Spatial and seasonal patterns in urban influence on regional concentrations of speciated aerosols across the United States

Abstract

Monthly, seasonal, and annual mean estimates of urban influence on regional concentrations of major aerosol species were computed using speciated aerosol data from the rural IMPROVE network (Interagency Monitoring of Protected Visual Environments) and the United States Environmental Protection Agency's urban Chemical Speciation Network for the 2008 through 2011 period. Aggregated for sites across the continental United States, the annual mean and one standard error in urban excess (defined as the ratio of urban to nearby rural concentrations) was highest for elemental carbon (3.3 ± 0.2), followed by ammonium nitrate (2.5 ± 0.2), particulate organic matter (1.78 ± 0.08), and ammonium sulfate (1.23 ± 0.03). The seasonal variability in urban excess was significant for carbonaceous aerosols and ammonium nitrate in the West, in contrast to the low seasonal variability in the urban influence of ammonium sulfate. Generally for all species, higher excess values in the West were associated with localized urban sources while in the East excess was more regional in extent. In addition, higher excess values in the western United States in winter were likely influenced not only by differences in sources but also by combined meteorological and topographic effects. This work has implications for understanding the spatial heterogeneity of major aerosol species near the interface of urban and rural regions and therefore for designing appropriate air quality management strategies. In addition, the spatial patterns in speciated mass concentrations provide constraints for regional and global models.

Sources and composition of PM2.5 in the Colorado Front Range during the DISCOVER‐AQ study

“…Hand et al . [] also found evidence for local sources of ammonium and nitrate affecting Denver aerosol. Figure is consistent with this finding, as ammonium showed a pronounced midday increase consistent with local emissions.…”

“…Both components showed relatively modest concentration enhancements during the day, with peak concentrations around 12:00–14:00 local time. Past studies suggest that OM and sulfate are predominantly regional during summer in the Colorado Front Range [ Hand et al ., ; Xie et al ., ]. Wind rose analyses showed no enhancements in either the OM or the sulfate concentration as a function of wind direction (not shown), consistent with a regional source for both components.…”

“…Hand et al . [] showed that EC is strongly affected by local sources in Denver during summer, as EC concentrations within the city are approximately three times higher than in surrounding rural areas.…”

“…Rapid expansion of oil and gas operations over the past decade has contributed to changing air quality in the region [ Pétron et al ., ; Thompson et al ., ]. On the regional scale, sulfate and secondary organic aerosols (SOA) from biogenic VOC emissions make important contributions to aerosol levels [ Hand et al ., ; Xie et al ., ]. Finally, aerosol concentrations in the region are subject to intermittent influences from the long‐range transport of fire, dust, and marine air [ Hallar et al ., ; Young et al ., ].…”

Regionalization based on spatial and seasonal variation in ground-level ozone concentrations across China

“…This topographic effect reflects near-surface air flow and meteorological conditions. Some studies had shown the topographic effects on air convection, winds, precipitation and aerosols components (Xiao and Wu, 1995;Sharman and Wurtele, 2004;Zhao et al, 2012;Smith and Barstad, 2004;Hand et al, 2014). Therefore we surmise that a regionalization based on ozone could be more appropriately determined through use of spatial distribution of the modes as well as topographic information.…”