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.     

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.     

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)     

Equilibrium sorption of gaseous organic chemicals to fiber filters used for aerosol studies

Fiber filters commonly used to collect aerosols for various analyses also collect gaseous organic chemicals during sampling. These sorbed chemicals can lead to serious artifacts, particularly when analyzing aerosols for organic compounds and organic carbonaceous material. To date, this sorption process has only been looked at for a few types of filters and compound classes. This work presents a comprehensive study of this sorption process for various, widely used fiber filters and a broad variety of compound classes. Furthermore, important factors have been investigated, including relative humidity, temperature, baking and exposure to ambient air during sampling. From these data, poly-parameter linear-free energy relationships were derived that allow for estimations of sorption constants of gaseous organic compounds on different filter types. Based on the results, recommendations are provided to help predict, minimize and ensure reproducibility of artifacts caused by gaseous organic compounds sorbing to fiber filters.     

Concentrations of decabromodiphenyl ether in air from Southern Ontario: implications for particle-bound transport

Atmospheric concentrations are reported for the main component of the brominated flame retardant decaBDE (BDE-209) in air samples collected from Southern Ontario for the period January 23-June 06, 2002. Levels ranged from below detection to 105pgm(-3) with virtually all of BDE-209 being trapped by the filter and thus deduced to be sorbed to aerosol particles. Thus, it is likely that the long-range atmospheric transport (LRAT) of BDE-209 is controlled by the transport characteristics of the aerosols. This conclusion that BDE-209 does not have the same potential for LRAT as other more volatile PBDEs is subject to possible complications arising from the uncertainties about the LRAT potential of aerosols.     

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.     

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.     

Planning A State-Wide Air Pollution Advisory Service

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°C) for 8 to 24 h and weighed prior to cryogenic storage. All filters were subsequently stored at ?70°C to ?80°C prior to a one-time extraction and Salmonella (Ames) mutagenicity bioassay of the entire sample set. Results indicate that the sample handling variations and collection period variables had no significant effect on recovery of organics or mutagens. However, a filter type difference was observed. The sonication extraction of organics and mutagens was significantly greater for TIGF filters than for glass fiber or quartz. Results from a second phase of study indicated differences in extracted organics and mutagens for these filter types.     

Retention of sulfur dioxide by nylon filters

Based on laboratory studies, recovery efficiencies of sulfur dioxide (SO₂) were determined for nylon filters. The nylon filters used in these experiments were found to retain SO₂. A relatively uniform amount (1.7%) was recoverable from each nylon filter, independent of relative humidity. An appreciable portion of SO₂ was unrecoverable, and this increased from 5 to 16% as the RH increased from 28 to 49%. This unrecoverable SO₂ may account for previous reports of a low bias for SO₂ determinations employing filter packs using nylon filters. Additional characterization of nylon filters is recommended prior to their future deployment as an integrative sampling medium for ambient air.     

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.     

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.     

Polycyclic aromatic hydrocarbons in the ambient air of suburban and industrial regions of central Taiwan

The concentrations of gas-phase and particle-bound polycyclic aromatic hydrocarbons (PAHs) were measured simultaneously at an industrial area (Taichung Industrial Park) and a suburban area (Tunghai University Campus) in Taichung, Taiwan. Twenty-four hours samplings for two consecutive days were performed between August and December 2002 at both sampling sites. Ambient air particle-bound PAHs were collected on quartz filters and gas-phase PAHs were collected on glass cartridges using a PUF Sampler, respectively. Both types of samples were extracted with a DCM/n-hexane mixture (50/50, v/v) for 24 h, then the extracts were subjected to gas chromatography-mass spectrometric (GC-MS) analysis. Total PAHs concentrations at the Taichung Industrial Park (TIP) sampling site and the Tunghai University Campus (THUC) sampling site were found to be 1232.3+/-963.6 and 609.8+/-356.3 ng/m(3), respectively. Stationary combustion processes were mainly responsible for PAHs sources at the TIP sampling site, while traffic vehicle exhaust was the largest contributor for PAHs sources at the THUC sampling site.     

Characterization of activated carbon fiber filters for pressure drop, submicrometer particulate collection, and mercury capture

The use of activated carbon fiber (ACF) filters for the capture of particulate matter and elemental Hg is demonstrated. The pressure drop and particle collection efficiency characteristics of the ACF filters were established at two different face velocities and for two different aerosols: spherical NaCl and combustion-generated silica particles. The clean ACF filter specific resistance was 153 kg m-2 sec-1. The experimental specific resistance for cake filtration was 1.6 x 10(6) sec-1 and 2.4 x 10(5) sec-1 for 0.5- and 1.5-micron mass median diameter particles, respectively. The resistance factor R was approximately 2, similar to that for the high-efficiency particulate air filters. There was a discrepancy in the measured particle collection efficiencies and those predicted by theory. The use of the ACF filter for elemental Hg capture was illustrated, and the breakthrough characteristic was established. The capacity of the ACF filter for Hg capture was similar to other powdered activated carbons.     

High-Volume Sampling: Effect of Windborne Particulate Matter Deposited during Idle Periods

For high volume air sampling, New York State uses a random once every six days schedule. To avoid double travel, this usually requires leaving filters mounted for five days before the actual sampling period of 24 hr. The starting and stopping of the sampling is controlled by a 7 day timer. (At the maximum, it is possible that a filter could be in place for 10 days with the motor idle.) The purpose of this investigation was to determine whether the filter collects a significant weight of particulate matter during the period the motor is idle, and what effect the collected windborne particulate matter has on computed TSP concentrations.     

