Calibration of a passive sampler for both gaseous and particulate phase polycyclic aromatic hydrocarbons

A novel passive air sampler was designed and tested that individually collects the gaseous and particulate phase polycyclic aromatic hydrocarbons (PAHs) in air. The sampler was calibrated against a conventional active sampler in an indoor environment. A PUF (polyurethane foam) disk and a piece of GFF (glass fiber filter) were installed in a sampling shelter for collecting gaseous and particulate phase PAHs, respectively. The passive samplers were deployed in seven indoor locations for 86 days. Six times during this period, 24-h conventional active sampling was conducted for calibration at an average interval of 17-days. Principle component analysis showed that the measured congener profile compositions were totally different between the gaseous and particulate phase PAHs, but similar between the passive and the active samples. This suggested that gaseous and particulate phase PAHs were primarily trapped by the PUF disk and GFF, respectively. Linear relationships between the passively and the actively measured and log-transformed concentrations were derived for calibration of both gaseous and particulate phase PAHs. The uptake rates of the sampler were 0.10 +/- 0.014 m3/d and 0.007 +/- 0.001 m3/d for gaseous and particulate phase PAHs, respectively. The rates were significantly lower than those reported in the literature using similar PUF samplers, mainly because of the special design with limited air circulation.     

Field testing passive air samplers for current use pesticides in a tropical environment

Air was sampled for one year in the central valley of Costa Rica using an active high-volume sampler as well as passive samplers (PAS) based on polyurethane foam (PUF) disks and XAD-resin filled mesh cylinders. Extracts were analyzed for pesticides that are either banned or currently used in Costa Rican agriculture. Sampling rates for PUF-based passive air samplers, determined from the loss of depuration compounds spiked on the disks prior to deployment averaged 5.9 +/- 0.9 m3 x d(-1) and were higher during the windier dry season than during the rainy season. Sampling rates for the XAD-based passive sampler were determined from the slopes of linear relationships that were observed between the amount of pesticide sequestered in the resin and the length of deployment, which varied from 4 months to 1 year. Those sampling rates increased with decreasing molecular size of a pesticide, and their average of 2.1 +/- 1.5 m3 x d(-1) is higher than rates previously reported for temperate and polar sampling sites. Even though the trends of the sampling rate with molecular size and temperature are consistent with the hypothesis that molecular diffusion controls uptake in passive samplers, the trends are much more pronounced than a direct proportionality between sampling rate and molecular diffusivity would suggest. Air concentrations derived by the three sampling methods are within a factor of 2 of each other, suggesting that properly calibrated PAS can be effective tools for monitoring levels of pesticides in the tropical atmosphere. In particular, HiVol samplers, PUF-disk samplers, and XAD-based passive samplers are suitable for obtaining information on air concentration variability on the time scale of days, seasons and years, respectively. This study represents the first calibration study for the uptake of current use pesticides by passive air samplers.     

Application of sorbent impregnated polyurethane foam (SIP) disk passive air samplers for investigating organochlorine pesticides and polybrominated diphenyl ethers at the global scale

As part of continued efforts under the Global Atmospheric Passive Sampling (GAPS) Network to develop passive air samplers applicable to a wide-range of compounds, sorbent-impregnated polyurethane foam (SIP) disk samplers were codeployed and tested against conventional polyurethane foam (PUF) disk samplers. The SIP disk sampler has a higher sorptive capacity compared to the PUF disk sampler, due to its impregnation with ground XAD resin. The two sampler types were codeployed at 20 sites during the 2009, 3-month long spring sampling period of the GAPS Network. Air concentrations for chlordanes (trans-chlordane, cis-chlordane, and trans-nonachlor) and endosulfans (endosulfan I, endosulfan II, and endosulfan sulfate) derived from PUF disk and SIP disk samplers showed near 1:1 agreement and confirmed previous results for polychlorinated biphenyls (PCBs). Discrepancies observed for α-HCH and γ-HCH in PUF disk versus SIP disk are attributed to lack of "comparability" of the PUF and SIP data sets, due to differences in effective air sampled by the two devices caused by saturation of these higher volatility compounds in the lower capacity PUF disk samplers. Analysis of PBDEs in PUF and SIP disks showed relatively good agreement but highlighted challenges associated with high blanks levels for PBDEs. The higher capacity SIP disk samplers allowed for the analysis of pentachlorobenzene (PeCBz) and hexachlorobenzene (HCBz) and revealed a relatively uniform global distribution of these compounds. The results of this study further validate the SIP disk sampler as a complement to the PUF disk sampler, with capabilities for a broad range of POPs targeted under international POPs treaties such as the Stockholm Convention on POPs and its Global Monitoring Plan.     

