Secondary organic aerosol

A secondary organic aerosol (SOA) is a molecule produced via oxidation over several generations of a parent organic molecule.[1] In contrast to primary organic aerosols, which are emitted directly from the biosphere, secondary organic aerosols are either formed via homogeneous nucleation through the successive oxidation of gas-phase organic compounds, or through condensation on pre-existing particles. These gas-phase species exert high vapor pressures, meaning they are volatile and stable in the gas-phase. Upon oxidation, the increased polarity, and thus reduced volatility, of the molecules results in a reduction of vapor pressure. After sufficient oxidation, the vapor pressure is sufficiently low that the gas-phase compound partitions into the solid-phase, producing secondary organic matter (the particle phase of secondary organic aerosol).

SOAs represent a significant proportion of aerosols contained in the troposphere.[1]

A common misconception is that the aerosol refers to the solid phase of the compound, where in reality, by definition, it is the combination of the gas- and solid-phases which constitute the aerosol.

References
  1. Yee, Lindsay D.; Craven, Jill S.; Loza, Christine L.; Schilling, Katherine A.; Ng, Nga Lee; Canagaratna, Manjula R.; Ziemann, Paul J.; Flagan, Richard C.; Seinfeld, John H. (2012-06-21). "Secondary Organic Aerosol Formation from Low-NOx Photooxidation of Dodecane: Evolution of Multigeneration Gas-Phase Chemistry and Aerosol Composition" (PDF). The Journal of Physical Chemistry A. 116 (24): 6211–6230. Bibcode:2012JPCA..116.6211Y. doi:10.1021/jp211531h. ISSN 1089-5639. PMID 22424261.

Bibliography
  • Lewis, Alastair C. (2018). "The changing face of urban air pollution" (PDF). Science. 359 (6377): 744–745. Bibcode:2018Sci...359..744L. doi:10.1126/science.aar4925. PMID 29449479.
  • McDonald, Brian C.; De Gouw, Joost A.; Gilman, Jessica B.; Jathar, Shantanu H.; Akherati, Ali; Cappa, Christopher D.; Jimenez, Jose L.; Lee-Taylor, Julia; Hayes, Patrick L.; McKeen, Stuart A.; Cui, Yu Yan; Kim, Si-Wan; Gentner, Drew R.; Isaacman-Vanwertz, Gabriel; Goldstein, Allen H.; Harley, Robert A.; Frost, Gregory J.; Roberts, James M.; Ryerson, Thomas B.; Trainer, Michael (2018). "Volatile chemical products emerging as largest petrochemical source of urban organic emissions". Science. 359 (6377): 760–764. Bibcode:2018Sci...359..760M. doi:10.1126/science.aaq0524. PMID 29449485.


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