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Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings Publication Acceptance Date: 8/31/2007 Publication Date: 11/1/2007 Citation: Wang, D. 2007. Estimating Plastic Film Permeability Under Field Conditions. International Conference on Methyl Bromide Alternatives and Emissions Reductions. Interpretive Summary: Use of plastic films is one of the acceptable means of reducing fumigant VOC emissions. However, recent field studies have shown large variations in the effectiveness of various films in reducing gas emissions. Unlike in the laboratory, there are increasing concerns on how film permeability would change under field conditions. In this literature review study, transfer coefficients of soil fumigants through various plastic films were calculated using field data. On average, field based transfer coefficients of plastic films were greater than the laboratory measured values. Virtually impermeable films (VIF) such as Bromostop and Hytibar illustrated lower permeability values than the conventional polyethylene films. Increasing air temperature also caused film permeability to increase, and this was a primary factor attributing to the diurnal variation in field measured emission fluxes when a plastic cover was used. Field aging effect due to weathering of the plastic films did not impact permeability of chloropicrin or 1,3-dichloropropene. More field studies are needed to validate the true potential of the VIF films for significantly reducing fumigant emissions. Technical Abstract: Fumigant emission is an important air quality and human health concern. Plastic films are used to reduce emissions. Laboratory tests have shown large differences in permeability between various films, including the typical polyethylene films (PEs), virtually impermeable films (VIFs), and semi-impermeable films (SIFs). How film permeability would change under field conditions, when subjected to wear and tear during film placement, diurnal temperature changes, weathering from UV radiation, and variations in film thickness or inconsistency in gluing the joining film sheets, has been a main concern for field adoption. In this study, transfer coefficients of soil fumigants through various plastic films were estimated using field measured fumigant emission and gas concentration data reported in the literature. Results indicated that field extrapolated transfer coefficients of plastic films were two-to-ten times greater than the laboratory reported values. The VIF films, e.g., Bromostop and Hytibar showed consistently lower permeability (0.01 to 0.46 cm/h) to fumigant emissions than the PE films (0.82 to 9.13 cm/h). The actual transfer coefficient or permeability of a particular film to a fumigant chemical is also temperature dependent. Higher temperature caused film permeability to increase under both laboratory and field conditions. No significant field aging effect (an increase or a decrease in transfer coefficient) was found for the PE films against chloropicrin or 1,3-dichloropropene. VIFs such as Bromostop or Hytibar appear to be most promising options for plastic films that will provide consistent result in reducing fumigant emissions. |