Aquatic passive sampling of herbicides on naked particle loaded membranes: accelerated measurement and empirical estimation of kinetic parameters

Water-sampler equilibrium partitioning coefficients and aqueous boundary layer mass transfer coefficients for atrazine, diuron, hexazionone and fluometuron onto C18 and SDB-RPS Empore disk-based aquatic passive samplers have been determined experimentally under a laminar flow regime (Re = 5400). The method involved accelerating the time to equilibrium of the samplers by exposing them to three water concentrations, decreasing stepwise to 50% and then 25% of the original concentration. Assuming first-order Fickian kinetics across a rate-limiting aqueous boundary layer, both parameters are determined computationally by unconstrained nonlinear optimization. In addition, a method of estimation of mass transfer coefficients--therefore sampling rates--using the dimension-less Sherwood correlation developed for laminar flow over a flat plate is applied. For each of the herbicides, this correlation is validated to within 40% of the experimental data.The study demonstrates that for trace concentrations (sub 0.1 microg/L) and these flow conditions, a naked Empore disk performs well as an integrative sampler over short deployments (up to 7 days) for the range of polar herbicides investigated. The SDB-RPS disk allows a longer integrative period than the C18 disk due to its higher sorbent mass and/or its more polar sorbent chemistry. This work also suggests that for certain passive sampler designs, empirical estimation of sampling rates may be possible using correlations that have been available in the chemical engineering literature for some time.     

Evolution of nitrogen species air pollutants along trajectories crossing the Los Angeles area

Ambient aerosol sampling was conducted in Diamond Bar, Mira Loma, and Riverside, CA, to observe at close range the effects of ammonia emissions on air quality. These sites are located upwind,within, and downwind, respectively, of the Chino dairy area, the largest single source of ammonia emissions in the Los Angeles area. Inertial impactors and bulk filter samplers provided 4-7-h measurements of aerosol chemical composition and size distribution. Daily average fine particle mass concentrations were in the range 22.4-143.0 microg m(-3). On some days the fine particulate matter concentrations were more than two times greater than the proposed 24-h Federal standard of 65 microg m(-3). Ammonium nitrate was the largest component of fine particle mass at all three sites; 24-h average fine particulate ammonium plus nitrate concentrations ranged from 11.7 to 75.4 microg m(-3). A single air mass was studied as it passed the Diamond Bar air monitoring site in the morning and stagnated near Mira Loma in the evening of the same day. Between these two sites NO was oxidized to NO2, and the ammonia concentration increased by a factor of 5. A second air parcel trajectory, which stagnated near Mira Loma during the early morning and passed near the Riverside site approximately 24 h later, showed a decrease in ammonia concentration over time that is consistent with dilution as the air mass moved downwind from the source of ammonia in the dairy area. Particulate NH4NO3 concentration in that air parcel remained approximately constant over time, consistent with a continued excess of NH3 relative to HNO3 downwind of the dairy area.     

