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Reactive gaseous mercury (RGM) was measured using an annular denuder coated with potassium chloride at three rural sites (Potsdam, Stockton, and Sterling) in New York State from April 2002 to April 2003. Concentrations of RGM ranged from 0.1 to 84.6 pg m(-3) with large spatial and temporal variation. Potential source contribution function (PSCF), a common receptor modeling tool, was used with these measurements, and source-receptor relationships were calculated using back-dispersion and deposition as well as back-trajectories. Modeling results were compared with the RGM emissions inventory, and Spearman rank-order correlation coefficients were calculated. PSCF results incorporating backward dispersion and deposition were better correlated with the emissions inventory than PSCF based on back-trajectories alone. This difference was determined to be mainly due to the inclusion of dispersion rather than deposition. The main sources of RGM were suggested to be coal-fired power plants in New York and Pennsylvania, the large copper smelter in Quebec, and the taconite mining areas around the Great Lakes.

An expanded factor analysis model (ME-2) that is capable of taking into account the influence of independent variables such as wind speed, wind direction, time of year and other variables of the measured fine particle matter (PM2.5) concentration data was utilized for identifying sources of airborne pollutants and providing quantitative estimations of the contribution of each source. The chemical composition data used in this study were obtained from PM2.5 samples collected using the Interagency Monitoring of Protected Visual Environments samplers from August 1999 to December 2001 at an urban monitoring site in Washington, DC. The expanded model has been applied to two different data sets based on the particulate carbon variables. Such an approach had been successfully applied previously and provided improved source resolution in simulated and ambient concentration data. Initially, total OC and EC were used in the expanded model and were compared to the results using conventional positive matrix factorization that had been done previously using the individual carbon fractions data. In the other expanded model analysis, the eight carbon fractions were used during the modeling in order to ascertain if additional source information could be extracted from the data. In both cases, it was possible to separate diesel from spark-ignition vehicles. The use of the individual carbon fractions in the model provides information on what appears to be secondary organic aerosol formation.

Samples of fine and coarse fractions of airborne particulate matter were collected at the Farm Gate area in Dhaka from July 2001 to March 2002. Dhaka is a hot spot area with very high pollutant concentrations because of the proximity of major roadways. The samples were collected using a "Gent" stacked filter unit in two fractions of 0- to 2.2-microm and 2.2- to 10-microm sizes. The samples were analyzed for elemental concentrations by particle-induced X-ray excitation (PIXE) and for black carbon by reflectivity methods, respectively. The data were analyzed by positive matrix factorization (PMF) to identify the possible sources of atmospheric aerosols in this area. Six sources were found for both the coarse and fine PM fractions. The data sets were also analyzed by an expanded model to explore additional sources. Seven and six factors were obtained for coarse and fine PM fractions, respectively, in these analyses. The identified sources are motor vehicle, soil dust, emissions from construction activities, sea salt, biomass burning/brick kiln, resuspended/fugitive Pb, and two-stroke engines. From the expanded modeling, approximately 50% of the total PM2.2 mass can be attributed to motor vehicles, including two-stroke engine vehicle in this hot spot in Dhaka, whereas the PMF modeling indicates that 45% of the total PM2.2 mass is from motor vehicles. The PMF2 and expanded models could resolve approximately 4% and 3% of the total PM2.2 mass as resuspended/fugitive Pb, respectively. Although, Pb has been eliminated from gasoline in Bangladesh since July 1999, there still may be substantial amounts of accumulated lead in the dust near roadways as well as fugitive Pb emissions from battery reclaimation and other industries. Soil dust is the largest component of the coarse particle fraction (PM2.2-10) accounting for approximately 71% of the total PM2.2-10 mass in the expanded model, whereas from the PMF modeling, the dust (undifferentiated) contribution is approximately 49%.

Currently, we have limited knowledge of the physical and chemical properties of emitted primary combustion aerosols and the changes in those properties caused by nucleation, condensation growth of volatile species, and particle coagulations under dilution and cooling in the ambient air. A dilution chamber was deployed to sample exhaust from a pilot-scale furnace burning various fuels at a nominal heat input rate of 160 kW/h(-1) and 3% excess oxygen. The formation mechanisms of particles smaller than 420 nm in electrical mobility diameter were experimentally investigated by measurement with a Scanning Mobility Particle Sizer (SMPS) as a function of aging times, dilution air ratios, combustion exhaust temperatures, and fuel types. Particle formation in the dilution process is a complex mixture of nucleation, coagulation, and condensational growth, depending on the concentrations of available condensable species and solid or liquid particles (such as soot, ash) in combustion exhausts. The measured particle size distributions in number concentrations measured show peaks of particle number concentrations for medium sulfur bituminous coal, No. 6 fuel oil, and natural gas at 40-50 nm, 70-100 nm, and 15-25 nm, respectively. For No. 6 fuel oil and coal, the particle number concentration is constant in the range of a dilution air ratio of 50, but the number decreases as the dilution air ratio decreases to 10. However, for natural gas, the particle number concentration is higher at a dilution air ratio of 10 and decreases at dilution air ratios of 20-50. At a dilution air ratio of 10, severe particle coagulation occurs in a relatively short time. Samples taken at different combustion exhaust temperatures for these fuel types show higher particle number concentrations at 645 K than at 450 K. As the aging time of particles increases, the particles increase in size and the number concentrations decrease. The largest gradient of particle number distribution occurs within the first 10 sec after dilution but shows only minor differences between 10 and 80 sec. The lifetimes of the ultrafine particles are relatively short, with a scale on the order of a few seconds. Results from this study suggest that an aging time of 10 sec and a dilution air ratio of 20 are sufficient to obtain representative primary particle emission samples from stationary combustion sources.

