Determination of the Atmospheric Volatility of Pesticides using Chemical Ionisation Mass Spectrometry

Abstract. Pesticides have been found to be transported through the atmosphere away from fields on application. A key indicator of a pesticide’s likelihood to reside in the atmosphere is its vapour pressure. Within this study we evaluate a novel method, the Filter Inlet for Gases and AEROsols (FIGAERO) coupled with a chemical ionisation mass spectrometer using a set of calibration compounds, poly-ethylene glycols (PEGs). Two methods of compound delivery onto the filter have been tested: atomisation and syringe deposition. Delivery results are consistent with previous studies, highlighting the lack of suitability of the syringe method. The successful calibration using the atomisation method was then used to determine the vapour pressure of 6 pesticides. This is the first-time particle phase pesticides have been measured with online mass spectrometry. The pesticides have then been compared to widely accepted standard literature values used in industry as well as values determined by a common environmental model also used in industry to give an indication of pesticide volatilities. Results showed that measurements from the FIGAERO-CIMS were consistent with reported literature values for some compounds, others differed by up to 2 orders of magnitude. Determinations of Dicamba, MCPA and MCPP volatility using the FIGAERO-CIMS showed them to be semi-volatile in agreement with literature values to be within an order of magnitude. Mesostrione exhibited the largest difference in volatility with the FIGAERO-CIMS measuring a low volatility of 4.12x10^-8 Pa at 298 K (compared to a literature value of 5.7x10^-6 Pa). The difference for 2,4-D of one order of magnitude perhaps can be explained by the smaller particles deposited on the FIGAERO filter compared to the aerosolised PEG calibration particles, leading to evaporation at lower Tmax values and a lower measured vapour pressure. The atmospheric implications of the pesticide volatilities are also discussed. A pesticide’s volatility is often a key indicator of the likelihood of the potential for short- or long-range transport occurring, thus determining a pesticide’s fate in the atmosphere and potential for environmental pollution from transportation in the air.