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Weekly UpdatesABSTRACT
The Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) has been previously verified as being capable of measuring total fine particulate matter ([PM.sub.2.5]), including semi-volatile species. The present study was conducted to determine if the simple modification of a commercial speciation sampler with a charcoal denuder followed by a filter pack containing a quartz filter and a charcoal-impregnated glass (CIG) fiber filter would allow for the measurement of total [PM.sub.2.5], including semi-volatile organic material. Data were collected using an R & P (Rupprecht and Pastasnik Co., Inc.) Partisol Model 2300 speciation sampler; an R & P Partisol speciation sampler modified with a BOSS denuder, followed by a filter pack with a quartz and a CIG filter; a Met One spiral aerosol speciation sampler (SASS); and the PC-BOSS from November 2001 to March 2002 at a U.S. Environmental Protection Agency (EPA) Science to Achieve Results (STAR) sampling site in Lindon, UT. Total [PM.sub.2.5] mass, ammonium nitrate (both nonvolatile and semi-volatile), ammonium sulfate, organic carbon (both nonvolatile and semi-volatile), and elemental carbon were determined on a 24-hr basis. Results obtained with the individual samplers were compared to determine the capability of the modified R & P speciation sampler for measuring total [PM.sub.2.5], including semi-volatile components. Data obtained with the modified speciation sampler agreed with the PC-BOSS results. Data obtained with the two unmodified speciation samplers were low by an average of 26% because of the loss of semi-volatile organic material from the quartz filter during sample collection.
INTRODUCTION
Human health endpoints associated with exposure to airborne particulate matter (PM) include increased mortality and morbidity from respiratory and cardiopulmonary disease. (1-3) These effects are observed with exposure to concentrations substantially below the U.S. coarse PM ([PM.sub.10]) ambient air quality standard. The observed exacerbation of health problems is believed to be associated more closely with exposure to fine particles (<2.5 [micro]m) than coarse particles (>2.5 [micro]m). As a result, the U.S. Environmental Protection Agency (EPA) has promulgated revised standards for PM, which establishes new annual and 24-hr fine particulate standards with fine PM ([PM.sub.2.5]), measured according to the Federal Reference Method (FRM) ([PM.sub.2.5] FRM), as the indicator. (4,5) This recognition of fine and coarse particles as different classes of PM pollutants is an advance in the understanding and control of PM. However, ambient [PM.sub.2.5] is not a single pollutant, but a mixture of many chemical species. Major components include: sulfate, nitrate, ammonium, and hydrogen ions; trace elements (including toxic and transition metals); organic material; elemental carbon (EC or soot); and crustal components. EPA has promulgated the use of commercial speciation samplers to determine the chemical composition of [PM.sub.2.5]. (4,5) Speciation samplers commonly use a variety of filter packs to collect stable species and a diffusion denuder system suitable for the determination of fine particulate nitrate. Stable species such as trace and crustal elements and sulfate can be measured by these filter samplers, and nitrate is measured with the diffusion denuder module in these systems. However, semi-volatile fine particulate organic material is not determined by these techniques. (6-8) Positive artifacts are seen in the collection of organic material, especially using quartz filters, due to adsoprtion of gas-phase organic compounds. (6,13) Negative artifacts occur because of the loss of particulate semi-volatile material during sampling. (6-9) Both of these artifact problems can be minimized using a diffusion denuder sampler to determine fine particulate organic material. (6-9) This study was initiated to compare speciation sampler and denuder measurement of fine particulate carbonaceous material and to see if a simple modification of a commercial speciation sampler would allow for the accurate determination of semi-volatile fine particulate organic material.
EXPERIMENTAL METHODS AND PROCEDURES
Sampling Site
The sampling site for this experiment is located next to the State of Utah Air Quality Monitoring site at Lindon Elementary School in Lindon, UT. Lindon is an urban community located approximately 20 km north of Provo, UT. During winter inversions the community is usually impacted by primary emissions and secondary components formed from combustion products from mobile sources and wood-burning stoves. (8) A nearby integrated steel mill was not operational during this study.
Sampling Period
A total of 24 sample sets were collected periodically during winter inversion conditions from November 15, 2001 until January 14, 2002. The 24-hr samples were collected each sampling day from 12:00 a.m. to 12:00 p.m. Samples were collected on days when stable inversions with no precipitation were meteorologically forecast. The composition and sources of the collected particles under these conditions have been previously described. (8,9)
Sampling Instruments
Three different speciation samplers were used for collection of [PM.sub.2.5]. These are shown schematically in Figure 1.
