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Characterization of Natural and Affected Environments
Seasonal and annual source appointment of carbonaceous ultrafine particulate matter (PM0.1) in polluted California cities Jian Xue, Wei Xue, Mohammad Sowlat, Constantinos Sioutas, Annabelle Lolinco, Alam S. Hasson, and Michael J. Kleeman Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b04404 • Publication Date (Web): 19 Nov 2018 Downloaded from http://pubs.acs.org on November 20, 2018
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Department of Civil and Environmental Engineering, University of California – Davis, Davis, California, USA, 95616 bDepartment of Civil and Environmental Engineering, University of Southern California, Los Angeles, California, USA, 90089 cDepartment of Chemistry, California State University – Fresno, Fresno, California, USA, 93740
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Department of Civil and Environmental Engineering
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University of California
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Davis, CA 95616
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Phone: 530 752 8386
Seasonal and annual source appointment of carbonaceous ultrafine particulate matter (PM0.1) in polluted California cities Jian Xuea, Wei Xuea, Mohammad H. Sowlatb, Constantinos Sioutasb, Annabelle Lolincoc, Alam Hassonc, and Michael J. Kleemana,* a
*corresponding author:
[email protected] 29 30 31 32 33 34 35 36 37 38 39 40 41
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Abstract
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in California: Los Angeles, East Oakland, San Pablo, and over six months at Fresno. Molecular
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markers adjusted for volatility and reactivity were used to calculate PM0.1 source contributions.
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Wood burning was a significant source of PM0.1 organic carbon (OC) during the winter months in
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northern California (17-47%) but made smaller contributions in other months (0-8%) and was
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minor in all seasons in Los Angeles (0-5%), expect December (17%) during holiday celebrations.
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Meat cooking was the largest source of PM0.1 OC across all sites (13-29%), followed by gasoline
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combustion (7-21%). Motor oil and diesel fuel combustion made smaller contributions to PM0.1
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OC (3-10% and 3-7%, respectively). Unresolved sources accounted for 22-56% of the PM0.1 OC.
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The lack of a clear seasonal profile for this unresolved OC suggests that it may be a primary source
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rather than secondary organic aerosol (SOA). PM0.1 elemental carbon (EC) was dominated by
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diesel fuel combustion with less than 15% contribution from other sources. All sources besides
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wood smoke exhibited relatively constant seasonal source contributions to PM0.1 OC reflecting
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approximately constant emissions over the annual cycle. Annual-average source contributions to
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PM0.1 OC calculated with traditional molecular markers were similar to the source contributions
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calculated with the modified molecular markers that account for volatility and reactivity.
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Samples of ultrafine particle matter mass (PM0.1) were collected over twelve months at three cities
Key word: Ultrafine particles, PM0.1, MOUDI, source apportionment
350 -3
PM0.1 EC/OC (ng m )
Average of four sampling sites across California PM0.1
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OC EC
200 150 100
-3
64 65 66 67 68 69 70 71 72 73
PM2.5 EC/OC (µg m )
300
50 0
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul
TOC
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1. Introduction
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because of their high surface area that can adsorb toxic substances, which may then be translocated
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to different regions of the body.1-4 The 1998 US National Research Council blueprint for
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particulate matter (PM) research identified ultrafine particles as a research priority5. Fifteen years
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later, the 2013 HEI Perspective on the Health Effects of Ultrafine Particles6 confirmed the robust
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evidence for the toxicity of ultrafine particles but noted that epidemiological studies were
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inconclusive due to inconsistencies and limitations in the findings from both short- and long-term
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studies.7 The lack of consistent epidemiologic results was also a factor in the 2009 US-EPA
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Integrated Science Assessment which concluded that the evidence was suggestive but not yet
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sufficiently developed to infer a causal relationship between ultrafine particles and human health.8
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A major limitation inherent in many epidemiological studies for ultrafine particles is simply
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lack of consistent long-term measurements necessary to support an accurate exposure assessment
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for all the features of interest. Ultrafine particle concentrations are typically quantified using
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number concentration (NX; number of particles with diameter ≥ X nm) or mass (PM0.1; mass of
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particles with diameter ≤ 0.1 µm). Total particle number concentration (NX) is continuously
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measured at multiple locations in major California cities9,
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ultrafine particle source contributions have been limited to shorter time periods (< 1 year) at a
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smaller number of sites. 11-23 Recent epidemiological studies have found multiple adverse health
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outcomes associated with PM0.1.
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broader range of cities would help to fully test the relevant hypotheses about the potential health
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effects of ultrafine particles.
