Assessing solvent impacts on ozone and VOC reactivity

As seen in Table 17.4.1, box model (single cell) simulations designed to represent summertime conditions in Los Angeles, California indicate that the amount of carbon associated with each class of compoimd only roughly corresponds to the amount of ozone formed from those compoxmds. Methane, which reacts veiy slowly but comprises most of the carbon, contributes httle to ozone formation. Alkenes and aromatics are only a small part of the total carbon, but lead to much of the ozone formation. 

Compound Class Percent of carbon in each specified class Percent of ozone due to specified organic class 

Two methods are generally employed to quantify the role pollutants play in forming ozone experimental and computational. Both types of estimation approaches have their limitations. In the case of physical experiments, it is difficult to fully simulate ambient conditions, so the results do not have general applicability. In the case of computational approaches, uncertainties and approximations in the model for airshed conditions, in its formulation, and in the chemical mechanism cause uncertainties in the predicted ozone impacts. For these reasons, modeling predictions and experimental measurements are used together. 

Given the limitations of physical experiments to simulate atmospheric conditions, computer models have been developed to assess the impact of emissions on ozone. These models, called airshed models, are computerized representations of the atmospheric processes responsible for air pollution, and are core to air quality management. They have been applied in two fashions to assess how solvents affect ozone. One approach is to conduct a number of simulations with varying levels of solvent emissions. The second approach is to evaluate individual compounds and then calculate the incremental reactivity of solvent mix-tures.  

While the types of simulations conducted by Derwent and Pearson are important to understanding the net effect of solvent emissions on ozone, there is an unanswered associated and important question, that being which specific solvents have the greatest impacts. 

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