Spatial and Temporal Variation in PM _2.5 Chemical Composition in the United States for Health Effects Studies

Abstract

BackgroundAlthough numerous studies have demonstrated links between particulate matter (PM) and adverse health effects, the chemical components of the PM mixture that cause injury are unknown.ObjectivesThis work characterizes spatial and temporal variability of PM2.5 (PM with aerodynamic diameter < 2.5 μm) components in the United States; our objective is to identify components for assessment in epidemiologic studies.MethodsWe constructed a database of 52 PM2.5 component concentrations for 187 U.S. counties for 2000–2005. First, we describe the challenges inherent to analysis of a national PM2.5 chemical composition database. Second, we identify components that contribute substantially to and/or co-vary with PM2.5 total mass. Third, we characterize the seasonal and regional variability of targeted components.ResultsStrong seasonal and geographic variations in PM2.5 chemical composition are identified. Only seven of the 52 components contributed ≥ 1% to total mass for yearly or seasonal averages [ammonium (NH4+), elemental carbon (EC), organic carbon matter (OCM), nitrate (NO3−), silicon, sodium (Na+), and sulfate (SO42−)]. Strongest correlations with PM2.5 total mass were with NH4+ (yearly), OCM (especially winter), NO3− (winter), and SO42− (yearly, spring, autumn, and summer), with particularly strong correlations for NH4+ and SO42− in summer. Components that co-varied with PM2.5 total mass, based on daily detrended data, were NH4+, SO42−, OCM, NO32−, bromine, and EC.ConclusionsThe subset of identified PM2.5 components should be investigated further to determine whether their daily variation is associated with daily variation of health indicators, and whether their seasonal and regional patterns can explain the seasonal and regional heterogeneity in PM10 (PM with aerodynamic diameter < 10 μm) and PM2.5 health risks.

Ionic Composition in Aqueous Extracts from PM2.5 in Ambient Air at the City of Cuernavaca, M&#233;xico

“…It is important to emphasize that these percentages may vary if the presence of other ion species is taken into account. [16] who, from a study of 187 communities in the United States noted that the sulfates and ammonium species were the main contributors to PM2.5, a similar situation to what was observed in this study.…”

“…Such a condition could be due to the warm climate that characterizes the city of Cuernavaca and does not favor the formation of nitrate in PM2.5 [21]. Aldabe et al (2011) [20] and Bell et al (2007) [16] report high concentration levels of nitrates in winter and low concentrations in summer in PM2.5, suggesting the likelihood that this condition is due to the low thermal stability of NH 4 NO 3 in summer, under warm conditions where HNO 3 formation is favored [20]. A longer study of the composition of ions associated with PM2.5 would confirm this condition in the city of Cuernavaca and also yield information about the temporal variation of nitrate in PM2.5.…”

“…Also it is observed that the presence of Cl − suggests that this may come from combustion emissions during cooking, coal cars, vegetation burning and incineration [25] [16] The presence of K + in the aqueous extracts from PM2.5 may well have a geological origin, or to be related to emissions from biomass burning [26]. It is likely that for the city of Cuernavaca part of the K + could be originated from soil particles, due to the significant correlation with Ca 2+ [26].…”

Long-term dust climatology in the western United States reconstructed from routine aerosol ground monitoring

“…for other purposes, such as monitoring visibility (Pitchford and Malm, 1994) and protecting human health (Bell et al, 2007). Therefore, it is difficult to utilize these monitors to identify dust events because the monitoring sites are either deployed far away from dust active regions (most likely collocated with dense population) or contaminated by anthropogenic sources.…”

Earth’s Climate System

“…Exposure to small (Dominici et al 2006) and/or toxic (Bell et al 2007) aerosols has deleterious effects on human health. As a consequence, movements are underway throughout the world to reduce both the direct emission of aerosols as well as the emission of aerosol precursors.…”