Smog chamber studies of ozone formation potentials for isopentane

The incremental reactivity and ozone formation potential of isopentane have been studied with chamber experiments and computer simulations. The chemical mechanism used in the computer simulations is an isopentane sub-mechanism from the Master Chemical Mechanism (MCM). The results from the chamber experiments suggest that the MCM can well simulate i-C₅H₁₂-NO _x chamber experiments. The heterogeneous reaction of NO₂ and water is an important source for OH radicals in the chamber experiments. The photolysis of HONO is responsible for the initiation of isopentane in photochemical reactions. The reaction rate constant for NO₂ → HONO was determined to be 3.9×10⁻⁴−5.9×10⁻³ min⁻¹ by conducting 3 sets of CO-NO _x -air irradiations. 5 sets of isopentane-NO _x irradiations under different conditions were performed in our chamber. Compared with the experiment with a low relative humidity (RH), an increase in RH can increase the reaction rate of NO₂ with H₂O, so that the peak ozone occurs earlier. When isopentane is predominant over NO _x , the peak ozone concentration is largely dependent on NO _x concentrations.