Environ. Sci. Technol. 2010, 44, 1911–1917
Spatial Variability of Carbonaceous Aerosol Concentrations in East and West Jerusalem ERIKA VON SCHNEIDEMESSER,† J I A B I N Z H O U , †,‡ E L I Z A B E T H A . S T O N E , † JAMES J. SCHAUER,† JACOB SHPUND,§ SHMUEL BRENNER,| RADWAN QASRAWI,⊥ ZIAD ABDEEN,⊥ AND J E R E M Y A . S A R N A T * ,# Environmental Chemistry and Technology Program, University of Wisconsin-Madison, Madison, Wisconsin, School of Resources and Environmental Engineering, Wuhan University of Technology, P.R. China, Israel Union for Environmental Defense (IUED), Tel Aviv, Israel, Arava Institute for Environmental Studies (AIES), Hevel Eilot, Israel, Al Quds University (AQU), East Jerusalem, Palestinian Authority, and Environmental and Occupational Health, Emory University, Atlanta, Georgia
Received May 11, 2009. Revised manuscript received August 10, 2009. Accepted September 1, 2009.
Carbonaceous aerosol concentrations and sources were compared during a yearlong study at two sites in East and West Jerusalem that were separated by a distance of approximately 4 km. One in six day 24-h PM2.5 elemental and organiccarbonconcentrationsweremeasured,alongwithmonthly average concentrations of particle-phase organic compound tracers for primary and secondary organic aerosol sources. Tracer compounds were used in a chemical mass balance (CMB) model to determine primary and secondary source contributions to organic carbon. The East Jerusalem sampling site at Al Quds University experienced higher concentrations of organic carbon (OC) and elemental carbon (EC) compared to the West Jerusalem site at Hebrew University. The annual average concentrations of OC and EC at the East Jerusalem site were 5.20 and 2.19 µg m-3, respectively, and at the West Jerusalem site were 4.03 and 1.14 µg m-3, respectively. Concentrations and trends of secondary organic aerosol and vegetative detritus were similar at both sites, but large differences were observed in the concentrations of organic aerosol from fossil fuel combustion and biomass burning, which was the cause of the large differences in OC and EC concentrations observed at the two sites.
Introduction Considerable progress has been made during the past decade toward understanding the specific components and sources of atmospheric aerosols responsible for observed health effects reported in the epidemiologic and toxicologic litera* Corresponding author phone: 404-712-9725; fax: 401-727-8744; e-mail:
[email protected]. † University of Wisconsin-Madison. ‡ Wuhan University of Technology. § Israel Union for Environmental Defense. | Arava Institute for Environmental Studies. ⊥ Al Quds University. # Emory University. 10.1021/es9014025 CCC: $40.75
Published on Web 10/05/2009
2010 American Chemical Society
ture. A remaining area of uncertainty concerns the spatial variability of these components and sources within urban settings. These variations may follow demographic gradients that influence susceptibility to exposure, further complicating this issue. Previous studies have shown, for example, that residents of poorer neighborhoods may live closer to point sources of industrial pollution or roadways with higher traffic density, and that using community averages can under- or overestimate the impact of air pollution on health (1-3). The city of Jerusalem provides a unique opportunity to examine urban aerosol spatial variability across divergent social and demographic affiliations. Jerusalem is a diverse city, comprising populations from very different religious, political, and socio-economic backgrounds, residing within close proximities. Previous research on air pollution and particulate matter in Jerusalem has focused primarily on characterizing ambient concentrations of nitrogen oxides (NOx), sulfur dioxide (SO2), carbon monoxide (CO), ozone (O3), and total suspended particles (TSP) (4, 5). Pollutants that are formed through atmospheric chemical transformations, such as particulate sulfate (SO42-) and O3, tend to have more uniform concentrations in urban areas as compared to pollutants that are dominated by primary emissions (2, 6, 7). Although elemental carbon is purely a primary pollutant, organic carbon has both primary and secondary sources. Much less work has been conducted examining the spatial variability of organic fine particulate matter (PM2.5), relative to gaseous pollutants, due to the fact that these measurements are more expensive, analytically intensive, and subsequently, less common than other ubiquitous urban air pollutants. Likewise, very limited data exist on the spatial variability of primary and secondary sources of organic and elemental carbon (OC and EC), key chemical components of PM2.5, in urban areas. These gaps in the research are particularly prominent given the emerging evidence linking the particulate carbon component to a range of adverse health outcomes (8). This analysis quantifies the seasonally resolved differences in carbonaceous PM2.5, as well as the primary and secondary sources of the carbonaceous fraction of the aerosol in two sites in Jerusalem located within close distance to each other. Results are presented and discussed that cover measurements from every-sixth-day sample collection conducted from January through December 2007. In addition to the 24-h integrated OC and EC measurements, monthly composites were analyzed for organic molecular markers of primary and secondary sources. The molecular markers were used in a source apportionment model to assess primary and secondary contributions to fine particulate matter (PM2.5) organic aerosol concentrations. Source contributions were compared across the two locations, which included a Palestinian University in East Jerusalem (al Quds University) and an Israeli University in West Jerusalem (Hebrew University). These source apportionment results provide a novel means for examining PM2.5 sources and how they affect different areas within an urban location. Understanding the microscale spatial variability of this important PM2.5 component can lead to improvements in estimating exposures and, ultimately, interpreting findings from health effect studies of PM2.5 sources and components.
