In situ measurements of gas-particle partitioning of organic compounds in Fairbanks.

Organic compounds were measured in both the gas and particle phases in Fairbanks, Alaska, using a real-time, high-resolution proton transfer reaction-time of flight mass spectrometer (PTR-ToF MS) during a wintertime campaign. The organic aerosol (OA) was dominated by semi-volatile organic compounds (SVOCs), followed by compounds in the low-volatile bin (LVOCs). Due to the persistently cold conditions, both heavy and highly oxygenated compounds showed a limited shift in partitioning with temperature change. In contrast, some semi-volatile compounds, such as methoxy phenols from wood combustion, presented some partitioning to the particle phase at lower temperatures. Laboratory studies or theoretical efforts rarely explore gas-particle partitioning at extremely low temperatures, and thus, their applicability under complex meteorological conditions remains to be assessed. A comparison of the observed and estimated volatilities at temperatures from 5 to -33 °C revealed a clear disagreement, with higher estimated volatility for light molecules (m/z below 120) and lower volatilities for heavier compounds (m/z above 300) with respect to the observed ones. Our findings from the Fairbanks winter campaign stress the need to extend the breadth of environmentally relevant conditions under which phase partitioning of organic compounds is generally explored.