Evaluation of passive samplers for assessment of community exposure to toxic air contaminants and related pollutants

The precision, accuracy, and sampling rates of Radiello and Ogawa passive samplers were evaluated in the laboratory using a flow-through chamber and under field conditions prior to their use in the 2007 Harbor Community Monitoring Study (HCMS), a saturation monitoring campaign in the communities adjacent to the Ports of Los Angeles and Long Beach. Passive methods included Radiello samplers for volatile organic compounds (benzene, toluene, ethylbenzene, xylenes, 1,3-butadiene), aldehydes (formaldehyde, acetaldehyde, acrolein) and hydrogen sulfide, and Ogawa samplers for nitrogen oxides and sulfur dioxide. Additional experiments were conducted to study the robustness of the passive sampling methods under variable ambient wind speed, sampling duration, and storage time before analysis. Our experimentally determined sampling rates were in agreement with the rates published by Radiello and Ogawa with the following exceptions: we observed a diffusion rate of 22.4 ± 0.1 mL/min for benzene and 37.4 ± 1.5 mL/min for ethylbenzene compared to the Radiello published values of 27.8 and 25.7 mL/min, respectively. With few exceptions, the passive monitoring methods measured one-week average ambient concentrations of selected pollutants with sensitivity and precision comparable to conventional monitoring methods averaged over the same period. Radiello Carbograph 4 VOC sampler is not suitable for the collection of 1,3-butadiene due to backdiffusion. Results for the Radiello aldehyde sampler were inconclusive due to lack of reliable reference methods for all carbonyl compounds of interest.     

Characterization of atmospheric ammonia emissions from a commercial chicken house on the Delmarva Peninsula

A three-dimensional sampling grid using passive collectors was used to characterize the downwind gas-phase ammonia plumes originating from a commercial chicken house on the Delmarva Peninsula in the Chesapeake Bay watershed. Inverse Gaussian plume modeling was used to determine the source strength of the chicken house and the corresponding chicken emission factors. A total of seven field deployments were performed during two different flocks with a sampling duration ranging from 6 to 12.6 h. The deployments occurred during weeks 3, 4, and 5 of the 6-week chicken grow-out period in the months of May-July 2002. The ammonia emission factors ranged from 0.27 to 2.17 g of NH3-N bird(-1) day(-1) with a mean of 1.18 g of NH3-N bird(-1) day(-1). Weighted emissions factors that accounted for the nonlinear increase in ammonia emissions over the 6-week grow-out period were also calculated and ranged from 0.14 to 1.65 g of NH3-N bird(-1) day(-1) with a mean of 0.74 g of NH3-N bird(-1) day(-1). These weighted emission values would correspond to an annual release of approximately 18 x 10(6) kg of NH3-N to the atmosphere from broiler production on the Delmarva Peninsula. This assumes that the emission factors in this study are representative for the entire year with varying meteorological conditions and are representative of all chicken husbandry practices. The Delmarva Peninsula could represent a significant source of nutrient nitrogen to the Chesapeake Bay and Delaware Bay watersheds through atmospheric deposition when considering the size of this annual release rate, the relative short atmospheric lifetime of ammonia due to deposition, and the proximity of the Delmarva Peninsula to the Chesapeake and Delaware Bays.     

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.     

Time-weighted average water sampling in Lake Ontario with solid-phase microextraction passive samplers

In this study, three types of solid-phase microextraction (SPME) passive samplers, including a fiber-retracted device, a polydimethylsiloxane (PDMS)-rod and a PDMS-membrane, were evaluated to determine the time weighted average (TWA) concentrations of polycyclic aromatic hydrocarbons (PAHs) in Hamilton Harbor (the western tip of Lake Ontario, ON, Canada). Field trials demonstrated that these types of SPME samplers are suitable for the long-term monitoring of organic pollutants in water. These samplers possess all of the advantages of SPME: they are solvent-free, sampling, extraction and concentration are combined into one step, and they can be directly injected into a gas chromatograph (GC) for analysis without further treatment. These samplers also address the additional needs of a passive sampling technique: they are economical, easy to deploy, and the TWA concentrations of target analytes can be obtained with one sampler. Moreover, the mass uptake of these samplers is independent of the face velocity, or the effect can be calibrated, which is desirable for long-term field sampling, especially when the convection conditions of the sampling environment are difficult to measure and calibrate. Among the three types of SPME samplers that were tested, the PDMS-membrane possesses the highest surface-to-volume ratio, which results in the highest sensitivity and mass uptake and the lowest detection level.     

