Chemical characterization of ambient particulate matter near the World Trade Center: elemental carbon, organic carbon, and mass reconstruction

Concentrations of elemental carbon (EC), organic carbon matter (OM), particulate matter less than 2.5 microm (PM2.5), reconstructed soil, trace element oxides, and sulfate are reported from four locations near the World Trade Center (WTC) complex for airborne particulate matter (PM) samples collected from September 2001 through January 2002. Across the four sampling sites, daily mean concentrations ranged from 1.5 to 6.8 microg/m3 for EC, from 10.2 to 31.4 microg/m3 for OM, and from 22.6 to 66.2 microg/m3 for PM2.5. Highest concentrations of PM species were generally measured north and west of the WTC complex. Total carbon matter and sulfate constituted the largest fraction of reconstructed PM2.5 concentrations. Concentrations of PM species across all sites decreased from the period when fires were present at the WTC complex (before December 19, 2001) to the period after the fires. Averaged over all sites, concentrations decreased by 25.6 microg/m3 for PM2.5, 2.7 microg/m3 for EC, and 9.2 microg/m3 for OM from the fire period to after fire period.     

Waterpipe-associated particulate matter emissions.

Waterpipe tobacco smoking is increasingly common worldwide, and evidence about its harmful effects to smokers is emerging. However, no studies have investigated the potential exposure of nonsmokers to waterpipe smoke. We measured particulate matter (PM) emissions (PM2.5, PM10) before and during laboratory sessions in which 20 individuals used a waterpipe to smoke tobacco and 20 individuals smoked a cigarette (10 for each particle-size/smoking-method), as well as 10 waterpipe and 10 cigarette smoldering sessions (i.e., without a smoker). A TSI-SidePak aerosol monitor obtained PM2.5, PM10 background, smoking, and maximum levels. Mean PM2.5 rose 447% for waterpipe (from 48 microg/m3 background to 264 microg/m3 smoking), and by 501% for cigarettes (from 44 microg/m3 to 267 microg/m3), whereas mean PM10 rose by 563% for waterpipe (from 55 microg/m3 to 365 microg/m3), and by 447% for cigarettes (from 52 microg/m3 to 287 microg/m3) (p<.05 for all). The increase in PM during cigarette smoking was due primarily to PM2.5, given that the proportion of PM2.5 from total PM10 increase was 95% compared with 70% for waterpipe (p<.05). Maximum PM2.5 was 908 microg/m3 for waterpipe and 575 microg/m3 for cigarettes, whereas maximum PM10 was 1052 microg/m3 for waterpipe and 653 microg/m3 for cigarettes. Mean PM2.5 and PM10 smoldering levels did not differ from background for waterpipe but were significantly higher for cigarettes (PM2.5: 33-190 microg/m3; PM10: 42-220 microg/m3). Policymakers considering clean air regulations should include waterpipe tobacco smoking, and the public should be warned about this source of smoke exposure.     

Determination of the sources of indoor PM2.5 in Amsterdam and Helsinki

Daily PM2.5 samples were repeatedly collected (1-8 times) in the homes of elderly nonsmoking individuals with coronary heart disease in Amsterdam, The Netherlands (33 individuals) and Helsinki, Finland (44 individuals). Sources of indoor PM2.5 were evaluated using a two-way multilinear engine model. Because the indoor elemental data lacked a traffic marker, separation of traffic related PM was attempted by combining the indoor data with fixed site outdoor data that also contained NO. Six outdoor sources, including long-range transport (LRT), urban mixture, oil combustion, traffic, sea-salt, and soil were identified, and three indoor sources were resolved: resuspension, potassium-rich and copper-rich sources. The average contribution of the indoor factors was 6% (1.1 microg m(-3)) and 22% (2.4 microg m(-3)) in Amsterdam and Helsinki, respectively. The highest longitudinal correlations between source-specific outdoor and indoor PM2.5 concentrations were found for LRT and urban mixture; the median R was above 0.6 for most sources. The longitudinal correlations were lower in Helsinki than in Amsterdam. Indoor-generated PM2.5 was not related to ambient concentrations. We conclude that using outdoor and indoor data together improved the source apportionment of indoor PM2.5. The results support the use of fixed site outdoor measurements in epidemiological time-series studies on outdoor air pollution.     

