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ABSTRACT: Organic aerosol measurements with high temporal resolution can differentiate primary organic carbon (POC) from secondary organic carbon (SOC) and can be used to distinguish morning rush hour traffic emissions and subsequent photo-oxidation. In the current study, five hour filter samples were collected during the Summer Study for Organic Aerosols at Riverside (SOAR-1 in CA, USA) for analysis of organic molecular markers. To achieve the low detection limits required for the high temporal resolution data, a laboratory-based in situ methylation thermal desorption gas chromatography-mass spectrometry method was developed. This enabled the measurement of potential markers of SOC, including phthalic acid, along with markers for traffic emissions, including norhopane. The aromatic acids correlated well with unapportioned OC from a molecular marker chemical mass balance model (SOC-cmb; r(2) = 0.46-0.70) and SOC from the elemental carbon tracer method (SOC-ec; r(2) = 0.40-0.56). The aromatic acid/norhopane ratio increased substantially over the course of each day. The average mid-day phthalic acid ratio compared to previously published roadway emissions was a factor of 4 times higher, while the average 1,2,3-benzenetricarboxylic acid ratio was a factor of 40 times higher than roadway emissions. Using correlation plots of SOC-cmb and phthalic acid, it was estimated that 2.9 ± 0.6 μg m(-3) SOC was associated with mid-day aromatic acid production in Riverside.
Environmental Science & Technology 12/2010; 44(24):9398-404. · 4.80 Impact Factor
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ABSTRACT: Carbonaceous atmospheric particulate matter (PM25) collected in the midwestern United States revealed that soot emissions from incomplete coal combustion were important sources of several organic molecular markers used in source apportionment studies. Despite not constituting a major source of organic carbon in the PM25, coal soot was an important source of polyaromatic hydrocarbons, hopanes, and elemental carbon. These marker compounds are becoming widely used for source apportionment of atmospheric organic PM, meaning that significant emissions of these marker compounds from unaccounted sources such as coal soot could bias apportionment results. This concept was demonstrated using measurements of atmospheric PM collected on a 1-in-6 day schedule at three monitoring sites in Ohio: Mingo Junction (near Steubenville), Cincinnati, and Cleveland. Impacts of coal sootwere measured to be significant at Mingo Junction and small at Cleveland and Cincinnati. As a result, biases in apportionment results were substantial at Mingo Junction and insignificant at Cleveland and Cincinnati. Misapportionments of organic carbon mass at Mingo Junction were significant when coal soot was detected in the particulate samples as identified bythe presence of picene, but when coal soot was not included in the model: gasoline engines (+8% to +58% of OC), smoking engines (0% to -17% of OC), biomass combustion (+1% to +11% of OC), diesel engines (-1% to -2% of OC), natural gas combustion (0% to -2% of OC), and unapportioned OC (0% to -47% of OC). These results suggest that the role of coal soot in source apportionment studies needs to be better examined in many parts of the United States and other parts of the world.
Environmental Science and Technology 10/2009; 43(20):7770-7. · 5.23 Impact Factor
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ABSTRACT: Primary and secondary sources contributing to atmospheric organic aerosol during the months of July and August were quantitatively assessed in three North American urban areas: Cleveland, Ohio, and Detroit, Michigan, in the Midwest region and Riverside, California, in the Los Angeles Air Basin. Organic molecular marker species unique to primary aerosol sources and secondarytracers derived from isoprene, alpha-pinene, beta-caryophyllene, and toluene were measured using gas chromatography-mass spectrometry. Source contributions from motor vehicles, biomass burning, vegetative detritus, and secondary organic aerosol (SOA) were estimated using chemical mass balance (CMB) modeling. In Cleveland, primary sources accounted for 37 +/- 2% of ambient organic carbon, measured biogenic and anthropogenic secondary sources contributed 46 +/- 6%, and other unknown sources contributed 17 +/- 4%. Similarly, Detroit aerosol was determined to be 44 +/- 5% primary and 37 +/- 3% secondary, while 19 +/- 7% was unaccounted for by measured sources. In Riverside, 21 +/- 3% of organic carbon came from primary sources, 26 +/- 5% was attributed to measured secondary sources, and 53 +/- 3% came from other sources that were expected to be secondary in nature. The comparison of samples across these two regions demonstrated that summertime SOA in the Midwestern United States was substantially different from the summertime SOA in the Los Angeles Air Basin and indicated the need to exert caution when generalizing about the sources and nature of SOA across different urban areas. Furthermore, the results of this study suggestthatthe contemporary understanding of SOA sources and formation mechanisms is satisfactory to explainthe majority of SOA in the Midwest Additional SOA sources and mechanisms of formation are needed to explain the majority of SOA in the Los Angeles Air Basin.
