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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 21 | Copyright
Atmos. Chem. Phys., 18, 15601-15622, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Oct 2018

Research article | 30 Oct 2018

Source apportionment of fine particulate matter in Houston, Texas: insights to secondary organic aerosols

Ibrahim M. Al-Naiema1, Anusha P. S. Hettiyadura1, Henry W. Wallace2, Nancy P. Sanchez2, Carter J. Madler1, Basak Karakurt Cevik2,3, Alexander A. T. Bui2, Josh Kettler1, Robert J. Griffin2,4, and Elizabeth A. Stone5 Ibrahim M. Al-Naiema et al.
  • 1Department of Chemistry, University of Iowa, Iowa City, IA 52242 USA
  • 2Department of Civil and Environmental Engineering, Rice University, Houston, TX 77005, USA
  • 3Department of Energy Systems Engineering, Faculty of Engineering, Yalova University, Yalova, 77100, Turkey
  • 4Department of Chemical and Biomolecular Engineering, Rice University, Houston, TX 77005, USA
  • 5Department of Chemical and Biochemical Engineering, University of Iowa, Iowa City, IA 52242, USA

Abstract. Online and offline measurements of ambient particulate matter (PM) near the urban and industrial Houston Ship Channel in Houston, Texas, USA, during May 2015 were utilized to characterize its chemical composition and to evaluate the relative contributions of primary, secondary, biogenic, and anthropogenic sources. Aerosol mass spectrometry (AMS) on nonrefractory PM1 (PM  ≤  1µm) indicated major contributions from sulfate (averaging 50% by mass), organic aerosol (OA, 40%), and ammonium (14%). Positive matrix factorization (PMF) of AMS data categorized OA on average as 22% hydrocarbon-like organic aerosol (HOA), 29% cooking-influenced less-oxidized oxygenated organic aerosol (CI-LO-OOA), and 48% more-oxidized oxygenated organic aerosol (MO-OOA), with the latter two sources indicative of secondary organic aerosol (SOA). Chemical analysis of PM2.5 (PM  ≤  2.5µm) filter samples agreed that organic matter (35%) and sulfate (21%) were the most abundant components. Organic speciation of PM2.5 organic carbon (OC) focused on molecular markers of primary sources and SOA tracers derived from biogenic and anthropogenic volatile organic compounds (VOCs). The sources of PM2.5 OC were estimated using molecular marker-based positive matric factorization (MM-PMF) and chemical mass balance (CMB) models. MM-PMF resolved nine factors that were identified as diesel engines (11.5%), gasoline engines (24.3%), nontailpipe vehicle emissions (11.1%), ship emissions (2.2%), cooking (1.0%), biomass burning (BB, 10.6%), isoprene SOA (11.0%), high-NOx anthropogenic SOA (6.6%), and low-NOx anthropogenic SOA (21.7%). Using available source profiles, CMB apportioned 41% of OC to primary fossil sources (gasoline engines, diesel engines, and ship emissions), 5% to BB, 15% to SOA (including 7.4% biogenic and 7.6% anthropogenic), and 39% to other sources that were not included in the model and are expected to be secondary.

This study presents the first application of in situ AMS-PMF, MM-PMF, and CMB for OC source apportionment and the integration of these methods to evaluate the relative roles of biogenic, anthropogenic, and BB-SOA. The three source apportionment models agreed that  ∼ 50% of OC is associated with primary emissions from fossil fuel use, particularly motor vehicles. Differences among the models reflect their ability to resolve sources based upon the input chemical measurements, with molecular marker-based methods providing greater source specificity and resolution for minor sources. By combining results from MM-PMF and CMB, BB was estimated to contribute 11% of OC, with 5% primary emissions and 6% BB-SOA. SOA was dominantly anthropogenic (28%) rather than biogenic (11%) or BB-derived. The three-model approach demonstrates significant contributions of anthropogenic SOA to fine PM. More broadly, the findings and methodologies presented herein can be used to advance local and regional understanding of anthropogenic contributions to SOA.

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Short summary
By integrating newly developed tracers for anthropogenic secondary organic aerosol in source apportionment for the first time, we estimate that this source contributes 28 % of fine particle organic carbon in the Houston Ship Channel. Our approach can be used to evaluate anthropogenic, biogenic, and biomass burning contributions to secondary organic aerosols elsewhere in the world. Because anthropogenic emissions are potentially controllable, they provide an opportunity to improve air quality.
By integrating newly developed tracers for anthropogenic secondary organic aerosol in source...