Apportionment of ambient primary and secondary fine particulate matter during a 2001 summer intensive study at the CMU Supersite and NETL Pittsburgh site.

ABSTRACT

Gaseous and particulate pollutant concentrations associated with five samples per day collected during a July 2001 summer intensive study at the Pittsburgh Carnegie Mellon University (CMU) Supersite were used to apportion fine particulate matter ([PM.sub.2.5]) into primary and secondary contributions using PMF2. Input to the PMF2 analysis included the concentrations of [PM.sub.2.5] nonvolatile and semivolatile organic material, elemental carbon (EC), ammonium sulfate, trace element components, gas-phase organic material, and N[O.sub.x], N[O.sub.2], and [O.sub.3] concentrations. A total of 10 factors were identified. These factors are associated with emissions from various sources and facilities including crustal material, gasoline combustion, diesel combustion, and three nearby sources high in trace metals. In addition, four secondary sources were identified, three of which were associated with secondary products of local emissions and were dominated by organic material and one of which was dominated by secondary ammonium sulfate transported to the CMU site from the west and southwest. The three largest contributors to [PM.sub.2.5] were secondary transported material (dominated by ammonium sulfate) from the west and southwest (49%), secondary material formed during midday photochemical processes (24%), and gasoline combustion emissions (11%). The other seven sources accounted for the remaining 16% of the [PM.sub.2.5]. Results obtained at the CMU site were comparable to results previously reported at the National Energy Technology Laboratory (NETL), located approximately 18 km south of downtown Pittsburgh. The major contributor at both sites was material transported from the west and southwest. Some difference in nearby sources could be attributed to meteorology as evaluated by HYSPLIT model back-trajectory calculations. These findings are consistent with the majority of the secondary ammonium sulfate in the Pittsburgh area being the result of contributions from distant transport, and thus decoupled from local activity involving organic pollutants in the metropolitan area. In contrast, the major local secondary sources were dominated by organic material.

INTRODUCTION

Organic carbonaceous material and ammonium sulfate are major components of ambient particles, and can be emitted directly in particulate form (primary aerosol) or formed in the atmosphere from products of gas-phase transformation reactions (secondary aerosol). It is important to be able to identify the composition and concentrations of fine particulate matter ([PM.sub.2.5]) associated with these primary and secondary sources to develop effective air quality control strategies. The estimation of primary and secondary contributions of ammonium sulfate in ambient air using a variety of receptor apportionment techniques has been documented. Approaches to apportion carbonaceous [PM.sub.2.5] include the use of the ratio of the particulate organic carbon (OC) to elemental carbon (EC) (1,2) or specific organic markers (3) to approximate the extent of secondary formation. Both secondary carbonaceous material and sulfate can be apportioned by chemical mass balance, (4) UNMIX (5), and probability mass function (PMF). (6,7) The PMF analyses results at the National Energy Technology Laboratory (NETL) previously reported by Eatough et al. (7) included the estimation of primary and secondary contributions of fine particulate mass, organic carbonaceous material, and ammonium sulfate using multiple Particle Concentrator-BYU Organic Sampling System (PC-BOSS) samples per day obtained at the NETL sampling site. The results obtained using data from a similar PC-BOSS sample set obtained at the Pittsburgh Air Quality Study (PAQS) Carnegie Mellon University (CMU) Supersite (8) during a July 2001 summer intensive study are reported here. The analysis is made using [PM.sub.2.5] composition including proton-induced X-ray emission (PIXE) used to determine elemental content, gas-phase volatile organic material (VOM), and tracer species usually monitored in ambient studies (e.g., nitrogen oxides [N[O.sub.x]], nitrogen dioxide [N[O.sub.2]], and ozone [[O.sub.3]]). PMF results from the NETL site and the CMU Supersite are compared.

