Modeling smog chamber measurements of incremental reactivities of volatileorganic compounds

A series of experiments performed at the GM chamber facility provided usefu l data for the evaluation of two current chemical mechanisms used in airshe d models (SAPRC97 and SAPRC93 mechanisms) and a test of their predictions o f maximum incremental reactivities which describe the change in ozone cause d by adding a small amount of a compound to a polluted urban mixture under high-NOx conditions. In general, the SAPRC97 detailed mechanism performed w ell in simulating the Volatile organic compound (VOC) reactivity experiment s for most test species; however, it had a tendency to underpredict increme ntal reactivities. For base-case runs containing a nine-component urban-sur rogate mixture under high-NOx conditions, where maximum concentrations of e ither O-3 or the smog produced (SP = the initial NO oxidized plus the ozone produced) were not attained during a 12-h irradiation, the SAPRC97 perform ed well while the SAPRC93 underestimated SP or O-3 significantly. Under low -NOx conditions where SP or O-3 maximums were attained, the SAPRC97 as well as the SAPRC93 underpredicted SP or O-3 for runs containing the urban-surr ogate mixture. Simulations of incremental reactivity experiments and specia l chamber runs showed that the SAPRC97 mechanism performed poorly for n-oct ane and some aromatic isomers such as ethylbenzene and p-xylene, while it p erformed well for other aromatic isomers such as toluene, m-xylene and 1,3, 5-trimethylbenzene. Although, additional chamber data for aromatic isomers is needed to further clarify the parameterized chemical mechanisms for arom atic isomers, the newer SAPRC97 mechanism appears to be much improved over the order SAPRC93 mechanism for simulating aromatic chemistry. (C) 1999 Els evier Science Ltd. All rights reserved.