Modeling smog chamber measurements of incremental reactivities of volatile organic compounds

A series of experiments performed at the GM chamber facility provided useful data for the evaluation of two current chemical mechanisms used in airshed models (SAPRC97 and SAPRC93 mechanisms) and a test of their predictions of maximum incremental reactivities which describe the change in ozone caused by adding a small amount of a compound to a polluted urban mixture under high-NOx conditions. In general, the SAPRC97 detailed mechanism performed well in simulating the Volatile organic compound (VOC) reactivity experiments for most test species; however, it had a tendency to underpredict incremental reactivities. For base-case runs containing a nine-component urban-surrogate mixture under high-NOx conditions, where maximum concentrations of either 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 performed 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-surrogate mixture. Simulations of incremental reactivity experiments and special chamber runs showed that the SAPRC97 mechanism performed poorly for n-octane and some aromatic isomers such as ethylbenzene and p-xylene, while it performed 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 aromatic isomers, the newer SAPRC97 mechanism appears to be much improved over the order SAPRC93 mechanism for simulating aromatic chemistry. (C) 1999 Elsevier Science Ltd. All rights reserved.