Methods Twenty-four-hour PM2.5 samples were collected, concurrently, every sixth day for the entire 2007 calendar year at VOL. 44, NO. 6, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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sites in both East and West Jerusalem. Multichannel air samplers, fabricated by URG Corp (Chapel Hill, NC) specifically for this project, comprised two PM2.5 sampling trains that operated at a total of 16.7 lpm. Each sampling train consisted of a sample inlet, a PM2.5 cyclone, a flow splitter, and two 8.35 lpm sample legs. All components of the sampler that were exposed to the aerosol sample flow were fabricated from Teflon-coated aluminum or Teflon-coated stainless steel. One sample train contained two filter holders that were used to collect samples on 47-mm Teflon membrane filters for mass determination and inorganic particulate matter components. The second sample leg contained one 47-mm quartz fiber filter (QFF) that collected particulate matter for OC and EC analysis and organic compound molecular markers. The fourth sample leg was not used for sampling, but replaced with a spacer to maintain standard flow rates and standard sampler construction. Air sampling flow rates were controlled with critical orifices and the samplers were started at midnight and shut off after 24 h using electronically controlled timers. Flow rates were measured with a rotameter before and after sampling. Monthly field and lab blanks were analyzed for quality control and quality assurance and to blank-correct measurements. The two sampling sites were located on the rooftops of university buildings in Jerusalem and were separated by a distance of 3.7 km. The East Jerusalem sampling site was located at the East Jerusalem campus of Al Quds University, approximately 760 m above sea level, with the sampler at 20 m above ground level, in the Shiekh Jarra neighborhood near the American Colony Neighborhood of Jerusalem. The sampler was 150 m from the nearest roadway, and land use around the East Jerusalem sampling site can be characterized as both residential and commercial (i.e., small shops, food markets) with some undeveloped dirt and gravel lots. It was also a few hundred meters from a main roadway transecting Jerusalem from Ramallah to Bethlehem and Hebron (Road 60). The West Jerusalem sampling site was located on a western hillside on the Givat Ram campus of the Hebrew University, which is approximately 770 m above sea level and 60 km from the Mediterranean Sea. The sampler was located on top of a building at 14 m above ground level, with the nearest building about 100 m away. The site was surrounded by land predominately used by the university, which included campus green space, public buildings, and residential neighborhoods. The West Jerusalem sampling site was within a few hundred meters of the Begin Expressway, one of Jerusalem’s major north-south highways, which at this point is located in a slightly sunken corridor relative to ground level. Importantly, both of these sites were chosen based on their ability to serve as broad indicators of ambient aerosol concentrations and composition for their respective neighborhoods. Both sampling stations were, therefore, located above ground level and were not influenced by any local, idiosyncratic point sources that could have distorted the measured distributions of the particle components. Prior to sample collection the QFFs were baked at 550 °C for a minimum of 16 h. Before and after sampling QFFs were stored in plastic Petri dishes sealed with Teflon tape, and kept frozen. Each sample collected on the quartz fiber filter was analyzed for elemental and organic carbon (ECOC) by thermal-optical analysis (Sunset Laboratory, Inc., Forest Grove, OR) (9). After the ECOC analysis, the remaining sections of the filters were composited on a monthly basis, solvent extracted with dichloromethane (DCM) and methanol by sonication, derivatized, and analyzed by gas chromatography-mass spectrometry (GC-MS) for molecular marker organic compounds (10). In addition, secondary organic aerosol (SOA) tracers were also quantified by GC-MS using the method adapted from Kleindienst, et al. (13) as described by Stone, 1912
