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Home > By DEPARTMENTS > Green Operations > Standard Operating Procedures for Green and Sustainable Business Operations > Pollution Prevention > Pollution Prevention - P2

How Pesticides Affect Atmospheric Ozone in California

Scientific results of research into the environmental impacts of pesticides not previously tested.

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california precipitation landscape and solar solutions The Air Resources Board announces the release of the final report titled, "Investigation of Atmospheric Ozone Impacts of Selected Pesticides" .

Researchers at the UC-Riverside, were successful in reducing uncertainties in atmospheric impacts of many types of pesticide-related VOCs used in California. Quantitative estimates of ozone impacts were developed for most of the chemicals in the California pesticide emissions profile. In addition, relative PM impacts of these compounds were assessed. For more details and study results, the final report (139 pages) is available at

This project was supported by the Air Resources Board under contract number 04-334. Any opinions, findings, and conclusions or recommendations expressed in this report are those of the author(s) and do not necessarily reflect the views of the Board. (EXCERPT)

Introduction and Background

Pesticides are widely used in agricultural operations in California and in addition to their other environmental impacts they may also be emitted into the atmosphere and contribute to the formation of ground-level ozone. Because ground-level ozone continues to be a problem in many areas of California, the California Air Resources Board (ARB) and the California Department of Pesticide Regulation need a means to quantify the ozone impacts of pesticide compounds that are used in the state. Because VOCs can react in the atmospheres at different rates and with different mechanisms, the different types of VOCs can vary significantly in their effects on air quality. An ability to quantify the effects of emissions of different types of VOCs on ozone formation is useful for assessing relative ozone impacts of various emissions sources such as pesticide use, and for developing cost-effective ozone control strategies. The effect of a VOC on ozone formation in a particular environment can be measured by its “incremental reactivity”, which is defined as the amount of additional ozone formed when a small amount of the VOC is added to the environment, divided by the amount added. Although this can be measured in environmental chamber experiments, incremental reactivities in such experiment cannot be assumed to be the same as incremental reactivities in the atmosphere (Carter and Atkinson, 1989; Carter et al., 1995a). This is because it is not currently practical to duplicate in an experiment all the environmental factors that affect relative reactivities; and, even if it were, the results would only be applicable to a single type of environment. The only practical means to assess atmospheric reactivity, and how it varies among different environments, is to estimate its atmospheric ozone impacts using airshed models.

However, airshed model calculations are no more reliable than the chemical mechanisms upon which they are based. Although several chemical mechanisms are used in airshed modeling applications in the United States (Gery et al, 1989; Stockwell et al, 1990, 1997; Carter, 2000a,b), the SAPRC-99 mechanism (Carter, 2000a) is considered to represent the current state of the art for model simulations of ozone impacts of individual VOCs. This is because it is the only one of these mechanisms that is designed to separately represent the reactions of several hundreds of different types of VOCs, while most other mechanisms use a limited number of “lumped species” to represent a broad classes of compounds assumed to have similar reactivity. The only other currently available state of the art mechanism that can be used to asses impacts of multiple VOCs is the European “Master Chemical Mechanism” (MCM) (Jenkin et al, 1997, 2003; Saunders et al, 2003, MCM, 2004), which explicitly represents the tropospheric degradations of over 130 volatile organic compounds. However, this mechanism is not widely used in the United States because it is not compatible with the multi-cell grid models that are currently used for regulatory applications in this country. For that reason, most of the discussion and analysis in this report will focus on use of the current version of the SAPRC-99 mechanism.

While the initial atmospheric reaction rates for many VOCs are reasonably well known or at least can be estimated, for most VOCs the subsequent reactions of the radicals formed are complex and have uncertainties that can significantly affect predictions of atmospheric impacts. Laboratory studies can reduce these uncertainties, but for most VOCs they will not provide the needed information in the time frame required for current regulatory applications. For this reason, environmental chamber experiments and other experimental measurements of reactivity are necessary to test and verify the predictive capabilities of the chemical mechanisms used to calculate atmospheric reactivities. They provide the only means to assess as a whole all the many mechanistic factors that might affect reactivity, including the role of products or processes that cannot be studied directly using currently available techniques. Because of this, the ARB and others have funded programs of environmental chamber studies to provide data needed to reduce uncertainties in ozone impact assessments of the major classes of VOCs present in emissions, and the development of the SAPRC-99 is based extensively on these data.

Although progress has been made in developing methods to estimate and quantify relative ozone impacts of the major classes of VOCs present in vehicle emissions and solvents, but the ozone impacts of many of the compounds used in pesticides are either unknown or very uncertain. The VOCs present in pesticides used in California, and the extent of our knowledge and ability to represent their atmospheric ozone impacts, are discussed in the following section....(continued)

William P. L. Carter, and Irina L. Malkina
January 10, 2007
Center for Environmental Research and Technology
College of Engineering
University of California
Riverside, California 92521

Edited by Carolyn Allen, owner/editor of California Green Solutions
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