| Presentations and Publications
Khlystov, A., Stanier, C., Takahama, S., and Pandis, S.N., “Water Content of Ambient Aerosol During the Pittsburgh Air Quality Study”, Journal of Geophysical Research – Atmospheres, 2005, Vol. 110, No. D7, D07S10, doi:10.1029/2004JD00465114.
The aerosol water content and volumetric growth factors of fine particulate matter
were measured during July–August 2001 and January–June 2002 in an urban park about
6 km from downtown Pittsburgh, Pennsylvania. Most of the aerosol during the study was
transported to the region from other areas, and its composition and concentration were
characteristic of the regional particulate matter in the northeastern United States. During the
summer months the ambient aerosol practically always contained water even when the
relative humidity (RH) was as low as 30%. In contrast, during the winter the aerosol was dry
below 60% RH. The spring months were characterized by a transitional behavior between
these two states. The observed seasonal behavior can be explained by the aerosol acidity. The summer aerosol was acidic and retained water at low RH. The winter aerosol was neutral
and became wet when the relative humidity reached the deliquescence point
of ammonium nitrate. The observations during July 2001 were compared with the
predictions of the thermodynamic Gibbs Free Energy Minimization (GFEMN) model and
the aerosol inorganics model (AIM), neglecting the organic aerosol contribution to water
absorption. The models under-predicted water concentrations by about 35%, but no clear
correlation between organic mass and the excess water was observed. On average, the
contribution of the organics to water absorption appeared to be higher during the afternoon
hours and when the aerosol was presumably more oxidized.
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