Temperature inversions ground base

Studies were initiated in 1980 to determine drift differences between air and ground applications, using one orchard location. Two climatic parameters were used, the presence and absence of a temperature inversion at the time of application. In 1980, as shown in Table I, five applications of a carbaryl/captan mixture, were made and in 1981, three applications of captan. The selection of carbaryl and captan was based on the need for exposure studies due to the uncertain registration status of the pesticides at the time of the studies. 

One possible explanation is offered by the results of a recent laboratory study (21) which showed that the mechanism of the DMS oxidation by OH is a function of temperature and that the OH addition mechanism dominates over H abstraction at temperatures below 285 K. Hynes et al. (21) speculated that OH addition to DMS may lead primarily to the formation of MSA and that the yield of MSA may increase inversely with temperature. Temperatures during our flights were around + 12°C at ground level and decreased to about -23°C at the highest flight altitude. If MSA is indeed the dominant product of the OH addition reaction we may calculate a corresponding increase of the MSA yield from 50% to 76%, respectively, based on tne data of Hynes et al. (21). The... 

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