PC-BOSS. The combination of technology used in the High-Volume Brigham Young University Organic Sampling System (10) (BIG BOSS) and the Harvard particle concentrator (11) resulted in the Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS). (6,7,12) The configuration and operation of the PC-BOSS as used in the Wasatch Front Environmental Monitoring for Public Awareness and Community Tracking (EMPACT) and Science to Achieve Results (STAR) programs, has been previously described. (8) The PC-BOSS was used for sample collection to determine fine particulate mass, sulfate, carbonaceous material (elemental and organic), nitrate, semi-volatile organic material, and semi-volatile nitrate. Inlet flow was 130 L/min. Samples for the chemical characterization of [PM.sub.2.5] in the minor flow following a particle concentrator and a BOSS diffusion denuder were collected in a filter pack containing a pre-fired 47-mm quartz filter (18 L/min, Pallflex) followed by 47-mm charcoal-impregnated glass (CIG) fiber filter (Schliecher and Schuell) to determine fine particulate carbonaceous material and nitrate, including semi-volatile species lost from the particles during sampling. A second parallel filter pack containing a 47-mm Teflon (12 L/min, Whatman) filter followed by a 47-mm nylon (Gelman, Nylasorb) filter was used to determine [PM.sub.2.5] filter-retained (nonvolatile) mass, sulfate, nitrate, and any nitrate lost from the particles during sample collection. A side-flow filter pack, before the particle concentrator, containing a 47-mm polycarbonate (10 L/min, Whatman, Nuclepore, 0.4-[micro]m pore size) filter followed by a 47-mm CIG fiber filter, collected particles (excluding semi-volatile species lost during sampling), and gas-phase organic material after the 2.5-[micro]m outlet cut. These data were compared with data from the minor flow filters to determine the particle concentrator efficiency. (7,12)
[FIGURE 1 OMITTED]
R & P Model 2300 Speciation Sampler. The R & P Partisol Model 2300 speciation sampler was used to determine fine particulate mass, sulfate, nitrate, and carbonaceous material. The sampler consists of three sampling channels, each subdivided into four sampling banks through which air can be pulled at the desired rate via internal pumps. The filter pack systems (ChemComb cartridges) include an anodized impactor plate followed by a vertical flow chamber. Samples were collected in four parallel ChemComb cartridges. The first cartridge was used to determine total [PM.sub.2.5] mass collected on a 47-mm Teflon (17 L/min, Whatman) filter. The second cartridge contained a 1% NaHC[O.sub.3]:1% glycerine-coated glass honeycomb denuder, which was used to determine concentrations of gas-phase nitric acid ([HNO.sub.3]) and sulfur dioxide (S[O.sub.2]). This was followed by a 47-mm nylon (17 L/min, Gelman, Nylasorb) filter used to determine concentrations of fine particulate nitrate and sulfate. The third cartridge used a Teflon-coated impactor plate followed by two pre-fired 47-mm quartz (10 L/min, Pallflex) filters to determine fine particulate sulfate and carbonaceous material after the tandem quartz filter protocols. (13) The fourth cartridge was modified from the original design of R & P by the addition of a short BOSS (14) diffusion denuder to the anodized inlet before the filters. The denuder consists of parallel strips of charcoal-impregnated cellulose fiber filters (CIF) (Schliecher and Schuell) with high capacity for interfering gas-phase organic compounds, ozone, [HNO.sub.3] and S[O.sub.2]. The denuder was followed by a 47-mm pre-fired quartz (10 L/min, Pallflex) filter followed by a 47-mm pre-fired CIG fiber (Schleicher and Schuell) filter to determine fine particulate sulfate and carbonaceous material, including any semi-volatile organic compounds (SVOCs) that may be removed from the particles during sampling.
Met One Speciation Sampler. The Met One spiral aerosol speciation sampler (SASS) consists of several individual channels through which air is sampled. These filter systems include a sharp cut cyclone followed by a short vertical flow chamber. The first chamber included a 47-mm Teflon (Whatman) filter to determine total [PM.sub.2.5] particulate mass and sulfate. A second parallel chamber consisted of an aluminum honeycomb denuder followed by a 47-mm nylon (Gelman, Nylasorb) filter used to determine fine [PM.sub.2.5] nitrate and sulfate material. The third parallel chamber used two pre-fired 47-mm quartz (Pallflex) filters to determine [PM.sub.2.5] fine particulate sulfate and carbonaceous material. Flow was 7 L/min in each of the systems channels.
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