Evaluation of high volume particle sampling and sample handling protocols for ambient urban air mutagenicity determinations.

An investigation of high volume particle sampling and sample handling procedures was undertaken to evaluate variations of protocols being used by the U.S. Environmental Protection Agency. These protocols are used in urban ambient air studies which collect ambient and source samples for subsequent mutagenicity analysis of the organic extracts of the aerosol fraction. Specific protocol issues investigated include: (a) duration of sampling period, (b) type of filter media used to collect air particles, (c) necessity for cryogenic field site storage and dry ice shipping of filter samples, and (d) sample handling at the receiving laboratory. Six PM10 Hi-Vol samplers were collocated at an urban site in downtown Durham, North Carolina and operated simultaneously to evaluate 12 h versus 24 h collection periods and filter media choices of glass fiber, Teflon impregnated glass fiber (TIGF), and quartz fiber. Filters from the samplers plus field blanks were collected during each of 25 sampling periods. TIGF filters from two samplers were immediately placed on dry ice in the field and transported directly to cryogenic storage. TIGF, quartz, and glass fiber filters from three samplers were transported at ambient and maintained at room temperature for three to six days prior to cryogenic storage. One TIGF sample, which was collected on a previously tared filter, was subjected to controlled environment equilibration (40 percent relative humidity, 22 degrees C) for 8 to 24 h and weighed prior to cryogenic storage. All filters were subsequently stored at -70 degrees C to -80 degrees C prior to a one-time extraction and Salmonella (Ames) mutagenicity bioassay of the entire sample set.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of post-sampling conditions on ambient carbon aerosol filter measurements

Ambient carbonaceous material collected on quartz filters is prone to measurement artifacts due to material gained or lost during post-sampling field latency, shipping, and storage. In seventeen sampling events over a one year period, ambient PM_2.5 aerosols were collected on quartz filters (without denuders) and subjected to various filter treatments to assess the potential for and extent of artifacts. The filter treatments simulated post-sampling environments that filters may be exposed to and included: storage at 40 °C for up to 96 h, storage at ?16 °C for 48 h, and storage at room temperature (～21 °C) for 48 h. Carbon mass on the filters was measured using a thermal-optical method. The total carbon (TC), total organic carbon (TOC) and total elemental carbon (TEC) as well as carbon thermal fraction masses were obtained. Statistical analyses were performed to identify significant differences in carbon fraction concentrations between filters analyzed immediately after sampling and after being subjected to treatment.TOC and TC concentrations decreased by on average 15 ± 5% and 10 ± 4%, respectively, for filters maintained at 40 °C for 96 h but did not change for filters stored at room temperature or frozen for 48 h. TEC did not change for any of the filter treatments. The mass concentration for the organic carbon thermal fraction that evolves at the lowest temperature step (OC1) decreased with increasing storage time at 40 °C with average losses of 70 ± 7% after 96 h. Therefore, OC1 is not a stable measurement due to post-sampling conditions that may be encountered. This work demonstrates that TOC and TC can have substantial measurement artifacts on filters subjected to field latency and other non-temperature controlled post-sampling handling, compared to the carbon loadings on the filter at the end of the sampling period.     

Use of Bioassay Methods to Evaluate Mutagenicity of Ambient Air Collected Near a Municipal Waste Combustor

An ambient air sampling study was conducted around a municipal waste combustor; a primary goal was to develop procedures and methods to evaluate the emissions of organic mutagens resulting from incomplete combustion of municipal waste. The products of Incomplete combustion from incineration include complex mixtures of organics, particularly polycycllc aromatic compounds, which are present after atmospheric dilution and cooling In emissions as semi-volatile or particle bound organic compounds. Combustion emissions are generally recognized as a potential cancer risk since they contain many carcinogenic and mutagenlc polycyclic aromatic hydrocarbons. Analyzing such a complex mixture for the presence of even a few selected chemicals is difficult and provides risk information on only a fraction of the chemicals present. Bioassay methods, however, may be directly applied to evaluate the mutagenic and potential carcinogenic activity of the complex organics from combustion emissions. The Salmonella (Ames) assay was used to determine the mutagenicity associated with particles from ambient air collected near a municipal waste combustor. Dose-response data was generated, and mutagenicity concentrations were calculated to demonstrate the utility of bioassay In assessing the potential Impact of emissions from municipal waste combustion. This phase of study quantified mutagenicity concentrations In ambient air but did not detect organic mutagens that could be attributed to Incinerator emissions.     

