Coarse particulate matter concentrations from residential outdoor sites associated with the North Carolina Asthma and Children's Environment Studies (NC-ACES)

Coarse particulate matter (PM${}_{10\text{-}2.5})$ concentration data from residential outdoor sites were collected using portable samplers as part of an exposure assessment for the North Carolina Asthma and Children's Environment Studies (NC-ACES). PM${}_{10\text{-}2.5}$ values were estimated using the differential between independent PM${}_{10}$ and PM${}_{2.5}$ collocated MiniVol measurements. Repeated daily 24-h integrated PM${}_{10}$ and PM${}_{2.5}$ residential outdoor monitoring was performed at a total of 26 homes during September 2003–June 2004 in the Research Triangle Park, NC area. This effort resulted in the collection of 73 total daily measurements. This assessment was conducted to provide data needed to investigate the association of exposures to coarse particle PM mass concentrations with observed human health effects. Potential instrument bias between the differential MiniVol methodology and a dichotomous sampler were investigated. Results indicated that minimal bias of PM${}_{10\text{-}2.5}$ mass concentration estimates (slope $=$ 0.8, intercept $=0.36\mathrm{\mu }$g m${}^{-3})$ existed between the dichotomous and differential MiniVol procedures. Residential outdoor PM${}_{10\text{-}2.5}$ mass concentrations were observed to be highly variable across measurement days and ranged from 1.1 to $12.6\mathrm{\mu }$g m${}^{-3}$ (mean of $5.4\mathrm{\mu }$g m${}^{-3})$. An average correlation coefficient of $r=0.75$ existed between residential outdoor PM${}_{10\text{-}2.5}$ mass concentrations and those obtained from the central ambient monitoring site. Temporal and spatial variability of PM${}_{10\text{-}2.5}$ mass concentrations during the study were observed and are described in this report.     

Ammonia and ammonium measurements from the southeastern United States

Twenty-four-hour integrated gaseous ${\mathrm{NH}}_3$ and fine particulate $({\mathrm{PM}}_{2.5}){\mathrm{NH}}_4^{+}$ were measured during 2004 at eight sites in the southeastern U.S. Mean ${\mathrm{NH}}_3$ concentrations for 2004 ranged from 2.44 ppbv at an urban-industrial site in North Birmingham, AL, to 0.23 ppbv at a rural-forested site near Centreville, AL. ${\mathrm{NH}}_3$ mixing ratios were found to be higher at urban sites than at nearby rural (or suburban sites) except for sites which were directly influenced by local sources. Only weak correlations with temperature were observed for ${\mathrm{NH}}_3$ at the sites; slightly greater correlations were observed for total ammonia $({\mathrm{NH}}_x={\mathrm{NH}}_3+{\mathrm{NH}}_4^{+})$ vs. temperature. A weak seasonal variation was observed for ${\mathrm{NH}}_3$ mixing ratios at all sites, with all but one site exhibiting biannual maxima in spring and late summer/fall. Mean ${\mathrm{PM}}_{2.5}$ ${\mathrm{NH}}_4^{+}$ concentrations ranged from $1.78\mathrm{\mu }\mathrm{g}{\mathrm{m}}^{-3}$ in Atlanta, GA, to $1.02\mathrm{\mu }\mathrm{g}{\mathrm{m}}^{-3}$ at Oak Grove, MS, and were more uniform across the network than ${\mathrm{NH}}_3$ mixing ratios, with only slightly larger values at urban sites as compared to nearby rural (or suburban) sites. All sites exhibited highest ${\mathrm{NH}}_x$ between July and September and lowest ${\mathrm{NH}}_x$ in November and December. The gaseous ${\mathrm{NH}}_3$ fraction $({\mathrm{NH}}_3/({\mathrm{NH}}_3+{\mathrm{NH}}_4^{+}))$ was observed to decrease with increasing values of ${\mathrm{PM}}_{2.5}$ ${\mathrm{SO}}_4^{2-}$ at all sites. At two rural-forested sites and two sites near the Gulf of Mexico, the ${\mathrm{NH}}_3$ gaseous fraction approached a relatively constant value of 5–10% as ${\mathrm{PM}}_{2.5}{\mathrm{SO}}_4^{2-}$ increased beyond 5–$7\mathrm{\mu }\mathrm{g}{\mathrm{m}}^{-3}$, suggesting that ${\mathrm{NH}}_3$ availability at these locations limits aerosol neutralization.