Federal Reference Method Research Articles

Improving the correlations of ambient tapered element oscillating microbalance PM2.5 data and SHARP 5030 Federal Equivalent Method in Ontario: A multiple linear regression analysis

Tapered element oscillating microbalances equipped with sample equilibration system (TEOM-SES) used by the province of Ontario for the ambient monitoring of PM2.5 (particulate matter with an aerodynamic diameter ≤2.5 µm) in its air quality index (AQI) network were collocated with the Synchronized Hybrid Ambient Real-time Particulate monitor (SHARP 5030) at two monitoring sites for a period spanning approximately 2 years to determine the similarities and differences between the measurement outputs of both instrumental systems. Due mainly to mass loss observed with the TEOM-SES in cooler months, the province has recently switched its PM2.5 instrumentation at all stations in its monitoring network from the TEOM-SES to the SHARP 5030, which has the U.S. Environmental Protection Agency (EPA) Federal Equivalent Method (FEM) Class III designation. Thus, it has become imperative to develop corrections for historical and future TEOM measurements for the purpose of making them more agreeable to the new FEM method. This work details the authors’ multiple linear regression analyses (MLRAs) of particulate matter data from both instrumental monitors, with the inclusion of operational parameters of physicochemical relevance for both cases of transformations of historical TEOM and TEOM measurements to be made in the future. For historical TEOM data, it was observed that the transformations only benefited winter and fall months. Furthermore, comparisons of the transformed historical TEOM data with PM2.5 concentrations determined from the Federal Reference Method (FRM) sampler at seven locations within the province showed marked improvements over the observed TEOM-FRM comparisons. Implications:This work provides a path to correcting the historically observed underreporting of particulate mass in winter and fall in Ontario by making the TEOM-based continuous data resemble the new FEM outputs (in this case, more SHARP-like). It is possible that the transformation of mainly winter TEOM data as detailed in this work may potentially lead to revisions in historical annual composite mean PM2.5 concentrations and total annual number of days PM2.5 exceeded the Canada-wide Standard (CWS) metric across the province.

Identification of potential source areas for elevated PM2.5, nitrate and sulfate concentrations

Extreme events or episodes of ambient fine particulate matter (PM2.5), in which daily mass concentrations are substantially higher than annual averages, have been frequently observed in southern Wisconsin, US. Determining the cause of events has been a great challenge to local governments responsible for protecting public health and complying with the 24-h PM2.5 standard. This study analyzed air parcel movements originating from emission source areas, and trends in PM2.5 concentrations in order to determine the important factors involved in elevated PM2.5 episodes in the region. A single backward trajectory analysis coupled with PM2.5 concentrations observed at Federal Reference Method Network (FRM) sites in Madison, Milwaukee and Waukesha; and nitrate and sulfate concentrations monitored at a Chemical Speciation Network (CSN) site in Milwaukee, Wisconsin, from 2002 to 2010 were examined. The PM2.5 concentrations from the FRM showed the total PM2.5 mass during the episodes were higher in Madison than in Milwaukee and Waukesha, while annual average concentrations were lower in Madison. However, the temporal trend in frequency of elevated PM2.5 episodes was remarkably similar across sites during the entire study period and high frequency episodes occurring from 2005 to 2007. Residence time analysis of backward trajectories calculated for all recorded data indicated episode changes were mainly driven by year-to-year variations of air mass movements originating in high emissions areas. Potential Source Contribution Function (PSCF) results showed the extreme events of PM2.5 occurred during times when trajectories passed over ammonia emissions hotspots as well as large stationary emissions. Enhanced nitrate and sulfate concentrations which were the major episode components were strongly influenced by air masses trajectories originating from the Ohio River Valley and adjacent states.

Statistical air quality predictions for public health surveillance: evaluation and generation of county level metrics of PM2.5 for the environmental public health tracking network