Aerosol samples were collected at the rural Burnt Island Ontario Integrated Air Deposition Network air sampling station on the northern shore of Lake Huron from 1992 through 1994. The samples were analyzed for trace elements by neutron activation analysis, and the air concentrations of over 30 elements were determined. Total potential source contribution function analysis (TPSCF) was used to determine the most probable geographical location of these aerosols' origin. The TPSCF results for As, In, Sb, Se, Sn, and Zn are highlighted in this paper. Source regions for these elements ranged from Alma, Quebec, Canada to Carrollton, GA. Because of large seasonal variations in the concentrations of the atmospheric concentrations of these elements, TPSCFvalues were calculated for the summer and winter halves of the year as well as the entire year.

Integrated ambient particulate matter < or =2.5 microm in aerodynamic diameter (PM2.5) samples were collected at a centrally located urban monitoring site in Washington, DC, on Wednesdays and Saturdays using Interagency Monitoring of Protected Visual Environments samplers. Particulate carbon was analyzed using the thermal optical reflectance method that divides carbon into four organic carbon fractions, pyrolyzed organic carbon, and three elemental carbon fractions. A total of 35 variables measured in 718 samples collected between August 1988 and December 1997 were analyzed. The data were analyzed using Positive Matrix Factorization and 10 sources were identified: sulfate (SO4(2-))-rich secondary aerosol I (43%), gasoline vehicle (21%), SO4(2-)-rich secondary aerosol II (11%), nitrate-rich secondary aerosol (9%), SO4(2-)-rich secondary aerosol III (6%), incinerator (4%), aged sea salt (2%), airborne soil (2%), diesel emissions (2%), and oil combustion (2%). In contrast to a previous study that included only total organic carbon and elemental carbon fractions, motor vehicles were separated into fractions identified as gasoline vehicle and diesel emissions containing carbon fractions whose abundances were different between the two sources. This study indicates that the temperature-resolved carbon fraction data can be utilized to enhance source apportionment, especially with respect to the separation of diesel emissions from gasoline vehicle sources. Conditional probability functions using surface wind data and deduced source contributions aid in the identifications of local sources.

Number concentrations and size distributions of particles in the size range of 0.010-0.500 microm were measured in Rochester, NY, from December 2001 to December 2002. The relationships between the number concentrations, gaseous pollutants, and meteorological parameters were examined during particle nucleation events. More than 70% of measured total number concentration was associated with ultrafine particles (UFP, 0.011-0.050 microm). Morning nucleation events typically peaking UFP number concentrations at around 08:00 were apparent in winter months with CO increases. These particles appear to be formed following direct emissions from motorvehicles during morning rush hour. There were also often observed increases in this smaller-sized range particles in the late afternoon during the afternoon rush hour, particularly in winter when the mixing heights remain lowerthan in summer. Strong afternoon nucleation events (> 30,000 cm(-3)) peaking at around 13: 00 were more likely to occur in spiring and summer months. During the prominent nucleation events, peaks of SO2 were strongly associated with the number concentrations of UFP, whereas there were no significant correlations between these events and PM2.5 and CO. Increased SO2 concentrations were observed when the wind direction was northwesterly where three SO2 sources were located. It is hypothesized that UFP formed during the events are sulfuric acid and water from the oxidation of SO2. There were also a more limited number of nucleation events followed by particle growth up to approximately 0.1 microm over periods of up to 18 h. The nucleation and growth events tended to be common in spring months especially in April.

The complexity of the volatile organic compound (VOC) mixture in the Houston area makes studies of the air quality in that area very challenging. In this paper, a novel factor analysis model, where the normal chemical mass balance model was augmented by a parallel equation that accounted for wind speed and direction, temperature, and weekend/weekday effects, was fitted with a multilinear engine (ME) to provide identification and apportionment of the VOC sources at the La Porte Municipal Airport site in Houston during the Texas Air Quality Study (TexAQS) 2000. The analysis determined the profiles and contributions of nine sources and the corresponding wind speed, wind direction, temperature, and weekend factors. The reasonableness of these results not only suggests the high resolving power of the expanded factor analysis model for source apportionment but also provides the novel and effective auxiliary information for more specific source identification. In addition, a new approach to estimate the measurement uncertainty and the details of determining the source number and dealing with missing values are also presented as important parts of the data analysis process. This study demonstrates the feasibility of the expanded model to identify sources in complex VOC systems and extract useful information for locating VOC emitters and controlling their emissions in the Houston area.

A multilinear model was developed for the analysis of the spatial patterns and possible sources affecting haze and its visual effects in the southwestern United States. The data from the project Measurement of Haze and Visual Effects (MOHAVE) collected during the late winter and mid-summer of 1992 at the monitoring sites in four states (i.e., California, Arizona, Nevada and Utah) were used in the study. The three-way data array was analyzed by a four-product-term model. This study makes a direct effort to include wind patterns as a component in the model in order to obtain the information of the spatial patterns of source contributions. The solution is computed using the conjugate gradient algorithm with applied non-negativity constraints. For the winter data set, reasonable solutions contained six sources and six wind patterns. The analysis of summer data required seven sources and seven wind patterns. The ME results are compared to the prior single-species empirical orthogonal function analysis results--and prior work describing the transport pathways.

On-road experiments were conducted to determine the sensitivities of rats to real-world aerosol. This article summarizes the on-road aerosol and gas measurements and provides background information for the companion paper on the rat exposures. Measurements were carried out over 10 days, 6 h/day, driving a route from Rochester to Buffalo. Aerosol instrumentation used in this study included two scanning mobility particle sizers (SMPS) to determine the aerosol size distribution from 10 to 300 nm, 2 stand-alone condensation particle counters to determine the total aerosol number concentration, and an electrical aerosol detector to determine the aerosol length concentration. A thermal denuder (TD) was used with one of the SMPS instruments to determine the size distribution of the non-volatile fraction. Filter samples were collected and analyzed for elemental carbon, and gas analyzers measured ambient levels of CO, CO(2), and NO. Average daily total aerosol number concentration ranged from 200,000 to 560,000 particles/cm(3). Past studies on urban highways have measured total number concentrations ranging between 10(4) and 10(6) particles/cm(3). The average daily NO concentration ranged from 0.10 to 0.24 ppm and the corresponding CO(2) concentration ranged from 400 to 420 ppm. The average daily geometric number mean particle size determined by the SMPS ranged from 15 to 20 nm. The TD reduced the average SMPS number concentration between 87 and 95% and the SMPS volume between 54 and 83%, suggesting that most of the particles consisted of volatile material. The TD also increased the geometric number mean diameter from 15 to 20 nm to 30 to 40 nm.

