Investigation of membrane dryers and evaluation of a new ozone scrubbing material for the sampling of organosulphur compounds in air

Development of a humidity pretreatment method for the measurement of ozone in ambient air

A frost filter (FRF) was developed as a humidity pretreatment device (HPD) to improve the measurement of ambient ozone (O₃). The FRF was produced in a tube, which was supercooled by a thermoelectric cooling device based on the Peltier effect. The relative humidity (RH) of the air samples varied from 30% to 80% at 25 °C, and the O₃ concentration was set as 100 ppbv. Besides O₃, SO₂ at 150 ppbv was used for comparison. The density of the FRF was evaluated. Comparison studies on the humidity removal efficiencies and loss ratios of analytes among a FRF HPD, a short Nafion™ tube (NS), and a long Nafion™ tube (NL) HPDs were conducted. As results, the density of the FRF was dependent on the temperature at a fixed sampling flow rate. The outlet humidity of both the FRF and the NL HPDs were less than 8% RH at 25 °C. The mean concentrations of O₃ and SO₂ after the FRF HPD were similar to the initial concentrations at all humidity levels, whereas they were significantly different for both the NS and NL HPDs at higher humidity. This suggests that the FRF HPD is a reliable humidity pretreatment for O₃ measurements.

Effects of Water Removal Devices on Ambient Inorganic Air Pollutant Measurements

Water vapor is a pivotal obstacle when measuring ambient air pollutants. The effects of water vapor removal devices which are called KPASS (Key-compound PASSer) and Cooler. On the measurement of O₃, SO₂, and CO at ambient levels were investigated. Concentrations of O₃, SO₂, and CO were 100 ppb, 150 ppb, and 25 ppm, respectively. The amount of water vapor varied at different relative humidity levels of 30%, 50%, and 80% when the temperature was 25 °C and the pressure was 1 atm. Water vapor removal efficiencies and recovery rates of target gases were also determined. The KPASS showed a better performance than the Cooler device, removing 93.6% of water vapor and the Cooler removing 59.2%. In terms of recovery, the KPASS showed a better recovery of target gases than the Cooler. Consequently, it is suggested that the KPASS should be an alternative way to remove water vapor when measuring O₃, SO₂, and CO.

Extractive FTIR spectroscopy with cryogen-free low-temperature inert preconcentration for autonomous measurements of atmospheric organics: 1: Instrument development and preliminary performance

In collaboration with the Jefferson County Department of Health and the Environmental Protection Agency (EPA), the University of Alabama in Huntsville developed a novel sensor for detecting very low levels of volatile organic compounds (VOCs). This sensor uses a commercial Fourier-transform infrared (FTIR) spectrometer, a commercial long-path IR gas cell, a commercial acoustic Stirling cyrocooler, and a custom cryogen-free cryotrap to improve sensitivity in an autonomous system with on-board quality control and quality assurance. Laboratory and initial field results show this methodology is sensitive to and well-suited for a wide variety of VOC atmospheric research and monitoring applications, including EPA National Air Toxics Trends Stations and the National Core monitoring network.

Evaluation of single column trapping/separation and chemiluminescence detection for measurement of methanethiol and dimethyl sulfide from pig production

Reduced sulfur compounds are considered to be important odorants from pig production due to their low odor threshold values and low solubility in slurry. The objective of the present study was to investigate the use of a portable method with a single silica gel column for trapping/separation coupled with chemiluminescence detection (SCTS-CL) for measurement of methanethiol and dimethyl sulfide in sample air from pig production. Proton-transfer-reaction mass spectrometry (PTR-MS) was used to evaluate the trapping/separation. The silica gel column used for the SCTS-CL efficiently collected hydrogen sulfide, methanethiol and dimethyl sulfide. The measurement of methanethiol by SCTS-CL was clearly interfered by the high concentration of hydrogen sulfide found in pig production, and a removal of hydrogen sulfide was necessary to obtain reliable results. Air samples taken from a facility with growing-finishing pigs were analyzed by SCTS-CL, PTR-MS, and a gas chromatograph with sulfur chemiluminescence detection (GC-SCD) to evaluate the SCTS-CL. The difference between the concentrations of methanethiol and dimethyl sulfide measured with SCTS-CL, PTR-MS, and GC-SCD was below 10%. In conclusion, the SCTS-CL is a portable and low-cost alternative to the commercial methods that can be used to measure methanethiol and dimethyl sulfide in sample air from pig production.

A review of methods for the determination of reduced sulfur compounds (RSCs) in air

The importance of reduced sulfur compounds (RSCs) in air is well-known for its significant effect on global atmospheric chemistry and malodor and quality of life. In this review, methodological approaches commonly employed for the analysis of RSCs such as hydrogen sulfide, methane thiol, dimethyl sulfide, carbon disulfide, and dimethyl disulfide in air are described. To this end, we focus on gas chromatography (GC) because it is the most feasible, frequently used, and widely accepted approach for the analysis of RSC in air. The advantages and possible limitations related to sampling and/or preconcentration methods are also discussed. The relative performance of different GC-based detection methodologies is evaluated in terms of basic quality assurance. Some alternative methods (i.e., other than GC) that deal with the determination of RSCs in air matrices are also discussed briefly. Finally, this review addresses the methodological developments of RSC analysis by highlighting current limitations and future developments.

Occurrence and abatement of volatile sulfur compounds during biogas production

Volatile sulfur compounds (VSCs) in biogas originating from a biogas production plant and from a municipal sewage water treatment plant were identified. Samples were taken at various stages of the biogas-producing process, including upgrading the gas to vehicle-fuel quality. Solid-phase microextraction was used for preconcentration of the VSCs, which were subsequently analyzed using gas chromatography in combination with mass spectrometry. Other volatile organic compounds present also were identified. The most commonly occurring VSCs in the biogas were hydrogen sulfide, carbonyl sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide, and hydrogen sulfide was not always the most abundant sulfur (S) compound. Besides VSCs, oxygenated organic compounds were commonly present (e.g., ketones, alcohols, and esters). The effect of adding iron chloride to the biogas reactor on the occurrence of VSCs also was investigated. It was found that additions of 500-g/m3 substrate gave an optimal removal of VSCs. Also, the use of a prefermentation step could reduce the amount of VSCs formed in the biogas process. Moreover, in the carbon dioxide scrubber used for upgrading the gas, VSCs were removed efficiently, leaving traces (ppbv levels). The scrubber also removed other organic compounds.