A photochemical kinetics mechanism for urban and regional scale computer modeling

A new chemical kinetics mechanism for simulating urban and regional photochemistry has been developed and evaluated. The mechanism, called the Carbon Bond Mechanism IV (CBM‐IV), was derived by condensing a detailed mechanism that included the most recent kinetic, mechanistic, and photolytic information. The CBM‐IV contains extensive improvements to earlier carbon bond mechanisms in the chemical representations of aromatics, biogenic hydrocarbons, peroxyacetyl nitrates, and formaldehyde. The performance of the CBM‐IV was evaluated against data from 170 experiments conducted in three different smog chambers. These experiments included NO x ‐air irradiations of individual organic compounds as well as a number of simple and complex organic mixtures. The results of the evaluation indicate substantial improvement in the ability of the CBM‐IV to simulate aromatic and isoprene systems with average overcalculation of ozone concentrations of 1% for the aromatic simulations and 6% for the isoprene simulations. The mechanism also performed well in simulating organic mixture experiments. Maximum ozone concentrations calculated for 68 of these experiments were approximately 2% greater than the observed values while formaldehyde values were low by 9%.