Evaluation of alternative filter media for particulate matter emission testing of residential wood heating devices

The performance of Teflon-coated glass fiber filter media (Pallflex Emfab TX40) is evaluated for particulate matter (PM) sampling of residential wood heating devices in a dilution tunnel. Thirty samples of varying duration and PM loading and concentration were collected from an U.S. Environmental Protection Agency (EPA) Method 28 dilution tunnel using dual Method 5G sample trains with untreated glass fiber and Emfab filters. Filters were weighed soon after the end of sampling and again the next day after equilibration at 35% relative humidity (RH). PM concentrations from both types of filters agreed very well with 1-day equilibration, demonstrating that Emfab filters are appropriate for use in measuring PM from residential wood burning appliances in a dilution tunnel and have performance equal to or better than the glass fiber filter media. Agreement between filter media without equilibration was erratic, with PM from glass fiber filter samples varying from slightly less than the Emfab samples to as much as 2.8 times higher. Some of the glass fiber filters lost substantial mass with equilibration, with the highest percent loss at lower filter mass loadings. Mass loss for Emfab samples was a small percentage of the mass and very consistent across the range of mass loadings. Taken together, these results may indicate water uptake on the glass fiber media that is readily removed with 1-day equilibration at moderate RH conditions.

Implications: EPA regulations now allow the use of either glass fiber or Teflon filter media for wood appliance PM emission testing. Teflon filter media minimizes the potential for acid-gas PM artifacts on glass fiber filters; this is important as EPA moves toward the use of locally sourced cordwood for testing that may have higher sulfur content. This work demonstrates that the use of Teflon-coated glass fiber filters can give similar PM measurement results to glass fiber filters after 1 day of equilibration. With no equilibration, measured PM from glass fiber filters was usually higher than from Teflon-coated glass fiber filters.     

Organic and inorganic sampling artefacts assessment

During collection on filter-based aerosol samplers, organic and inorganic aerosol compounds both contribute to positive and negative artefacts, significantly affecting chemical analyses results for single species and PM mass concentrations. Up to now, studies on organic or inorganic artefacts have been conducted in Europe but very scarce data are available for both in a single study.The field study was carried out in Milan, which is located in the Po valley (Northern Italy) one of the major pollution hot spots in Europe. As sampling artefacts depend on many factors, such as filter type, face velocity, sampling duration, and ambient conditions, in this field study two different filter types have been considered (i.e. quartz fibre filters and Teflon filters) for the assessment of both inorganic and organic artefacts during two different seasons (performing also some samplings at different flow-rates).Results showed that positive artefacts due to OC adsorption on quartz filters accounted for 39% of the OC measured concentration in summer, and 23% in winter. Negative artefact due to nitrate volatilisation by the filters was 51% on Teflon and 22% on the quartz filters in summer, and no or negligible losses were observed in winter. A significant improvement in the PM mass comparability obtained in parallel samplings on different filters was obtained taking into account the artefact estimates performed in this study.     

Comparison of speciation sampler and PC-BOSS fine particulate matter organic material results obtained in Lindon, Utah, during winter 2001-2002

The Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) has been previously verified as being capable of measuring total fine particulate matter (PM2.5), including semi-volatile species. The present study was conducted to determine if the simple modification of a commercial speciation sampler with a charcoal denuder followed by a filter pack containing a quartz filter and a charcoal-impregnated glass (CIG) fiber filter would allow for the measurement of total PM2.5, including semi-volatile organic material. Data were collected using an R&P (Rupprecht and Pastasnik Co., Inc.) Partisol Model 2300 speciation sampler; an R&P Partisol speciation sampler modified with a BOSS denuder, followed by a filter pack with a quartz and a CIG filter; a Met One spiral aerosol speciation sampler (SASS); and the PC-BOSS from November 2001 to March 2002 at a U.S. Environmental Protection Agency (EPA) Science to Achieve Results (STAR) sampling site in Lindon, UT. Total PM2.5 mass, ammonium nitrate (both nonvolatile and semi-volatile), ammonium sulfate, organic carbon (both non-volatile and semi-volatile), and elemental carbon were determined on a 24-hr basis. Results obtained with the individual samplers were compared to determine the capability of the modified R&P speciation sampler for measuring total PM2.5, including semi-volatile components. Data obtained with the modified speciation sampler agreed with the PC-BOSS results. Data obtained with the two unmodified speciation samplers were low by an average of 26% because of the loss of semi-volatile organic material from the quartz filter during sample collection.     