Hourly averaged particle size distributions measured at a centrally located urban site in Seattle were analyzed through the application of bilinear positive matrix factorization (PMF) and Unmix to study underlying size distributions and their daily patterns. A total of 1051 samples each with 16 size intervals from 20 to 400 nm were obtained from a differential mobility particle sizer operating between December 2000 and February 2001. Both PMF and Unmix identify four similar underlying factors in the size distributions. Factor 1 is an accumulation mode particle size spectrum that shows a regular nocturnal pattern, and factor 2 is a larger particle distribution. Factor 3 is assigned as a traffic-related particle distribution, based on its correlations with accompanying gas-phase measurements, and has a regular weekday-high rush-hour pattern. Factor 4 is a traffic-related particle size distribution that has a regular rush-hour pattern on weekdays as well as weekends. Conditional probability functions (CPF) were computed using wind profiles and factor contributions. The results of CPF analysis suggest that these factors are correlated with surrounding particle sources of wood burning, secondary aerosol, diesel emissions, and motor vehicle emissions.

Using a modified turbulent mixing CNC, the heterogeneous nucleation of different compounds (working fluids) on nanometer sized carbon particles was examined. The working fluids were dibutyl phthalate, octadecane, octadecanol, and octadecanoic acid. Based on the particle size distributions measured with a scanning mobility particle sizer system, nucleation and consequent growth were examined with respect to different temperature and vapor pressure for each working fluid. Nucleation rates for all conditions were calculated from the fitted size distribution data by subtracting the residual nonactivated particle concentration for each condition. Experimental nucleation rates were compared to the calculated ones based on Fletcher's heterogeneous nucleation theory. This theory matches well with the experiments with octadecanol and octadecanoic acid, and at high supersaturation ratios for dibutyl phthalate. However, the theory shows discrepancies with the observed phenomena at low supersaturation for dibutyl phthalate, and especially for octadecane. Several possible hypotheses for the discrepancies and observed particle growth are discussed.

Mean silver concentrations in weekly particle samples collected at Kevo, northern Finland, were determined for the period of October 1964-March 1978 by neutron activation analysis. Two distinct periods were observed in the silver concentration levels over this time frame. During 1964-1970, mean weekly silver concentration levels were found in the range of 0.01-190 ng/m3 with an arithmetic mean of 2.19 ng/m3. A few very high silver concentration levels (>10 ng/m3) were observed in this period, some of which simultaneously occurred with some of the highest bromine and iodine concentration levels. During 1971-1978, silver concentration levels were in the range of 0.02-0.89 ng/m3 with a mean value of 0.09 ng/m3. The observed concentration levels in the later period matched well the data from the early 1990s reported at Sevettijärvi, northern Finland, about 60 km east of Kevo. Data analysis, historical records for this region, and residence time analysis (RTA) using wind back-trajectories show that occasional smelting of silver-rich Norilsk ores at the Nikel smelter, Kola Peninsula, was probably a significant contributor to elevated mean silver concentration levels during 1964-1970. RTA alone was not able to unambiguously identify the most probable source region for highest silver impacts at Kevo due to the weekly integrated nature of the samples collected. Critical examination of wind back-trajectories (24 per day) for specific high silver, bromine, and iodine concentration weeks was carried out to supplement the ensemble RTA analysis (2 back-trajectories per day). The supplemental back-trajectory analysis revealed that deposition of the smelter component silver as well as the sea components (bromine and iodine) could occur together at Kevo during these weekly sampling periods. The study implies that data from weekly integrated samples are insufficiently time-resolved for RTA methods alone to unambiguously resolve the sources contributing to ambient atmospheric concentrations at Kevo, Finland.

Data characterizing daily integrated particulate matter (PM) samples collected at the Jefferson Street monitoring site in Atlanta, GA, were analyzed through the application of a bilinear positive matrix factorization (PMF) model. A total of 662 samples and 26 variables were used for fine particle (particles < or = 2.5 microm in aerodynamic diameter) samples (PM2.5), and 685 samples and 15 variables were used for coarse particle (particles between 2.5 and 10 microm in aerodynamic diameter) samples (PM10-2.5). Measured PM mass concentrations and compositional data were used as independent variables. To obtain the quantitative contributions for each source, the factors were normalized using PMF-apportioned mass concentrations. For fine particle data, eight sources were identified: SO4(2-) -rich secondary aerosol (56%), motor vehicle (22%), wood smoke (11%), NO(3-) -rich secondary aerosol (7%), mixed source of cement kiln and organic carbon (OC) (2%), airborne soil (1%), metal recycling facility (0.5%), and mixed source of bus station and metal processing (0.3%). The SO4(2-) -rich and NO(3-) -rich secondary aerosols were associated with NH(4+). The SO4(2-) -rich secondary aerosols also included OC. For the coarse particle data, five sources contributed to the observed mass: airborne soil (60%), NO(3-)-rich secondary aerosol (16%), SO4(2-) -rich secondary aerosol (12%), cement kiln (11%), and metal recycling facility (1%). Conditional probability functions were computed using surface wind data and identified mass contributions from each source. The results of this analysis agreed well with the locations of known local point sources.

