The Experts below are selected from a list of 654 Experts worldwide ranked by ideXlab platform
Allen L Robinson - One of the best experts on this subject based on the ideXlab platform.
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positive and negative artifacts in particulate organic carbon measurements with denuded and undenuded sampler configurations special issue of aerosol science and technology on findings from the fine particulate matter supersites program
Aerosol Science and Technology, 2004Co-Authors: R. Subramanian, Juan C Cabada, Andrey Khlystov, Allen L RobinsonAbstract:Measurement of ambient particulate organic carbon (POC) with quartz Filters is prone to positive and negative sampling artifacts. One approach for estimating these artifacts is to sample with a Backup quartz Filter placed behind either the main quartz Filter or a Teflon Filter in a parallel line. Another approach is to use a denuder to reduce the positive artifact in combination with a highly adsorbent Backup Filter to capture any negative artifact. Results obtained using both of these approaches in parallel for over one year in Pittsburgh, PA are presented in this article. A sampler using an activated carbon monolith denuder has been developed and tested extensively. Transmission losses were found to be negligible, and the denuder is on average 94% efficient at removing gas-phase organics. Denuder breakthrough is corrected for each run using a dynamic blank in parallel with the sample line. Comparisons with the dynamic blank indicate that the denuder almost eliminates the positive artifact on the quartz ...
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positive and negative artifacts in particulate organic carbon measurements with denuded and undenuded sampler configurations
Aerosol Science and Technology, 2004Co-Authors: R. Subramanian, Juan C Cabada, Andrey Khlystov, Allen L RobinsonAbstract:Measurement of ambient particulate organic carbon (POC) with quartz Filters is prone to positive and negative sampling artifacts. One approach for estimating these artifacts is to sample with a Backup quartz Filter placed behind either the main quartz Filter or a Teflon Filter in a parallel line. Another approach is to use a denuder to reduce the positive artifact in combination with a highly adsorbent Backup Filter to capture any negative artifact. Results obtained using both of these approaches in parallel for over one year in Pittsburgh, PA are presented in this article. A sampler using an activated carbon monolith denuder has been developed and tested extensively. Transmission losses were found to be negligible, and the denuder is on average 94% efficient at removing gas-phase organics. Denuder breakthrough is corrected for each run using a dynamic blank in parallel with the sample line. Comparisons with the dynamic blank indicate that the denuder almost eliminates the positive artifact on the quartz Filter. Negative artifact from the denuded quartz Filter is quantified using a carbon-impregnated glass fiber (CIG) Backup Filter and was found to be small, typically less than 10% of the ambient POC. Compared to the denuded sampler POC, 24 h bare quartz samples showed an almost constant positive artifact of 0.5 μg-C/m 3 for samples taken throughout the year-long study period. Sampling for shorter durations (4-6 h) resulted in a larger positive artifact. A quartz Filter behind a Teflon Filter (QBT) provides a consistent estimate of the positive artifact on the bare quartz Filter irrespective of sample duration, though it overcorrects for the positive artifact by 16-20% (attributed to particulate matter volatilizing off the upstream Teflon Filter). The quartz behind quartz (QBQ) approach provides a reasonable estimate of the positive artifact on the bare quartz Filter for the 24 h samples but not for the shorter samples. A slight seasonal variation is observed in the absolute value of the positive artifact, with higher values observed during the summer months.
R. Subramanian - One of the best experts on this subject based on the ideXlab platform.
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positive and negative artifacts in particulate organic carbon measurements with denuded and undenuded sampler configurations special issue of aerosol science and technology on findings from the fine particulate matter supersites program
Aerosol Science and Technology, 2004Co-Authors: R. Subramanian, Juan C Cabada, Andrey Khlystov, Allen L RobinsonAbstract:Measurement of ambient particulate organic carbon (POC) with quartz Filters is prone to positive and negative sampling artifacts. One approach for estimating these artifacts is to sample with a Backup quartz Filter placed behind either the main quartz Filter or a Teflon Filter in a parallel line. Another approach is to use a denuder to reduce the positive artifact in combination with a highly adsorbent Backup Filter to capture any negative artifact. Results obtained using both of these approaches in parallel for over one year in Pittsburgh, PA are presented in this article. A sampler using an activated carbon monolith denuder has been developed and tested extensively. Transmission losses were found to be negligible, and the denuder is on average 94% efficient at removing gas-phase organics. Denuder breakthrough is corrected for each run using a dynamic blank in parallel with the sample line. Comparisons with the dynamic blank indicate that the denuder almost eliminates the positive artifact on the quartz ...