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The CMU and NETL Sampling Sites

The CMU PAQS Supersite is located at 40.44 N latitude and 79.94 W longitude on an open hill (elevation 310 m) just east of the CMU campus and 6 km east of downtown Pittsburgh. Thus it is in the central city area (see Figure 1). The NETL site is located at 40.31 N latitude and 79.98 W longitude on an open hill (elevation 325 m) at the NETL facility (see Figure 1) at the southern portion of the Pittsburgh metropolitan area. Major coal-fired power plants, iron and coke processing facilities, and chemical manufacturing plants are located mainly to the southwest through northwest of both sites. The closer of these industrial facilities is shown relative to the CMU and NETL sampling sites in Figure 1. Facilities named in Figure 1 are those specifically mentioned in the following text. A major incinerator, a secondary Zn smelter, a major power plant, and several small chemical and metallurgical industries are located along the Ohio River close to the Ohio-Pennsylvania border to the northwest. Coal-fired power plants and a coke processing facility are in the same direction closer to the sampling sites. Additional coal-fired power plants as well coke and iron processing facilities are located along the Monongahela River, south of the city. These are all potential sources of local and transported pollutants at the two sites.

EXPERIMENTAL TECHNIQUES

Sampling Protocols

Five sample sets were collected each day at the CMU Supersite using a PC-BOSS sampler. (8,9) The sampling periods (EDT) were midnight to 6:00 a.m.; 6:00 a.m. to 10:00 a.m.; 10:00 a.m. to 2:00 p.m.; 2:00 p.m. to 6:00 p.m.; and 6:00 p.m. to midnight each next day.

As previously reported, (7,8) four sample sets were collected each day at the NETL site using a PC-BOSS sampler. The sampling time periods at NETL (EDT) were: 5:00 a.m. to 10:00 a.m.; 10:00 a.m. to 2:00 p.m.; 2:00 p.m. to 7:00 p.m.; and 7:00 p.m. to 5:00 a.m. the next day.

PC-BOSS Sampler Results

The PC-BOSS sampler and analysis of the collected samples at the CMU site during the July 2001 summer intensive have been previously described. (8,9) The PC-BOSS included a [PM.sub.2.5] inlet (140 L/min flow), a particle concentrator (lower cut point of less than 0.1 [micro]m, major flow 90 L/min) and a diffusion denuder (35 L/m flow) comprised of parallel strips of charcoal-impregnated cellulose fiber filters (CIF, Schleicher and Schuell) to remove gas-phase organic material, sulfur dioxide (S[O.sub.2]), nitric acid (HN[O.sub.3]), [O.sub.3], and N[O.sub.x], followed by two filter packs to determine [PM.sub.2.5] components.

Before the particle concentrator, a side-flow manifold (sampled at 10 L/m) held a single filter pack containing a 47-mm diameter Whatman nuclepore filter (0.4-[micro]m pore, Whatman Inc.) for sulfate and elemental analysis, and a 47-mm diameter charcoal-impregnated glass fiber filter (CIG) (Schleicher and Schuell) for VOM analysis. The sulfate concentration measured on the side-flow nuclepore filter allowed for the determination of the particle concentrator efficiency and losses. (9,10) Samples collected on the nuclepore filters were concentrated in a 4-[cm.sup.2] area on the filter using a stainless steel masking disk, positioned underneath the nuclepore filter. The reduced sample collection area maximized the PIXE detection limits.

The denuder was followed by two parallel filter packs. One contained a 47-mm Pallflex quartz filter (Gelman Sciences) followed by a 47-mm diameter CIG filter. The quartz filter was used to determine fine particulate EC, nonvolatile organic material (NVOM), and sulfate concentrations. The CIG filter was used to capture semivolatile organic material (SVOM) evolved from particles collected on the quartz filter. In this paper, NVOM and SVOM are identified based on the filter on which they were collected. Particulate samples collected on both of these filters were concentrated on a 4-[cm.sup.2] area on the filters using the mask described earlier for the Nuclepore filter. The reduced sample collection area maximizes the PIXE detection limits.

The other parallel filter pack contained a 47-mm diameter ring-supported Teflon filter (Whatman Inc.) followed by a 47-mm diameter Nylasorb filter (Gelman Sciences). Unlike sample collection on the quartz and CIG filter packs, collection on the Teflon and Nylasorb filters was over the entire surface of the filters. The Teflon filters were analyzed for sulfate and nonvolatile nitrate, and the Nylasorb filters were analyzed for nitrate lost from particles during sampling. With this combination of sample analysis techniques on both parallel channels of the minor flow of the sampler, negative and positive sampling artifacts were minimized.

Gas-Phase Data

N[O.sub.x], N[O.sub.2], and [O.sub.3] data were obtained through the PAQS air-monitoring program in Pittsburgh. (11)

Filter Pretreatment