BackgroundThe Centers for Disease Control and Prevention (CDC) developed county level metrics for the Environmental Public Health Tracking Network (Tracking Network) to characterize potential population exposure to airborne particles with an aerodynamic diameter of 2.5 μm or less (PM2.5). These metrics are based on Federal Reference Method (FRM) air monitor data in the Environmental Protection Agency (EPA) Air Quality System (AQS); however, monitor data are limited in space and time. In order to understand air quality in all areas and on days without monitor data, the CDC collaborated with the EPA in the development of hierarchical Bayesian (HB) based predictions of PM2.5 concentrations. This paper describes the generation and evaluation of HB-based county level estimates of PM2.5.MethodsWe used three geo-imputation approaches to convert grid-level predictions to county level estimates. We used Pearson (r) and Kendall Tau-B (τ) correlation coefficients to assess the consistency of the relationship, and examined the direct differences (by county) between HB-based estimates and AQS-based concentrations at the daily level. We further compared the annual averages using Tukey mean-difference plots.ResultsDuring the year 2005, fewer than 20% of the counties in the conterminous United States (U.S.) had PM2.5 monitoring and 32% of the conterminous U.S. population resided in counties with no AQS monitors. County level estimates resulting from population-weighted centroid containment approach were correlated more strongly with monitor-based concentrations (r = 0.9; τ = 0.8) than were estimates from other geo-imputation approaches. The median daily difference was −0.2 μg/m3 with an interquartile range (IQR) of 1.9 μg/m3 and the median relative daily difference was −2.2% with an IQR of 17.2%. Under-prediction was more prevalent at higher concentrations and for counties in the western U.S.ConclusionsWhile the relationship between county level HB-based estimates and AQS-based concentrations is generally good, there are clear variations in the strength of this relationship for different regions of the U.S. and at various concentrations of PM2.5. This evaluation suggests that population-weighted county centroid containment method is an appropriate geo-imputation approach, and using the HB-based PM2.5 estimates to augment gaps in AQS data provides a more spatially and temporally consistent basis for calculating the metrics deployed on the Tracking Network.

Comparison of Locomotive Emissions Measured during Dynamometer versus Rail Yard Engine Load Tests

For environmental emissions certification, locomotive prime mover engines undergo rigorous measurements with the use of federal reference methods (FRMs). However, there are nonregulatory reasons for engine emissions measurement, such as to compare relative differences in fuel use and emissions as a result of engine rebuild or between engines in a fleet. Portable emissions measurement systems (PEMSs) are widely used for highway vehicle and nonroad construction equipment but have had limited locomotive applications. The objectives are to (a) demonstrate an approach for quantifying locomotive emission rates with a PEMS during dynamometer and rail yard engine load tests, (b) compare the emissions measured in dynamometer versus rail yard load tests, and (c) assess the relative change in fuel use and emissions from engine rebuild. Measurements were conducted on 3,000-hp prime movers, including an EMD 16-645 for a GP40 and two EMD 12-710s for F59PHs. Fuel use and PEMS-based emission rates for nitric oxide, carbon monoxide, hydrocarbons, and particulate matter were compared between dynamometer and rail yard load tests and with data from previous literature. Fuel use and oxides of nitrogen (NOx) emission rates after engine rebuild were lower for the GP40 prime mover, and the fuel use and NOx emission rates for the F59PH rebuilt engines were lower than those of the rebuilt GP40 engine. PEMS is not a substitute for locomotive FRMs if compliance certification is needed but provides useful data for comparative assessment.

Spatial and seasonal variations of fine particle water-soluble organic carbon (WSOC) over the southeastern United States: implications for secondary organic aerosol formation

Abstract. Secondary organic aerosol (SOA) in the southeastern US is investigated by analyzing the spatial-temporal distribution of water-soluble organic carbon (WSOC) and other PM2.5 components from 900 archived 24-h Teflon filters collected at 15 urban or rural EPA Federal Reference Method (FRM) network sites throughout 2007. Online measurements of WSOC at an urban/rural-paired site in Georgia in the summer of 2008 are contrasted to the filter data. Based on FRM filters, excluding biomass-burning events (levoglucosan < 50 ng m−3), WSOC and sulfate were highly correlated with PM2.5 mass (r2~0.7). Both components comprised a large mass fraction of PM2.5 (13% and 31%, respectively, or ~25% and 50% for WSOM and ammonium sulfate). Sulfate and WSOC both tracked ambient temperature throughout the year, suggesting the temperature effects were mainly linked to faster photochemistry and/or synoptic meteorology and less due to enhanced biogenic hydrocarbon emissions. FRM WSOC, and to a lesser extent sulfate, were spatially homogeneous throughout the region, yet WSOC was moderately enhanced (27%) in locations of greater predicted isoprene emissions in summer. A Positive Matrix Factorization (PMF) analysis identified two major source types for the summer WSOC; 22% of the WSOC were associated with ammonium sulfate, and 56% of the WSOC were associated with brown carbon and oxalate. A small urban excess of FRM WSOC (10%) was observed in the summer of 2007, however, comparisons of online WSOC measurements at one urban/rural pair (Atlanta/Yorkville) in August 2008 showed substantially greater difference in WSOC (31%) relative to the FRM data, suggesting a low bias for urban filters. The measured Atlanta urban excess, combined with the estimated boundary layer heights, gave an estimated Atlanta daily WSOC production rate in August of 0.55 mgC m−2 h−1 between mid-morning and mid-afternoon. This study characterizes the regional nature of fine particles in the southeastern US, confirming the importance of SOA and the roles of both biogenic and anthropogenic emissions.