Exposure to secondhand smoke in Germany: air contamination due to smoking in German restaurants, bars, and other venues.

This study quantified exposure to secondhand smoke in German restaurants, bars, and entertainment venues by determining the concentration of respirable suspended particles measuring 2.5 microm or less (PM2.5) in indoor air. The measurements were taken using an inconspicuous device placed on the investigator's table in the venue. The concentration of particulate matter in the indoor air was measured for a minimum of 30 min. A total of 39 restaurants, 20 coffee bars, 12 bars, 9 discothèques, and 20 restaurant cars in trains were visited throughout Germany from September 30 to October 31, 2005. The readings disclosed a median PM2.5 of 260 microg/m3 and an arithmetic mean PM2.5 of 333 microg/m3. Median values were 378 microg/m3 in bars, 131 microg/m3 in cafes, and 173 microg/m3 in restaurants. The highest medians were measured in discothèques and restaurant cars, with values averaging 432 microg/m3 and 525 microg/m3 PM2.5, respectively. This study was the first to show the magnitude and extent of exposure to secondhand smoke on such an extensive scale in Germany. The contaminated air due to smoking is a human carcinogenic and major health hazard, which would be prevented most effectively and completely by implementing a ban on smoking. This study is important for the ongoing national debate in Germany as well as for debates in all countries without smoke-free air legislation, which includes most countries around the world.     

Airborne respirable silica near a sand and gravel facility in central California: XRD and elemental analysis to distinguish source and background quartz

Despite the potential toxicity of respirable quartz to humans, little is known about the transport of airborne quartz from sources to receptors and how to distinguish anthropogenically generated quartz from natural background in a receptor sample. Airborne quartz emissions near a sand and gravel facility were determined using PM10 and PM2.5 filter samples collected at four downwind sites (D1: 22 m, D2: 62 m, D3: 259 m, and D4: 745 m from the facility) as well as one upwind site (U1: 1495 m) during summer sampling. X-ray diffraction was used to determine quartz concentration and elemental composition was analyzed using PIXE, XRF, PESA, and HIPS techniques. Elemental composition of the PM samples was used to determine the X-ray mass absorption coefficients that are essential for accurate quartz quantification by XRD. Elemental composition was found to be a useful tool to distinguish source and background crystalline silica. Both PM10 and PM2.5 samples collected at the D1, D2, and D3 sites contained more Si, Al, and Fe and less H, Na, and S, compared to those at the U1 site, whereas site D4 sample compositions were similar to those at the U1 site. A composite variable, SOIL/(H+Na+S), where SOIL = 2.20Al + 2.49Si + 1.63Ca + 1.94Ti + 2.42Fe, was used to distinguish source materials from background. Average dry season quartz concentrations in replicate PM10 samples were 4.6 +/- 0.9) microg m(-3) at U1, 60.6 (+/- 5.4) microg m(3) at D1, 62.4 (+/- 3.6) at D2, 32.6 (+/- 2.1) microg m(-3) at D3, and 9.41 (+/- 0.9) microg m(-3) at D4. The mass fraction of quartz was the highest at the D1 site and decreased with increasing distance from the facility. The mass of PM2.5 samples was too low to determine quartz concentrations. These results identify the facility as the main source of quartz and other silicate minerals downwind of the plant and that the air quality of the most remote sampling site, located approximately 750 m downwind, was still impacted by the facility's activity.     

Exposure assessment for estimation of the global burden of disease attributable to outdoor air pollution

Ambient air pollution is associated with numerous adverse health impacts. Previous assessments of global attributable disease burden have been limited to urban areas or by coarse spatial resolution of concentration estimates. Recent developments in remote sensing, global chemical-transport models, and improvements in coverage of surface measurements facilitate virtually complete spatially resolved global air pollutant concentration estimates. We combined these data to generate global estimates of long-term average ambient concentrations of fine particles (PM(2.5)) and ozone at 0.1° × 0.1° spatial resolution for 1990 and 2005. In 2005, 89% of the world's population lived in areas where the World Health Organization Air Quality Guideline of 10 μg/m(3) PM(2.5) (annual average) was exceeded. Globally, 32% of the population lived in areas exceeding the WHO Level 1 Interim Target of 35 μg/m(3), driven by high proportions in East (76%) and South (26%) Asia. The highest seasonal ozone levels were found in North and Latin America, Europe, South and East Asia, and parts of Africa. Between 1990 and 2005 a 6% increase in global population-weighted PM(2.5) and a 1% decrease in global population-weighted ozone concentrations was apparent, highlighted by increased concentrations in East, South, and Southeast Asia and decreases in North America and Europe. Combined with spatially resolved population distributions, these estimates expand the evaluation of the global health burden associated with outdoor air pollution.     

