Applications of a regional chemical transport modeling system: Operational air quality forecast, Arctic spring near-surface ozone depletion, and continental outflow from North America

A regional chemical transport modeling system is developed for simulations of regional tropospheric chemistry and air quality. Meteorological data assimilation (forecast) is conducted using the NCAR/Penn State MM5 with NCEP reanalysis (NOAA AVN forecast). The regional chemistry and transport model simulates emission, transport, chemistry, and deposition processes. The lateral and upper boundary conditions of trace gases are specified using the results from the global GEOS-CHEM model. We will discuss three specific applications of the modeling system. First, daily 48-hour air quality forecast over the continental U.S. using this system has been operational since August, 2003. The forecast is available online at http://apollo.eas.gatech.edu/forecast.html. Second, we applied the modeling system to simulate surface O3 depletion catalyzed by bromine radicals at northern high latitudes in spring 2000. Satellite observations of BrO column by GOME were processed to specify the BrO concentrations in the lower troposphere. The model reproduces the observed ozone depletions. The model captures reasonably well the O3 depletion events observed at surface sites and by airborne in situ and DIAL instrument during the TOPSE experiments at northern high latitudes. Model results indicate that low O3 concentrations (<20 ppbv) near the surface cover ~60% of the northern high latitudes and that the depleted O3 concentrations (<10ppbv) cover ~20% of the region in April. The high BrO events tend to be large-scale and persistent (1-2 weeks). Lastly, we applied the modeling system to analyze column observations of NO2 by GOME and CO by MOPITT over North America and surrounding oceans for April. Transient enhancements in these measurements due to lightning NOx production or convective transport are examined. Evidence is found for lightning enhancements of NO2 over the continent and western North Atlantic and for convective transport enhancements of CO over the ocean. The two independent satellite measurements show consistent enhancements related to convective events.