A High Volume Stack Sampler

This paper deals with the development design, and trial application of a sampling train to gather a relatively large amount of particulate sample in a short period of time. With air pollution sources installing control equipment to reduce emissions to the required low levels, it becomes necessary to use a sampling device which can collect a representative sample in a reasonable period of time. Some of the sampling trains currently being specified are expensive, awkward, and nearly impossible to use under field conditions. The high-volume train overcomes ail of these shortcomings and has some additional advantages. It uses the same glass fiber filter that is specified for ambient air particulate sampling so the emission test results are directly comparable to ambient air sampling data. The laboratories currently weighing and analyzing the glass filters need no additional equipment for the emission sampling analysis. The sample collected by the high-volume probe may be analyzed microscopically for size and characteristics of the particles. This is very important if control equipment is to be specified for the process or source. The high-volume sampler was evaluated on field tests of wood fired boilers, incinerators, wigwam burners, asphalt batching plants, seed cleaning plants, and wood fiber filtration systems. The results of several typical tests using the sampler on these sources are included in the paper.     

Further Evaluation of Glass Fiber Filters for Sampling Hydrogen Fluoride

Tests were conducted to determine the limitations of glass fiber filters in sampling atmospheric hydrogen fluoride. Filters without latex binder were more efficient collectors than those with the binder. Up to 75 μg F/in.² of filter area was collected by a single filter before the loss reached 5 percent. Two filters, one behind the other, collected over 250 μg F/in.² of filter area before loss through them reached five percent. By controlling the sampling rate and time to avoid exceeding the saturation limit, it is possible to use glass fiber filters for sampling over a wide range of fluoride concentrations.     

The measurement of fine particulate semivolatile material in urban aerosols

Ammonium nitrate and semivolatile organic material (SVOM) are significant components of fine particles in urban atmospheres. These components, however, are not properly determined with methods such as the fine particulate matter (PM2.5) Federal Reference Method (FRM) or other single filter samplers because of significant losses of semivolatile material (SVM) from particles collected on the filter during sampling. The R&P tapered element oscillating microbalance (TEOM) monitor also does not measure SVM, because this method heats the sample to remove particle bound water, which also results in evaporation of SVM. Recent advances in monitoring techniques have resulted in samplers for both integrated and continuous measurement of total PM2.5, including the particle concentrator-Brigham Young University organic sampling system (PC-BOSS), the real-time total ambient mass sampler (RAMS), and the R&P filter dynamics measurement system (FDMS) TEOM monitor. Results obtained using these samplers have been compared with those obtained with either a PM2.5 FRM sampler or a TEOM monitor in studies conducted during the past five years. These studies have shown the following: (1) the PC-BOSS, RAMS, and FDMS TEOM are all comparable. Each instrument measures both the nonvolatile material and the SVM. (2) The SVM is not retained on the heated filter of a regular TEOM monitor and is not measured by this sampling technique. (3) Much of the SVM is also lost during sampling from single filter samplers such as the PM2.5 FRM sampler. (4) The amount of SVM lost from single filter samplers can vary from less than one-third of that lost from heated TEOM filters during cold winter conditions to essentially all during warm summer conditions. (5) SVOM can only be reliably collected using an appropriate denuder sampler. (6) A PM2.5 speciation sampler can be easily modified to a denuder sampler with filters that can be analyzed for semivolatile organic carbon (OC), nonvolatile OC, and elemental carbon using existing OC/elemental carbon analytical techniques. The research upon which these statements are based for various urban studies are summarized in this paper.     

Sampling of carbonaceous particles in the atmosphere—II

A laboratory study was conducted to test the ability of various sorbents to remove vapor-phase atmospheric carbonaceous materials otherwise retained by sorption on quartz filters, a ‘positive artifact’ in sampling atmospheric particulate C. A dual quartz filter strategy, in which the C recovered from the after-filter is used to correct for the positive artifact, was also assessed. Sorbents such as activated Al₂O₃ and quartz fiber can reduce by up to 60% the positive artifact in sampling at 20 ℓ min⁻ with 47-mm Pallflex 2500 QAO quartz filters. On the assumption, defended herein, that a quartz fiber profilier was unlikely to influence the ratio of C retained by sorption on downstream tandem quartz filters, the dual filter strategy permitted correction for this positive artifact within, on average, 12%. Conclusions from an initial study suggesting extensive loss by volatilization of previously collected particulate C are reassessed.     