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positive and negative artifacts in particulate organic carbon measurements with denuded and undenuded sampler configurations
Aerosol Science and Technology, 2004Co-Authors: R. Subramanian, Juan C Cabada, Andrey Khlystov, Allen L RobinsonAbstract:Measurement of ambient particulate organic carbon (POC) with quartz Filters is prone to positive and negative sampling artifacts. One approach for estimating these artifacts is to sample with a Backup quartz Filter placed behind either the main quartz Filter or a Teflon Filter in a parallel line. Another approach is to use a denuder to reduce the positive artifact in combination with a highly adsorbent Backup Filter to capture any negative artifact. Results obtained using both of these approaches in parallel for over one year in Pittsburgh, PA are presented in this article. A sampler using an activated carbon monolith denuder has been developed and tested extensively. Transmission losses were found to be negligible, and the denuder is on average 94% efficient at removing gas-phase organics. Denuder breakthrough is corrected for each run using a dynamic blank in parallel with the sample line. Comparisons with the dynamic blank indicate that the denuder almost eliminates the positive artifact on the quartz Filter. Negative artifact from the denuded quartz Filter is quantified using a carbon-impregnated glass fiber (CIG) Backup Filter and was found to be small, typically less than 10% of the ambient POC. Compared to the denuded sampler POC, 24 h bare quartz samples showed an almost constant positive artifact of 0.5 μg-C/m 3 for samples taken throughout the year-long study period. Sampling for shorter durations (4-6 h) resulted in a larger positive artifact. A quartz Filter behind a Teflon Filter (QBT) provides a consistent estimate of the positive artifact on the bare quartz Filter irrespective of sample duration, though it overcorrects for the positive artifact by 16-20% (attributed to particulate matter volatilizing off the upstream Teflon Filter). The quartz behind quartz (QBQ) approach provides a reasonable estimate of the positive artifact on the bare quartz Filter for the 24 h samples but not for the shorter samples. A slight seasonal variation is observed in the absolute value of the positive artifact, with higher values observed during the summer months.
Brian T Mader - One of the best experts on this subject based on the ideXlab platform.
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sampling methods used for the collection of particle phase organic and elemental carbon during ace asia
Atmospheric Environment, 2003Co-Authors: Brian T Mader, James J Schauer, John H Seinfeld, Richard C Flagan, Jian Zhen Yu, Hong Yang, Barbara J Turpin, Jeffrey T Deminter, G Heidemann, P K QuinnAbstract:Abstract The semi-volatile nature of carbonaceous aerosols complicates their collection, and for this reason special air sampling configurations must be utilized. ACE-Asia provided a unique opportunity to compare different sampling techniques for collecting carbonaceous aerosols. In this paper detailed comparisons between Filter-based carbonaceous aerosol sampling methods are made. The majority of organic carbon (OC) present on a Backup quartz fiber Filter (QFF) in an undenuded-Filter sampler resulted from the adsorption of native gaseous OC rather than OC evaporated from collected particles. The level of OC on a Backup QFF placed behind a QFF was lower than the level present on a Backup QFF placed behind a Teflon membrane Filter (TMF) indicating that gas/Filter equilibrium may not be achieved in some QFF front and Backup Filter pairs. Gas adsorption artifacts can result in a 20–100% overestimation of the ambient particle-phase OC concentration. The gas collection efficiency of XAD-coated and carbon-impregnated Filter-lined denuders were not always 100%, but, nonetheless, such denuders minimize gas adsorption artifacts. The median fraction of particle-phase OC that is estimated to evaporate from particles collected by denuder-Filter samplers ranged from 0 to 0.2; this value depends on the sampler configuration, chemical composition of the OC, and sampling conditions. After properly correcting for sampling artifacts, the measured OC concentration may differ by 10% between undenuded- and denuder-Filter samplers. Uncorrected, such differences can be as large as a factor two, illustrating the importance of sampling configurations in which gas adsorption or evaporation artifacts are reduced or can be corrected.