Comparison of light scattering devices and impactors for particulate measurements in indoor,outdoor, and personal environments

Short-term monitoring of individual particulate matter (PM) exposures on subjects and inside residences in health effect studies have been sparse due to the lack of adequate monitoring devices. The recent development of small and portable light scattering devices, including the Radiance nephelometer (neph) and the personal DataRAM (pDR) has made this monitoring possible. This paper evaluates the performance of both the passive pDR and neph (without any size fractionation inlet) against measurements from both Harvard impactors (HI2.5) and Harvard personal environmental monitors (HPEM2.5) for PM2.5 in indoor, outdoor, and personal settings. These measurements were taken at the residences and on the person of nonsmoking elderly subjects across the metropolitan Seattle area and represent a wide range of light scattering measurements directly related to exposures and health effects. At low PM levels, nephs provided finer resolution and more precise measurements (precision = 3-8% and uncertainty = 2.8 x 10(-7) m(-1) or <1 microg/m3) than the pDRs. The unbiased precision of pDRs above 10 microg/m3 is around 5% (with an unbiased uncertainty of 4.4 microg/m3). The 24-h average responses of the pDR and neph, as compared to 24-h integrated gravimetric measurements, are not affected by indoor sources of PM. When regressed against 24-h gravimetric measurements, nephs showed higher coefficients of determination (R2 = 0.81-0.93) than pDRs (R2 = 0.77-0.84). The default mass calibration on the pDRs generally overestimated indoor HI2.5 measurements by 56%. When carried by subjects, the pDR overestimated the HPEM2.5 measurements by approximately 27%. Collocated real-time indoor nephs and pDRs at diverse residential sites had varied coefficients of determination across homes (R2 = 0.75-0.96), and the difference between pDR and neph responses increased during cooking hours. This difference was larger during baking or frying episodes than during other cooking or cleaning activities. Relative humidity, ranging between 25% and 64% indoors in our study, was not a significant factor affecting the differences in neph or pDR response. In summary, for nonsmoking residences, the mass scattering efficiency (m2/g) of a stationary indoor neph on a 24-h basis does not vary by residence, including residences with and without cooking activities. This is also true forthe pDR. These same stationary indoor pDRs and nephs correlate well with each other, even on a 10-min basis, in the absence of indoor source activities. The fact that these activities comprised a relatively small percentage (cooking + cleaning = 2.3%) of the overall sampling time meant that the overall correlation between these two instruments for all time periods was good. However, when examining the cooking and cleaning periods separately, the correlation was not very good. Thus, during these short-term PM episodes, the 24-h average calibrations versus gravimetric mass should be used with caution. Both devices should be potentially useful in future exposure assessment and health effects studies.     

Development and evaluation of a personal particulate organic and mass sampler

Accurate measurement of personal exposure to particulate matter and its constituents requires samplers that are accurate, compact, lightweight, inexpensive, and convenient to use. The personal particulate organic and mass sampler (PPOMS) has been developed to meet these criteria. The PPOMS uses activated carbon-impregnated foam as a combined 2.5-microm size-selective inlet and denuder for assessment of fine particle mass and organic carbon. Proof of the PPOMS concept has been established by comparing mass and organic carbon in particles collected with collocated samplers in Seattle, at a central outdoor site, and in residences. Daily particulate mass concentrations averaged 10.0 +/- 5.2, 12.0 +/- 5.3, and 11.2 +/- 5.1 microg m(-3) for the Federal Reference Method, the Harvard Personal Exposure Monitor, and the PPOMS, respectively, for 10 24-h sampling periods. During a series of PM2.5 indoor organic carbon (OC) measurements from single quartz filters, the apparent indoor OC averaged 7.7 +/- 0.8 microg of C m(-3), which was close to the indoor PM2.5 mass from collocated Teflon filters (7.3 +/- 2.3 microg of C m(-3)), indicating the presence of a large positive OC artifact. In collocated measurements, the PPOMS eliminated this artifact just as well as the integrated gas and particle sampler that incorporated a macroreticular polystyrene-divinylbenzene (XAD-4) resin-coated denuder, yielding OC concentrations of 2.5 +/- 0.4 and 2.4 +/- 1.0 microg of C m(-3), respectively. Thermal analysis for OC indicated that the indoor positive artifact was due to adsorption of gas-phase semivolatile organic compounds (SVOC). This study shows that the PPOMS design provides a 2.5-microm size-selective inlet that also prevents the adsorption of gas-phase SVOC onto quartz filters, thus eliminating the filter positive artifact The PPOMS meets a significant current challenge for indoor and personal sampling of particulate organic carbon. The PPOMS design can also simplify accurate ambient sampling for PM2.5.     