In situ measurement of PCB pore water concentration profiles in activated carbon-amended sediment using passive samplers

Vertical pore water profiles of in situ PCBs were determined in a contaminated mudflat in San Francisco Bay, CA, 30 months after treatment using an activated carbon amendment in the upper layer of the sediment. Pore water concentrations were derived from concentrations of PCBs measured in two passive samplers; polyethylene (PE, 51 μm thick) and polyoxymethylene (POM, 17 μm thick) at different sediment depths. To calculate pore water concentrations from PCB contents in the passive samplers, an equilibrium approach and a first-order uptake model were applied, using five performance reference compounds to estimate pore water sampling rates. Vertical pore water profiles showed good agreement among the measurement and calculation methods with variations within a factor of 2, which seems reasonable for in situ measurements. The close agreements of pore water estimates for the two sampler materials (PE and POM) and the two methods used to translate uptake in samplers to pore water concentrations demonstrate the robustness and suitability of the passive sampling approach. The application of passive samplers in the sediment presents a promising method for site monitoring and remedial treatment evaluation of sorbent amendment or capping techniques that result in changes of pore water concentrations in the sediment subsurface.     

Rapidly equilibrating micrometer film sampler for priority pollutants in air

Modified polymer-coated glass samplers (POGs), termed EVA samplers, consist of micrometer-thin layers of ethylene vinyl acetate (EVA) coated onto a glass fiber filter or aluminum foil substrate. These samplers were designed to equilibrate rapidly with priority pollutants in air, making them ideal for short-term spatial studies in ambient or indoor air. The EVA sampler was calibrated by measuring the uptake of polychlorinated biphenyls (PCBs) over 8 weeks in an indoor environment, and four different film thicknesses were monitored that ranged from 0.1 to 30 μm. The results were used to calculate the average mass transfer coefficient (50.5 m/day) and generate contour maps that provide guidance in choosing an appropriate EVA sampler for a particular study based on film thickness, deployment time, and the log K(OA) of the anlayte. A range of air pollutant classes was also added to the EVA sampler prior to deployment to assess depuration rates. These included polychlorinated biphenyls (PCBs), current-use pesticides (CUPs), perfluorinated compounds (PFCs), and polybrominated diphenyl ethers (PBDEs). On the basis of the depuration profiles, the EVA sampler was a suitable equilibrium sampler for several CUPs and PCBs; however, for the high molecular weight PCBs and PBDEs, the EVA sampler operates as a linear uptake sampler. Samplers were also evaluated for their use as a rapid screening tool for assessing concentrations of siloxanes in indoor air. The EVA sampler was used to estimate air concentrations for D4 and D5 in laboratory air to be 118 and 89 ng/m(3), respectively. Analyses were performed directly using thermal desorption gas chromatography/mass spectrometry (TDS-GC-MS). EVA samplers show promise due to their relatively low cost and ease of deployment and applicability to a wide range of priority chemicals. The ability to alter the film thickness, and hence the sorption capacity and performance of the EVA sampler, allows for a versatile sampler that can be used under varying sampling conditions and deployment times.     