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gas solid partitioning of semivolatile organic compounds socs to air Filters 3 an analysis of gas adsorption artifacts in measurements of atmospheric socs and organic carbon oc when using teflon membrane Filters and quartz fiber Filters
Environmental Science & Technology, 2001Co-Authors: Brian T Mader, James F. PankowAbstract:Adsorption of gaseous semivolatile organic compounds (SOCs) onto the Filter(s) of a Filter/sorbent sampler is a potential source of measurement error when determining specific SOCs as well as organic carbon (OC) levels in the atmosphere. This work examines partitioning to both Teflon membrane Filters (TMFs) and quartz fiber Filters (QFFs) for purposes of predicting the magnitude of the compound-dependent gas adsorption artifact as a function of various sampling parameters. The examination is based on values of K_(p,face) (m^3 cm^(-2)), the gas/Filter partition coefficient expressed as [ng sorbed per cm^2 of Filter face]/[ng per m^3 in the gas phase]. Values of K_(p,face) were calculated based on literature values of the gas/solid partition coefficient K_(p,s) [ng sorbed per m^2 of Filter]/[ng per m^3 in gas phase] for the adsorption of various polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) to TMFs, and for the adsorption of PAHs to QFFs. At relative humidity (RH) values below ≈50%, the K_(p,face) values for PAHs are lower on TMFs than on ambient-Backup QFFs. The gas adsorption artifact will therefore be lower for PAHs with TMFs than with QFFs under these conditions. In the past, corrections for the gas/Filter adsorption artifact have been made by using a Backup Filter, and subtracting the mass amount of each compound found on the Backup Filter from the total (particle phase + sorbed on Filter) amount found on the front Filter. This procedure assumes that the ng cm^(-2) amounts of each SOC sorbed on the front and Backup Filters are equal. That assumption will only be valid after both Filters have reached equilibrium with each of the gaseous SOCs in the incoming sample air. The front Filter will reach equilibrium first. The minimum air sample volume V_(min,f+b) required to reach gas/Filter sorption equilibrium with a pair of Filters is 2K_(p,face)A_(Filter) where A_(Filter) (cm^2) is the per-Filter face area. K_(p,face) values, and therefore V_(min,f+b) values, depend on the compound, relative humidity (RH), temperature, and Filter type. Compound-dependent V_(min,f+b) values are presented for PAHs and PCDD/Fs on both TMFs and QFFs. Compound-dependent equations which give the magnitude of the Filter adsorption artifact are presented for a range of different sampling arrangements and circumstances. The equations are not intended for use in actually correcting field data because of uncertainties in actual field values of relevant parameters such as the compound-dependent K_(p,face) and gas/particle K_p values, and because of the fact that the equations assume ideal step-function chromatographic movement of gas-phase compounds through the adsorbing Filter. Rather, the main utility of the equations is as guidance tools in designing field sampling efforts that utilize Filter/sorbent samplers and in evaluating prior work. The results indicate that some Backup-Filter-based corrections described in the literature were carried out using sample volumes that were too small to allow proper correction for the gas adsorption artifact for some specific SOCs of interest. Similar conclusions are reached regarding artifacts associated with the measurement of gaseous and particulate OC.
Jihua Tan - One of the best experts on this subject based on the ideXlab platform.
