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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 24 | Copyright
Atmos. Chem. Phys., 17, 15055-15067, 2017
https://doi.org/10.5194/acp-17-15055-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 Dec 2017

Research article | 20 Dec 2017

Formation of secondary organic aerosol coating on black carbon particles near vehicular emissions

Alex K. Y. Lee1, Chia-Li Chen2, Jun Liu2, Derek J. Price2, Raghu Betha2, Lynn M. Russell2, Xiaolu Zhang3,a, and Christopher D. Cappa3 Alex K. Y. Lee et al.
  • 1Department of Civil and Environmental Engineering, National University of Singapore, Singapore
  • 2Scripps Institution of Oceanography, University of California, San Diego, USA
  • 3Department of Civil and Environmental Engineering, University of California, Davis, USA
  • anow at: Crocker Nuclear Laboratory, University of California, Davis, USA

Abstract. Black carbon (BC) emitted from incomplete combustion can result in significant impacts on air quality and climate. Understanding the mixing state of ambient BC and the chemical characteristics of its associated coatings is particularly important to evaluate BC fate and environmental impacts. In this study, we investigate the formation of organic coatings on BC particles in an urban environment (Fontana, California) under hot and dry conditions using a soot-particle aerosol mass spectrometer (SP-AMS). The SP-AMS was operated in a configuration that can exclusively detect refractory BC (rBC) particles and their coatings. Using the −log(NOxNOy) ratio as a proxy for photochemical age of air masses, substantial formation of secondary organic aerosol (SOA) coatings on rBC particles was observed due to active photochemistry in the afternoon, whereas primary organic aerosol (POA) components were strongly associated with rBC from fresh vehicular emissions in the morning rush hours. There is also evidence that cooking-related organic aerosols were externally mixed from rBC. Positive matrix factorization and elemental analysis illustrate that most of the observed SOA coatings were freshly formed, providing an opportunity to examine SOA coating formation on rBCs near vehicular emissions. Approximately 7–20wt% of secondary organic and inorganic species were estimated to be internally mixed with rBC on average, implying that rBC is unlikely the major condensation sink of SOA in this study. Comparison of our results to a co-located standard high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) measurement suggests that at least a portion of SOA materials condensed on rBC surfaces were chemically different from oxygenated organic aerosol (OOA) particles that were externally mixed with rBC, although they could both be generated from local photochemistry.

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Understanding the mixing state of ambient black carbon (BC) and the chemical characteristics of its associated coatings is important to evaluate BC fate and environmental impacts. This study reports fresh secondary organic aerosol (SOA) formation near traffic emissions during daytime. Our observations suggest that BC was unlikely the major condensation sink of SOA, and a portion of SOA condensed on BC surface was chemically different from other SOA particles that were externally mixed with BC.
Understanding the mixing state of ambient black carbon (BC) and the chemical characteristics of...
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