Quantitative Analysis of Environmental Factors in Differential Weighing of Blank Teflon Filters (original) (raw)
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Development of a Reliable and Cost-Effective Weighing Chamber for Aerosol Sample Analyses
Aerosol and Air Quality Research, 2015
Reliable gravimetric analysis of particulate matter filters is of great importance in exposure and risk assessment in industrial hygiene and environmental health, especially for light weight fine particles like PM 2.5. Weighing bias may be caused by a number of environmental and operational factors. Among them, the humidity effect is most often addressed. This study proposes a cost-effective weighing chamber with humidity control by using a saturated magnesium chloride solution to meet the USEPA requirements for filter weighing. To exclude the interference of electrostatic charges, filter samples are treated with a radioactive source, Am 241 , on a microbalance pan before weighing. The results of long term monitoring showed that the relative humidity inside the weighing chamber is between 31-35%, when the temperature is between 18-21°C. The air pressure inside the weighing chamber is kept slightly positive by adjusting the air supply of the humidity control unit at 15 L/min during filter conditioning and at 25 L/min during filter weighing to maintain a stable humidity condition and prevent aerosol contamination from outside. Moreover, the operator should wear gloves to prevent hand moisture evaporation. We suggest that filter samples to be stored and conditioned in a weighing chamber with the filter holder's lid open to expedite and enhance the filter conditioning. When a hygroscopic filter, such as an MCE, is used to collect about 0.5 mg of hygroscopic NaCl particles, a mass increase of 0.5 mg results occurs due to the filter. An additional 1.2 mg mass increase occurs due to collected NaCl particles, when the weighing is performed under RH 85% rather than in the environmentally-well-controlled weighing chamber. With the use of the weighing chamber and the recommended practices, this study demonstrates excellent weighing quality. The mass determination limits are below 3 µg for 37-mm particle-laden filter samples commonly encountered in practical situations.
Aerosol and Air Quality Research, 2013
Mass concentration and chemical composition of PM 10 and PM 2.5 was measured during eight one-month winter and summer field studies carried out in the Po Valley (Northern Italy). PM was daily collected on Teflon (T) and on quartz (Q) filters set side-by-side. During the summer periods the differences between the mass concentrations measured on the two filters (T-Q) were within the range of experimental error, while statistically significant positive differences were detected during the winter periods. The sum of the chemical analyses (elements, ions, elemental and organic carbon) allowed the achievement of satisfactory mass closure during the summer periods, while unaccounted masses of the order of 10-20% of the PM mass measured on Teflon were detected during the winter periods. Unaccounted mass and T-Q differences increased during periods of high atmospheric stability, when the ammonium nitrate concentration also increased rapidly. Unaccounted masses and T-Q differences can be attributed to PM-bound and PM-adsorbed water.
Future trends in laboratory methods to predict HVAC in service filter performance
2019
Air filters installed in ventilation systems face various types of aerosols during their service life, both in residential and in commercial buildings. Their particle size is the most important characteristic and ranges from a few nanometers to a few micrometers. Different physicochemical properties, such as phase state, hygroscopicity, and morphology are also important to determine the impact of particulate matter on the behavior of air filters during their service life. Therefore, the performance of air filters installed in a Heating, Ventilation and AirConditioning (HVAC) system is strongly dependent on the properties of the particles captured during their service life and not only on the characteristics of the materials and technologies used to manufacture the air cleaning equipment. Current laboratory test methods for evaluating HVAC filter performance include the determination of their fractional particle removal efficiency on a limited size range, typically between 300 nm and 10000 nm. Such information is useful and meaningful for clean filters. However, air filters performance (i.e. airflow resistance and removal efficiency) changes during their service life because of particle loading. For this reason, air filters are artificially clogged in laboratory with the intent to compare one product to another and to predict their behavior while they age in HVAC systems. Current standardized air filter loading procedures use synthetic dusts with particle size distributions very different from typical urban atmospheric aerosols. Consequently, the results obtained in this way differ from the air filter performance measured in real HVAC installations and the designers cannot use them to predict quantitatively the in-situ air filter performance. Standards writers are aware of the problem and this limitation is stated explicitly in EN ISO 16890 and ANSI/ASHRAE 52.2 standards. However, there is a need to perform the test in a short time. Moreover, the filtration industry consolidated this approach during the past decades and a lot of data is available with those dusts.
Journal of the Air & Waste Management Association
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.
Evaluation of Continuous and Filter-Based Methods for Measuring PM 2.5 Mass Concentration
Aerosol Science and Technology, 2005
Real-time continuous PM2.5 mass measurements were made by a continuous ambient mass monitor (CAMM), a real-time total ambient mass sampler (RAMS), and a tapered element oscillating microbalance (TEOM) in Houston during summer and in Seattle during winter. Hourly PM2.5 mass concentrations measured by the three samplers were compared with one another to evaluate the sampling performance for total ambient PM2.5 mass measurements. Reasonably good agreement was observed between pairs of the continuous mass samplers. The regression parameters were calculated between PM2.5 mass concentrations of the instruments.