Field evaluation of particulate matter measurements using tapered element oscillating microbalance in a layer house

The tapered element oscillating microbalance (TEOM) is one type of continuous ambient particulate matter (PM) monitor. Adsorption and desorption of moisture and semivolatile species may cause positive or negative artifacts in TEOM PM mass measurement. The objective of this field study was to investigate possible uncertainties associated with TEOM measurements in the poultry operation environment. For comparisons of TEOM with filter-based gravimetric method, four instruments (TEOM-PM10, low-volume PM10 sampler, TEOM-PM2.5, and PM2.5 speciation sampler) were collocated and tested inside a poultry house for PM2.5 and PM10 (PM with aerodynamic equivalent diameter ≤2.5 and ≤10 μm, respectively) measurements. Fifteen sets of 24-hr PM10 concentrations and 13 sets of 24-hr PM2.5 measurements were obtained. Results indicate that compared with filter-based gravimetric method, TEOM gave significantly lower values of both PM10 and PM2.5 mass concentrations. For PM10, the average ratio of TEOM to the gravimetric method was 0.936. For PM2.5, the average ratio of TEOM to the gravimetric method was 0.738. Particulate matter in the poultry houses possibly contains semivolatile compounds and moisture due to high levels of relative humidity (RH) and gas pollutants. The internal heating mechanism of the TEOM may cause losses in mass through volatilization. To investigate the effects of TEOM settings on concentration measurements, the heaters of two identical TEOMs were set at 50 °C, 30 °C, or no heating at all. They were collocated and tested for total suspended particle (TSP), PM10, and PM2.5 measurements in layer house for 6 weeks. For all TSP, PM10, and PM2.5 measurements, the internal TEOM temperature setting had a significant effect (P < 0.05). Significantly higher PM mass concentrations were measured at lower temperature settings. The effects of environmental (i.e., temperature, RH, NH3 and CO2 concentrations) and instrumental (i.e., filter loading and noise) parameters on PM measurements were also assessed using regression analysis. Implications Because of its potential health and environmental effects, particulate matter (PM) emissions from animal feeding operations (AFOs) have been a great concern to the public and to the regulatory agencies. The tapered element oscillating microbalance (TEOM) PM monitor has been was adapted for continuous PM measurements in some AFO air quality studies. This study investigated possible uncertainties associated with TEOM measurements in an egg production environment. It was discovered that there was a significant bias in TEOM measurements of PM10 as compared with federal reference method. Internal temperature settings of a TEOM have significant impact on its PM measurement.

Uncertainties in PM2.5 Gravimetric and Speciation Measurements and What We Can Learn from Them

ABSTRACT The U.S. Environmental Protection Agency (EPA) and the federal land management community (National Park Service, United States Fish and Wildlife Service, United States Forest Service, and Bureau of Land Management) operate extensive particle speciation monitoring networks that are similar in design but are operated for different objectives. Compliance (mass only) monitoring is also carried out using federal reference method (FRM) criteria at approximately 1000 sites. The Chemical Speciation Network (CSN) consists of approximately 50 long-term-trend sites, with about another 250 sites that have been or are currently operated by state and local agencies. The sites are located in urban or suburban settings. The Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring network consists of about 181 sites, approximately 170 of which are in nonurban areas. Each monitoring approach has its own inherent monitoring limitations and biases. Determination of gravimetric mass has both negative and positive artifacts. Ammonium nitrate and other semivolatiles are lost during sampling, whereas, on the other hand, measured mass includes particle-bound water. Furthermore, some species may react with atmospheric gases, further increasing the positive mass artifact. Estimating aerosol species concentrations requires assumptions concerning the chemical form of various molecular compounds, such as nitrates and sulfates, and organic material and soil composition. Comparing data collected in the various monitoring networks allows for assessing uncertainties and biases associated with both negative and positive artifacts of gravimetric mass determinations, assumptions of chemical composition, and biases between different sampler technologies. All these biases are shown to have systematic seasonal characteristics. Unaccounted-for particle-bound water tends to be higher in the summer, as does nitrate volatilization. The ratio of particle organic mass divided by organic carbon mass (Roc) is higher during summer and lower during the winter seasons in both CSN and IMPROVE networks, and Roc is lower in urban than nonurban environments. IMPLICATIONS Particulate matter less than 2.5 microns in size (PM2.5) National Ambient Air Quality Standards (NAAQS) are based on gravimetric analysis of particulate matter collected on a Teflon substrate, using federal reference methodologies, whereas compliance under the Regional Haze Rule (RHR) is based on atmospheric extinction, derived from measurements of individual aerosol species. Gravimetric mass can be over- or underestimated because of volatilization issues and water retention by inorganic species, whereas species-specific estimates of mass are dependent on assumptions concerning their detailed chemical composition. Over- or underestimation of aerosol species or gravimetric mass could result in violation of standards or failure to meet visibility goals established under the RHR.

