Fundamental basis of incremental reactivities of organics in ozone formation in VOC/NOₓ mixtures
The incremental reactivity of a particular organic species refers to the change in the ozone generated upon addition of a small amount of the organic to a complex organic/NOₓ, mixture undergoing photooxidation. It is known that the values of the incremental reactivities of organic species depend on the composition of the particular organic/NOₓ, mixture, the hydrocarbon-to-NOₓ, ratio, and other environmental conditions. Using a method that enables the assignment of the ozone produced in the photo-oxidation of a complex organic/NOₓ, mixture to each of the individual organics present, we show how the incremental ozone reactivity of any one organic species results from changes in the ozone generated by each of the organics present. Thus, we demonstrate explicitly the dependence of the incremental reactivity of each organic present on the nature of the organic/NOₓ, mixture. Calculations are presented using the SAPRC 90 chemical mechanism to explain the origin of the variation of incremental reactivities with initial hydrocarbon-to-NOₓ ratio.
This work was supported by the Coordinating Research Council and the National Renewable Energy Laboratory. The authors wish to acknowledge the referee for helpful comments.