sphere. Depressed stratospheric ozone levels increase the flux of ultraviolet radiation to the troposphere; under conditions of high ambient NOx levels, this can increase tropospheric OH/HO2 and lead to increased tropospheric ozone production.
Within the troposphere, changes in the vertical temperature structure may affect the evolution and dynamics of the boundary layer and associated mixing processes that influence the dispersion and transport of air pollutants. Changes in the thermal structure of the troposphere and stratosphere may also affect the location of the tropopause and cross-tropopause transport of ozone and its precursors (IPCC, 1996). 1
Climate can affect the emissions of many biogenic compounds that play an influential role in tropospheric chemistry. For example, changes in temperature, soil moisture, and solar radiation can all lead to changes in the emission of ozone precursors such as isoprene and terpenes (Tingley et al., 1979; Lamb et al., 1985). Changes in temperature could also affect biological activity in the oceans and the resulting emissions of halogenated hydrocarbons such as methyl bromide, and sulfur compounds such as dimethyl sulfide.
1 This reference is to the IPCC's second assessment report. The IPCC's third assessment report is in press and will be available by late 2001. The Summary for Policymakers is currently available online at www.ipcc.ch .