A literature review of concentrations and size distributions of ambient airborne Pb-containing particulate matter

Abstract The final 2008 lead (Pb) national ambient air quality standards (NAAQS) revision maintains Pb in total suspended particulate matter as the indicator. However, the final rule permits the use of low-volume PM10 (particulate matter sampled with a 50% cut-point of 10 μm) Federal Reference Method (FRM) monitors in lieu of total suspended particulate (TSP) monitors for some non-source-oriented monitoring. PM10 FRM monitors are known to provide more reliable concentration measurements than TSP samplers because they are omni-directional samplers and so are not biased by wind conditions. However, by design they exclude the upper tail of the particle size distribution. Hence, each monitor produces uncertainties about measured concentrations of Pb-bearing PM. Uncertainties in reported Pb data are also related to spatiotemporal variation of the concentration and size distribution of Pb-bearing PM. Therefore, a comprehensive literature review was performed to summarize the current knowledge regarding the concentration and size distribution of Pb particles in the atmosphere. The objectives of this review were to compile data that could shed light on these uncertainties, to provide insights useful during future Pb NAAQS reviews, and to identify areas where more research is needed. Results of this review indicated that Pb size distribution data are relatively limited and often outdated. Thirty-nine articles were found to have sufficiently detailed information regarding airborne Pb concentrations, study location, sample collection methods, and analytical techniques; only 16 of those papers reported Pb concentration data for multiple size fractions. For the most part, U.S. and European studies from the last forty years illustrate that the largest mode of the size distribution of airborne particle-bound Pb has shifted to larger sizes while airborne Pb concentrations have decreased in urban areas. This shift occurred as tetraethyl Pb additives in gasoline were phased out and industrial emissions and resuspended road dust became more important sources of Pb. Several studies also suggested the occurrence of long-range transport of Pb-bearing PM from industrial emissions. Uncertainties associated with these studies include influence of wind speed and direction on captured concentrations and variability in analytical techniques used to quantify Pb concentrations on the reported size distributions.

Field evaluation of portable and central site PM samplers emphasizing additive and differential mass concentration estimates

The US Environmental Protection Agency (EPA) published a National Ambient Air Quality Standard (NAAQS) and the accompanying Federal Reference Method (FRM) for PM10 in 1987. The EPA revised the particle standards and FRM in 1997 to include PM2.5. In 2005, EPA proposed revisions to this NAAQS to include PM10–2.5 but only finalized revisions with a PM2.5 FRM and the development of a national monitoring network in 2006. Presently, no EPA designated reference or equivalent method sampler has the ability to directly measure the mass concentrations of PM10, PM10–2.5, and PM2.5 simultaneously. An additive approach has been used for samplers like the dichotomous monitors to calculate PM10 mass concentrations from independent measures of PM10–2.5 and PM2.5 (i.e. PM10 = PM10–2.5 + PM2.5). A differential approach has been used to calculate PM10–2.5 from identical collocated PM10 and PM2.5 samplers (i.e. PM10–2.5 = PM10–PM2.5). Since these two approaches have been used widely for PM measurements, it is informative to evaluate their precision and comparability. EPA performed collocated tests of five different particle samplers in the Research Triangle Park area of North Carolina to evaluate the comparability and to characterize the additive and differential approaches used to determine particle mass concentrations. The intra-sampler precision of MiniVol, Omni, and dichotomous samplers was less than 8.4%. The precision of PM10 measurements using the additive approach with dichotomous samplers was less than 3.5%. The poorest precision of the various PM10–2.5 differential approaches was less than 15.1%. No zero or negative PM10–2.5 concentrations were calculated using the differential approach. A coefficient of determination of 0.81 or higher was obtained for all paired comparison of PM10–2.5. The reported test results show that concentrations calculated from both the additive and differential approaches generally agree among the portable samplers, the more established dichotomous sampler and the Federal Reference Methods