This work analyzes PM2.5 24-h average concentrations measured every third day at over 300 locations in the eastern United States during 2000. The non-negative factor analytic model, Positive Matrix Factorization, has been enhanced by modeling the dependence of PM2.5 concentrations on temperature, humidity, pressure, ozone concentrations, and wind velocity vectors. The model comprises 12 general factors, augmented by 5 urban-only factors intended to represent excess concentration present in urban locations only. The computed factor components or concentration fields are displayed as concentration maps, one for each factor, showing how much each factor contributes to the average concentration at each location. The factors are also displayed as flux maps that illustrate the spatial movement of PM2.5 aerosol, thus enabling one to pinpoint potential source areas of PM2.5. The quality of the results was investigated by examining how well the model reproduces especially high concentrations of PM2.5 on specific days at specific locations. Delimiting the spatial extent of all such factors that exhibit a clear regional maximum surrounded by an almost-zero outer domain lowered the uncertainty in the computed results.

Potential source contribution function (PSCF) modeling using polychlorinated biphenyl (PCB) concentrations measured in the Chicago area resolved three PCB source sectors. They were (i) the direction northwest of Chicago, (ii) the direction southwest of Chicago, and (iii) the south side of Chicago in the neighborhood of Lake Calumet. The area south of Chicago was further examined by taking upwind/ downwind samples near a landfill and sludge drying beds. Results identified the sludge drying beds and a large landfill as PCB sources to the atmosphere. Another PCB source identified in Chicago was a transformer storage yard. This site had the highest upwind/downwind concentration increments in this study (downwind PCB concentrations were more than 5 times those in the upwind air). These PCB sources were characterized in terms of inventories, emission rates, contributions, and PCB congener profiles (fingerprints). Preliminarily results indicate that the sludge may emit up to 90 kg/yr of PCBs to the air. This amount is probably not a significant contribution of PCBs to the Chicago atmosphere on the basis of dispersion modeling results and a simple box model.

Daily PM2.5 samples, Hg0 and speciated polycyclic aromatic hydrocarbon (PAH) were simultaneously collected at Potsdam and Stockton site in NY during the summers of 2000 and 2001. Samples for determination of the mass concentration and chemical composition of the PM2.5 were obtained with a speciation network PM2.5 sampler. Chemical composition including trace elemental composition, water-soluble ions, and elemental carbon were analyzed. Elemental mercury and PAHs were sampled separately. Daily PM2.5 concentrations ranged from 0.47 to 53.7 microg m(-3) at the Potsdam site, and from 0.82 to 47.23 microg m(-3) at the Stockton site with large daily differences between the two sites. Potsdam consistently had lower mass values than Stockton. The greatest contributors to the PM2.5 mass (generally >0.1 microg/m(3)) were sulfate, nitrate, ammonium, and BC at both sites. Seventeen PAHs were identified at each site in 2000 and the average total concentrations were 3.2 ng/m(3) and 2.9 ng/m(3) at the Potsdam and Stockton sites, respectively. The mean vapor phase mercury concentration at the Potsdam site (2.4 +/-1.2 ng m(-3), n=93) was higher than that at the Stockton site (1.2 +/- 1.0 ng m(-3), n=60) in 2000, whereas in 2001, the average concentrations were 1.1 ng m(-3) and 1.6 ng m(-3) at the Potsdam and Stockton sites, respectively. In general, vapor phase mercury concentrations increased with increasing ambient temperature at the Stockton site in 2000. These differences in values between 2000 and 2001 can be largely explained by distinct differences in the meteorological regimes that dominated in the different years.

Source types or source regions contributing to the concentration of atmospheric fine particles measured at Brigantine National Wildlife Refuge, NJ, were identified using a factor analysis model called Positive Matrix Factorization (PMF). Cluster analysis of backward air trajectories on days of high- and low-factor concentrations was used to link factors to potential source regions. Brigantine is a Class I visibility area with few local sources in the center of the eastern urban corridor and is therefore a good location to study Mid-Atlantic regional aerosol. Sulfate (expressed as ammonium sulfate) was the most abundant species, accounting for 49% of annual average fine mass. Organic compounds (22%; expressed as 1.4 x organic carbon) and ammonium nitrate (10%) were the next abundant species. Some evidence herein suggests that secondary organic aerosol formation is an important contributor to summertime regional aerosol. Nine factors were identified that contributed to PM2.5 mass concentrations: coal combustion factors (66%, summer and winter), sea salt factors (9%, fresh and aged), motor vehicle/mixed combustion (8%), diesel/Zn-Pb (6%), incinerator/industrial (5%), oil combustion (4%), and soil (2%). The aged sea salt concentrations were highest in springtime, when the land breeze-sea breeze cycle is strongest. Comparison of backward air trajectories of high- and low-concentration days suggests that Brigantine is surrounded by sources of oil combustion, motor vehicle/mixed combustion, and waste incinerator/industrial emissions that together account for 17% of PM2.5 mass. The diesel/Zn-Pb factor was associated with sources north and west of Brigantine. Coal combustion factors were associated with coal-fired power plants west and southwest of the site. Particulate carbon was associated not only with oil combustion, motor vehicle/mixed combustion, waste incinerator/industrial, and diesel/Pb-Zn, but also with the coal combustion factors, perhaps through common transport.

This study applies and compares results of four receptor modeling techniques to a common set of speciated fine particle measurement data collected ata remote site in northwestern Vermont between 1988 and 1995. Two multivariate mathematical models, positive matrix factorization and UNMIX, were applied to the measurement data and identified seven "common" sources that had similar compositions and similar fine mass contributions in both models. Two ensemble backward trajectory techniques, potential source contribution function and residence-time analysis, were also applied to evaluate and interpret the mathematical model results. The trajectory techniques indicate a strong regional character to the upwind locations associated with aerosol contributions from most of the sources identified independently by the mathematical models and help in the interpretation of those results. The process of model comparison provides insights on the strengths and limitations of the individual and combined source attribution techniques. Convergent results among the multiple methods provide a degree of confidence that each of the receptor methods may represent useful tools for future air quality management. Divergent or inconsistent results among the models can help identify limitations of the individual models and of the underlying aerosol and meteorological data sets.

