506 Phys. Chem. Chem. Phys., 2011, 13, 506–517 This journal is c the Owner Societies 2011 Heterogeneous oxidation of the insecticide cypermethrin as thin film and airborne particles by hydroxyl radicals and ozone M. Segal-Rosenheimer,* R. Linker and Y. Dubowski Received 20th June 2010, Accepted 8th October 2010 DOI: 10.1039/c0cp00931h Evaluation of pesticides’ fate in the atmosphere is important in terms of environmental effects on non-target areas and risk assessments analysis. This evaluation is usually done in the laboratory using analytical grade materials and is then extrapolated to more realistic conditions. To assess the effect of the pesticide purity level (i.e. analytical vs. technical) and state (i.e. sorbed film vs. airborne particles), we have investigated the oxidation rates and products of technical grade cypermethrin as thin film and in its airborne form, and compared it with our former results for analytical grade material. Technical grade thin film kinetics for both ozone and OH radicals revealed reaction rates similar to the analytical material, implying that for these processes, the analytical grade can be used as a good proxy. Oxidation products, however, were slightly different with two additional condensed phase products: formanilide, N-phenyl and 2-biphenyl carboxylic acid, which were seen with the technical grade material only. OH experiments revealed spectral changes that suggest the immediate formation of surface products containing OH functionalities. For the ozonolysis studies of airborne material, a novel set-up was used, which included a long-path FTIR cell in conjugation with a Scanning Mobility Particle Sizer (SMPS) system. This set-up allowed monitoring of real-time reaction kinetics and product formation (gas and condensed phases) together with aerosol size distribution measurements. Similar condensed phase products were observed for airborne and thin film technical grade cypermethrin after ozonolysis. Additionally, CO, CO 2 and possibly acetaldehyde were identified as gaseous oxidation products in the aerosols experiments only. A kinetic model fitted to our experimental system enabled the identification of both primary and secondary products as well as extraction of a formation rate constant. Kinetic calculations (based on gaseous products formation rate) have revealed values similar to that of the thin film experiments. Interestingly, heterogeneous oxidation of cypermethrin was also found to generate ultra fine secondary organic aerosols. Again, no significant difference was observed between analytical and technical grade materials. However, particle size distribution was much broader when films were exposed to OH and ozone than to ozone alone. Introduction Pyrethroids are synthetic pyrethrins, which are gaining popu- larity as replacements for organophosphate insecticides due to their low avian and mammalian toxicity. As such, they are widely used both indoor and outdoor. Having low vapour pressures, these pesticides are likely to reside in the atmosphere in the airborne particulate phase or on stagnant surfaces, such as soil and leaves. 1 While adsorbed on atmospheric interfaces, these compounds interact with solar radiation and atmospheric oxidants, yielding products that may still pose health and environmental concerns (sometimes even more than the parent compound). 2,3 In order to model pesticides’ fate in the atmosphere or to conduct risk analysis regarding their influence on non-target communities, there is a need to quantitatively assess their degradation pathways and to acquire knowledge on their degradation products. Our former investigations were focused on the heterogeneous reactions of analytical grade a-cypermethrin, which is a common member of the pyrethroid family. Thin films of the pure material were tested under different ozone concentrations and under UV radiation (254 and 313 nm) at various atmospheric like environments. 2,3 However, a question arose whether laboratory analytical grade pesticides can serve as a good proxy for the real materials that are being used in the field (from hereafter referred to as technical grade pesticides). It is long established that pesticides have numerous formulations, which can greatly affect the behaviour of the active material in the field. 4 Also, as our former investigations were done on thin films, a question remained regarding the difference between the reactivity of thin films and airborne particles (i.e., submicron aerosols). The main goal of the present study was to gain quantitative insight regarding ozonolysis and OH oxidation of a technical grade cypermethrin, both as a film and in its aerosolized form, and to compare its oxidation rates to that of its analytical grade analogue. In general, quantitative information on hetero- geneous ozonolysis of pesticides is limited, and the knowledge Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, Technion City, 32000, Haifa, Israel. E-mail: segalm@tx.technion.ac.il; Fax: +972 4-822-8898; Tel: +972 4-829-2808 PAPER www.rsc.org/pccp | Physical Chemistry Chemical Physics Downloaded by Technion - Israel Institute of Technology on 24 October 2012 Published on 08 November 2010 on http://pubs.rsc.org | doi:10.1039/C0CP00931H View Online / Journal Homepage / Table of Contents for this issue