Environ. Sci. Technol. 2008, 42, 3524–3530
Source Apportionment and Spatial Distributions of Coarse Particles During the Regional Air Pollution Study I N J O H W A N G , †,§ P H I L I P K . H O P K E , * ,† AND JOSEPH P. PINTO‡ Department of Chemical and Biomolecular Engineering, Clarkson University, Potsdam, New York 13699-5708 and U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711
Received July 2, 2007. Revised manuscript received January 25, 2008. Accepted February 7, 2008.
To identify the coarse particle sources and to estimate the variability in their contributions to coarse particle mass (CPM) concentrations across the St. Louis metropolitan area, positive matrix factorization (PMF) was applied to historic ambient coarse particle compositional data from 10 Regional Air Pollution Study/Regional Air Monitoring System (RAPS/RAMS) monitoring sites in St. Louis. Coarse particles in this study had aerodynamic sizes between 2.4 and 20 µm. The sources were qualitatively identified, and the source contributions were quantitatively estimated. Nine sources were identified for 8 of the 10 sampling sites (except rural sites 122 and 124) including soil, cement kiln/quarry, iron and steel, motor vehicle, incinerator, pigment plant, primary/secondary lead smelter, zinc smelter, and copper production, respectively. At site 122, five sources were identified as soil, cement kiln/quarry, motor vehicle, incinerator, and zinc smelter. At site 124, six sources were identified as soil, cement kiln/quarry, motor vehicle, incinerator, primary/secondary lead smelter, and zinc smelter. Soil was the largest coarse particle source across the study area (6.15 µg/m3, 29.3%). Cement kiln/quarry, iron and steel, and motor vehicle sources were the other large contributions to the coarse particles mass (5.27 µg/m3, 25.1%; 3.53 µg/m3, 16.8%; 2.72 µg/m3, 12.9%). The results of this study suggest there can be significant potential for exposure misclassification in timeseries epidemiologic studies when regressing health outcomes against source contributions if they were to be estimated at a single central monitoring site.
Introduction The U.S. Environmental Protection Agency (EPA) issued the first National Ambient Air Quality Standards (NAAQS) for total suspended particles in 1971 in order to protect public health and welfare. Since issuance of the NAAQS in 1971, the EPA revised particulate matter (PM) standards to PM10 in 1987, and added PM2.5 in 1997. Recently the U.S. EPA considered the promulgation of a NAAQS for inhalable coarse * E-mail address:
[email protected] (P.K. Hopke). † Clarkson University. ‡ U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, USA. § Current address: Department of Environmental Engineering, Daegu University, Gyeongsan, Gyeongbuk, South Korea. 3524
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particulate matter (smaller than 10 µm in diameter but larger than PM2.5). The new standard would have been limited to urban areas, excluding agricultural sources, mining sources, and other similar sources of crustal materials (1, 2). Although the EPA ultimately chose not to establish a new indicator at this time, there is a need to better understand the spatial variability of coarse particles and the variation in exposure to coarse particles arising from different sources across urban areas. Unfortunately, there are very limited data sets available in which coarse particle compositions are provided at multiple sites within a given urban area. Only the Regional Air Pollution Study (RAPS) of the mid-1970s provides such data. Although these data were collected 30 years ago, many of the major sources present at that time are still in operation, and the results provide insights into the distribution of coarse particles from multiple sources across a complex urban area as no other data set does. The Regional Air Pollution Study/Regional Air Monitoring System (RAPS/RAMS) (3–5) conducted in St. Louis, Missouri between 1975 and 1977 is a study with enough data to evaluate the spatial heterogeneity of PM20–2.4 (particulate matter between 2.4 and 20.0 µm in aerodynamic diameter), its components, and its source contributions across an urban area. Kim et al. (6) evaluated the spatial heterogeneity in source contributions to the RAPS/RAMS PM2.5 data set. Although the upper size cutoff of the dichotomous