Influence of uncertain reaction rates on ozone sensitivity to emissions |
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Authors: | Daniel S. Cohan Bonyoung Koo Greg Yarwood |
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Affiliation: | 1. Department of Geography and Resource Management, The Chinese University of Hong Kong, Sha Tin, N.T., Hong Kong;2. Institute of Environment, Energy and Sustainability, The Chinese University of Hong Kong, Sha Tin, N.T., Hong Kong;3. Stanley Ho Big Data Decision Analytics Research Centre, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong;4. Computational Exposure Division, National Exposure Research Laboratory, US Environmental Protection Agency, United States of America;5. The Jockey Club School of Public Health and Primary Care, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong |
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Abstract: | Air quality models rely upon simplified photochemical mechanisms to efficiently represent the thousands of chemical species that interact to form air pollution. Uncertainties in the chemical reaction rate constants and photolysis frequencies that comprise those mechanisms can generate uncertainty in the estimation of pollutant concentrations and their responsiveness to emission controls. A high-order sensitivity analysis technique is applied to quantify the extent to which reaction rate uncertainties influence estimates of ozone concentrations and their sensitivities to precursor emissions during an air pollution episode in Houston, Texas. Several reactions were found to have much larger proportional effects on ozone’s sensitivities to emissions than on its concentrations. In particular, uncertainties in photolysis frequencies and in the rate of reaction between NO2 and OH to form nitric acid can significantly influence the magnitude and sign of peak ozone sensitivity to nitrogen oxide (NOx) emissions. Ozone sensitivity to VOCs exhibits a much more muted response to uncertainties in the reaction rate constants and photolysis frequencies considered here. The results indicate the importance of accurate reaction rate constants to predicting the ozone impacts resulting from NOx emission controls. |
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