| The horizontal and vertical distributions of ozone and its precursors over North America during the spring and the summer are frequently determined by several factors: cloud convection, lightning NOX production, mixing depth, and long-range transport. The critical factors that contribute to the spatial distribution of air pollutants are studied using the Regional chEmical trAnsport Model (REAM) with diverse satellite measurements as well as in-situ surface and aircraft measurements. Among the space-borne measurements, GOME and OMI NO2 column measurements show enhanced lightning NO X over the continent and the western North Atlantic. Concurrent convective transport-causing CO column peaks and high CO enhancements in the upper troposphere (UT) over the ocean are shown from the modeling analysis of the CO column by MOPITT and UT CO by TES. Likewise, TOMS-SAGE II and OMI-MLS O3 column peaks and TES UT O3 enhancements due to convective outflow and lightning NOX are also observed. Lightning NOX production in REAM is much larger than that in GEOS-CHEM, resulting in better simulations of GOME NO2 columns over the western North Atlantic. Consequently, REAM simulates larger O3 increasing trends in better agreement with TOMS-SAGE II and OMI-MLS O3 columns over the southern United States and the western North Atlantic than GEOS-CHEM. Another factor, mixing depth, is a key parameter for the boundary layer structure of the model. Simulated spring to summer transitions of O3 and its precursors over North America indicate that the simulated boundary layer structure plays a key role in differentiating REAM from GEOS-CHEM. Large enhancements of columns and upper tropospheric O3 comparable to those over the eastern United States are found over the western North Atlantic in the satellite measurements and REAM simulations. The O3 enhancement region migrates northward from the spring to the summer. A model analysis indicates that the northward shift is driven by O3 in the stratospheric flux, convective outflow and production from lightning NOX. In addition, long-range transport affects the spatial distributions of air pollutants, particularly during the spring. During the late spring, large enhancements of NOX, PAN, O3, CO, CFCs, and Halon-1211 in UT are found over North America due to a surge of trans-Pacific pollutant transport from observations during the TOPSE 2000 experiment. The transition occurs later than that of the typical low-altitude trans-Pacific transport, which peaks around March or April.;Surface and aircraft measurements show a large amount of reactive nitrogen tracers over the Antarctic plateau during the summer. These enhanced measurements are investigated, and their photochemical impact is assessed by 1-D CTM and 3-D CTM, REAM. The 1-D model and REAM reasonably simulate the surface measurements of NO, HNO3, HNO4, and balloon NO measurements at the South Pole. However, compared with the Twin Otter NO measurements, REAM underestimates NO concentrations over plateau regions because parameterization based on surface measurements at the South Pole underestimates emissions in higher-elevation plateau regions. After all, around 50% of reactive nitrogen is scavenged by deposition, and the other is lost by transport. Thus, a shallow but highly active oxidizing canopy surrounds the Antarctic plateau due to snow NO X emissions. |