Measurements of Primary Sulfates with an Acid Condensation System

Two techniques were used to measure primary sulfuric acid and sulfate emissions from two small package boilers burning nominal 0.3% sulfur fuels, one with 11 ppm vanadium and one with 4.3 ppm vanadium. Several of the particulate fractions from both sampling methods were analyzed for sulfuric acid using a selective solvent determination (SSD) procedure. The sulfuric acid present on the filters accounted for a minimum of 11% of the particulate emission rates. The observed conversion of sulfur dioxide to primary sulfate or primary sulfuric acid is reduced considerably when sulfate ion detected in an isopropanol impinger is attributed to sulfur dioxide conversion in the solution rather than to primary sulfuric acid. An additional reduction occurs when the method of calculating the conversion is based solely on sulfur weight. This study gives a fourfold reduction in percent conversion when compared to a similar study conducted earlier. Suggestions are offered for improvements in measurement methods and for a consistent technique for calculating sulfur conversion.     

Characterization of aerosols from biomass burning--a case study from Mizoram (Northeast), India

Physical and optical properties of biomass burning aerosols in Northeastern region, India analyzed based on measurements made during February 2002. Large spatial extent of Northeastern Region moist tropical to moist sub-tropical forests in India have high frequency of burning in annual dry seasons. Characterization of resultant trace gases and aerosols from biomass burning is important for the atmospheric radiative process. Aerosol optical depth (AOD) observed to be high during burning period compared to pre- and post-burning days. Peak period of biomass burning is highly correlated with measured AOD and total columnar water vapor. Size distribution of aerosols showed bimodal size distribution during burning day and unimodal size distribution during pre- and post-burning days. Size distribution retrievals from biomass burning aerosols show dominance of accumulation mode particles. Weighted mean radius is high (0.22 microm) during burning period. Columnar content of aerosols observed to be high during burning period in addition to the drastic reduction of visibility. During the burning day Anderson sampler measurements showed dominance of accumulation mode particles. The diurnal averaged values of surface shortwave aerosol radiative forcing af biomass burning aerosols varies from -59 to -87 Wm(-2) on different days. Measured and modeled solar irradiances are also discussed 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.     

Applicability of a modified MCE filter method with Button Inhalable Sampler for monitoring personal bioaerosol inhalation exposure

In this study, a “modified” mixed cellulose ester (MCE) filter culturing method (directly placing filter on agar plate for culturing without extraction) was investigated in enumerating airborne culturable bacterial and fungal aerosol concentration and diversity both in different environments. A Button Inhalable Sampler loaded with a MCE filter was operated at a flow rate of 5 L/min to collect indoor and outdoor air samples using different sampling times: 10, 20, and 30 min in three different time periods of the day. As a comparison, a BioStage impactor, regarded as the gold standard, was operated in parallel at a flow rate of 28.3 L/min for all tests. The air samples collected by the Button Inhalable Sampler were directly placed on agar plates for culturing, and those collected by the BioStage impactor were incubated directly at 26 °C. The colony forming units (CFUs) were manually counted and the culturable concentrations were calculated both for bacterial and fungal aerosols. The bacterial CFUs developed were further washed off and subjected to polymerase chain reaction–denaturing gradient gel electrophoresis (DGGE) for diversity analysis. For fungal CFUs, microscopy method was applied to studying the culturable fungal diversity obtained using different methods. Experimental results showed that the performance of two investigated methods varied with sampling environments and microbial types (culturable bacterial and fungal aerosols). For bacterial aerosol sampling, both methods were shown to perform equally well, and in contrast the “modified” MCE filter method was demonstrated to enumerate more culturable fungal aerosols than the BioStage impactor. In general, the microbial species richness (number of gel bands) was observed to increase with increasing collection time. For both methods, the DGGE gel patterns were observed to vary with sampling time and environment despite of similar number of gel bands. In addition, an increase in sampling time from 20 to 30 min was found not to substantially alter the species richness. Regardless of the sampling methods, more species richness was observed in the outdoor environment than the indoor environment. This study described a new personal bioaerosol exposure assessment protocol, and it was demonstrated applicable in monitoring the personal bioaerosol exposure in replace of an Andersen-type impactor.     

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.     

A Technique for Respirable Sampling

The purpose of this paper is to describe instrumentation to aerodynamically size suspended particulates found in ambient air and to summarize results of field testing utilizing the new technique.

A four-stage, multiorifice high-volume fractionating impactor with backup filter, which can be operated as a component of the standard high-volume sampler, collects particulate matter in five separate aerodynamic size ranges: 7 micrometer (μm) or larger, 3.3 to 7 μm, 2.0 to 3.3 μm, 1.1 to 2.0 μm, and 0.01 to 1.1 μm.

Comparative field tests utilizing duplicate sampling techniques were conducted to determine the feasibility of using the size fractionator on a routine basis in field operations. Verification of the actual particle size separation was not undertaken; however, earlier tests utilizing laboratory-generated aerosols have been performed with satisfactory results.

The results of field tests indicate that the fractionator can be used to determine the aerodynamic size distribution of particulate matter. A glass fiber surface with a pH of 11.0 was found to adsorb atmospheric acid gases during sampling and thus gave erroneous mass concentration results when compared to the standard high-volume sampler. Glass fiber filters with a pH of 6.5 eliminated the acid gas adsorption.