Passive air sampling using semipermeable membrane devices at different wind-speeds in situ calibrated by performance reference compounds

Semipermeable membrane devices (SPMDs) are passive samplers used to measure the vapor phase of organic pollutants in air. This study tested whether extremely high wind-speeds during a 21-day sampling increased the sampling rates of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), and whether the release of performance reference compounds (PRCs) was related to the uptakes at different wind-speeds. Five samplers were deployed in an indoor, unheated, and dark wind tunnel with different wind-speeds at each site (6-50 m s(-1)). In addition, one sampler was deployed outside the wind tunnel and one outside the building. To test whether a sampler, designed to reduce the wind-speeds, decreased the uptake and release rates, each sampler in the wind tunnel included two SPMDs positioned inside a protective device and one unprotected SPMD outside the device. The highest amounts of PAHs and PCBs were found in the SPMDs exposed to the assumed highest wind-speeds. Thus, the SPMD sampling rates increased with increasing wind-speeds, indicating that the uptake was largely controlled by the boundary layer at the membrane-air interface. The coefficient of variance (introduced by the 21-day sampling and the chemical analysis) for the air concentrations of three PAHs and three PCBs, calculated using the PRC data, was 28-46%. Thus, the PRCs had a high ability to predict site effects of wind and assess the actual sampling situation. Comparison between protected and unprotected SPMDs showed that the sampler design reduced the wind-speed inside the devices and thereby the uptake and release rates.     

Sensitivity of particulate matter nitrate formation to precursor emissions in the California San Joaquin Valley

The formation of secondary ammonium nitrate during the 1995 Integrated Monitoring Study (IMS95) in San Joaquin Valley, CA was investigated using a box model that simulates the atmospheric chemistry and gas/particle partition of inorganic compounds. The concentration of particulate matter (PM) nitrate was found to be sensitive to reductions in VOC emissions. Nitric acid, rather than ammonia, was the limiting reagent in the formation of PM nitrate. The formation of nitric acid was more sensitive to the availability of oxidants than that of NOx. Oxidant chemistry in wintertime conditions in the San Joaquin Valley was shown to be VOC-sensitive. In fact, a decrease in NOx emissions may have the counter-intuitive effect of increasing PM nitrate.     

Assessing the influence of meteorological parameters on the performance of polyurethane foam-based passive air samplers

Polyurethane foam (PUF) disk passive air samplers were evaluated under field conditionsto assessthe effect of temperature and wind speed on the sampling rate for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs). Passive samples integrated over 28-day periods were compared to high-volume air samples collected for 24 h, every 7 days. This provided a large data set of 42 passive sampling events and 168 high-volume samples over a 3-year period, starting in October 2003. Average PUF disk sampling rates for gas-phase chemicals was approximately 7 m3 d(-1) and comparable to previous reports. The high molecular weight PAHs, which are mainly particle-bound, experienced much lower sampling rates of approximately 0.7 m3 d(-1). This small rate was attributed to the ability of the sampling chamber to filter out coarse particles with only the fine/ultrafine fraction capable of penetration and collection on the PUF disk. Passive sampler-derived data were converted to equivalent air volumes (V(EQ), m3) using the high-volume air measurement results. Correlations of V(EQ) against meteorological data collected on-site yielded different behavior for gas- and particle-associated compounds. For gas-phase chemicals, sampling rates varied by about a factor of 2 with temperature and wind speed. The higher sampling rates at colder temperatures were explained bythe wind effecton sampling rates. Temperature and wind were strongly correlated with the greatest winds at coldertemperatures. Mainly particle-phase compounds (namely, the high molecular weight PAHs) had more variable sampling rates. Sampling rates increased greatly atwarmertemperatures as the high molecular weight PAH burden was shifted toward the gas phase and subject to higher gas-phase sampling rates. At colder temperatures, sampling rates were reduced as the partitioning of the high molecular weight PAHs was shifted toward the particle phase. The observed wind effect on sampling for the particle-phase compounds is believed to be tied to this strong temperature dependence on phase partitioning and hence sampling rate. For purposes of comparing passive sampler derived data for persistent organic pollutants, the factor of 2 variability observed for mainly gas-phase compounds is deemed to be acceptable in many instances for semiquantitative analysis. Depuration compounds may be used to improve accuracy and provide site-specific sampling rates, although this adds a level of complexity to the analysis. More research is needed to develop and test passive air samplers for particle-associated chemicals.     

