title: Organic particulate material levels in the atmosphere: conditions favoring sensitivity to varying relative humidity and temperature.
abstract: This study examines the sensitivity in predicted levels of atmospheric organic particulate matter (M(o), microg m(-3)) as those levels may potentially be affected by changes in relative humidity and temperature. In a given system, for each partitioning compound, f(g) and f(p) represent the gaseous and particulate fractions (f(g) + f(p) = 1). Sensitivity in the M(o) levels becomes dampened as the compounds contributing significantly to M(o) are increasingly found in the particle phase (f(p) --> 1). Thus, although local maxima in sensitivity can be encountered as M(o) levels increase, because as M(o) increases each f(p) --> 1, then increasing M(o) levels generally tend to reduce sensitivity in M(o) levels to changes in relative humidity and temperature. Experiments designed to elucidate the potential magnitudes of the effects of relative humidity and temperature on M(o) levels must be carried out at M(o) levels that are relevant for the ambient atmosphere: The f(p) values for the important partitioning compounds must not be elevated above ambient-relevant values. Systems in which M(o) levels are low (e.g., 1-2 microg 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].
authors.affiliation: Department of Civil and Environmental Engineering, Portland State University, Portland, OR 97207, USA. pankowj@pdx.edu
authors.forename: James F
authors.initials: JF
authors.lastname: Pankow
mesh_terms: D000336:Aerosols / Q000737:chemistry; D000393:Air Pollutants; D000465:Algorithms; D001272:Atmosphere; D002621:Chemistry / Q000379:methods; D002625:Chemistry, Organic / Q000379:methods*; D004784:Environmental Monitoring / Q000379:methods*; D005740:Gases; D006813:Humidity; D015233:Models, Statistical; D010316:Particle Size; D052638:Particulate Matter; D013696:Temperature
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D005740:Gases; D052638:Particulate Matter