Optical remote sensing to quantify fugitive particulate mass emissions from stationary short-term and mobile continuous sources: part II. Field applications

Quantification of emissions of fugitive particulate matter (PM) into the atmosphere from military training operations is of interest by the United States Department of Defense. A new range-resolved optical remote sensing (ORS) method was developed to quantify fugitive PM emissions from puff sources (i.e., artillery back blasts), ground-level mobile sources (i.e., movement of tracked vehicles), and elevated mobile sources (i.e., airborne helicopters) in desert areas that are prone to generating fugitive dust plumes. Real-time, in situ mass concentration profiles for PM mass with particle diameters <10 μm (PM(10)) and <2.5 μm (PM(2.5)) were obtained across the dust plumes that were generated by these activities with this new method. Back blasts caused during artillery firing were characterized as a stationary short-term puff source whose plumes typically dispersed to <10 m above the ground with durations of 10-30 s. Fugitive PM emissions caused by artillery back blasts were related to the zone charge and ranged from 51 to 463 g PM/firing for PM(10) and 9 to 176 g PM/firing for PM(2.5). Movement of tracked vehicles and flying helicopters was characterized as mobile continuous sources whose plumes typically dispersed 30-50 m above the ground with durations of 100-200 s. Fugitive PM emissions caused by moving tracked vehicles ranged from 8.3 to 72.5 kg PM/km for PM(10) and 1.1 to 17.2 kg PM/km for PM(2.5), and there was no obvious correlation between PM emission and vehicle speed. The emission factor for the helicopter flying at 3 m above the ground ranged from 14.5 to 114.1 kg PM/km for PM(10) and 5.0 to 39.5 kg PM/km for PM(2.5), depending on the velocity of the helicopter and type of soil it flies over. Fugitive PM emissions by an airborne helicopter were correlated with helicopter speed for a particular soil type. The results from this range-resolved ORS method were also compared with the data obtained with another path-integrated ORS method and a Flux Tower method.     

Use of personal-indoor-outdoor sulfur concentrations to estimate the infiltration factor and outdoor exposure factor for individual homes and persons

A study of personal, indoor, and outdoor exposure to PM2.5 and associated elements has been carried out for 37 residents of the Research Triangle Park area in North Carolina. Participants were selected from persons expected to be at elevated risk from exposure to particles, and included 29 persons with hypertension and 8 cardiac patients with implanted defibrillators. Participants were monitored for 7 consecutive days in each of four seasons. One goal of the study was to estimate the contribution of outdoor PM2.5 to indoor concentrations. This depends on the infiltration factor Finf, the fraction of outdoor PM2.5 remaining airborne after penetrating indoors. After confirming with our measurements the findings of previous studies that sulfur has few indoor sources, we estimated an average Finf for each house based on indoor/outdoor sulfur ratios. These estimates ranged from 0.26 to 0.87, with a median value of 0.55. Since these estimates apply only to particles of size similar to that of sulfur particles (0.06-0.5 microm diameter), and since larger particles (0.5-2.5 microm) have lower penetration rates and higher deposition rates, these estimates are likely to be higher than the true infiltration factors for PM2.5 as a whole. In summer when air conditioners were in use, the sulfur-based infiltration factor was at its lowest (averaging 0.50) for most homes, whereas the average Finf for the other three seasons was 0.62-0.63. Using the daily estimated infiltration factor for each house, we calculated the contribution of outdoor PM2.5 to indoor air concentrations. The indoor-generated contributions to indoor PM2.5 had a wider range (0-33 microg/m3) than the outdoor contributions (5-22 microg/m3). However, outdoor contributions exceeded the indoor-generated contributions in 27 of 36 homes. A second goal of the study was to determine the contribution of outdoor particles to personal exposure. This is determined by the "outdoor exposure factor" Fpex, the fraction of outdoor PM2.5 contributing to personal exposure. As with Finf, we estimated Fpex by the personal/outdoor sulfur ratios. The estimates ranged from 0.33 to 0.77 with a median value of 0.53. Outdoor air particles were less important for personal exposures than for indoor concentrations, with the median outdoor contribution to personal exposure just 49%. We regressed the outdoor contributions to personal exposures on measured outdoor PM2.5 at the central site. The regressions had R2 values ranging from 0.19 to 0.88 (median = 0.73). These values provide an indication of the extent of misclassification error in epidemiological estimates of the effect of outdoor particles on health.     

