Secondary organic aerosols (SOA) produced by the photooxidation of volatile organic represent a dominant fraction of particulate matter. SOA undergo chemical change by various mechanisms, including condensed-phase photochemical processes driven by absorption of ultraviolet radiation from the sun. Absorption spectrum of the organic compounds in SOA particles is one of the factors that controls the photochemical rate. The absorption spectra of SOA compounds are sometimes obtained by spectrophotometry on extracted SOA in solutions. However, this method fails to capture the effect of intramolecular and charge transfer interactions between SOA molecules in particles. This paper reports mass absorption coefficients (MACs) of SOA from four common VOCs in the UV-Visible range measured with two different methods: in the solid phase, directly on the filter, and dissolved in three common solvents (methanol, nanopure water, acetonitrile). Solid data is acquired by collecting the SOA particles on teflon filters, recording their absorption spectra on a highly-sensitive UV-Visible-Near IR spectrometer, calculating MAC values, and and comparing the MAC values to those of the same SOA dissolved in one of three different solvents. The results indicate that SOA in the solid phase exhibit higher MACs in the visible and near-IR range than when dissolved in solution, potentially affecting the rate and extent of photochemistry undergone by these SOA in the atmosphere compared to previous projections.<br/>

Solid versus solution phase ultraviolet-visible absorption of secondary organic aerosols

2019 Fall National Meeting

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