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Blanchard C.L.,Envair | Hidy G.M.,AeroChem Research Laboratories | Shaw S.,EPRI | Baumann K.,Atmospheric Research and Analysis Inc. | Edgerton E.S.,Atmospheric Research and Analysis Inc.
Atmospheric Chemistry and Physics | Year: 2016

Long-term (1999 to 2013) data from the Southeastern Aerosol Research and Characterization (SEARCH) network are used to show that anthropogenic emission reductions led to important decreases in fine-particle organic aerosol (OA) concentrations in the southeastern US On average, 45 % (range 25 to 63 %) of the 1999 to 2013 mean organic carbon (OC) concentrations are attributed to combustion processes, including fossil fuel use and biomass burning, through associations of measured OC with combustion products such as elemental carbon (EC), carbon monoxide (CO), and nitrogen oxides (NOx). The 2013 mean combustion-derived OC concentrations were 0.5 to 1.4 μg-3 at the five sites operating in that year. Mean annual combustion-derived OC concentrations declined from 3.8 ± 0.2 μg-3 (68 % of total OC) to 1.4 ± 0.1 μg-3 (60 % of total OC) between 1999 and 2013 at the urban Atlanta, Georgia, site (JST) and from 2.9 ± 0.4 μg-3 (39 % of total OC) to 0.7 ± 0.1 μg-3 (30 % of total OC) between 2001 and 2013 at the urban Birmingham, Alabama (BHM), site. The urban OC declines coincide with reductions of motor vehicle emissions between 2006 and 2010, which may have decreased mean OC concentrations at the urban SEARCH sites by > 2 μg-3. BHM additionally exhibits a decline in OC associated with SO2 from 0.4 ± 0.04 μg-3 in 2001 to 0.2 ± 0.03 μg-3 in 2013, interpreted as the result of reduced emissions from industrial sources within the city. Analyses using non-soil potassium as a biomass burning tracer indicate that biomass burning OC occurs throughout the year at all sites. All eight SEARCH sites show an association of OC with sulfate (SO4) ranging from 0.3 to 1.0 μg-3 on average, representing ∼25 % of the 1999 to 2013 mean OC concentrations. Because the mass of OC identified with SO4 averages 20 to 30 % of the SO4 concentrations, the mean SO4-associated OC declined by ∼0.5 to 1 μg-3 as SO4 concentrations decreased throughout the SEARCH region. The 2013 mean SO4 concentrations of 1.7 to 2.0 μg-3 imply that future decreases in mean SO4-associated OC concentrations would not exceed ∼0.3 to 0.5 μg-3. Seasonal OC concentrations, largely identified with ozone (O3), vary from 0.3 to 1.4 μg-3 (∼20 % of the total OC concentrations). © Author(s) 2016.

Blanchard C.L.,Envair | Hidy G.M.,Envair Aerochem | Tanenbaum S.,Envair | Edgerton E.S.,Atmospheric Research and Analysis Inc.
Atmospheric Environment | Year: 2011

Carbonaceous compounds constitute a major fraction of the fine particle mass at locations throughout North America; much of the condensed-phase organic carbon (OC) is produced in the atmosphere from NMOC reactions as " secondary" OC (SOC). Ten years of particulate carbon and speciated non-methane organic compound (NMOC) data combined with other measurements from Southeastern Aerosol Research and Characterization (SEARCH) and other sites provide insight into the association between elemental carbon (EC), OC and NMOCs. Data are analyzed to characterize the OC and SOC contrasts between urban Atlanta, Georgia, and nearby non-urban conditions in the Southeast. Analysis of the monitoring record indicates that the mean Atlanta urban excess of total carbon (TC) is 2.1-2.8μgm -3. The OC/EC ratio of the Atlanta urban excess is in the range 1.3 to 1.8, consistent with OC/EC ratios observed in motor vehicle emissions and a fossil carbon source of urban excess TC. Carbon isotope analysis of a subset of particle samples demonstrates that the urban excess is mainly fossil in origin, even though the majority of the TC is modern at both urban and non-urban sites. Temperature-dependent partitioning of OC between gas and condensed phases cannot explain the observed diurnal and seasonal variations of OC/CO, EC/CO, and OC/EC ratios. Alternatively, a hypothesis involving vertical mixing of OC-enriched air from aloft is supported by the seasonal and diurnal OC, isopentane, aromatic and isoprene observations at the ground. A statistical model is applied to indicate the relative significance of aerometric factors affecting OC and EC concentrations, including meteorological and pollutant associations. The model results demonstrate strong linkages between fine particle carbon and pollutant indicators of source emissions compared with meteorological factors; the model results show weaker dependence of OC on meteorological factors than is the case for ozone (O 3) concentrations. © 2010 Elsevier Ltd.