Characterization of aerosols containing Zn, Pb, and Cl from an industrial region of Mexico City

Recent ice core measurements show lead concentrations increasing since 1970, suggesting new nonautomobile-related sources of Pb are becoming important worldwide (1). Developing a full understanding of the major sources of Pb and other metals is critical to controlling these emissions. During the March, 2006 MILAGRO campaign, single particle measurements in Mexico City revealed the frequent appearance of particles internally mixed with Zn, Pb, Cl, and P. Pb concentrations were as high as 1.14 microg/m3 in PM10 and 0.76 microg/m3 in PM2.5. Real time measurements were used to select time periods of interest to perform offline analysis to obtain detailed aerosol speciation. Many Zn-rich particles had needle-like structures and were found to be composed of ZnO and/or Zn(NO3)2 x 6H2O. The internally mixed Pb-Zn-Cl particles represented as much as 73% of the fine mode particles (by number) in the morning hours between 2-5 am. The Pb-Zn-Cl particles were primarily in the submicrometer size range and typically mixed with elemental carbon suggesting a combustion source. The unique single particle chemical associations measured in this study closely match signatures indicative of waste incineration. Our findings also show these industrial emissions play an important role in heterogeneous processing of NO(y) species. Primary emissions of metal and sodium chloride particles emitted by the same source underwent heterogeneous transformations into nitrate particles as soon as photochemical production of nitric acid began each day at approximately 7 am.     

Evaluation of urinary methoxyphenols as biomarkers of woodsmoke exposure

Urinary methoxyphenols have been proposed as biomarkers for woodsmoke exposure, but the relationship between exposure and urinary methoxyphenol concentrations has not been characterized. We collected personal particulate matter2.5 and urine samples from 9 adults experimentally exposed to smoke from an open wood fire to characterize this relationship. Personal exposures (PM2.5 mean 1500 microg/ m3) varied 3.5-fold. Twenty-two methoxyphenols, levoglucosan, and 17 polynuclear hydrocarbons were quantified by gas chromatography/mass spectrometry assays for personal filter samples and urine samples. Most methoxyphenols had measurable preexposure levels. Propylguaiacol, syringol, methylsyringol, ethylsyringol, and propylsyringol had peak urinary concentrations after the woodsmoke exposure. Eight subjects had peak urinary elimination of methoxyphenols within 6 h (t1/2 3-5 h), whereas one had delayed elimination. Several metrics for urinary excretion were evaluated. Analyte concentration was greatly affected by diuresis. Excretion rate and analyte concentrations normalized by creatinine gave a clearer signal and were equivalent in predictive ability. Twelve-hour average creatinine-normalized concentrations of each of the 5 methoxyphenols gave a Pearson correlation > or = 0.8 with their particle-phase concentration. The sum of urinary concentrations for the 5 methoxyphenols versus levoglucosan on personal filters gave a regression coefficient of 0.75. This sum versus PM2.5 gave a regression coefficient of 0.79. The intercept of this regression suggests that the threshold for detection of an acute exposure event would be approximately 760 microg/m3 particulate matter from woodsmoke. The signal-to-noise (12-h postexposure average/preexposure average) ranged from 1.1 to 8 for the 5 methoxyphenols. Analysis of multiple compounds provided assurance that elevations were not artifactual due to food or other products.     

