On the nonlinearity of the tropospheric ozone production

The relationship of photochemical ozone production versus photochemical loss of an ozone precursor, that is, either NO x or nonmethane hydrocarbons (NMHCs), is studied by using a box model with particular emphasis on the nonlinearity problem of the relationship with respect to the concentration of the precursor. Model calculations indicate that the composition of NMHCs, the ratio of NMHCs to NO x , and the background concentrations of natural hydrocarbons, CO, and CH 4 all play important roles in determining the nonlinearity of O 3 production with respect to the loss of NO x . In addition, influences on the nonlinearity due to radical loss via reactions of HO 2 with RO 2 , exchanges between PAN and NO 2 , and inclusion of nighttime NO x loss processes are also investigated. Mechanisms that contribute to the nonlinearity are discussed. The nonlinear property of O 3 production versus loss of hydrocarbons and CO is different from that of NO x . When the sum of CO and all hydrocarbons, including CH 4 , natural NMHCs, and anthropogenic NMHCs, is used as the reference O 3 precursor, the nonlinearity is much less pronounced for ambient conditions usually found in rural air.