Ultrafine particles (with aerodynamic diameter ≤ 0.1 µm) have toxic properties, possibly
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but measurements for PM0.1 and
Longer-term (≥ 1 year) PM0.1 measurements spanning a
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Here we describe a network of PM0.1 measurements and source apportionment calculations
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carried out in four polluted California cities: Los Angeles (twelve months), East Oakland in the
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San Francisco Bay Area (SFBA) (twelve months), San Pablo in the SFBA (twelve months), and
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Fresno in the San Joaquin Valley (SJV) (six months). We focus on PM0.1 organic carbon (OC)
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and elemental carbon (EC) concentrations at all locations since these two components are expected
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to comprise +90% of the total PM0.1 mass.13 Source contributions to PM0.1 OC and EC are
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calculated using molecular markers. Semi-volatile PM0.1 source profiles are developed to account
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for partial evaporation of OC and molecular markers after dilution in the atmosphere. A method
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to account for photochemical reaction is developed to account for the observed seasonal variation.
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The effects of these modifications on calculated PM0.1 source contributions are evaluated and
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trends in PM0.1 concentrations and source contributions are discussed as a function of season and
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location. To the best of our knowledge, this is the first demonstration of an annual PM0.1 sampling
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network with source apportionment in the world.
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concentrations and source contributions will be a useful resource for testing PM0.1 exposure models
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that can support future epidemiological studies.
The resulting dataset describing PM0.1
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2. Sampling and analysis
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2.1 Sampling sites and periods
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The PM0.1 sampling network was deployed across four polluted cities spanning the wide range
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of air quality issues experienced in California. Los Angeles is the largest city in California and the
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second largest city in the United States. The Los Angeles (LA) site was located, on the campus of
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the University of Southern California (USC), approximately 3 km to the south of downtown Los
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Angeles. The LA site was 1 km from a major, heavily congested, interstate freeway (i.e., I-110)
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and approximately 13 km from the Los Angeles International Airport (LAX). Fresno is the largest
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city in California’s heavily polluted San Joaquin Valley (SJV). The Fresno (FR) site was located
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on the campus of California State University, Fresno, which is within 3 km of a moderately busy
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highway (i.e., State Highway 99). The FR site was bounded by commercial/residential
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neighborhoods on 3 sides and agricultural fields on the remaining side. The San Francisco Bay
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Area has the highest population density in California. The San Pablo (SP) and East Oakland (EO)
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monitoring sites were approximately 30 km apart in the Bay Area. Both SP and EO were
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influenced by traffic, commercial, and residential sources, but their proximity to industrial sources
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differed. Most notably, the SP location is within 5 km of a major chemical refinery, while the EO
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location is within 5km of the Oakland International Airport and within 15 km of the Port of
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Oakland. All the sampling locations are shown in Figure S4 in supporting information (SI).
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The sampling period covered one year from August 2015 to July 2016 at the SP, EO and
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LA sites, and 6 months (January-April, June-July 2016) at the FR site. Each sample collection
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event lasted for 70-71 hours to collect sufficient PM0.1 mass for chemical analysis. Quality control
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/ quality assurance checks were performed at the conclusion of each sample collection event prior
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to the collection of the subsequent sample. Overall, 102, 110, 95 and 42 valid samples were
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collected at SP, EO, LA and FR sites, respectively, covering 70-90% of the total sampling periods.
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2.2 Sampling Methods
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The detailed PM0.1 measurement methods used in this study have been described previously13,
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(MOUDIs) were operated in parallel to collect PM0.1 samples that could be tested for both
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carbonaceous speciation and elemental analysis. The first MOUDI was equipped with pre-baked
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aluminum substrates (Foil 0100-96-0573A-X; MSP Corp., Shoreview, MN, USA) and quartz fiber
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after-filters (Tissuquartz filters; Pall Corp., Port Washington, NY, USA) that were analyzed for
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elemental carbon (EC), organic compounds (OC), and organic molecular markers, such as
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cholesterol, levoglucosan, alkanes, etc. The second MOUDI was equipped with Teflon membrane
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substrates (Teflo R2PJ047; Pall Corp., Port Washington, NY, USA) that were analyzed for trace
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elements. Measurements from the aluminum MOUDI substrates are used for the analysis in the
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current paper.
and so only a brief summary is presented here. Two Micro-Orifice Uniform Deposit Impactors
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Each MOUDI was operated at the flow rate recommended by the manufacturer (30 L min-1)
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with an AIHL-design cyclone placed upstream to remove particles with diameter larger than 1.8
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µm due to their tendency to bounce off uncoated impaction stages.27 Ultrafine particles (DpEO>SP>FR. PM0.1 EC concentrations in downtown LA were higher than those
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measured at other sites (p