Herbicide sorption to fine particulate matter suspended downwind of agricultural operations: field and laboratory investigations

Tillage-induced erosion of herbicides bound to airborne soil particles has not been quantified as a mechanism for offsite herbicide transport. This study quantifies the release of two preemergent herbicides, metolachlor and pendimethalin, to the atmosphere as gas- and particle-phase species during soil incorporation operations. Fine particulate matter (PM2.5) and gas-phase samples were collected at three sampling heights during herbicide disking into the soil in Davis, CA, in May 2000 and May 2001 using filter/PUF sampling. Quartz fiber filters (QFFs) were used in May 2000, and Teflon membrane filters (TMFs) were used in May 2001. The field data were combined with laboratory filter/PUF partitioning experiments to account for adsorption to the filter surfaces and quantify the mass of PM2.5-bound herbicides in the field samples. Laboratory results indicate a significant adsorption of metolachlor, but not pendimethalin, to the quartz filter surfaces. Metolachlor partitioning to PM2.5 collected on TMF filters resulted in corrected PM2.5 field partition coefficient values, Kp,corr = Cp/Cg, of approximately 10(-3.5) m3/microg, indicating its preference for the gas phase. Pendimethalin exhibited more semivolatile behavior,with Kp,corr values that ranged from 10(-3) to 10(-1) m3/ microg and increased with sampling height and distance downwind of the operation. An increase in pendimethalin enrichment at a height of 5 m suggests winnowing of finer, more sorptive soil components with corresponding higher transport potential. Pendimethalin was enriched in the PM2.5 samples by up to a factor of 250 compared to the field soil, indicating thatfurther research on the processes controlling the generation of PM-bound herbicides during agricultural operations is warranted to enable prediction of off-site mass fluxes by this mechanism.     

Source contributions to atmospheric gases and particulate matter in the southeastern United States

A new approach for determining the contributions of emission sources to concentrations of particulate matter and gases is developed using the chemical mass balance (CMB) method and the U.S. EPA's National Emission Inventory (NEI). The approach apportions combined gas-phase and condensed-phase concentrations of individual compounds as well as PM(2.5) mass. Because the NEI is used to provide source emission profiles for CMB analysis, the method generates information on the consistency of the NEI with ambient monitoring data. The method also tracks secondary species to primary source emissions, permitting a more complete accounting of the impact of aggregated source types on PM(2.5) mass concentrations. An example application is presented using four years of monitoring data collected at eight sites in the Southeastern Aerosol Research and Characterization (SEARCH) network. Including both primary and secondary species, area sources contributed 2.0-3.7 μg m(-3) (13-26%), point sources contributed 3.0-4.6 μg m(-3) (22-33%), and mobile sources contributed 1.0-6.0 μg m(-3) (9-42%) to mean PM(2.5) mass concentrations. Whereas the NEI generally accounts for the ambient concentrations of gases and particles, certain anomalies are identified, especially related to carbonaceous compounds and dust.     

Impact of the 2002 Canadian forest fires on particulate matter air quality in Baltimore city

With increasing evidence of adverse health effects associated with particulate matter (PM), the exposure impact of natural sources, such as forest fires, has substantial public health relevance. In addition to the threat to nearby communities, pollutants released from forest fires can travel thousands of kilometers to heavily populated urban areas. There was a dramatic increase in forest fire activity in the province of Quebec, Canada, during July 2002. The transport of PM released from these forest fires was examined using a combination of a moderate-resolution imaging spectroradiometer satellite image, back-trajectories using a hybrid single-particle Lagrangian integrated trajectory, and local light detection and ranging measurements. Time- and size-resolved PM was evaluated at three ambient and four indoor measurement sites using a combination of direct reading instruments (laser, time-of-flight aerosol spectrometer, nephelometer, and an oscillating microbalance). The transport and monitoring results consistently identified a forest fire related PM episode in Baltimore that occurred the first weekend of July 2002 and resulted in as much as a 30-fold increase in ambientfine PM. On the basis of tapered element oscillating microbalance measurements, the 24 h PM25 concentration reached 86 microg/m3 on July 7, 2002, exceeding the 24 h national ambient air quality standard. The episode was primarily comprised of particles less than 2.5 microm in aerodynamic diameter, highlighting the preferential transport of the fraction of PM that is of greatest health concern. Penetration of the ambient episode indoors was efficient (median indoor-to-outdoor ratio 0.91) such that the high ambient levels were similarly experienced indoors. These results are significant in demonstrating the impact of a natural source thousands of kilometers away on ambient levels of and potential exposures to air pollution within an urban center. This research highlights the significance of transboundary air pollution and the need for studies that assess the public health impacts associated with such sources and transport processes.     