Aerosol chemical composition data for PM2.5 samples collected during the period from 1988 to 1995 at Underhill, VT, were analyzed. Sulfur and black carbon mass concentrations ranged from 0.01 to 6.5 microg m(-3) and from 0.05 to 2.2 microg m(-3), respectively, while the total fine aerosol mass concentration ranged from 0.2 to 51.1 microg m(-3). Seasonal variations with maxima during the summer and minima in winter/spring were observed for sulfur and the fine mass concentrations. No annual pattern was observed for black carbon. Seasonal variations for most of the other anthropogenic species had maxima in winter and spring and minima in the summer. A factor analysis method, positive matrix factorization (PMF), utilizing error estimates of the data to provide optimum data point scaling was used to obtain information about possible sources of the aerosol. An 11-factor solution was obtained. The six sources representing wood burning, coal and oil combustion, coal combustion emissions plus photochemical sulfate production, metal production plus municipal waste incineration, and emissions from motor vehicles were identified. Emissions from smelting of nonferrous metal ores, arsenic smelting, and soil particles and particles with high concentrations of Na were also identified by PMF. Potential source contribution function (PSCF) analysis combines the aerosol data with the air parcel backward trajectories. PSCF was applied to identify possible source areas and pathways that give rise to the observed high particulate mass concentrations from these 11 sources. The CAPITA Monte Carlo trajectory model was used to obtain 10 sets of 5-day air parcel back trajectories arriving every 2 h for the 7-yr period from 1988 to 1995. The PSCF plot for the black carbon factor shows high probabilities in the area surrounding the sampling site, indicating a strong local influence from residential wood combustion in northern New England and southwestern Quebec. Similar large potential source areas in the midwestern United States were identified for the two coal combustion factors. The midwestern United States was also identified as the source region for the Zn-Pb factor. The oil combustion factor was associated with the east coast of the United States. The results for the Pb-Mn factor suggests high probability over the nearby Montreal urban area and the areas in the midwestern United States. The windblown dust emissions from the areas to the north are significant contributors for the soil factor. Canadian Ni smelters are the main sources for the As factor, although there is some contribution from coal-fired power plants to the south and west of Underhill, VT. It is concluded that the combination of the two receptor modeling methods, PMF and PSCF, provides an effective way in identifying atmospheric aerosol sources and their likely locations. Emissions from different anthropogenic activities as well as secondary aerosol production are the main sources of aerosol measured in Vermont. Fuel combustion, local wood smoke, municipal waste incineration, and the secondary sulfate production collectively accounted for about 87% of the fine mass concentrations measured in Vermont.

Aerosol data consisting of condensation nuclei (CN) counts, black carbon (BC) mass concentration, and aerosol light scattering coefficient at the wavelength of 450 nm (SC) measured at Barrow, AK, from 1986 to 1997 have been analyzed. BC and SC show an annual cycle with the Arctic haze maxima in the winter and spring and the minima in the summer. The CN time series shows two maxima in March and August. Potential source contribution function (PSCF) that combines the aerosol data with air parcel backward trajectories was applied to identify potential source areas and the preferred pathways that give rise to the observed high aerosol concentrations at Barrow. Ten-day isentropic back trajectories arriving twice daily at 500 and 1500 m above sea level were calculated for the period from 1986 to 1997. The PSCF analyses were performed based on the 80th percentile criterion values for the 2- and 24-h averages of the measured aerosol parameters. There was a good correspondence between PSCF maps for the 2- and 24-h averages, indicating that 1-day aerosol sampling in the Arctic adequately represents the aerosol source areas. In winter, the high PSCF values for BC and SC are related to industrial source areas in Eurasia. The trajectory domain in winter and spring is larger than in summer, reflecting weaker transport in summer. No high PSCF areas for BC and SC can be observed in summer. The result is related to the poor transport into the Arctic plus the strong removal of aerosol by precipitation in summer. In contrast to the BC and SC maps, the CN plot for summer shows high PSCF areas in the North Pacific Ocean. High CN values appearto be mostly connected with the long-range transport from Eurasia in winter and spring and with the reduced sulfur compound emission from biogenic activities in the ocean in the summer. PSCF analysis was found to be effective in identifying potential aerosol source areas.

Aerosol time-of-flight mass spectrometry (ATOFMS) is capable of measuring the sizes and chemical compositions of individual polydisperse aerosol particles in real time. A qualitative estimate of the particle composition is acquired in the form of a mass spectrum that must be subsequently interpreted in order to draw conclusions regarding atmospheric relevance. The actual problem involves developing a calibration that allows the mass spectral data to be transformed into estimates of the composition of the atmospheric aerosol. A properly calibrated ATOFMS system should be able to quantitatively determine atmospheric concentrations of various species. Ideally, it would be able to accomplish this more rapidly, accurately, with higher size and time resolution, and at a far lower marginal cost than the manual sampling methods that are currently employed. Attempts have already been made at using ATOFMS and similar techniques to extract the bulk chemical species concentration present in an ensemble of particles. This study represents the use of a multivariate calibration method, two-dimensional partial least-squares analysis, for calibrating single-particle mass spectral data. The method presented here is far less labor-intensive than the univariate methods attempted to date and allows for less observer bias. Because of the labor savings, this is also the most comprehensive calibration performed to date, resulting in the quantification of 44 different chemical species.

Many chemical and environmental data sets are complicated by the existence of fully missing values or censored values known to lie below detection thresholds. For example, week-long samples of airborne particulate matter were obtained at Alert, NWT, Canada, between 1980 and 1991, where some of the concentrations of 24 particulate constituents were coarsened in the sense of being either fully missing or below detection limits. To facilitate scientific analysis, it is appealing to create complete data by filling in missing values so that standard complete-data methods can be applied. We briefly review commonly used strategies for handling missing values and focus on the multiple-imputation approach, which generally leads to valid inferences when faced with missing data. Three statistical models are developed for multiply imputing the missing values of airborne particulate matter. We expect that these models are useful for creating multiple imputations in a variety of incomplete multivariate time series data sets.