SARA Title III,Section 313 —Looking Ahead

This study performed a workplace evaluation of emission control using available air sampling filters and characterized the emitted particles captured in filters. Characterized particles were contained in the exhaust gas released from carbon nanotube (CNT) synthesis using chemical vapor deposition (CVD). Emitted nanoparticles were collected on grids to be analyzed using transmission electron microscopy (TEM). CNT clusters in the exhaust gas were collected on filters for investigation. Three types of filters, including Nalgene surfactant-free cellulose acetate (SFCA), Pall A/E glass fiber, and Whatman QMA quartz filters, were evaluated as emission control measures, and particles deposited in the filters were characterized using scanning transmission electron microscopy (STEM) to further understand the nature of particles emitted from this CNT production. STEM analysis for collected particles on filters found that particles deposited on filter fibers had a similar morphology on all three filters, that is, hydrophobic agglomerates forming circular beaded clusters on hydrophilic filter fibers on the collecting side of the filter. CNT agglomerates were found trapped underneath the filter surface. The particle agglomerates consisted mostly of elemental carbon regardless of the shapes. Most particles were trapped in filters and no particles were found in the exhaust downstream from A/E and quartz filters, while a few nanometer-sized and submicrometer-sized individual particles and filament agglomerates were found downstream from the SFCA filter. The number concentration of particles with diameters from 5 nm to 20 µm was measured while collecting particles on grids at the exhaust piping. Total number concentration was reduced from an average of 88,500 to 700 particle/cm³ for the lowest found for all filters used. Overall, the quartz filter showed the most consistent and highest particle reduction control, and exhaust particles containing nanotubes were successfully collected and trapped inside this filter.

Implications: As concern for the toxicity of engineered nanoparticles grows, there is a need to characterize emission from carbon nanotube synthesis processes and to investigate methods to prevent their environmental release. At this time, the particles emitted from synthesis were not well characterized when collected on filters, and limited information was available about filter performance to such emission. This field study used readily available sampling filters to collect nanoparticles from the exhaust gas of a carbon nanotube furnace. New agglomerates were found on filters from such emitted particles, and the performance of using the filters studied was encouraging in terms of capturing emissions from carbon nanotube synthesis.     

The Recovery of Selenious Acid Aerosols on Glass Fiber Filters

Previous workers have shown that selenium is only partially trapped on a filter during air sampling. In some cases, these losses have been attributed to volatilization of selenium dioxide. Our results demonstrate that selenium dioxide, In the presence of moist air, is completely recovered (apparently as selenious acid aerosols) and that the previous shortfalls must be due to other selenium species as yet unidentified. Selenious acid aerosols In our study were formed by volatilizing selenium dioxide (≈3 mg) Into a stream of moist ambient air (relative humidity, >50%), and trapped on glass fiber filters using a high-volume air sampler. Selenium(IV) was ultrasonlcally extracted from the filter with water and analyzed by atomic absorption spectrometry. Selenious acid aerosols were trapped on the filters with high efficiency (105 ± 5 percent) using a 50 minute sampling period. With an extended sampling period (24 hours) the recovery was 103 ± 6 percent.     

A Comparison of Filter Types in the Collection and Gravimetric Determination of Airborne Particulate Matter Less than 2.5 Microns (PM25)

ABSTRACT

Five identical, collocated, low-volume samplers were operated to collect airborne particulate matter less than 2.5 microns (PM₂₅). Five commercially available filter types were installed in the samplers to compare the gravimetric determination of PM_2.5 concentrations in the atmosphere. The filters were rotated through the five samplers for two study periods—one in summer and one in winter. The study was performed in Sheridan, WY, in close proximity to a gravimetric laboratory to minimize the introduction of errors associated with sample handling. Rigorous quality assurance procedures were employed throughout the study.Four of the five filter types provided comparable gravimetric determinations of airborne PM_2.5.     

The Magnitude of Bias in the Measurement of PM25 Arising from Volatilization of Particulate Nitrate from Teflon Filters

ABSTRACT

Because the Federal Reference Method for PM₂₅ specifies the collection of ambient particles on Teflon filters, we have examined the loss of a known volatile species, particulate nitrate, during sampling. Data are presented from two studies in southern California for which parallel samples were collected by different methods. Differences in collected nitrate are modeled using an evaporation model based on the work of Zhang and McMurry. The average nitrate obtained from sampling with Teflon filters was 28% lower on average than that measured by denuded nylon filters. In contrast, cascade impactor samples were within 5% of the denuded nylon filter on average. A simple model is presented that accounts for the particulate nitrate loss from Teflon filters either by scavenging nitric acid and ammonia in the sampler inlet or by heating the filter substrate during sampling. The observed magnitude of loss is explained by any of the following situations: (1) 100% nitric acid and ammonia vapor loss in the inlet, (2) 5 °C heating of the filter substrate above ambient temperature during sampling, or (3) a combination of these factors, such as 50% vapor loss in the inlet and 3 °C heating of the filter.     