Spatial and Temporal Characterization of PM2.5 Mass Concentrations in California, 1980–2007

ABSTRACT Systematic measurement of fine particulate matter (aerodynamic diameter less than 2.5 μm [PM2.5]) mass concentrations began nationally with implementation of the Federal Reference Method (FRM) network in 1998 and 1999. In California, additional monitoring of fine particulate matter (PM) occurred via a dichotomous sampler network and several special studies carried out between 1982 and 2002. The authors evaluate the comparability of FRM and non-FRM measurements of PM2.5 mass concentrations and establish conversion factors to standardize fine mass measurements from different methods to FRM-equivalent concentrations. The authors also identify measurements of PM2.5 mass concentrations that do not agree with FRM or other independent PM2.5 mass measurements. The authors show that PM2.5 mass can be reconstructed to a high degree of accuracy (r 2 > 0.9; mean absolute error ∼2 μg m−3) from PM with an aerodynamic diameter ≤10 μm (PM10) mass and species concentrations when site-specific and season-specific conversion factors are used and a statewide record of fine PM mass concentrations by combining the FRM PM2.5 measurements, non-FRM PM2.5 measurements, and reconstructions of PM2.5 mass concentrations. Trends and spatial variations are evaluated using the integrated data. The rates of change of annual fine PM mass were negative (downward trends) at all 22 urban and 6 nonurban (Interagency Monitoring of Protected Visual Environments [IMPROVE]) monitoring locations having at least 15 yr of data during the period 1980–2007. The trends at the IMPROVE sites ranged from -0.05 to -0.25 μg m−3 yr−1 (median -0.11 μg m−3 yr−1), whereas urban-site trends ranged from -0.13 to -1.29 μg m−3 yr−1 (median -0.59 μg m−3 yr−1). The urban concentrations declined by a factor of 2 over the period of record, and these decreases were qualitatively consistent with changes in emissions of primary PM2.5 and gas-phase precursors of secondary PM. Mean PM2.5 mass concentrations ranged from 3.3 to 7.4 μg m−3 at IMPROVE sites and from 9.3 to 37.1 μg m−3 at urban sites. IMPLICATIONS Mean measured and reconstructed fine particulate matter mass concentrations declined by about a factor of 2 in California over the period 1980 to 2007 and varied by about a factor of 4 among air basins. The integrated data record is of interest for epidemiological studies and for assessments of emission control programs.

Measurement System Evaluation for Upwind/Downwind Sampling of Fugitive Dust Emissions

Eight different PM10 samplers with various size-selective inlets and sample flow rates were evaluated for upwind/ downwind assessment of fugitive dust emissions from two sand and gravel operations in southern California during September through October 2008. Continuous data were acquired at one-minute intervals for 24 hours each day. Integrated filters were acquired at five-hour intervals between 1100 and 1600 PDT on each day because winds were most consistent during this period. High-volume (hivol) size-selective inlet (SSI) PM10 Federal Reference Method (FRM) filter samplers were comparable to each other during side-by-side sampling, even under high dust loading conditions. Based on linear regression slope, the BGI low-volume (lovol) PQ200 FRM measured ~18% lower PM10 levels than a nearby hivol SSI in the source-dominated environment, even though tests in ambient environments show they are equivalent. Although the TSI DustTrak DRX PM10 concentrations did not equal those from the hivol SSI, both instruments were highly correlated (R = 0.9) at the two downwind sites. Multiple size ranges from the TSI DustTrak DRX and Grimm optical particle counters (OPC) allowed the identification of spatial non-uniformity for sources within and outside the facilities. Narrow dust plumes were only detected by some of the continuous instruments across the sampler array. Upwind PM10 concentrations at one of the locations were higher than the downwind concentrations owing to a high concentration of industrial and vehicular activities. The shorter-duration measurements and quantification of super-coarse (> 10 µm) particles with high deposition velocities available from optical particle counters is needed to evaluate the effects of local emissions on both upwind and downwind samples.

