Characterization of atmospheric aerosol in the US Southeast from ground- and space-based measurements over the past decade

Abstract

Abstract. This study examines how aerosols measured from the ground and space over the US Southeast change temporally over a regional scale during the past decade. PM 2.5 (particulate matter with aerodynamic diameter > 2.5 micrometers) data consist of two datasets that represent the measurements that are used for regulatory purposes by the US EPA (Environmental Protection Agency) and continuous measurements used for quickly disseminating air quality information. AOD (aerosol optical depth) data come from three NASA sensors: the MODIS sensors onboard Terra and Aqua satellites and the MISR sensor onboard the Terra satellite. We analyze all available data over the state of Georgia from 2000-2009 of both types of aerosol data. The analysis reveals that during the summer the large metropolitan area of Atlanta has average PM 2.5 concentrations that are 50 % more than the remainder of the state. Strong seasonality is detected in both the AOD and PM 2.5 datasets, as evidenced by a threefold increase of AOD from mean winter values to mean summer values, and the increase in PM 2.5 concentrations is almost twofold over the same period. Additionally, there is agreement between MODIS and MISR onboard the Terra satellite during the spring and summer, having correlation coefficients of 0.64 and 0.71, respectively. Monthly anomalies were used to determine the presence of a trend in all considered aerosol datasets. We found negative linear trends for both the monthly AOD anomalies from MODIS onboard Terra and the PM 2.5 datasets, which are statistically significant. Decreasing trends were also found for MISR onboard Terra and MODIS onboard Aqua, but those trends were not statistically significant. The observed decrease in AOD and PM 2.5 concentrations may be indicative of the brightening over the study region during the past decade.

Aerosol loading in the Southeastern United States: reconciling surface and satellite observations

“…1 shows that the measured surface concentrations exhibit only a fraction of the seasonality in the column AOD observed by the satellite instruments, suggesting that changes in surface concentrations do not dictate the seasonality observed in AOD. This is in agreement with Alston et al (2012), who show that the summertime enhancement in surface PM 2.5 in Georgia is considerably less than the AOD enhancement over the region. This presents an intriguing disconnect between surface and column measurements of aerosol loading in the SEUS.…”

“…This is consistent with Alston et al (2012), who find a threefold increase in summertime AOD over wintertime, although they use a finer resolution product and therefore show greater spatial variability. The magnitude of both the seasonal mean and the relative enhancement differs among instruments as shown in the figure, but is spatially consistent.…”

“…Edgerton et al (2005) note a 15-20 % decrease in surface PM 2.5 mass in the region over the five-year period from 1999-2003, mainly attributable to declines in sulfate and organic matter. Using satellite measurements of AOD and surface PM 2.5 measurements over Georgia, Alston et al (2012) also suggest that aerosol loading over the Southeastern US declined from [2000][2001][2002][2003][2004][2005][2006][2007][2008][2009]. Additionally, Leibensperger et al (2012) suggest that anthropogenic aerosols are responsible for regional cooling over the Eastern US over the last century but that this radiative forcing has declined since 1990 mainly due to decreases in domestic emissions of sulfur dioxide.…”

Simulation of the interannual variations of aerosols in China: role of variations in meteorological parameters

“…Habib et al (2006) found by using the Total Ozone Mapping Spectrometer absorbing aerosol index data sets that the absorbing aerosol column burdens averaged over April-May of 1981-1992 exhibited a RSD of 16-30 % in different regions of India. Alston et al (2012) showed by using ground-based measurements at 41 sites in the southeastern United States (29 sites of PM 2.5 measurements provided by Environmental Protection Agency and 12 sites by Georgia Dept. of Natural Resources) that monthly mean PM 2.5 concentrations in that region had APDM values of 5-10 % over 2000-2009.…”

A Comparison of Meteorology-Driven Interannual Variations of Surface Aerosol Concentrations in the Eastern United States, Eastern China, and Europe

“…Observational and modeling studies have reported high aerosol concentrations in the eastern United States (US) (Malm 2004;Park et al 2003Park et al , 2004Walker et al 2012), eastern China (Zhang et al 2012b;Wang et al 2013;Mu and Liao 2014), and Europe (Megaritis et al 2014;Andersson et al 2007) as a result of the large anthropogenic emissions of aerosols and aerosol precursors in these regions (Dutkiewicz et al 2000;Vestreng et al 2007;Hand et al 2012;Mijling et al 2013). Previous studies also showed that the interannual variations (IAVs) of aerosols were significant in the eastern US (Alston et al 2012), eastern China (Yang et al 2011;Mu and Liao 2014), and Europe (Andersson et al 2007). The IAVs in aerosol concentrations were found to be sensitive to the IAVs in anthropogenic emissions of aerosols and aerosol precursors (Mylona 1996;Irie 2005;Ohara et al 2007;Vestreng et al 2007;Xing et al 2013) and in meteorological conditions, since the meteorology modulates the processes of dilution, transport, deposition, and chemical reaction (Andersson et al 2007;Zhao et al 2012;Mu and Liao 2014).…”