Organic particulate material levels in the atmosphere: Conditions favoring sensitivity to varying relative humidity and temperature

摘要

This study examines the sensitivity in predicted levels of atmospheric organic particulate matter (Mo, μg m-3) as those levels may potentially be affected by changes in relative humidity and temperature. In a given system, for each partitioning compound, fg and fp represent the gaseous and particulate fractions (fg + fp = 1). Sensitivity in the Mo levels becomes dampened as the compounds contributing significantly to Mo are increasingly found in the particle phase (fp → 1). Thus, although local maxima in sensitivity can be encountered as Mo levels increase, because as Mo increases each fp → 1, then increasing Mo levels generally tend to reduce sensitivity in Mo levels to changes in relative humidity and temperature. Experiments designed to elucidate the potential magnitudes of the effects of relative humidity and temperature on Mo levels must be carried out at Mo levels that are relevant for the ambient atmosphere: The fp values for the important partitioning compounds must not be elevated above ambient-relevant values. Systems in which Mo levels are low (e.g., 1–2 μg m-3) and/or composed of unaged secondary organic aerosol are the ones most likely to show sensitivity to changing relative humidity and temperature. Results from two published chamber studies are examined in the above regard: [Warren B, et al. (2009) Atmos Environ 43:1789–1795] and [Prisle NL, et al. (2010) Geophys Res Lett 37:L01802].