Environmental Science and Technology 06/2009; 43(10):3448-54. · 5.23 Impact Factor
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Kenneth S Docherty,
Elizabeth A Stone,
Ingrid M Ulbrich,
Peter F DeCarlo, David C Snyder,
James J Schauer,
Richard E Peltier,
Rodney J Weber,
Shane M Murphy,
John H Seinfeld,
Brett D Grover,
Delbert J Eatough,
Jose L Jimenez
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ABSTRACT: Ambient sampling was conducted in Riverside, California during the 2005 Study of Organic Aerosols in Riverside to characterize the composition and sources of organic aerosol using a variety of state-of-the-art instrumentation and source apportionmenttechniques. The secondary organic aerosol (SOA) mass is estimated by elemental carbon and carbon monoxide tracer methods, water soluble organic carbon content, chemical mass balance of organic molecular markers, and positive matrix factorization of high-resolution aerosol mass spectrometer data. Estimates obtained from each ofthese methods indicate that the organic fraction in ambient aerosol is overwhelmingly secondary in nature during a period of several weeks with moderate ozone concentrations and that SOA is the single largest component of PM1 aerosol in Riverside. Average SOA/OA contributions of 70-90% were observed during midday periods, whereas minimum SOA contributions of approximately 45% were observed during peak morning traffic periods. These results are contraryto previous estimates of SOAthroughout the Los Angeles Basin which reported that, other than during severe photochemical smog episodes, SOA was lower than primary OA. Possible reasons for these differences are discussed.
Environmental Science and Technology 11/2008; 42(20):7655-62. · 5.23 Impact Factor
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ABSTRACT: Gaseous elemental mercury (GEM), particulate mercury (PHg) and reactive gaseous mercury (RGM) were measured every other hour at a rural location in south central Wisconsin (Devil's Lake State Park, WI, USA) between April 2003 and March 2004, and at a predominantly downwind urban site in southeastern Wisconsin (Milwaukee, WI, USA) between June 2004 and May 2005. Annual averages of GEM, PHg, and RGM at the urban site were statistically higher than those measured at the rural site. Pollution roses of GEM and reactive mercury (RM; sum of PHg and RGM) at the rural and urban sites revealed the influences of point source emissions in surrounding counties that were consistent with the US EPA 1999 National Emission Inventory and the 2003-2005 US EPA Toxics Release Inventory. Source-receptor relationships at both sites were studied by quantifying the impacts of point sources on mercury concentrations. Time series of GEM, PHg, and RGM concentrations were sorted into two categories; time periods dominated by impacts from point sources, and time periods dominated by mercury from non-point sources. The analysis revealed average point source contributions to GEM, PHg, and RGM concentration measurements to be significant over the year long studies. At the rural site, contributions to annual average concentrations were: GEM (2%; 0.04 ng m(-3)); and, RM (48%; 5.7 pg m(-3)). At the urban site, contributions to annual average concentrations were: GEM (33%; 0.81 ng m(-3)); and, RM (64%; 13.8 pg m(-3)).
Journal of Environmental Monitoring 02/2008; 10(1):102-8. · 1.99 Impact Factor
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ABSTRACT: Speciated measurements of atmospheric mercury plumes were obtained at an industrially impacted residential area of East St. Louis, IL. These plumes were found to result in extremely high mercury concentrations at ground level that were composed of a wide distribution of mercury species. Ground level concentrations as high as 235 ng m(-3) for elemental mercury (Hg0) and 38 300 pg m(-3) for reactive mercury species (reactive gaseous (RGM) plus particulate (PHg) mercury) were measured. The highest mercury concentrations observed during the study were associated with plumes that contained high concentrations of all mercury species (Hg0, RGM, and PHg) and originated from a source located southwest of the sampling site. Variations in proportions of Hg0/RGM/PHg among plumes, with Hg0 dominating some plumes and RGM and/or PHg dominating others, were attributed to differences in emissions from different sources. Correlations between mercury plumes and elevated NO(x) were not observed; however, a correlation between elevated SO2 and mercury plumes was observed during some but not all plume events. Despite the presence of six coal-fired power plants within 60 km of the study site, wind direction data along with Hg/SO2 and Hg/NO(x) ratios suggest that high-concentration mercury plumes impacting the St. Louis-Midwest Particle Matter Supersite are attributable to local point sources within 5 km of the site.