Chemical composition data for fine and coarse particles collected in Phoenix, AZ, were analyzed using positive matrix factorization (PMF). The objective was to identify the possible aerosol sources at the sampling site. PMF uses estimates of the error in the data to provide optimum data point scaling and permits a better treatment of missing and below-detection-limit values. It also applies nonnegativity constraints to the factors. Two sets of fine particle samples were collected by different samplers. Each of the resulting fine particle data sets was analyzed separately. For each fine particle data set, eight factors were obtained, identified as (1) biomass burning characterized by high concentrations of organic carbon (OC), elemental carbon (EC), and K; (2) wood burning with high concentrations of Na, K, OC, and EC; (3) motor vehicles with high concentrations of OC and EC; (4) nonferrous smelting process characterized by Cu, Zn, As, and Pb; (5) heavy-duty diesel characterized by high EC, OC, and Mn; (6) sea-salt factor dominated by Na and Cl; (7) soil with high values for Al, Si, Ca, Ti, and Fe; and (8) secondary aerosol with SO4(-2) and OC that may represent coal-fired power plant emissions. For the coarse particle samples, a five-factor model gave source profiles that are attributed to be (1) sea salt, (2) soil, (3) Fe source/motor vehicle, (4) construction (high Ca), and (5) coal-fired power plant. Regression of the PM mass against the factor scores was performed to estimate the mass contributions of the resolved sources. The major sources for the fine particles were motor vehicles, vegetation burning factors (biomass and wood burning), and coal-fired power plants. These sources contributed most of the fine aerosol mass by emitting carbonaceous particles, and they have higher contributions in winter. For the coarse particles, the major source contributions were soil and construction (high Ca). These sources also peaked in winter.

The apportionment of ambient aerosol mass to different sources of airborne soil is a difficult problem because of the similarity of the chemical composition of crustal sources. However, additional information can be obtained using individual particle analysis. A novel approach based on the combination of two neural networks, the adaptive resonance theory-based neural network (ART-2a) and the back-propagation (BP) neural network with electron microscopy data, has been developed to apportion the mass contributions of the crustal sources to ambient particle samples. The crustal source samples were analyzed using computer-controlled scanning electron microscopy (CCSEM). CCSEM provides elemental compositions and size parameters for individual particles as well as estimates of the shape and density from which the volume and mass of each particle can be estimated. The ART-2a neural network was first used to partition particles into homogeneous classes based on the elemental composition data. After the different particle type classes were produced by ART-2a, their mass fractions were calculated. In this way, the source profiles for the crustal dust sources can be obtained in terms of the mass fractions for different particle types. Then the BP neural network was applied to build the model between the mass fractions of different particle types and the mass contributions. Using the three physical source samples prepared for this study, artificial ambient samples were generated by randomly mixing particles from the three source samples. These samples were then used to examine the proposed method. Satisfactory predictions for the mass contributions of the three sources to the ambient samples have been obtained, indicating the proposed method is a promising tool for the source apportionment of chemically similar soil samples.

Radon, a naturally occurring gas found at some level in most homes, is an established risk factor for human lung cancer. The U.S. National Research Council has recently completed a comprehensive evaluation of the health risks of residential exposure to radon and developed models for projecting radon lung cancer risks to the general population. This analysis suggests that radon may play a role in the etiology of 10-15% of all lung cancer cases in the United States, although these estimates are subject to considerable uncertainty. In this article, we present a detailed analysis of uncertainty and variability in estimates of lung cancer risk due to residential exposure to radon. We use a general framework for the analysis of uncertainty and variability that we developed previously. Specifically, we focus on estimates of the age-specific excess relative risk (ERR) and lifetime relative risk (LRR), both of which vary substantially among individuals. We also consider estimates of the population attributable risk (PAR), which reflects the proportion of the lung cancer burden attributable to radon. Variability in the ERR and LRR is largely determined by variability in residential exposure levels and in the dosimetric K-factor used to extrapolate from occupational to environmental settings. Uncertainty in the ERR and LRR is due to uncertainty in the model parameters, notably those reflecting the carcinogenic potency of radon and the modifying effect of attained age. Uncertainty in the PAR is determined by uncertainty about the values of the parameters in the risk models used to estimate the PAR. Uncertainty in radon levels in homes and the dosimetric K-factor contribute comparatively little to uncertainty in the PAR. These results suggest that reduction in uncertainty about the PAR for radon induced lung cancer can only be achieved if more reliable risk projection models can be developed.

Two types of potential source contribution function analysis- Potential Source Contribution Function (PSCF) and Total Potential Source Contribution Function (TPSCF) analysiswere employed to study the source-receptor relationships for several trace elements (vanadium, selenium, arsenic, manganese, and indium) found in precipitation and airborne particles collected at Dorset, Ontario. This study identified areas in the United States and Canada as possible emission source areas that could contribute to the trace element concentrations observed at Dorset. The identified regions in the United States generally coincide well with the locations of known emission sources, whereas the possible source regions revealed in Canada could not be adequately explained because of the absence of emission source information. The likely emission sources for these trace elements include oiland coal-fired power plants, incinerators, motor vehicles, nonferrous metal smelters, iron and steel mills, ferrous-Mn alloy plants, and Mn chemicals production.

The Potential Source Contribution Function (PSCF) receptor model combines both chemical and meteorological information. In this study, PSCF was employed to identify the potential source emission regions for aerosol compositions measured at Tjörn, Sweden (58.01 ∘N, 11.36 ∘E). PSCF was for the first time applied on a European scale. One hundred and fifty-two four-day air parcel backward trajectories were combined with concentrations of sixteen elements determined in 33 coarse and fine aerosol samples. The observations were made between February 17 and March 26, 1985. The modeling results of the heavy metals V, Pb, Zn, and As are presented and compared with available emission inventory data. A number of known industrialized regions in the former USSR and Europe are found of high potential to be the emission source areas. These areas are in good agreement with the known emission information. The PSCF maps of total sulfur, Non-Seasalt-Sulfur (N.S.S.) and chlorine are also presented. High potential regions in the Arctic area exist in the PSCF map for total sulfur wheres they do not occur in that for N.S.S.

