Computer Simulation of the Chemistry of a Simple Analogue to the Sunlight-Irradiated Auto-Exhaust Polluted Atmosphere

Abstract

Computer simulations have been made of the chemistry of a simple analogue to the sunlight-irradiated, auto-exhaust polluted atmosphere: a mixture of 0.075 ppm NO, 0.025 ppm NO₂, 1.5 ppm CH₄, 10 ppm CO, 0.10 ppm trans-2-butene, 0.10 ppm CH₂O and 0.06 ppm CH₃CHO in air with a relative humidity of 50% (25°C). The relative importance towards attack on trans-2-butene of the various possible reactive intermediates has been calculated as a function of time. O(³P), O₃, HO₂ and HO all seem to be important during some stage of the reaction with trans-2-butene.

The question of which reactions trigger the NO to NO₂ conversion is considered by examining the relative importance of the several possible sources of the HO (or HO₂) radicals which initiate the olefin oxidation. In the simulated system in which the rate of HONO forming reaction is assumed to be zero, the major initial push to oxidize NO and the olefin comes from aldehyde photolyses. While in the system in which HONO is formed at an appreciable rate, its presence and subsequent photolysis enhances the initial rate of the smog forming reactions, although HONO is not a necessary component of the polluted atmosphere to account for the general features of the smog-forming reactions.

Key Words:

• photochemical smog
• photooxidation
• trans-2-butene
• aldehydes
• nitrogen oxides
• computer simulation
• reactive intermediates