OFF - TARGET DRIFT OF MCPA : “ REAL - TIME ” AIR SAMPLING bY

. The drift of MCPA downwind of an aerial application was measured using short air sampling intervals in an attempt to estimate “real-time” concentrations. Prior drift studies examined deposition patterns or measured air concentrations downwind of pesticide applications using long sampling intervals (1 to 24 hours). This preliminary study was designed to determine: 1) the Eeasibility of “real-t ime” sampling and 2) iE these “real-time” concentrations were signiffcantly different from long-term concentrations. At present, no apparatus measures instantaneous pesticide concentrations in air, therefore conventional air sampling equipment operated at 5-minute intervals was employed to estimate “real-time” concentrations. High and low volume air samplers were employed, with high volume samplers yielding more consistent results. Concentrations as highas 52.30, 30.46 and 31.10 pgg/m3 were measured at 25, 50 and 100 m downwind of the application, respectively, using “real-time” sampling techniques. An analysis of variance indicated a significant linear decline in air concentrations with distance Erom the field and significantly higher concentrations from high VS. low volume samplers. A polynomial regression of the form: concentration = 693 551(log distance) + 114(log distanceJ2 best described the relationship between air concentration and distance downwind. Comparisons between “real-time” and long-term concentrations were confounded by a marked change in wind direction during application therefore results for this objective were not conclusive. Another field trial will be conducted to determine if “real-time’ and long-term concentrations are signiftcantly different.