Correction factor for continuous monitoring of wood smoke fine particulate matter.

The US Environmental Protection Agency (EPA) has designated a handful of instruments as Federal Reference or Federal Equivalency Methods (FRM and FEM, respectively) for the monitoring of fine particulate matter (PM2.5). More commonly used for indoor exposure assessment studies are optical scanning devices such as the DustTrak (TSI) due to the their portability and affordability. It is recommended by the manufacturer of these instruments that a "correction factor" be applied when assessing source-specific conditions. In this study, DustTraks were collocated with multiple samplers in various environments in an effort to establish an indoor, wood smoke-source specific correction factor. The DustTrak was found to report PM2.5 levels on average 1.6 times higher than a filter based method in two indoor sampling programs. The DustTrak also reported indoor PM2.5 concentrations 1.7 times higher than a FRM sampler during a regional forest fire event. These real-world scenarios give a correction factor within a reasonable range of the results of a controlled laboratory experiment in which DustTraks reported PM2.5 approximately 2 times higher than a FEM. Our indoor wood smoke-specific correction factor of 1.65 will allow for DustTraks to be confidently used in quantifying PM2.5 exposures within indoor environments predominantly impacted by wood smoke.

A Re-Examination of Ambient Air Ozone Monitor Interferences

Attaining the National Ambient Air Quality Standard (NAAQS) for ozone (O3) could cost billions of dollars nationwide. Attainment of the NAAQS is judged on O3 measurements made by the Federal Reference Method (FRM), ethylene chemiluminescence, or a Federal Equivalent Method (FEM), predominantly ultraviolet (UV) absorption. Starting in the 1980s, FRM monitors were replaced by FEMs so that today virtually all monitoring in the United States uses the UV methodology. This report summarizes a laboratory and collocated ambient air monitoring study of interferences in O3 monitors. Potential interferences examined in the laboratory included water vapor, mercury, o-nitrophenol, naphthalene, p-tolualdehyde, and mixed reaction products from smog chamber simulations of urban atmospheric photochemistry. UV absorption O3 monitors modified for humidity equilibration were also collocated with UV FEM O3 monitors at six sites in Houston, TX, during the 2007 summer O3 season. The results suggest that humidity and interfering species can positively bias (overestimate) O3 measured by FEM monitors used to determine compliance with the O3 standards. The results also suggest that humidity equilibration can mitigate this bias.

Miniature Personal Ozone Monitor Based on UV Absorbance.

A new portable instrument has been developed that offers rapid detection of ozone at the ppb level for personal exposure monitoring. The Personal Ozone Monitor is based on the EPA Federal Reference Method of UV absorbance and has the advantage of being small (10 × 7.6 × 3.8 cm), light-weight (0.3 kg), low power (2.9 watts), and battery-operated. The instrument can be worn by an individual during normal daily activities because it is unaffected by humidity, physical orientation, temperature, and vibration. In order to eliminate any significant interference from water vapor, Nafion(®) tubing was installed before the detection cell, and the optical path was lined with quartz. A precision of 1.5 ppbv and limit of detection of 4.5 ppbv (S/N = 3) was demonstrated with the instrument making measurements every 10 seconds.

Biomass burning impact on PM&amp;lt;sub&amp;gt; 2.5&amp;lt;/sub&amp;gt; over the southeastern US during 2007: integrating chemically speciated FRM filter measurements, MODIS fire counts and PMF analysis

Abstract. Archived Federal Reference Method (FRM) Teflon filters used by state regulatory agencies for measuring PM2.5 mass were acquired from 15 sites throughout the southeastern US and analyzed for water-soluble organic carbon (WSOC), water-soluble ions and carbohydrates to investigate biomass burning contributions to fine aerosol mass. Based on over 900 filters that spanned all of 2007, levoglucosan and K+ were studied in conjunction with MODIS Aqua fire count data to compare their performances as biomass burning tracers. Levoglucosan concentrations exhibited a distinct seasonal variation with large enhancement in winter and spring and a minimum in summer, and were well correlated with fire counts, except in winter when residential wood burning contributions were significant. In contrast, K+ concentrations had no apparent seasonal trend and poor correlation with fire counts. Levoglucosan and K+ only correlated well in winter (r2=0.59) when biomass burning emissions were highest, whereas in other seasons they were not correlated due to the presence of other K+ sources. Levoglucosan also exhibited larger spatial variability than K+. Both species were higher in urban than rural sites (mean 44% higher for levoglucosan and 86% for K+). Positive Matrix Factorization (PMF) was applied to analyze PM2.5 sources and four factors were resolved: biomass burning, refractory material, secondary light absorbing WSOC and secondary sulfate/WSOC. The biomass burning source contributed 13% to PM2.5 mass annually, 27% in winter, and less than 2% in summer, consistent with other souce apportionment studies based on levoglucosan, but lower in summer compared to studies based on K+.