A flow-through sampler for semivolatile organic compounds in air

A widely acknowledged limitation of current passive air sampling designs for semivolatile organic chemicals is their relatively low sampling rate, severely constraining the temporal resolution that can be achieved. Addressing the need for an improved sampling design which achieves significantly faster uptake while maintaining the capability of providing quantitative information, a new sampler has been developed that provides greatly increased sampling rates by forcing the wind to blow through the sampling medium. The sampler consists of a horizontally oriented, aerodynamically shaped, stainless steel flow tube mounted on a post with ball bearings, which turns into the wind with the help of vanes. A series of polyurethane foam (PUF) discs with relatively large porosity mounted inside the flow tube serve as the sampling medium. The sampled air volume is calculated from wind speed, which is measured outside the sampler and after passage through the sampling medium using precalibrated vortex rotor and turbine anemometers mounted on top of the sampler and at the exit of the flow tube, respectively. Small battery-operated data loggers are used for data storage. Under typical wind speed conditions, the sampler can collect 100 m(3)/ day, which is approaching the sampling rates of conventional high volume samplers. Controlled experiments in the laboratory and frontal chromatography theory yield the theoretical plate number and breakthrough volumes for polychlorinated biphenyls and polycyclic aromatic hydrocarbons in the PUF plugs and allow for the estimation of breakthrough levels for relatively volatile organic chemicals. After correction for breakthrough, the air concentration obtained with the new flow-through sampler are independent of sampling length and volume and compare favorably with those obtained from conventional pumped high volume samples.     

Development and calibration of a passive sampler for perfluorinated alkyl carboxylates and sulfonates in water

Perfluorinated chemicals (PFCs) are emerging environmental contaminants with a global distribution. Due to their moderate water solubility, the majority of the environmental burden is assumed to be in the water phase. This work describes the application of the first passive sampler for the quantitative assessment of concentrations of perfluorinated alkylcarboxylates (PFCAs) and sulfonates (PFSAs) in water. The sampler is based on a modified Polar Organic Chemical Integrative Sampler (POCIS) with a weak anion exchange sorbent as a receiving phase. Sampling rates were between 0.16 and 0.37 L d(-1), and the duration of the kinetic sampling stage was between 2.2 and 13 d. A field deployment in the most urbanized estuary in Australia (Sydney Harbour) showed trace level concentrations from passive samplers (0.1-12 ng L(-1)), in good agreement with parallel grab sampling (0.2-16 ng L(-1)). A separate field comparison of the modified POCIS with standard POCIS suggests the latter may have application for PFC sampling, but with a more limited range of analytes than the modified POCIS which contains a sorbent with a mixed mode of action.     

Filter and electrostatic samplers for semivolatile aerosols: physical artifacts

Adsorptive and evaporative artifacts often bias measurements of semivolatile aerosols. Adsorption occurs when the sampling method disrupts the gas-particle partitioning equilibrium. Evaporation occurs because concentrations of semivolatiles are rarely constant over time. Filtration is subject to both adsorptive and evaporative artifacts. By comparison, electrostatic precipitation reduces these artifacts by minimizing the surface area of collected particles without substantially disrupting the gas-particle equilibrium. The extent of these artifacts was determined for filter samplers and electrostatic precipitator samplers for semivolatile alkane aerosols in the laboratory. Adsorption of gas-phase semivolatiles was lower in electrostatic precipitators by factors of 5-100 compared to the filter method. Particle evaporation from the electrostatic sampler was 2.3 times lower than that from TFE-coated glass-fiber filters. Use of a backup filter to correct for compound-specific adsorption artifacts can introduce positive or negative errors to the measured particle-phase concentration due to competition among the adsorbates for available adsorption sites. Adsorption of evaporated particles from the front filter onto the backup filter increased the measured evaporative artifact by a factor of 1.5-2.     

