Global Modeling Studies of Potential Climate Change Effects on U.S. Air Quality—Part 1: How Well can PCM Drive the Chemical Transport Model?

Driven by NCAR-DOE Parallel Climate Model (PCM) meteorology, the global chemical transport model MOZART-2.4 (Model for OZone And Related chemical Tracers version 2.4) is used to simulate the global current and future summertime air quality, focusing on the continental U.S. It is shown here that MOZART-2.4 driven by the present-day PCM meteorology produces tropospheric ozone and precursors concentrations that are overall comparable to those driven by the NCEP/DOE AMIP II reanalysis (R-2). However, as compared with the R-2-driven run, the PCM-driven simulation yields higher NOx and ozone concentrations off the western coasts of the major continents and larger CO values over most of the globe. In North America, the main disagreement occurs in the areas with high anthropogenic emissions such as the New York area and California, where PCM tends to produce a photochemical environment that suppresses local air pollution. These disagreements due to PCM climate biases may have important consequences on the U.S. air quality study using a regional modeling system that requires the specification of lateral boundary conditions of the chemistry from the MOZART-2.4 output, especially the inflow CO, NOx and ozone background concentrations off the southwestern coast. In addition, the biofuels and biomass burning emissions of CO are scaled by a factor of 1.55 in order to comply with the IPCC (2001) budget analyses. A sensitivity experiment shows that this scaling has little impact on the MOZART-2.4 simulation of the CO, NOx and ozone concentrations outside the areas dominated by biofuels or biomass burning emissions.