Blanchard C.L.,Envair | Hidy G.M.,Envair Aerochem | Tanenbaum S.,Envair | Edgerton E.S.,Atmospheric Research and Analysis Inc. | Hartsell B.E.,Atmospheric Research and Analysis Inc.
Journal of the Air and Waste Management Association | Year: 2013

The SEARCH study began in mid 1998 with a focus on particulate matter and gases in the southeastern United States. Eight monitoring sites, comprising four urban/nonurban pairs, are located inland and along the coast of the Gulf of Mexico. Downward trends in ambient carbon monoxide (CO), sulfur dioxide (SO2), and oxidized nitrogen species (NOy) concentrations averaged 1.2 ± 0.4 to 9.7 ± 1.8% per year from 1999 to 2010, qualitatively proportional to decreases of 4.7 to 7.9% per year in anthropogenic emissions of CO, SO2, and oxides of nitrogen (NOx) in the SEARCH region. Downward trends in mean annual sulfate (SO4) concentrations ranged from 3.7 ± 1.1 to 6.2 ± 1.1% per year, approximately linear with, but not 1:1 proportional to, the 7.9 ± 1.1% per year reduction in SO2 emissions from 1999 to 2010. The 95th percentile of the March-October peak daily 8-hr ozone (O3) concentrations decreased by 1.1 ± 0.4 to 2.4 ± 0.6 ppbv per year (1.5 ± 0.6 to 3.1 ± 0.8% per year); O3 precursor emissions of NOx and volatile organic compounds (VOC) decreased at rates of 4.7 and 3.3% per year, respectively. Ambient particulate nitrate (NO3) concentrations decreased by 0.6 ± 1.2 to 5.8 ± 0.9% per year, modulated in comparison with mean annual ambient NOy concentration decreases ranging from 6.0 ± 0.9 to 9.0 ± 1.3% per year. Mean annual organic matter (OM) and elemental carbon (EC) concentrations declined by 3.3 ± 0.8 to 6.5 ± 0.3 and 3.2 ± 1.4 to 7.8 ± 0.7% per year. The analysis demonstrates major improvements in air quality in the Southeast from 1999 to 2010. Meteorological variations and incompletely quantified uncertainties for emission changes create difficulty in establishing unambiguous quantitative relationships between emission reductions and ambient air quality.Emissions and secondary pollutants show complex relationships that depend on year-to-year variations in dispersion and atmospheric chemistry. The observed response of O3 to NOx and VOC emissions in the Southeast implies that continuing reductions of precursor emissions, probably achieved through vehicle fleet turnover and emission control measures, will be needed to attain the National Ambient Air Quality Standard for O3. Reductions in fine particle concentrations have resulted from reductions of primary PM, especially EC and a portion of OM, and from reduction of gas precursors known to form particles, especially SO4 from SO2. Continued reduction of PM2.5 mass concentrations will require attention to organic constituents, which may be complicated by potentially unmanageable biogenic species present in the Southeast. © 2013 Copyright 2013 A&WMA.

