of lightning flashes to tropospheric NO2 release has been parameterized in several ways.

Satellites have allowed mapping of other important tropospheric trace gases and have been essential in solving the mystery of “polar sunrise” tropospheric ozone depletion. Since the 1980s, Arctic ozone has been known to disappear at the surface in the first few weeks of spring (Barrie et al. 1988). Organic halogen in some form was originally implicated, but the mechanisms were unclear until GOME detection of BrO (Richter et al. 1998, Hollwedel et al. 2004) in the first sunlit days (Figure 5.10). Reactions with highly saline surface associated with annual sea ice are now believed to be the source of airborne labile halogen compounds, which cause the surface ozone depletion (Rankin et al. 2002). The same phenomenon is detected at the edge of the Antarctic continent in austral spring.

For many years satellite measurements of stratospheric composition have advanced our understanding of the chemistry and dynamics of the region above the tropopause. As this region continues to respond to changes in halocarbon concentrations and global temperature, the measurements will continue to be vital to monitoring the health of the planet. Furthermore, the present growth of greenhouse gases leads not only to warming of the troposphere but also to cooling of the stratosphere, which is predicted to affect the rate and extent of ozone recovery. Continuation of the types of measurements described above is essential to monitoring the progress of ozone recovery and to further the understanding of the complex role of ozone in the climate system.

Although satellite measurements of tropospheric species are more difficult, rapid advances in measurements of tropospheric composition are providing insights into the sources, mechanisms, and transport of many species. Combined with data assimilation schemes, continuing tropospheric chemistry observations from satellites will lead to a better understanding of the factors affecting air quality and the ability to predict its interactions with the stratosphere and climate system.

FIGURE 5.10 BrO from GOME (April monthly averages, 1996-2002) SCIAMACHY (2003-2007). Total column BrO includes more or less uniform stratospheric and free tropospheric contributions. The majority signal is from boundary layer BrO that forms from heterogeneous processes associated with the annual sea ice (Richter et al. 1998, Hollwedel et al. 2004). SOURCE: Figure courtesy of A. Richter and J.P. Burrows, University of Bremen, Germany.

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