Impact of Extended Chemistry for Non-Methane Volatile Organic Compounds on Tropospheric Ozone and Implications for Radiative Forcing

Integrating a complicated photochemical scheme into a global climate model increases the CPU time needed for calculations. For this reason, a number of chemical species and their reactions are often simplified in global chemistry/transport models. To increase the accuracy and reduce the uncertainty in the models, it is essential that the simplified model provide the same results as up-to-date chemical mechanisms on a global scale. Here, we show an evaluation of extended chemistry for non-methane volatile organic compounds (NMVOC) on tropospheric ozone and the implications for the calculation of radiative forcing from 1890 to 1995 in a global climate model. The model is the newest version of CHASER developed at CCSR/NIES and subsequently modified at FRCGC. Simplified chemistry using lumped species has been compared to more complicated calculations using the extended photochemistry in which the species that are emitted into the model atmosphere are specified with more explicit surrogates. Deviations in the calculated abundances of O3 and the radiative forcing between the two simulations were within ~10% in most regions. The use of more efficient simplified chemical scheme is acceptable for global scale simulations of the radiative effects of tropospheric O3 changes in a GCM, since the differences between the simplified and extended simulations are small, especially relative to other uncertainties such as the quantification of major sources of O3 precursors.