Supplementary material to "Formation of secondary organic aerosol coating on black carbon particles near vehicular emissions"

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(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-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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Secondary Organic Aerosol Coating Formation and Evaporation: Chamber Studies Using Black Carbon Seed Aerosol and the Single-Particle Soot Photometer

Aerosol Science and Technology ◽

10.1080/02786826.2012.750712 ◽

2012 ◽

Vol 47 (3) ◽

pp. 326-347 ◽

Cited By ~ 29

Author(s):

Andrew R. Metcalf ◽

Christine L. Loza ◽

Matthew M. Coggon ◽

Jill S. Craven ◽

Haflidi H. Jonsson ◽

...

Keyword(s):

Black Carbon ◽

Single Particle ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Evaporation Chamber ◽

Coating Formation ◽

Chamber Studies ◽

Aerosol Coating ◽

Seed Aerosol

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

10.5194/acp-2017-665 ◽

2017 ◽

Cited By ~ 1

Author(s):

Alex K. Y. Lee ◽

Chia-Li Chen ◽

Jun Liu ◽

Derek J. Price ◽

Raghu Betha ◽

...

Keyword(s):

Black Carbon ◽

Mass Spectrometer ◽

Secondary Organic Aerosol ◽

Spectral Characteristics ◽

Organic Aerosol ◽

Vehicular Emissions ◽

Aerosol Mass Spectrometer ◽

Diurnal Cycles ◽

Aerosol Mass ◽

Inorganic Species

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 are 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 detect refractory BC (rBC) particles and their coatings exclusively. 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 missions 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 rBC 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 sinks of SOA in this study. Diurnal cycles of oxygenated organic aerosol (OOA) observed by a co-located standard high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-MS) correlated well with that of SOA coatings on rBC, but their mass spectral characteristics were different from each other. Our results suggest that at least a portion of SOA materials condensed on rBC surface were chemically different from OOA particles that were externally mixed with rBC, although they are both generated from local photochemistry.

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