‐phase photochemical secondary organic aerosol formation in summer Fontana than winter Fresno. Uncommon trace organic fragments, elevated inorganic, and alcohol group submicron mass concentrations persisted at Fontana for more than 5 days after 4 July fireworks. These unique aerosol chemical compositions at Fresno and Fontana show substantial and extended air‐quality impacts from residential burning and fireworks.
Abstract. Regional concentrations and source contributions are calculated for airborne
particle number concentration (Nx) and ultrafine particle mass
concentration (PM0.1) in the San Francisco Bay Area (SFBA) and the
South Coast Air Basin (SoCAB) surrounding Los Angeles with 4 km spatial
resolution and daily time resolution for selected months in the years 2012,
2015, and 2016. Performance statistics for daily predictions of N10
concentrations meet the goals typically used for modeling of PM2.5
(mean fractional bias
(MFB) < ±0.5 and mean fractional error
(MFE) < 0.75). The relative ranking and
concentration range of source contributions to PM0.1 predicted by
regional calculations agree with results from receptor-based studies that
use molecular markers for source apportionment at four locations in
California. Different sources dominated regional concentrations of N10
and PM0.1 because of the different emitted particle size distributions
and different choices for heating fuels. Nucleation (24 %–57 %) made the
largest single contribution to N10 concentrations at the 10 regional
monitoring locations, followed by natural gas combustion (28 %–45 %),
aircraft (2 %–10 %), mobile sources (1 %–5 %), food cooking (1 %–2 %), and
wood smoke (0 %–1 %). In contrast, natural gas combustion (22 %–52 %) was
the largest source of PM0.1 followed by mobile sources (15 %–42 %),
food cooking (4 %–14 %), wood combustion (1 %–12 %), and aircraft
(2 %–6 %). The study region encompassed in this project is home to more than
25 million residents, which should provide sufficient power for future
epidemiological studies on the health effects of airborne ultrafine
particles. All of the PM0.1 and N10 outdoor exposure fields
produced in the current study are available free of charge at http://webwolf.engr.ucdavis.edu/data/soa_v3/hourly_avg/ (last access: 20 November 2019).
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