The mechanism of growth of secondary organic aerosol (SOA) is often described in atmospheric models by instantaneous thermodynamic equilibrium partitioning of semi-volatile organic compounds (SVOC) into liquid pre-existing organic particles.  When compared with field measurements, these models tend to underpredict SOA concentrations.  One possible source for this discrepancy could reside in the assumption that the SOA is indeed a liquid which allows equilibrium with the gas phase to be rapidly attained.  However, there is an increasing evidence that at least some SOA can adopt an amorphous solid or highly viscous state instead of an ideal liquid.  A previous study from our group showed that, in the case of alpha-pinene simultaneous oxidation by ozone and nitrate radicals, the uptake of organic nitrates products into the formed SOA does not follow thermodynamic equilibrium partitioning but is consistent with a kinetically limited/condensation growth mechanism.  We report here a series of new experiments performed using a large volume slow flow aerosol flow tube system to measure the partitioning of organic nitrates products into SOA formed from simultaneous oxidation by ozone and nitrate radicals of a series of atmospherically relevant monoterpenes.  Particle mass concentrations, and organic nitrate product concentrations in both the gas phase and in particles were experimentally measured using scanning mobility and aerodynamic particle sizers, long path cell FTIR and by collection of the particles on quartz fiber filter followed by LC-UV analysis.  Interpretations of the data in terms of partitioning and particle growth will be presented, along with the implications for model development for SOA.

Uptake of organic nitrates in SOA from the simultaneous oxidation of monoterpenes by ozone and nitrate radicals

243rd National Meeting (2012)

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