A passive system using an electret ion chamber to measure dissolved radon in a water sample has been recently described. In the current work, an electret ion chamber has been used to measure time-averaged concentration of dissolved radon in water. A steady concentration of radon in water is generated by bubbling radon gas into water in a 20-L jar and maintaining constant rates of feed and bleed of the water. To perform the measurement, the outgoing water flows into a 4-L cylindrical chamber. Air is bubbled at 1 L min-1 through a 10 cm long sintered stainless steel tube immersed in this water releasing the radon from water into the chamber volume. A 1-L electret ion chamber ("H" chamber) loaded with an electret is hung in the 4-L chamber. Radon diffuses into the "H" chamber through its tyvek (carbon-coated) covered openings. The radon concentration in air is measured from the change in electret voltage. The concentration of radon in water is then obtained from the concentration of radon in air and the air and water flow rates. For comparison, the radon concentration in water was measured using a standard liquid scintillation counting method. For the concentration range covered (4.7 to 72 Bq L-1), there was a good agreement between the two methods.

This paper reports charge neutralization phenomena of 212Pb particles in nitrogen or oxygen atmospheres with trace amounts of other gases. Newly produced thoron or radon progeny are positively charged, stable molecular clusters that are subsequently neutralized by several mechanisms. The charged clusters have a smaller diffusion coefficient than neutral clusters of the same size due to the interaction of the charge with the surrounding gas molecules. In this study, we have found that the diffusion coefficients of 212Pb in O2, N2, NH3/O2, NH3/N2, and C6H12/N2 (IPs between 15.58 and 9.8 eV) ranged between 0.015 and 0.030 cm2 s-1. In the case of C6H12/O2, NO2/O2, NO/O2, and dimethylamine/O2 (ionization potential between 9.8 and 8.23 eV), the diffusion coefficients have increased to between 0.046 and 0.69 cm2 s-1. These results are consistent with previous results of 218Po, indicating that charged progeny are neutralized by electron transfer from a gas molecule with a lower ionization potential than lead oxide. We estimate the ionization potential of lead oxide to range between 9.8 and 10.2 eV. 212Pb was also neutralized by an electron scavenging mechanism in NO2/nitrogen.

This work examines the potential connections between extreme value statistics, problems in aerosol science, and a recent technique of solving ill-posed inversion problems, called EVE (Extreme Value Estimation). EVE estimates functional of the unknown solution by searching the extreme (maximum and minimum) values of that functional within a set of acceptable solutions. The statistics of occurrence of extreme values in real life were not considered when this method was developed. The results of this technique are more con servative than those of the other methods used to solve the problem of aerosol size distribution estimation like non-linear least squares, expectation-maximization, regularization, etc. The utilization of the customary methods of deconvolution may lead to an underestimation of the possibility of occurrence of extreme values in real life. It is suggested that consideration of extreme value statistics might aid in better defining the limits to be placed on the physically acceptable solutions in the EVE deconvolution. Other problems could also benefit from the application of extreme value statistics including the estimation of the second highest value of measured airborne particle mass in the context of the ambient air quality standard for particulate matter less than 10 μm and the determination of the Maximally Exposed Individual as required under the 1990 revisions to the Clean Air Act.

Over the past 5 y, there have been significant improvements in measurement of activity-weighted size distributions of airborne radon decay products. The modification of screen diffusion batteries to incorporate multiple screens of differing mesh number, called graded screen arrays, have permitted improved size resolution below 10 nm such that the size distributions can now be determined down to molecular sized activities (0.5 nm). In order to ascertain the utility and reliability of such systems, several intercomparison tests have been performed in a 2.4 m3 radon chamber in which particles of varying size have been produced by introducing SO2 and H2O along with the radon to the chamber. In April 1988, intercomparison studies were performed between direct measurements of the activity-weighted size distributions as measured by graded screen arrays and an indirect measurement of the distribution obtained by measuring the number size distribution with a differential mobility analyzer and multiplying by the theoretical attachment rate. Good agreement was obtained in these measurements. A second set of intercomparison studies among a number of groups with graded screen array systems was made in April 1989 with the objective of resolving spectral structure below 10 nm. Again, generally good agreement among the various groups was obtained although some differences were noted. It is thus concluded that such systems can be constructed and can be useful in making routine measurements of activity-weighted size distributions with reasonable confidence in the results obtained.

A problem exists in the meaning and use of the term "unattached fraction" to describe the highly diffusive portion of the airborne radon progeny. The term was originally developed to aid in lung dosimetry but now that more detailed size measurements can be made, there are ambiguities in its definition between a physical size basis and a dosimetric definition. Some possible ways to resolve these ambiguities are presented and discussed. It is suggested that the term only be used in the context of complete size information rather than as the conventional operationally defined term.

The development of an automated system for activity-weighted size distribution measurements now permits more complete exposure and dose assessment for indoor radon decay products. Exposures characterized by the semi-continuous measurement of activity-weighted size distributions of radon decay products were obtained over four test periods in three normally occupied houses, two of which were occupied by cigarette smokers. These measured activity size distributions were used to calculate exposure-dose conversion coefficients and the annual effective doses. These doses were found to be approximately two-fold higher than the values derived conventionally from the measured radon concentration, on the assumption that indoor exposure to 20 Bq m-3 radon gas concentration corresponds to an annual effective dose 1 mSv y-1. The degree to which aerosol-measurement-based dose estimates were higher than radon-gas-based estimates was found to be influenced if the study house occupant was a cigarette smoker. Reassessment of the measured PAEC-weighted radon progeny particle size distribution in terms of the classical "unattached" and "attached" modes yielded lower estimates of the exposure-effective dose conversion coefficient that were similar to the reference values derived from a recent study by the National Research Council. Thus, by not resolving the measured radon progeny PAEC that is associated with particles intermediate in size between the two classical radon progeny modes, the estimated annual effective doses were also found to be similar to the values derived conventionally from the measured radon gas concentration. It is concluded that the observed presence of 4 to 13% of the radon progeny PAEC in the size-range 1.5 to 15 nm diameter is a dosimetrically significant factor that appears to be commonplace in various home environments.

