Secondary Organic Aerosols

Multiday production of SOA in urban and forest outflow

Regional pollution around Mexico City - photo by NASA

Secondary organic aerosol (SOA) production in urban and biogenic outflow was investigated using the explicit gas-phase chemical mechanism generator GECKO-A [Lee-Taylor et al., 2015]. Urban outflow simulations show several-fold increases in SOA mass continuing for multiple days, whereas forest outflow simulations showed only modest SOA mass increases, and no long-term growth. The multiday SOA production in urban-origin air stems from multigenerational oxidation products of gas-phase precursors which persist in equilibrium with the particle phase.

Gas-Phase Dry Deposition as a Major Removal Mechanism for Secondary Organic Aerosols (SOA)

Water droplets on a leaf, by Siddharth Patil at Wikimedia Commons

Removal of secondary organic aerosols (SOA) from the atmosphere has been studied far less than its equal, production.  In current regional and global chemistry models rainout is the dominant loss of SOA. Here we show the importance of a less direct pathway, in which large scale evaporation of SOA particles occurs as a re-adjustment to gas-particle partitioning when semi-volatile organic gases are lost by dry deposition to the Earth’s surface.

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