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et al. (12). Briefly, the DCM/methanol extracts were blown to dryness, reconstituted in pyridene, derivatized with silylation reagent (11), and analyzed by positive chemical ionization GC-MS. The SOA compounds were quantified as pinonic acid, relative to the ketopinic acid internal standard. The pinonic acid functioned as a surrogate, since identical quantification standards were unavailable (12, 13). Teflon membrane filters (Pall Life Sciences) were used to collect and measure PM2.5 mass gravimetrically. Watersoluble ionic and trace metal concentrations were determined by analyzing the collected PM2.5 mass using ion chromatography and by X-ray fluorescence (XRF), respectively. The mass and water-soluble data are not discussed in this paper, but nickel (Ni), vanadium (V), aluminum (Al), and silicon (Si) data from the XRF analysis were used in the molecular marker source apportionment model. The XRF analysis was conducted at Desert Research Institute (DRI) in Reno, Nevada using the EPA Compendium Method 10-3.3 (14). Source apportionment analyses were performed using the U.S. EPA Chemical Mass Balance (CMB) model (CMB8.2) which used an effective variance weighted least-squares solution generated from known source contributions and experimentally determined source compositions (15). The molecular marker source profiles included in the model were vegetative detritus, biomass burning, diesel and gasoline vehicles, residual fuel oil, a local dust profile, low-temperature coal combustion, and secondary organic aerosol sources from the following gas-phase precursors: isoprene, R-pinene, β-caryophyllene, and toluene (13, 16-20). The model was configured to apportion PM2.5 organic carbon and used the following tracer compounds: EC, n-alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes, levoglucosan, SOA markers, and select trace elements. A full list of the individual organic compounds and trace elements included can be found in Supporting Information (Table S1), as well as a table of the complete CMB results and model performance statistics (Tables S2 and S3). The compounds listed in Table S1 are components of the characteristic fingerprints that comprise the source profiles, and are not necessarily quantified in every sample. A summary of the literature on the sources of these compounds is provided in the Supporting Information. The SOA apportioned from the R-pinene derivatives was statistically insignificant in the model and therefore will not be discussed further. The fitting statistics for entire data set were as follows: R2 values ranged from 0.79 to 1.0, indicating good agreement between the measured compounds and the source profiles; and χ2 values, correlating to the uncertainty of measured species relative to the uncertainties in the source profiles, ranged from 2.7 to 5.6, which were comparable to results from similar molecular marker CMB analyses (21). On average, West Jerusalem and East Jerusalem had an R2 of 0.95 and 0.96, and an χ2 value of 4.2 and 3.9, respectively. The average mass apportioned was 81% (West Jerusalem) and 89% (East Jerusalem). The same source profiles were included in the model for East and West Jerusalem, with the exception of the smoking vehicle profile. The CMB model results showed the smoking vehicle contribution was statistically insignificant for all months for West Jerusalem and was therefore removed. The difference in the amount of OC attributed to the gasoline vehicle source with and without the inclusion of the smoking vehicle source in West Jerusalem was within the overlap of the standard error. The smoking vehicle source contributions were statistically significant in 8 of the 12 months in East Jerusalem; only those statistically significant values were included in the gasoline vehicle source. For the four months where the smoking vehicle contribution was insignificant, the gasoline vehicle contribution was statistically the same within the uncertainty of the model, when the CMB model was run with and without
amount of organic carbon. In these cases there is a source that was not included in the CMB model that is having an impact during these months. The source may be additional SOA that was not captured with the derivatives quantified in this study.
Results and Discussion
FIGURE 1. Monthly average fine particle organic carbon (OC) and elemental carbon (EC) concentrations for 2007 for (a) West Jerusalem and (b) East Jerusalem. the inclusion of the smoking vehicle profile. As demonstrated by Lough et al. (17), smoking vehicle emissions are important to include in molecular marker CMB models to obtain an accurate vehicular source apportionment, but the exact split between organic particulate matter emissions from gasoline vehicles and smoking vehicles contains considerable uncertainty. For this reason, the smoking vehicle profile source contributions are combined with the gasoline vehicle contributions in the presented results. For a limited number of months at both sites, there remains an unapportioned
Monthly PM2.5, OC, and EC concentrations for the East and West Jerusalem sites are shown in Figure 1. Despite being separated by a distance of less than 4 km, concentrations of both OC and EC were significantly different between the East and West Jerusalem sampling sites. The annual mean EC concentrations in West and East Jerusalem were 4.03 and 5.20 µg/m3, respectively (p-value ) 0.0007), with annual mean OC concentrations measured in West and East Jerusalem of 1.14 and 2.19 µg m-3, respectively (p-value
