Submitted to: Atmospheric Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2011
Publication Date: 6/3/2011
Publication URL: http://dx.doi.org/10.1016/j.atmosenv.2011.04.075
Citation: Gao, S., Pflaum, T.J., Qin, R. 2011. Trapping Efficiency of 1,3-Dichloropropene Isomers by XAD-4 Sorbent Tubes for Air Sampling. Atmospheric Environment. 45: 4322-4327. Interpretive Summary: Accurate measurements of fumigant emissions are important in determining the impact of soil fumigation on the environment. Emission monitoring often involves the use of sampling tubes filled with sorbents to trap fumigants from gas samples. As alternative fumigants to methyl bromide, 1,3-dichloropropene (1,3-D) and chloropicrin (CP) are being increasingly used in combination to maximize pest control efficacy. Two types of sorbent materials (charcoal and XAD-4) have been used for independent trapping of 1,3-D and CP resulting in twice the number of samples, doubles the amount of work, and higher material costs in comparison with a single sampling tube if used for both fumigants. As an effective material for adsorbing CP, XAD-4 was tested in this study for its trapping efficiency of both cis- and trans- 1,3-D isomers at different flow rates (100-1000 ml/min) and sampling time periods (10-360 min) with varying loading amounts (up to 3.0 mg). The results indicate that small XAD-4 (120 mg) sorbent tubes can effectively trap 1,3-D isomers from soil-gas and emission sampling at any flow rate during a short sampling time period (<30 min). Longer sampling time resulted in significant breakthrough from small XAD-4 sorbent tubes. Large XAD-4 (600 mg) sorbent tubes should be used for extended sampling time periods at low flow rates (100 ml/min) as no breakthrough was found up to 6 h. However, at high flow rates (1000 ml/min), significant breakthrough was observed from large XAD-4 tubes in laboratory tests, suggesting that short sampling time intervals and/or use of back-up tubes are preferred in field sampling regimes to avoid the potential high loss of fumigants from the sampling tubes that may result in underestimating the amount of fumigants in natural samples. This research provides an efficient sampling method for monitoring both 1,3-D and CP emissions or concentrations in air/gas samples.
Technical Abstract: Emission monitoring is necessary to evaluate the impact of air pollutants such as soil fumigants on the environment. Quantifying fumigant emissions often involves the use of air sampling tubes filled with sorbents to trap fumigants. 1,3-dichloropropene (1,3-D) and chloropicrin (CP) are being increasingly used in combination in soil fumigation since the phase-out of methyl bromide. Charcoal and XAD-4 resins are used for trapping 1,3-D, and CP, respectively. If one sampling tube can trap both chemicals, the number of samples, the amount of work, and associated costs can be significantly reduced. The objective of this research was to determine the efficiency of XAD-4 sorbent tubes for trapping cis- and trans-1,3-D isomers as a function of flow rate (100–1000 ml/min) and sampling time period (10 – 360 min). The results show that XAD-4 can trap 1,3-D isomers as efficiently as charcoal and breakthrough occurs depending on the amount of sorbent materials in a tube, fumigant amount, flow rate and sampling time period. No significant breakthrough was observed from either small (120 mg) or large (600 mg) XAD-4 sorbent tubes during short sampling time periods (<30 min) at any flow rate. For longer sampling (3-6 h) at low flow rates (100 ml/min), breakthrough (> 50%) was observed from the small tubes during a 3 h sampling period; but no breakthrough was observed from the large XAD-4 tubes up to the 6 h sampling period when 3.0 mg 1,3-D isomers were tested. At high flow rates (1000 ml/min) during a 3 h laboratory test, however, significant breakthrough was observed from large XAD-4 sorbent tubes suggesting that short sampling time intervals and/or back-up tubes are preferred to avoid potential breakthrough of fumigants from the sampling tubes that can result in underestimating fumigant emissions or concentrations in gas samples.