Blanchard C.L.,Envair | Hidy G.M.,Envair Aerochem | Tanenbaum S.,Envair | Edgerton E.S.,Atmospheric Research and Analysis Inc. | Hartsell B.E.,Atmospheric Research and Analysis Inc.
Journal of the Air and Waste Management Association | Year: 2013

The Southeastern Aerosol Research and Characterization (SEARCH) study, which has been in continuous operation from 1999 to 2012, was implemented to investigate regional and urban air pollution in the southeastern United States. With complementary data from other networks, the SEARCH measurements provide key knowledge about long-term urban/nonurban pollution contrasts and regional climatology affecting inland locations and sites along the Gulf of Mexico coastline. Analytical approaches ranging from comparisons of mean concentrations to the application of air mass trajectories and principal component analysis provide insight into local and area-wide pollution. Gases (carbon monoxide, sulfur dioxide, nitrogen oxides, ozone, and ammonia), fine particle mass concentration, and fine particle species concentrations (including sulfate, elementary carbon, and organic carbon) are affected by a combination of regional conditions and local emission sources. Urban concentrations in excess of regional baselines and intraurban variations of concentrations depend on source proximity, topography, and local meteorological processes. Regional-scale pollution events (95th percentile concentrations) involving more than 6 of the 8 SEARCH sites are rare (< 2% of days), while subregional events affecting 4-6 sites occur on ~10% of days. Regional and subregional events are characterized by widely coincident elevated concentrations of ozone, sulfate, and particulate organic carbon, driven by persistent synoptic-scale air mass stagnation and higher temperatures that favor formation of secondary species, mainly in the summer months. The meteorological conditions associated with regional stagnation do not favor long-range transport of polluted air masses during episodes. Regional and subregional pollution events frequently terminate with southward and eastward penetration of frontal systems, which may initially reduce air pollutant concentrations more inland than along the Gulf Coast.Regional distribution of emission sources and synoptic-scale meteorological influences favoring stagnation lead to high regionwide pollution levels. The regional influence is greatest with secondary species, including ozone (O3) particulate sulfate (SO4), and particulate organic matter, some of which is produced by atmospheric oxidation of volatile organic compounds (VOCs) from vegetation and anthropogenic sources. Other species, many of which are from primary emissions, are more influenced by local sources, especially within the Atlanta, GA, and Birmingham, AL, metropolitan areas. Limited measurements of modern and fossil total carbon point to the importance of biological and biogenic emissions in the Southeast. © 2013 Copyright 2013 A&WMA.

Blanchard C.L.,Envair | Tanenbaum S.,Envair | Hidy G.M.,Envair Aerochem
Atmospheric Environment | Year: 2014

Quantification of the spatial and temporal variations of outdoor air pollutant concentrations provides important information for epidemiological and other air-pollution studies, many of which have relied in the past on data from a single, centrally-located air pollution monitoring site. A method is developed for combining air pollution measurements from multiple monitors and monitoring networks to generate daily air pollution concentration fields representing spatial variations over distances of approximately 1-10km. Meteorological and co-pollutant data are used to estimate missing site measurements, yielding more realistic concentration fields as the number of monitoring locations with available data increases. Monitoring data are interpolated with weights computed from intersite pollutant correlations, which decay with distance, so distances between interpolation points and monitoring sites are factored into the interpolation weights. The approach minimizes the influence of source-oriented sites that represent limited areas, because data from such sites exhibit low intersite correlations and yield interpolation weights that decay rapidly to zero. Interpolated values represent pollutant concentrations averaged over spatial scales that depend on intersite distances and the interpolation grid, and do not delineate sharp spatial gradients associated with roadside or near-source conditions. The approach yields quantified interpolation errors the values of which depend on measurement uncertainties, intersite distances, and the representativeness of monitoring site locations. The method is illustrated using an 11-year period of measurements of ozone, PM2.5, and PM10 concentrations from Jefferson County, Alabama. The principal city is Birmingham, which is influenced by regional-scale air pollution and by local emissions from mobile sources, industrial facilities, and residential communities. Emission sources are not distributed uniformly throughout Birmingham, the ridge-and-valley topography complicates dispersion of local emissions, and monitoring data indicate that air pollutant concentrations vary spatially as well as temporally. No single monitor represents air quality across the entire study area. © 2014 Elsevier Ltd.

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