Water-Soluble Organic Aerosol material and the light-absorption characteristics of aqueous extracts measured over the Southeastern United States

Abstract. Light absorption of fine particle (PM2.5) aqueous extracts between wavelengths of 200 and 800 nm were investigated from two data sets: 24-h Federal Reference Method (FRM) filter extracts from 15 Southeastern US monitoring sites over the year of 2007 (900 filters), and online measurements from a Particle-Into-Liquid Sampler deployed from July to mid-August 2009 in Atlanta, Georgia. Three main sources of soluble chromophores were identified: biomass burning, mobile source emissions, and compounds linked to secondary organic aerosol (SOA) formation. Absorption spectra of aerosol solutions from filter extracts were similar for different sources. Angstrom exponents were ~7±1 for biomass burning and non-biomass burning-impacted 24-h filter samples (delineated by a levoglucosan concentration of 50 ng m−3) at both rural and urban sites. The absorption coefficient from measurements averaged between wavelength 360 and 370 nm (Abs365, in units m−1) was used as a measure of overall brown carbon light absorption. Biomass-burning-impacted samples were highest during winter months and Abs365 was correlated with levoglucosan at all sites. During periods of little biomass burning in summer, light absorbing compounds were still ubiquitous and correlated with fine particle Water-Soluble Organic Carbon (WSOC), but comprised a much smaller fraction of the WSOC, where Abs365/WSOC (i.e., mass absorption efficiency) was typically ~3 times higher in biomass burning-impacted samples. Factor analysis attributed 50% of the yearly average Abs365 to biomass burning sources. Brown carbon from primary urban emissions (mobile sources) was also observed and accounted for ~10% of the regional yearly average Abs365. Summertime diurnal profiles of Abs365 and WSOC showed that morning to midday increases in WSOC from photochemical production were associated with a decrease in Abs365/WSOC. After noon, this ratio substantially increased, indicating that either some fraction of the non-light absorbing fresh SOA was rapidly (within hours) converted to chromophores heterogeneously, or that SOA from gas-particle partitioning later in the day was more light-absorbing. Factor analysis on the 24-h integrated filter data associated ~20 to 30% of Abs365 over 2007 with a secondary source that was highest in summer and also the main source for oxalate, suggesting that aqueous phase reactions may account for the light-absorbing fraction of WSOC observed throughout the Southeastern US in summer.

Particulate Matter Sample Deposit Geometry and Effective Filter Face Velocities

Aerosol filter face velocities can be underestimated when the sample deposit area does not cover the entire face of the filter. In many aerosol samplers, Teflon filters are backed with a metal support screen. In these samplers, air flows through the filter only in the small area upstream of each hole in the screen, resulting in a sample deposit that is an array of tiny dots that mimics the array of holes. Thus, the filter deposit area is smaller than the total filter area and the effective face velocity is greater than that calculated from the sample deposit envelope. The Inter-agency Monitoring of Protected Visual Environments (IMPROVE) network has used filter holders with two different screen hole arrays. The U.S. Environmental Protection Agency’s Chemical Speciation Network (CSN) and the Federal Reference Method samplers also use a metal support screen, but with much smaller screen holes than IMPROVE. These networks also use larger filters and lower flow rates than those used in IMPROVE. Filter face velocities for all of these networks that are calculated using the actual deposit array area range from 1.6 to 3.5 times larger than those calculated incorrectly using the entire sample deposit envelope.

