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

TitleFormation of secondary organic aerosol coating on black carbon particles near vehicular emissions
Publication TypeJournal Article
Year of Publication2017
AuthorsLee A.KY, Chen C.L, Liu J., Price D.J, Betha R., Russell LM, Zhang X.L, Cappa CD
JournalAtmospheric Chemistry and Physics
Date Published2017/12
Type of ArticleArticle
ISBN Number1680-7316
Accession NumberWOS:000418423700002
Keywordsabsorption; environments; mass-spectrometer data; mixing state; motor-vehicle emissions; optical-properties; positive matrix factorization; quantification; Soot; sp-ams

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(NOx / NOy) 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 7-20 wt% 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-off-light aerosol mass spectrometer (HR-ToF-AMS) measurement suggests that at least a portion of SOA materials con-densed 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.

Short TitleAtmos. Chem. Phys.
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