Journal of the Air & Waste Management Association, 2004
The extent of mass loss on Teflon filters caused by ammonium nitrate volatilization can be a substantial fraction of the measured particulate matter with an aerodynamic diameter less than 2.5 m (PM 2.5) or 10 m (PM 10) mass and depends on where and when it was collected. There is no straightforward method to correct for the mass loss using routine monitoring data. In southern California during the California Acid Deposition Monitoring Program, 30-40% of the gravimetric PM 2.5 mass was lost during summer daytime. Lower mass losses occurred at more remote locations. The estimated potential mass loss in the Interagency Monitoring of Protected Visual Environments network was consistent with the measured loss observed in California. The biased mass measurement implies that use of Federal Reference Method data for fine particles may lead to control strategies that are biased toward sources of fugitive dust, other primary particle emission sources, and stable secondary particles (e.g., sulfates). This analysis clearly supports the need for speciated analysis of samples collected in a manner that preserves volatile species. Finally, although there is loss of volatile nitrate (NO 3 Ϫ) from Teflon filters during sampling, the NO 3 Ϫ remaining after collection is quite stable. We found little loss of NO 3 Ϫ from Teflon filters after 2 hr under vacuum and 1 min of heating by a cyclotron proton beam.
Gas-phase filters breakthrough models at low concentration-Effect of relative humidity
Building and Environment, 2014
Indoor air quality (IAQ) is a major concern in non-industrial buildings since it influences occupants’ health, comfort and productivity. Adsorption-based granular activated carbon (GAC) filters are commonly being used to purify indoor air by removing indoor air pollutants. Predicting the breakthrough time of filters is necessary for scheduling their maintenance and/or regeneration. However, the pollutants’ concentrations that typically encounter in indoor environment are very low thus increasing the influence of humidity on the filter performance. Also, the existing standard recommends the test to be carried out at 100 ppm, which is much higher than the actual volatile organic compounds (VOC) concentration in buildings. This paper reports the development of a framework for predicting the breakthrough curve of activated carbon filters at low concentration and different levels of relative humidity applying accelerated test data. The procedure is based on two well-known empirical models: Wheeler-Jonas and Yoon-Nelson equations. The overall mass transfer coefficient in the Wheeler-Jonas equation and the proportionality constant in the Yoon-Nelson equation (both as a function of adsorption capacity) are a function of humidity level. Results show that the proposed framework allows the breakthrough time at humid condition and low contaminant concentration to be estimated using the data obtained from the existing standard test procedure.
To guide the selection of gas phase filtration media in the air cleaning devices, it is important to understand and estimate the media performance under usage concentrations. Filters for improving indoor air quality are typically subject to low volatile organic compounds (VOCs) concentration levels (e.g., ∼50 ppb), while the current standard tests per ASHRAE 145.1 . are performed at relatively high challenge concentrations (∼1-100 ppm level). The primary objective of this study was to determine if media that perform well at the high concentration test condition would also perform well under the low concentration. The secondary objective was to investigate if and how existing models of filtration by media bed can be applied to extrapolate the results from the high concentration tests to the low concentration condition. Experiments and simulations were carried out at both high concentrations (100 ppm for toluene and 1 ppm for formaldehyde) and low concentrations (0.05 ppm for toluene and formaldehyde) for six selected filtration media. The results show that (1) the high concentration test data were able to differentiate the relative performance among the media at the low concentration properly, confirming the validity of using ASHRAE 145.1 (ANSI/ASHRAE 2008) for relative performance comparison; (2) significant initial breakthrough observed at high concentration tests of large pellet media was not present at the low concentration tests, indicating the dependency of the adsorption capability of the sorbent media on the concentration level as well as the possible "by-pass" effects (i.e., not all the VOC molecules in the air stream had the same chance to contact with the sorbent media); and (3) existing models need to be improved by incorporating the concentration dependency of the partition coefficient and the by-pass effect in order to predict the breakthrough curve at low concentrations properly. Such an improved model was proposed, evaluated with the measured data, and was found to be promising for physical sorbent, but requires further development for chemical, catalytic sorbent and large pellet sorbent. The study provides previously unavailable experimental data and new insight into the behavior of the filtration media for volatile organic compounds as well as evidence in support of the application of ASHRAE Standard 145.1 (ANSI/ASHRAE 2008) for media performance evaluation.
Analytical and Bioanalytical Chemistry, 2011
In this research, the two most common filter media, quartz and Teflon, were tested to obtain information about the possible adsorption of gas-phase compounds onto filters during long sample collection of atmospheric aerosols. Particles of nanometer-size for off-line chemical characterization were collected using a recently introduced differential mobility analyzer for size separation. Samples were collected at an urban site (Helsinki, SMEARIII station) during spring 2010. Sampling time was 4 to 10 days for particles 50, 40, or 30 nm in diameter. Sample air flow was 4 L/min. The sampling setup was arranged so that two samples were obtained for each sampling period almost simultaneously: one containing particles and adsorbed gasphase compounds and one containing adsorbed gas-phase compounds only. Filters were extracted and analyzed for the presence of selected carboxylic acids, polyols, nitrogencontaining compounds, and aldehydes. The results showed that, in quartz filter samples, gas-phase adsorption may be responsible for as much as 100% of some compound masses. Whether quartz or Teflon, simultaneous collection of gas-phase zero samples is essential during the whole sampling period. The dependence of the adsorption of gasphase compounds on vapor pressure and the effect of adsorption on the deposited aerosol layer are discussed.
2022
The particle filtration efficiency (PFE) of a respirator or face mask is one of its key properties. While the physics of particle filtration results in the PFE being size-dependent, measurement standards are specified using a single, integrated PFE, for simplicity. This integrated PFE is commonly defined with respect to either the number (NBFE) or mass (MBFE) distribution of particles as a function of size. This relationship is non-trivial; it is influenced by both the shape of the particle distribution and the fact that multiple practical definitions of particle size are used. This manuscript discusses the relationship between NBFE and MBFE in detail, providing a guide to practitioners. Our discussion begins with a theoretical discussion of the underlying principles. We then present experimental results for a database of size-resolved PFE (SPFE) measurements for over 900 candidate respirators and filter media, including filter media with systematically varied properties and commerc...