sampler used in the RAPS study was 20 µm, the coarse particle behavior for PM20–2.4 and the variability of the source emissions across the region permit the exploration of the issues of spatial heterogeneity of the source impacts and the problem of the extent of impact of coarse urban particles. Although there will be some additional deposition of 10-20 µm particles relative to PM10 deposition, respiration of particles into larger sizes does occur. Inhalable particles include sizes all the way up to 100 µm and, thus, these data are relevant for understanding the spatial distribution of PM10 and related exposure issues. There has been limited prior analyses of the RAPS coarse particle data. Alpert and Hopke (3) examined several small subsets of the data, including two months of data at one site and one week of data at all of the sites. There has not previously been a comprehensive study of all of the data from all of the sites. Epidemiologic studies of the effects of exposure to pollutants typically use the concentrations measured at a single site as being representative of the exposure across the urban area. If the concentrations differ across an urban area, there is a potential for exposure misclassification in these epidemiologic studies. Particularly, if materials from specific sources are important in inducing or exacerbating health effects or if there are major differences in the source contributions across an urban area, then low site-to-site correlations among source contributions or exposure misclassification could be important in interpreting health effects model results for coarse particles. Therefore, the objective of this study is to characterize the spatial uniformity in coarse particle source contributions so that the potential for exposure characterization error in health outcome studies can be better understood. Positive matrix factorization (PMF) was applied to an ambient coarse particles compositional data from the 10 RAPS/RAMS sites to identify the coarse particle sources and to estimate their contributions to coarse particles mass concentrations in the St. Louis metropolitan area. The spatial variability in these source contributions is discussed. 10.1021/es0716204 CCC: $40.75
2008 American Chemical Society
Published on Web 04/05/2008
FIGURE 1. Location of the 10 sampling sites with site numbers and major point sources.
TABLE 1. Summary of RAPS Sampling Sites and Statistics for the Coarse Particles Concentrations at Each Site in St. Louis, Missouri between 1975 and 1977 Location site
latitude
longitude
No. of Samples
AMa
SDb
GMc
Min
Max
103 105 106 108 112 115 118 120 122 124
38.658 38.605 38.616 38.736 38.648 38.793 38.486 38.695 69.081 38.244
-90.155 -90.201 -90.259 -90.142 -90.312 -90.040 -90.213 -90.435 -90.207 -90.152
482 506 382 397 467 451 451 439 464 362
29.74 24.69 22.64 23.08 23.61 17.99 16.60 16.82 16.45 13.83
17.09 14.09 11.76 13.57 16.06 10.67 9.47 8.83 11.03 7.85
24.38 20.59 19.43 18.46 18.68 14.61 13.77 14.42 12.78 11.67
1.90 0.90 2.50 0.25 1.60 0.30 0.80 1.25 0.60 0.50
106.80 87.68 61.65 69.85 114.40 63.55 59.99 49.60 52.40 46.00
a
Arithmetic mean.
b
Standard deviation. c Geometric mean.
Experimental Methods Sample Collection and Data Analysis. The ambient coarse particle samples were collected at 10 sampling sites in St. Louis metropolitan area as part of the St. Louis RAPS (3, 4). Figure 1 shows the location of the 10 sampling sites with site numbers and major point sources. Industries located in the St. Louis metropolitan area include steel mills, a secondary lead smelter, and nonferrous metal facilities (7). Coarse and fine particle samples were collected using automatic dichotomous samplers between May 1975 and April 1977 (8). The normal sampling procedure consisted of integrated 12 h sampling intervals at all sites except sites 103 and 105, where
6 h samples were standard. During intensive study periods in the summer of 1975, 6 h samples were obtained at 7 sites (sites 106, 108, 115, 118, 120, 122, and 124) and 2 h samples were obtained at 3 sites (sites 103, 105, and 112) (9). Table 1 shows a summary of sampling sites and statistics for the coarse particles concentrations at each site in St. Louis, Missouri over the sampling period from 1975 to 1977. A two-stage virtual impactor sampler separated particles into two size fractions: fine particles (
