Quantitative investigation of source and elemental composition of indoor and outdoor fine particulate air pollution in Houston.
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An investigation was undertaken to determine the chemical characterization of inhalable particulate matter in the Houston area, with special emphasis on source identification and apportionment of outdoor and indoor atmospheric aerosols using multivariate statistacal analyses. Fine (< 2.5 um) particle aerosol samples were collected by means of dichotomous samplers at two fixed site (Clear Lake and Sunnyside) ambient monitoring stations and one mobile monitoring van in the Houston area during June-October 1981 as part of the Houston Asthma Study. The mobile van allowed particulat sampling to take place both inside and outside of twelve homes. The samples collected for 12-h sampling on a 7 am-7 pm and 7 pm-7 am (CDT) schedule were analyzed for mass, trace elements, and two anions. Mass was determined gravimetrically. An energydispersive x-ray fluorescence (XRF) spectrometer was used for determination of elemental composition. Ion chromatography (IC) was used to determine sulfate and nitrate. Average chemical composition of fine aerosol at each site were presented. Sulfate was found to be the largest single component of the fine fraction mass, comprising the approximately 30% of the fine mass outdoors and 12% indoors, respectively. Principal components analysis (PCA) was applied to identify sources of aerosols and to assess the role of meteorological factors on the variation in particulat samples. The results sug- gested that meteorological parameters were not associated with sources of aerosol samples collected at these Houston sites. Source factor contributions to fine mas were calculated using a combination of PCA and stepwise multivariate regression analysis. It was found that much of the total fine mass was apparently contributed by sulfate-related aerosols. The average contributions to the fine mass coming from the sulfate-related aerosols were 56% of the Houston outdoor ambient fine particulate matter and 26% of the indoor fine particulate matter. Characterization of indoor aerosol in residential environments was compared with the results for outdoor aerosols. It was suggested that much of the indoor aerosol may be due to outdoor sources, but there may be important contributions from common indoor sources in the home environment such as smoking and gas cooking.