Spatial variability of fine particle mass, components, and source contributions during the regional air pollution study in St. Louis

Community time-series epidemiology typically uses either 24-hour integrated particulate matter (PM) concentrations averaged across several monitors in a city or data obtained at a central monitoring site to relate PM concentrations to human health effects. If the day-to-day variations in 24-hour integrated concentrations differ substantially across an urban area (i.e., daily measurements at monitors at different locations are not highly correlated), then there is a significant potential for exposure misclassification in community time-series epidemiology. If the annual average concentration differs across an urban area, then there is a potential for exposure misclassification in epidemiologic studies that use annual averages (or multi-year averages) as an index of exposure across different cities. The spatial variability in PM2.5 (particulate matter < or = 2.5 microm in aerodynamic diameter), its elemental components, and the contributions from each source category at 10 monitoring sites in St. Louis, Missouri were characterized using the ambient PM2.5 compositional data set of the Regional Air Pollution Study (RAPS) based on the Regional Air Monitoring System (RAMS) conducted between 1975 and 1977. Positive matrix factorization (PMF) was applied to each ambient PM2.5 compositional data set to estimate the contributions from the source categories. The spatial distributions of components and source contributions to PM2.5 at the 10 sites were characterized using Pearson correlation coefficients and coefficients of divergence. Sulfur and PM2.5 are highly correlated elements between all of the site pairs Although the secondary sulfate is the most highly correlated and shows the smallest spatial variability, there is a factor of 1.7 difference in secondary sulfate contributions between the highest and lowest site on average. Motor vehicles represent the next most highly correlated source component. However, there is a factor of 3.6 difference in motor vehicle contributions between the highest and lowest sites. The contributions from point source categories are much more variable. For example, the contributions from incinerators show a difference of a factor of 12.5 between the sites with the lowest and highest contributions. This study demonstrates that the spatial distributions of elemental components of PM2.5 and contributions from source categories can be highly heterogeneous within a given airshed and thus, there is the potential for exposure misclassification when a limited number of ambient PM monitors are used to represent population-average ambient exposures.     

Interannual variations in PM2.5 due to wildfires in the Western United States

In this study we have evaluated the role of wildfires on concentrations of fine particle (d < 2.5 microm) organic carbon (OC) and particulate mass (PM2.5) in the Western United States for the period 1988-2004. To do this, we examined the relationship between mean summer PM2.5 and OC concentrations at 39 IMPROVE sites with a database of fires developed from federal fire reports. The gridded database of area burned was used to generate a database of biomass fuel burned using ecosystem-specific fuel loads. The OC, PM2.5, and fire data were evaluated for five regions: Northern Rocky Mountains (Region 1), Central Rocky Mountains (Region 2), Southwest (Region 3), California (Region 4), and Pacific Northwest (Region 5). In Regions 1, 2, and 5, we found good correlations of seasonal mean PM2.5 concentrations among the sites within each region. This indicates that a common influence was important in determining the PM concentration at all sites across each region. In Regions 1 and 2, we found a significant correlation between PM2.5 and both the area burned and biomassfuel burned in each region. This relationship is statistically significant using either the area burned or fuel burned, but the correlations are stronger using the biomass fuel burned. In all five regions we found a statistically significant relationship between biomass burned and organic carbon. Using these relationships, we can estimate the amount of PM2.5 due to fires in each region during summer. For the Regions 1 through 5, the average summer-long enhancement of PM2.5 due to fires is 1.84, 1.09, 0.61, 0.81, and 1.21 microg/m3, respectively, and approximately twice these values during large fire years.     