Combining numerical model output and particulate data using Bayesian space–time modeling

AbstractOver the past few years, Bayesian models for combining output from numerical models and air monitoring data have been applied to environmental data sets to improve spatial prediction. This paper develops a new hierarchical Bayesian model (HBM) for fine particulate matter (PM2.5) that combines U. S. EPA Federal Reference Method (FRM) PM2.5 monitoring data and Community Multi‐scale Air Quality (CMAQ) numerical model output. The model is specified in a Bayesian framework and fitted using Markov Chain Monte Carlo (MCMC) techniques. We find that the statistical model combining monitoring data and CMAQ output provides reliable information about the true underlying PM2.5 process over time and space. We base these conclusions on results of a validation exercise in which independent monitoring data were compared with predicted values from the HBM and predictions from a standard kriging model based solely on the monitoring data. Copyright © 2009 John Wiley &amp; Sons, Ltd.

The Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) field study methodology

The Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) field study examined indoor and outdoor exposure to traffic-generated air pollution by studying the individual processes of generation of traffic emissions, transport and dispersion of air contaminants along a roadway, and infiltration of the contaminants into a residence. Real-time instrumentation was used to obtain highly resolved time-series concentration profiles for a number of air pollutants. The B-TRAPPED field study was conducted in the residential Sunset Park neighborhood of Brooklyn, NY, USA, in May 2005. The neighborhood contained the Gowanus Expressway (Interstate 278), a major arterial road (4(th) Avenue), and residential side streets running perpendicular to the Gowanus Expressway and 4(th) Avenue. Synchronized measurements were obtained inside a test house, just outside the test house façade, and along the urban residential street canyon on which the house was located. A trailer containing Federal Reference Method (FRM) and real-time monitors was located next to the Gowanus Expressway to assess the source. Ultrafine particulate matter (PM), PM(2.5), nitrogen oxides (NO(x)), sulfur dioxide (SO(2)), carbon monoxide (CO), carbon dioxide (CO(2)), temperature, relative humidity, and wind speed and direction were monitored. Different sampling schemes were devised to focus on dispersion along the street canyon or infiltration into the test house. Results were obtained for ultrafine PM, PM(2.5), criteria gases, and wind conditions from sampling schemes focused on street canyon dispersion and infiltration. For comparison, the ultrafine PM and PM(2.5) results were compared with an existing data set from the Los Angeles area, and the criteria gas data were compared with measurements from a Vancouver epidemiologic study. Measured ultrafine PM and PM(2.5) concentration levels along the residential urban street canyon and at the test house façade in Sunset Park were demonstrated to be comparable to traffic levels at an arterial road and slightly higher than those in a residential area of Los Angeles. Indoor ultrafine PM levels were roughly 3-10 times lower than outdoor levels, depending on the monitor location. CO, NO(2), and SO(2) levels were shown to be similar to values that produced increased risk of chronic obstructive pulmonary disease hospitalizations in the Vancouver studies.

Atmospheric Emissions from a Passenger Ferry with Selective Catalytic Reduction

The two main propulsion engines on Staten Island Ferry Alice Austen (Caterpillar 3516A, 1550 hp each) were fitted with selective catalytic reduction (SCR) aftertreatment technology to reduce emissions of oxides of nitrogen (NOx). After the installation of the SCR system, emissions from the ferry were characterized both pre- and post-aftertreatment. Prior research has shown that the ferry operates in four modes, namely idle, acceleration, cruise, and maneuvering modes. Emissions were measured for both engines (designated NY and SI) and for travel in both directions between Manhattan and Staten Island. The emissions characterization used an analyzer system, a data logger, and a filter-based particulate matter (PM) measurement system. The measurement of NOx, carbon monoxide (CO), and carbon dioxide (CO2) were based on federal reference methods. With the existing control strategy for the SCR urea injection, the SCR provided approximately 64% reduction of NOx for engine NY and 36% reduction for engine SI for a complete round trip with less than 6.5 parts per million by volume (ppmv) of ammonia slip during urea injection. Average reductions during the cruise mode were 75% for engine NY and 47% for engine SI, which was operating differently than engine NY. Reductions for the cruise mode during urea injection typically exceeded 94% from both engines, but urea was injected only when the catalyst temperature reached a 300 °C threshold pre- and postcatalyst. Data analysis showed a total NOx mass emission split with 80% produced during cruise, and the remaining 20% spread across idle, acceleration, and maneuvering. Examination of continuous NOx data showed that higher reductions of NOx could be achieved on both engines by initiating the urea injection at an earlier point (lower exhaust temperature) in the acceleration and cruise modes of operation. The oxidation catalyst reduced the CO production 94% for engine NY and 82% for engine SI, although the high CO levels during acceleration did cause analyzers to over-range. No clear, quantitative conclusions could be made regarding the effects of the SCR on PM