Abstract
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).
Highlights
Numerous epidemiological studies have identified positive correlations between exposure to ambient particulate matter (PM) and increased risk of respiratory and cardiovascular diseases, premature mortality, and hospitalization (Pope et al, 2002, 2004, 2009; Dockery and Stone, 2007; Ostro et al, 2006, 2010, 2015; Brunekreef and Forsberg, 2005; Fann et al, 2012; Gauderman et al, 2015; Miller et al, 2007)
Measurements conducted in parallel with the current study found that particles emitted from natural gas combustion in home appliances were semi-volatile when diluted by a factor of 25 in clean air, but particles emitted from reciprocating engines did not evaporate under the same conditions (Xue et al, 2018a)
In order to account for the uncertainty in predicted wind fields and spatial surrogates used to place emissions, “bestfit” model results were created by identifying the closest match within three grid cells of each measurement location
Summary
Numerous epidemiological studies have identified positive correlations between exposure to ambient particulate matter (PM) and increased risk of respiratory and cardiovascular diseases, premature mortality, and hospitalization (Pope et al, 2002, 2004, 2009; Dockery and Stone, 2007; Ostro et al, 2006, 2010, 2015; Brunekreef and Forsberg, 2005; Fann et al, 2012; Gauderman et al, 2015; Miller et al, 2007) Most of these studies have not fully addressed ultrafine particles (UFPs; Dp < 0.1 μm) because these particles make a very small contribution to total ambient PM mass (Ogulei et al, 2007). Yu et al.: Regional sources of airborne ultrafine particle number
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