Methyl Bromide Emissions from a Covered Field: II. Volatilization

Abstract

An experiment to investigate the environmental fate and transport of methyl bromide in agricultural fields is described. The methyl bromide volatilization rate was determined as a function of time for conditions where methyl bromide was applied at a rate of 843 kg in a 3.5‐ha (i.e., 240 kg/ha) field covered with plastic at a depth of 25 cm. Three methods were used to estimate the methyl bromide volatilization rate, including: the aerodynamic, theoretical profile shape and integrated horizontal flux methods. The highest methyl bromide volatilization rates were at the beginning of the experiment. Within the first 24 h, approximately 36% of the applied methyl bromide mass was lost. Diurnally, the largest volatilization rates occurred during the day when temperatures were high and the atmosphere was unstable. Cooler temperatures, light winds, and neutral to stable atmospheric conditions were present at night, reducing the flux. The total emission calculated using these methods was found to be approximately 64% (±10%)of the applied mass. A mass balance was calculated using each flux estimation technique and several methods for analyzing the data. The average mass recovery using all the flux methods was 867 kg (±83 kg), which was 102.8% (±9.8%) of the applied mass (i.e., 843 kg). The range in the mass balance percent (i.e., percent of applied mass that is measured) is from 88 to 112%. The averaged mass balance percent for the aerodynamic method, which involved using the measured data directly, was approximately 100.8%. The total emission calculated using the aerodynamic method was found to be approximately 62% (± 11%) of the applied mass.

Measuring Herbicide Volatilization from Bare Soil

“…Similar observations were made by Yates et al (10) for methyl bromide emissions and by Majewski et al (11) for chlorpyrifos. The correspondence between the IHF and TPS volatilization rates suggest that these are a more accurate representation of the volatilization rate compared to the chamber method.…”

“…The TPS method has advantages in that the large fetch requirement is not necessary and only a single-height measurement of the concentration in air and wind speed is necessary. Numerous investigators (10)(11)(20)(21) have used the theoretical profile shape method, among others, to determine the rate of pesticide from field experiments. The pesticide volatilization rate is obtained from where average values of the wind speed, u j(Zinst) and triallate concentration in air, C h (Zinst) are obtained at the instrument height, Zinst.…”

“…Volatilization is an important route of dissipation for pesticides with large vapor pressures or, similarly, large Henry's Law constants (5,9,10). Volatilization has also been shown to be important for pesticides with low to moderate volatility (11)(12)(13).…”

Analytical solutions for the transport of volatile organic chemicals in unsaturated layered systems

“…Gas-phase transport and volatilization have been shown to be important processes affecting the environmental fate of volatile organic chemicals (VOC) [Jury et al, 1983;Taylor and Spencer, 1990]. For many VOCs, such as methyl bromide, 1,3-dichloropropene (1,3-D), methyl isothiocyanate, and methyl iodide, volatilization is one of the most important processes governing movement during agricultural use [Majewski et al, 1995;van den Berg et al, 1992van den Berg et al, , 1993Jin and Jury, 1996;Gan et al, 1996], accounting for up to 70% of the applied mass [Yates et al, 1996b]. Gas-phase transport is also very important in characterizing the production of climate-affecting gases such as CO2, NO, and N20 [Suarez, 1999;Healy et al, 1996;Jury et al, 1991].…”

Microbial Transformations at Aqueous-Solid Phase Interfaces: A Bioremediation Approach

“…Due to its gaseous nature it may have an effect on the stratospheric ozone layer [281,402,404]. After injection into soil for fumigation, methyl bromide rapidly diffuses through the soil pore space to the soil surface and then into the atmosphere [159,162,163,405,406]. Since a plastic sheet typically covers the soil surface, the rate of emission into the atmosphere depends upon the thickness and density of the plastic, if other conditions are the same [159,406].…”