The recovery of selenious acid aerosols on glass fiber filters

Previous workers have shown that selenium is only partially trapped on a filter during air sampling. In some cases, these losses have been attributed to volatilization of selenium dioxide. Our results demonstrate that selenium dioxide, in the presence of moist air, is completely recovered (apparently as selenious acid aerosols) and that the previous shortfalls must be due to other selenium species as yet unidentified. Selenious acid aerosols in our study were formed by volatilizing selenium dioxide (approximately 3 mg) into a stream of moist ambient air (relative humidity, greater than 50%), and trapped on glass fiber filters using a high-volume air sampler. Selenium(IV) was ultrasonically extracted from the filter with water and analyzed by atomic absorption spectrometry. Selenious acid aerosols were trapped on the filters with high efficiency (105 +/- 5 percent) using a 50 minute sampling period. With an extended sampling period (24 hours) the recovery was 103 +/- 6 percent.     

Flexibility of X-Ray Emission Spectrography as Adapted to Microanalysis of Air Pollutants

Methods previously published by this laboratory for analyzing thin dust coatings of airborne particulates have been further evaluated, as applied to vast air pollution surveys. It was demonstrated that choice of glass fiber filters adapted to high-volume samplers restricts the analysis to a limited number of elements, such as lead. More flexibility and versatility are attained through the use of organic membrane filters mounted in small plastic monitors which permit multi-elemental analysis at least as accurately as with other popular but time-consuming techniques. These qualities of speed and accuracy allow shorter intervals of sampling which are normally required for better statistical assessment of broad air pollution surveys. Sensitivity of the technique reaches a value close to 0.05 μg/m³, while time of analysis required is about five minutes per element after receipt of the sample.     

Simultaneous Sampling of Gas- and Aerosol-Phase TDI with a Triple Filter System

Abstract

A new triple filter system sampler/model is proposed for the precise and accurate simultaneous sampling and determination of gas- and aerosol-phase 2,4-toluene diisocyanate (TDI). The system consists of two front Teflon filters for sampling aerosol-phase TDI and a final coated glass fiber filter to collect gas-phase TDI. The aerosol-phase TDI is collected on the first Teflon filter, while the second Teflon filter is used to estimate gaseous TDI adsorbed by the first. According to the gas adsorption test of two Teflon filters in series, the TDI gas adsorption fraction of the two filters is almost the same. Results of the evaporation test using pure TDI aerosols collected on the Teflon filter show that significant evaporation of the compound does not occur during sampling. These two findings allow the use of a model to estimate accurate gasand aerosol-phase TDI concentrations. The comparison test with an annular denuder shows that the triple filter system can minimize the TDI sampling bias between the dual filter and the annular denuder systems.     

Simultaneous sampling of gas- and aerosol-phase TDI with a triple filter system

A new triple filter system sampler/model is proposed for the precise and accurate simultaneous sampling and determination of gas- and aerosol-phase 2,4-toluene diisocyanate (TDI). The system consists of two front Teflon filters for sampling aerosol-phase TDI and a final coated glass fiber filter to collect gas-phase TDI. The aerosol-phase TDI is collected on the first Teflon filter, while the second Teflon filter is used to estimate gaseous TDI adsorbed by the first. According to the gas adsorption test of two Teflon filters in series, the TDI gas adsorption fraction of the two filters is almost the same. Results of the evaporation test using pure TDI aerosols collected on the Teflon filter show that significant evaporation of the compound does not occur during sampling. These two findings allow the use of a model to estimate accurate gas- and aerosol-phase TDI concentrations. The comparison test with an annular denuder shows that the triple filter system can minimize the TDI sampling bias between the dual filter and the annular denuder systems.     

A High-Volume Sampler for the Determination of Particle Size Distributions in Ambient Air

A size selective particle sampler has been developed for continuous sampling of the urban aerosol over periods ranging from hours to weeks, providing relatively large sample weights. The system, which is now operating in New York City, uses a parallel array of two-stage samplers. The cyclones used as the first stage collectors have 50% particle retention at 3.5,2.5,1.5 and 0.5 µm aerodynamic diameter, respectively. Undersize particles which pass through the cyclones are captured on glass fiber filters. Equal intake velocities are assured by using flow equalizers on the inlets to the cyclones. Accurate control of the flow through the cyclones is obtained by the use of an integrated circuit pressure transducer in conjunction with a specially designed feedback control circuit. The collection efficiencies of the cyclone were calibrated using monodisperse ferric oxide test aerosols tagged with Tc-99m. Mass balances of the par-ticulates collected on the cyclones and filters are obtained for the five sampling stages. Preliminary results show the distributions of the total suspended particulates in New York City to be bimodal. The distributions of lead, copper, and manganese with particle size are also discussed.