| Summary: | A thermal volatility technique was used in the boreal forest environment to examine accumulation mode (0.05–0.35 µm radius) physico-chemical properties as a function of air mass origin. Three primary aerosol species were identified in all air masses: (1) a semi-volatile organic component, (2) ammonium sulphate, and (3) a non-volatile component thought to comprise mostly of soot carbon. Under some conditions, sulphuric acid was also identified, as was sea salt. Following nucleation and growth of new particles into accumulation mode sizes, the organic fraction of accumulation mode aerosol, by mass, was observed to increase from 30%, prior to and during the nucleation event, up to 75% by the end of the growth period, indicating a substantial fraction of organic mass condensing onto newly formed particles.
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