Environmental Science and Technology 09/2007; 41(16):5626-33. · 5.23 Impact Factor
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ABSTRACT: Considerable uncertainty still exists regarding the contribution of resuspended soil and road dust to PM2.5 organic carbon (OC) in US urban areas. Contributing factors are the limited knowledge of the OC content of resuspended soils and road dusts, and the variability of the ratio of OC to traditional soil markers such as silicon and aluminum. This study investigates the composition of resuspended soils and road dusts in the Midwestern US, and the contributions of these soils to atmospheric PM2.5 OC. Paved road dust and soil samples were resuspended in a residence chamber from which PM2.5 size fractions were collected and analyzed to generate source profiles. Differences significant to 1 standard deviation were observed in the mass ratios between OC, and silicon and aluminum across different soil types which were larger between soil types within each city (61–97%), than between samples of the same soil type collected in different cities (29–57%). CMB 8.2 source apportionment results revealed large biases in soil apportionments, but these did not greatly affect the overall OC apportionments in six Midwest cities due to the small contributions of soil to total OC (ranging between 0.01 and 0.1 μg m−3). Apportionments of total PM2.5 mass were more greatly affected: biases up to 0.7 μg m−3 for total PM2.5 masses ranging between 7 and 14 μg m−3 were observed when soil profiles were interchanged.
Atmospheric Environment. 45(2):514-518.
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ABSTRACT: Semi-continuous and 24-h averaged measurements of fine carbonaceous aerosols were made concurrently at three sites within each of two U.S. Midwestern Cities; Detroit, Michigan and Cleveland, Ohio; during two, one-month intensive campaigns conducted in July of 2007 and January & February of 2008. A comparison of 24-h measurements revealed substantial intra-urban variability in carbonaceous aerosols consistent with the influence of local sources, and excesses in both PM2.5 organic carbon (OC) and elemental carbon (EC) were identified at individual sites within each city. High time-resolved black carbon (BC) measurements indicated that elemental carbon concentrations were higher at sites adjacent to freeways and busy surface streets, and temporal patterns suggested that excess EC at sites adjacent to freeways was dominated by mobile source emissions while excesses in EC away from traffic corridors was dominated by point/area source emissions. The site-to-site variability in OC concentrations was approximately 7% within the neighborhood scale (0.5–4 km) and between 4 and 27% at the urban scale (4–100 km). In contrast, measurements of organic source tracers, in conjunction with a Chemical Mass Balance (CMB) source-apportionment model, indicated that the spatial variation in the contribution of both mobile and stationary sources to PM2.5 OC often exceeded the variation in OC mass concentration by a factor of 3 or more. Markers for mobile sources, biomass smoke, natural gas, and coal combustion differed by as much as 60% within the neighborhood scale and by greater than 200% within the urban scale. The observations made during this study suggest that the urban excess of carbonaceous aerosols is much more complex than has been previously reported and that a more rigorous, source-oriented approach should be taken in order to assess the risk associated with exposure to carbonaceous aerosols within the industrialized environments of the Midwestern United States.
Atmospheric Environment.
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ABSTRACT: Single-particle mass spectra were collected using an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) during December of 2003 and February of 2004 at an industrially impacted location in East St. Louis, IL. Hourly integrated peak areas for twenty ions were evaluated for their suitability in representing metals/metalloids, particularly those reported in the US EPA Toxic Release Inventory (TRI). Of the initial twenty ions examined, six (Al, As, Cu, Hg, Ti, and V) were found to be unsuitable due to strong isobaric interferences with commonly observed organic fragments, and one (Be) was found to have no significant signal. The usability of three ions (Co, Cr, and Mn) was limited due to suspected isobaric interferences based on temporal comparisons with commonly observed organic fragments. The identity of the remaining ions (Sb, Ba, Cd, Ca, Fe, Ni, Pb, K, Se, and Zn) was substantiated by comparing their signals with the integrated hourly signals of one or more isotope ions. When compared with one-in-six day integrated elemental data as determined by X-ray fluorescence spectroscopy (XRF), the daily integrated ATOFMS signal for several metal ions revealed a semi-quantitative relationship between ATOFMS peak area and XRF concentrations, although in some cases comparison of these measurements were poor at low elemental concentrations/ion signals due to isobaric interferences. A method of estimating the impact of local point sources was developed using hourly integrated ATOFMS peak areas, and this method attributed as much as 85% of the concentration of individual metals observed at the study site to local point sources. Hourly surface wind data were used in conjunction with TRI facility emissions data to reveal likely point sources impacting metal concentrations at the study site and to illustrate the utility of using single-particle mass spectral data to characterize atmospheric metals and identify point sources.
Atmospheric Environment.
