Atmospheric gas phase oxidation processes produce low volatility species that can homogeneously nucleate particles or condense onto existing seed-particles.  Once formed, these particles can grow by uptake of semi-volatile compounds to sizes capable of scattering light and impacting visibility, human health, and climate.  Recent studies from laboratory and field observations show that many atmospheric organic particles are more viscous than initially proposed, exhibiting a high viscosity and semi-solid nature.  The phase state of the particles is an important property to characterize, as it will affect how they interact with water and trace gases, and how they take up semi-volatile organic compounds in the atmosphere.  In the present work, we characterize the phase of atmospheric particles by investigating the incorporation of semi-volatile organic nitrates into secondary organic aerosol formed from the ozonolysis of a-pinene in a large-volume aerosol flow chamber at room temperature.  Size distributions of particles were characterized using an SMPS/APS combined system.  Particles were impacted onto an ATR-FTIR germanium crystal using a custom-built impactor, and the infrared peaks due to the nitrate group were used to quantify the uptake of organic nitrates into the particles.  In addition, evaporation of the nitrate from the particles was followed by ATR-FTIR as a function of time while dry clean air flowed over the impacted particles, providing a measure of diffusion coefficients within the SOA matrix and insights into its phase state.  Implications for particle growth processes in the atmosphere will be discussed.

Investigating particle phase and growth mechanisms: Studying organic nitrate uptake into secondary organic aerosol

251st National Meeting (2016)

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