Environmental Health Perspectives Volume 105, Number 8, August 1997
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The Metropolitan Acid Aerosol Characterization Study: Results from the Summer 1994 Washington, D.C. Field Study
Helen H. Suh,
1
Yurika Nishioka,
1
George A. Allen,
1
Petros Koutrakis,
1
and Robert M. Burton
2
1
Harvard University, School of Public Health, Boston, MA 02115 USA;
2
National Exposure Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 USA
Abstract
An ambient particle monitoring study was conducted in Washington, D.C. during the summer of 1994 as part of the Metropolitan Acid Aerosol Characterization Study (MAACS). Acid aerosol and inhalable (particulate matter with aerodynamic diameters <10 µm; PM
10
) and fine (particulate matter with aerodynamic diameters <2.5 µm; PM
2.5
) particle samples were collected for 24-hr periods (9 a.m.-9 a.m. EDT) on alternate days at six monitoring sites located throughout the greater Washington, D.C. area. Monitoring sites were located in both urban and rural areas and were generally situated along a southwest to northeast line due to the prevailing winds. Information on site characteristics, including population density and distance from the city center, was also obtained, as were data on meteorological parameters. Results from this study show strong correlations among the particulate measures, PM
10
, PM
2.5
, SO
4
2-
, and H
+
. These strong correlations resulted from the fact that PM
2.5
comprised 77% of PM
10
, with SO
4
2-
-related species accounting for 49% of total PM
2.5
. PM
10
, PM
2.5
, SO
4
2-
, and H
+
concentrations were found to be uniform across the metropolitan Washington area. Spatial variation was found, however, for coarse particles (PM
2.5-10
) and NH
3
concentrations. In our previous Philadelphia study, population density was an important determinant of spatial variation in coarse particles and NH
3
concentrations; however, in Washington, D.C., population density was not associated with observed spatial patterns in coarse particle concentrations, but was an important determinant of NH
3
concentrations. When data from one site (Reservoir) was excluded from the analysis, population density explained a larger percentage of the variability in NH
3
levels and became an important determinant of the H
+
/SO
4
2-
ratio as well. Ambient H
+
models developed from Philadelphia data were found to predict H
+
concentrations in Washington, D.C. reasonably well, representing an improvement over measurements made at a single stationary ambient monitoring site.
Key words
: ambient concentrations, ammonia, particulate matter, population density, spatial variation.
Environ Health Perspect
105:826-834 (1997)
Address correspondence to H.H. Suh, Harvard University, School of Public Health, 665 Huntington Avenue, Boston, MA 02115 USA.
The authors would like to thank M. Davey and D. Krask of the Washington, D.C. Air Resources Management Division, R. McIntyre of the Fairfax County Health Department, and D. Belliveau and G. Magil for their help. This study was funded by EPA (#CR-822050). Funding for H.H.S. was provided by the Center for Indoor Air Research.
This study was subjected to EPA's peer and administrative review and has been approved as an EPA document.
Received 15 January 1997; accepted 18 March 1997.
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