Determination of methoxyphenols in ambient atmospheric particulate matter: tracers for wood combustion

Combustion of wood and other biomass fuels produces source-specific organic compounds arising from pyrolysis of lignin, including substantial amounts of 4-substituted methoxylated phenolic compounds (methoxyphenols). These compounds have been used as atmospheric markers to determine the contribution of wood smoke to ambient atmospheric fine particulate matter (PM). However, reliable quantification of methoxyphenols represents an analytical challenge because these compounds are polar, semi-volatile, and somewhat reactive. We reportherein an improved gas chromatographic-mass spectrometric (GC/MS) method for the sensitive and reliable determination of methoxyphenols in low-volume ambient PM samples. Deuterated standard compounds are added to the environmental samples prior to extraction to determine analyte recoveries in each sample. Analytical figures of merit for the assay, as applied to ambient PM2.5 and PM10 samples are as follows: recovery = 63-100%; precision = 2-6%; analytical limit of detection (S/N 2) = 0.002 microg/mL; limit of quantitation = 0.07-0.45 ng/m3 (assuming a 14 m3 sample). The improved method was applied to ambient PM samples collected between 1999 and 2000 in Seattle, WA. Particle-bound methoxyphenol concentrations in the range <0.1 to 22 ng/m3 were observed and the methoxyphenols were present almost exclusively in the fine (PM2.5) size fraction. We also demonstrated that XRF analysis of samples of atmospheric PM collected on Teflon filters significantly reduced the levels of methoxyphenols measured in the PM samples in subsequent assay of the same filters. Therefore, XRF analysis of filters, commonly undertaken to obtain trace element concentrations for use in source apportionment analyses, would preclude the subsequent analysis of those filters for methoxyphenols and other similarly semivolatile or reactive organic chemicals.     

Household concentrations and exposure of children to particulate matter from biomass fuels in The Gambia

Particulate matter (PM) is an important metric for studying the health effects of household air pollution. There are limited data on PM exposure for children in homes that use biomass fuels, and no previous study has used direct measurement of personal exposure in children younger than 5 years of age. We estimated PM(2.5) exposure for 1266 children in The Gambia by applying the cookhouse PM(2.5)-CO relationship to the child's CO exposure. Using this indirect method, mean PM(2.5) exposure for all subjects was 135 ± 38 μg/m(3); 25% of children had exposures of 151 μg/m(3) or higher. Indirectly estimated exposure was highest among children who lived in homes that used firewood (collected or purchased) as their main fuel (144 μg/m(3)) compared to those who used charcoal (85 μg/m(3)). To validate the indirect method, we also directly measured PM(2.5) exposure on 31 children. Mean exposure for this validation data set was 65 ± 41 μg/m(3) using actual measurement and 125 ± 54 μg/m(3) using the indirect method based on simultaneously-measured CO exposure. The correlation coefficient between direct measurements and indirect estimates was 0.01. Children in The Gambia have relatively high PM(2.5) exposure. There is a need for simple methods that can directly measure PM(2.5) exposure in field studies.     

Origins of primary and secondary organic aerosol in Atlanta: results of time-resolved measurements during the Atlanta Supersite Experiment

Time-resolved ambient particulate organic (OC) and elemental carbon (EC) data measured in Atlanta, GA, during the Atlanta Supersite Experiment (August3-September 1, 1999) were investigated to determine the temporal trends of atmospheric carbonaceous aerosol and to examine the relative contributions of primary and secondary OC to measured particulate OC. Mean 1-h average concentrations (ranges in parentheses) of PM2.5 OC, EC, and total carbon were 8.3 (3.6-15.8), 2.3 (0.3-9.6), and 10.6 (4.6-24.6) microg of C m(-3), respectively, based on Rutgers University/Oregon Graduate Institute in situ thermal-optical carbon analyzer measurements. Carbonaceous matter (organic material 40%; EC 8%) comprised approximately 48% of PM2.5 mass in Atlanta. Primary and secondary OC concentrations were estimated using an EC tracer method. Secondary OC contributed approximately 46% of measured particulate OC, and 1-h average contributions ranged up to 88%. Vehicle emissions appear to be the dominant contributors to measured EC and primary OC concentrations based on temporal patterns of EC, primary OC, and CO. This research suggests that secondary OC concentrations in Atlanta were influenced by (1) "fresh" secondary organic aerosol formed by photochemical reactions locally in the early afternoons as seen in the Los Angeles air basin and (2) "aged" secondary organic aerosol transported from upwind regions or formed on previous days. Nocturnal peaks in secondary OC and ozone concentrations were observed on several days. The most probable explanation for this is the favorable partitioning of semivolatile organic compounds to the particulate phase driven by temperature decreases and relative humidity increases at night and vertical transport of regional pollutants from above to ground level.