%0 Journal Article
%T Spatial and Temporal Trends in PM2.5 Organic and Elemental Carbon across the United States
%A J. L. Hand
%A B. A. Schichtel
%A W. C. Malm
%A N. H. Frank
%J Advances in Meteorology
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/367674
%X The rural/remote IMPROVE network (Interagency Monitoring of Protected Visual Environments) and the Environmental Protection Agency's urban Chemical Speciation Network have measured PM2.5 organic (OC) and elemental carbon (EC) since 1989 and 2000, respectively. We aggregated OC and EC data from 2007 to 2010 at over 300 sites from both networks in order to characterize the spatial and seasonal patterns in rural and urban carbonaceous aerosols. The spatial extent of OC and EC was more regional in the eastern United States relative to more localized concentrations in the West. The highest urban impacts of OC and EC relative to background concentrations occurred in the West during fall and winter. Urban and rural carbonaceous aerosols experienced a large (although opposite) range in seasonality in the West compared to a much lower seasonal variability in the East. Long-term (1990¨C2010) trend analyses indicated a widespread decrease in rural TC (TC = OC + EC) across the country, with positive, though insignificant, trends in the summer and fall in the West. Short-term trends indicated that urban and rural TC concentrations have both decreased since 2000, with the strongest and more spatially homogeneous urban and rural trends in the West relative to the East. 1. Introduction Carbonaceous aerosols, including organic (OC) and elemental (EC) carbon, are ubiquitous in the atmosphere and therefore contribute significantly to particulate matter, both the PM2.5 fraction [1] and coarse (PM10£¿PM2.5) fraction [2, 3], and they contribute to visibility degradation [4, 5] and climate forcing due to their ability to scatter and absorb solar radiation [6, 7]. Carbonaceous aerosols also adversely affect health [8, 9]. Organic carbon can be emitted directly from combustion activities or produced from secondary processes such as gas-to-particle formation. Elemental carbon, also known as light absorbing carbon or black carbon depending on the measurement method, is emitted directly from combustion sources. EC plays a significant role in climate forcing, and a recent review [10] suggests that the climate warming effects of EC are greater than previously thought, although large uncertainties still exist. Characterizing and predicting the complex nature of OC and EC are challenging from both a measurement and modeling framework. However, this characterization is necessary given the importance of OC and EC to many atmospheric processes and climate impacts. Comprehensive speciation of carbonaceous aerosols is expensive and time-consuming and therefore usually possible only at a
%U http://www.hindawi.com/journals/amete/2013/367674/