Browsing by Author "Takahama, S"

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    Semi-continuous PM2.5 inorganic composition measurements during the Pittsburgh Air Quality Study
    (Atmospheric Environment, 2004-06-01) Wittig, AE; Takahama, S; Khlystov, AY; Pandis, SN; Hering, S; Kirby, B; Davidson, C
    A method for semi-continuous (10min time resolution) PM2.5 nitrate and sulfate measurements, based on the humidified impaction with flash volatilization design of Stolzenburg and Hering (Environ. Sci. Technol. 34 (2000) 907), was evaluated during the Pittsburgh Air Quality Study (PAQS) from July 2001 to August 2002. The semi-continuous measurements were corrected for several operating parameters. The overall corrections were less than 10% on average, but could be quite large for individual 10min measurements. These corrections resulted in an improvement in the agreement of the measurements with the filter-based measurements, with a major axis regression relationship of y=0.83x+0.20μgm-3 and R2 of 0.84 for nitrate and y=0.71x+0.42μgm-3 and R2 of 0.83 for sulfate. The corrected semi-continuous measurements were calibrated over the entire year using collocated denuder/filter-pack-based measurements. These calibrated semi-continuous measurements are used in conjunction with temporally resolved gas-phase measurements of total (gas- and aerosol-phase) nitrate and meteorological measurements to investigate short-term phenomena at the Pittsburgh Supersite. The gas-to-particle partitioning of nitrate varied daily and seasonally, with a majority of the nitrate in the particle phase at night and during the winter months. © 2004 Elsevier Ltd. All rights reserved.
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    Water content of ambient aerosol during the Pittsburgh air quality study
    (JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 2005) Khlystov, A; Stanier, CO; Takahama, S; Pandis, SN
    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.