Field comparison of particulate PAH measurements using a low-flow denuder device and conventional sampling systems

Polyaromatic hydrocarbons (PAHs) are complex carbonaceous compounds emitted to the atmosphere by various combustion processes. Because the toxicity of many of them is now well recognized and documented, the determination of their atmospheric concentrations is of great interest to better understand and develop future atmospheric pollution control strategies. Hence, a common sampling protocol has to be defined to homogenize the results. With this goal in mind, field studies were carried out under different environmental conditions (74 samples) by simultaneously operating both a conventional sampler and a sampler equipped with a denuder tube upstream from the filter. The experimental results presented in this work show that the atmospheric particulate PAH concentrations are underestimated at least by a factor of 2 using a conventional sampler. The discrepancy between the two kinds of samplers used varied a lot from one compound to another and from one field campaign to another. This discrepancy may be explained by a simple degradation of particulate PAH in the natural atmosphere and on the filter. This is particularly worrisome because, based on the results presented in this work, the atmospheric PAH concentrations measured using conventional samplers not equipped with an ozone trap can underestimate the PAH concentration by more than 200%. This is especially true when the samples are collected in the vicinity of the point source of particulate PAHs and for highly reactive compounds such as benzo[a]pyrene.     

Sampling atmospheric carbonaceous aerosols using an integrated organic gas and particle sampler

Measurement of particle-bound organic carbon (OC) may be complicated by sampling artifacts such as adsorption of gas-phase species onto particles or filters or evaporation of semivolatile compounds off the particles. A denuder-based integrated organic gas and particle sampler (IOGAPS), specifically designed to minimize sampling artifacts, has been developed to sample atmospheric carbonaceous aerosols. IOGAPS is designed to first remove gas-phase chemicals via sorption to the XAD-coated denuder, and subsequently particles are trapped on a quartz filter. A backup sorbent system consisting of sorbent- (XAD-4 resin) impregnated filters (SIFs) was used to capture the semivolatile OC that evaporates from the particles accumulated on the upstream quartz filter. A traditional filter pack (FP) air sampler, which uses a single quartz filter to collect the particles, was employed for comparison in this study. Elemental and organic carbon were determined from filter punches by a thermal optical transmittance aerosol carbon analyzer. Field measurements show that there was no significant difference between the elemental carbon concentrations determined by the FP and IOGAPS, indicating that particle loss during the transit through the denuder tube was negligible. Compared with the OC determined by FP (3.9-12.6 microg of C/m3), the lower OC observed on the quartz filter in the IOGAPS (2.2-6.0 microg of C/m3) was expected because of the removal of gas-phase organics by the denuder. Higher semivolatile organic carbon (SVOC) on the backup SIFs during the night (1.24-8.43 microg of C/m3) suggests that more SVOC, emitted from primary sources or formed as secondary organic compounds, partitions onto the particles during the night because of the decreased ambient temperature. These data illustrate the utility of an IOGAPS system to more accurately determine the particle-bound OC in comparison to FP-based systems.     

Heterogeneity of coarse particles in an urban area

The variation in composition and concentration of coarse particles in Rochester, a medium-sized city in western New York, was studied using UNC passive samplers and computer-controlled scanning electron microscopy (CCSEM). The samplers were deployed in a 5 × 5 grid (2 km × 2 km per grid cell) for 2-3 week periods in two seasons (September 2008 and May 2009) at 25 different sites across Rochester. CCSEM analysis yielded size and elemental composition for individual particles and analyzed more than 800 coarse particles per sample. Based on the composition as reflected in the fluoresced X-ray spectrum, the particles were grouped into classes with similar chemical compositions using an adaptive resonance theory (ART) network. The mass fractions of particles in the identified classes were then used to assess the homogeneity of composition and concentration across the measurement domain. These results illustrate how particle sampling using the UNC passive sampler coupled with CCSEM/ART can be used to determine the concentration and source of the coarse particulate matter at multiple sites. The particle compositions were dominated by elements suggesting that the major particle sources are road dust and biological particles. Considerable heterogeneity in both composition and concentration were observed between adjacent sites as indicated by cofficient of divergence analyses.