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improved measurement of carbonaceous aerosol evaluation of the sampling artifacts and inter comparison of the thermal optical analysis methods
Atmospheric Chemistry and Physics, 2010Co-Authors: Yuan Cheng, Fengkui Duan, Mei Zheng, Jihua TanAbstract:Abstract. The sampling artifacts (both positive and negative) and the influence of thermal-optical methods (both charring correction method and the peak inert mode temperature) on the split of organic carbon (OC) and elemental carbon (EC) were evaluated in Beijing. The positive sampling artifact constituted 10% and 23% of OC concentration determined by the bare quartz Filter during winter and summer, respectively. For summer samples, the adsorbed gaseous organics were found to continuously evolve off the Filter during the whole inert mode when analyzed by the IMPROVE-A temperature protocol. This may be due to the oxidation of the adsorbed organics during sampling (reaction artifact) which would increase their thermal stability. The Backup quartz approach was evaluated by a denuder-based method for assessing the positive artifact. The quartz-quartz (QBQ) in series method was demonstrated to be reliable, since all of the OC collected by QBQ was from originally gaseous organics. Negative artifact that could be adsorbed by quartz Filter was negligible. When the activated carbon impregnated glass fiber (CIG) Filter was used as the denuded Backup Filter, the denuder efficiency for removing gaseous organics that could be adsorbed by the CIG Filter was only about 30%. EC values were found to differ by a factor of about two depending on the charring correction method. Influence of the peak inert mode temperature was evaluated based on the summer samples. The EC value was found to continuously decrease with the peak inert mode temperature. Premature evolution of light absorbing carbon began when the peak inert mode temperature was increased from 580 to 650 °C; when further increased to 800 °C, the OC and EC split frequently occurred in the He mode, and the last OC peak was characterized by the overlapping of two separate peaks. The discrepancy between EC values defined by different temperature protocols was larger for Beijing carbonaceous aerosol compared with North America and Europe, perhaps due to the higher concentration of brown carbon in Beijing aerosol.
Juan C Cabada - One of the best experts on this subject based on the ideXlab platform.
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positive and negative artifacts in particulate organic carbon measurements with denuded and undenuded sampler configurations special issue of aerosol science and technology on findings from the fine particulate matter supersites program
Aerosol Science and Technology, 2004Co-Authors: R. Subramanian, Juan C Cabada, Andrey Khlystov, Allen L RobinsonAbstract:Measurement of ambient particulate organic carbon (POC) with quartz Filters is prone to positive and negative sampling artifacts. One approach for estimating these artifacts is to sample with a Backup quartz Filter placed behind either the main quartz Filter or a Teflon Filter in a parallel line. Another approach is to use a denuder to reduce the positive artifact in combination with a highly adsorbent Backup Filter to capture any negative artifact. Results obtained using both of these approaches in parallel for over one year in Pittsburgh, PA are presented in this article. A sampler using an activated carbon monolith denuder has been developed and tested extensively. Transmission losses were found to be negligible, and the denuder is on average 94% efficient at removing gas-phase organics. Denuder breakthrough is corrected for each run using a dynamic blank in parallel with the sample line. Comparisons with the dynamic blank indicate that the denuder almost eliminates the positive artifact on the quartz ...
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positive and negative artifacts in particulate organic carbon measurements with denuded and undenuded sampler configurations
Aerosol Science and Technology, 2004Co-Authors: R. Subramanian, Juan C Cabada, Andrey Khlystov, Allen L RobinsonAbstract:Measurement of ambient particulate organic carbon (POC) with quartz Filters is prone to positive and negative sampling artifacts. One approach for estimating these artifacts is to sample with a Backup quartz Filter placed behind either the main quartz Filter or a Teflon Filter in a parallel line. Another approach is to use a denuder to reduce the positive artifact in combination with a highly adsorbent Backup Filter to capture any negative artifact. Results obtained using both of these approaches in parallel for over one year in Pittsburgh, PA are presented in this article. A sampler using an activated carbon monolith denuder has been developed and tested extensively. Transmission losses were found to be negligible, and the denuder is on average 94% efficient at removing gas-phase organics. Denuder breakthrough is corrected for each run using a dynamic blank in parallel with the sample line. Comparisons with the dynamic blank indicate that the denuder almost eliminates the positive artifact on the quartz Filter. Negative artifact from the denuded quartz Filter is quantified using a carbon-impregnated glass fiber (CIG) Backup Filter and was found to be small, typically less than 10% of the ambient POC. Compared to the denuded sampler POC, 24 h bare quartz samples showed an almost constant positive artifact of 0.5 μg-C/m 3 for samples taken throughout the year-long study period. Sampling for shorter durations (4-6 h) resulted in a larger positive artifact. A quartz Filter behind a Teflon Filter (QBT) provides a consistent estimate of the positive artifact on the bare quartz Filter irrespective of sample duration, though it overcorrects for the positive artifact by 16-20% (attributed to particulate matter volatilizing off the upstream Teflon Filter). The quartz behind quartz (QBQ) approach provides a reasonable estimate of the positive artifact on the bare quartz Filter for the 24 h samples but not for the shorter samples. A slight seasonal variation is observed in the absolute value of the positive artifact, with higher values observed during the summer months.