The seasonal fluctuations of antimony, arsenic, indium, manganese and vanadium have been measured in airborne particulate matter from 1982-1987 at Alert in the Canadian high Arctic. Calculations of enrichment factors have shown that arsenic and antimony are very enriched in the wintertime aerosol. While wintertime ratios of non-crustal manganese/non-crustal vanadium were in agreement with previously published work, summertime ratios often resulted in negative values. A re-evaluation of the crustal Mn/V ratio was undertaken by looking at this ratio during the summertime and assuming that nearly all the airborne particulate matter was derived from crustal matter. Principal Source Contribution Function Analyses were performed for arsenic, indium and manganese. The results suggested that these important regional signatures can now be characterized as coming from distinct European and Asian areas. This improvement in area resolution is much more satisfactory than citing the usual attribution of an overall Eurasian source.

A number of investigators have reported the formation of radiolytic ultrafine particles produced by the interaction of ionizing radiation with atmospheric trace gases. Previous studies have suggested that a very high localized concentration of the OH radical produced by the radiolysis of water can react with atmospheric trace gas, like SO2, to produce lower vapor pressure compounds that can then nucleate. To determine trace-gas dependence of the active, positively charged, first decay product of radon, the mobility spectrum of the decay products in the range of 0.06-3.0 cm2 V-1s-1 was measured in a flow-through radon chamber using a specially designed mobility spectrometer. Measurements were taken for different relative humidities and concentrations of SO2 in purified laboratory compressed air. The resultant mobility spectra were compared with radiolytic ultrafine particle activity distribution data. In the case of low humidities, the reduction of available OH concentration and hence neutralization rate led to the increasing intensity of the shoulder around 1.35 cm2 V-1s-1 with increasing SO2, suggesting SO2 clustering around the PoOx+ ion. For high humidity conditions (5 ppm SO2, 30% RH), there was clear droplet formation, H2SO4, clustering around the ion, and also an increase in the background level between the high mobility peak and droplet peak.

Field evaluations of an air filtration system and an electronic air cleaner to remove Rn decay products were performed in a single-family house located in the Northford, CT area. Field measurements included the Rn concentration, particle number concentration, and concentration and activity size distribution of Rn decay products. A semi-continuous screen diffusion battery system with six parallel sampler/detector units was used to determine the concentrations and size distributions of the Rn decay products. Indoor particles were generated by common activities such as vacuuming, washing and drying clothes, opening the outside door, and cooking. Influences on the size distributions over the size range from 0.5 nm to 500 nm of Rn decay products were investigated in the domestic environment. The effect of the air cleaners was to decrease the concentration of the decay products and to reduce the equilibrium fraction. For the filtration system in particular, the activity fractions in the smallest size range were increased. However, the overall effect of the air cleaners was to reduce the median dose. The filtration unit was found to be more effective than the electronic air cleaner.

Three mechanisms of neutralization of Po(+)--electron transfer, electron scavenging, and small ion recombination--have previously been suggested. Considerable work has been conducted on the first two mechanisms. However, little information about small ion recombination is available. In the present study, this mechanism was studied by examining the neutralization rates of different Rn concentrations in N2, Ar, and O2 with the aid of a continuous Rn progeny monitoring system. The results showed that the neutralization rates in the three gases are of the order 1-4 s-1 at high Rn concentrations (higher than 40,000 Bq m-3). A linear relationship between the neutralization rate and the square root of Rn concentration (from 40,000 Bq m-3 to 810,000 Bq m-3) was obtained. Neutralization rates were higher in the gas with lower ionization potential. Further, the existence of a neutralization rate plateau at high Rn concentrations was strongly suggested.

A receptor modeling study was performed to identify and apportion the sources of PM10 mass in Granite City, Illinois, an area of historic TSP nonattainment. Samples of the ambient aerosol were collected using a dichotomous sampler. Each sample was analyzed by x-ray fluorescence and instrumental neutron activation analysis. To begin the study, a factor analysis was performed. Two different chemical mass balance (CMB) analyses were then made. The first CMB analysis used only source profiles available from the literature while the second included twelve source profiles developed from dust samples collected in Granite City. Both CMB analyses used 20 of the 33 analyzed elements since many of the source profiles in the literature did not include the other thirteen elements. The results from both sets of CMB analyses were grouped by the predominate wind direction at the site during the time each sample was taken to identify the direction of each source relative to the sampler. It was found that regional sources were the primary contributors to the fine fraction while the coarse fraction was composed of material from local industries. These sources were generally the ones identified during the Regional Air Pollution Study previously conducted in the area. However, the emission profiles from these sources were observed to have changed between the studies. It was also found that the use of the locally generated profiles greatly improved the results of the CMB analysis.

Using models of particle deposition in the nasal cavity and in the tracheobronchial region of the respiratory tract, it is possible to design a measurement system based on wire screen penetration theory. This system provides direct estimates for the quantities of Rn decay product activity deposited in the nasal cavity and in the tracheobronchial region. Historically, measurements of the "unattached" fraction of the airborne Rn decay product size distribution have been made in order to better estimate the dose resulting from the deposition of these 222Rn progeny in the human respiratory tract. However, previous measurement systems have been developed based on choices of screen parameters and sampling flow conditions in an attempt to separate the "unattached" fraction from the rest of the activity size distribution. By taking into consideration the deposition behavior of particles in the respiratory tract, a specific choice of wire screens and flow rates can be made that can provide better information for the estimation of deposited dose in the respiratory tract.