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E. Linacre and B. Geerts |
10/'97 |
The upward transport of boundary-layer air within a deep convective cloud also lifts pollutants such as nitric and sulphuric-acid gases from the PBL into clouds, where they acidify the droplets or ice crystals, leading to acid rain some distance downwind (1).
In addition, deep convection mixes another pollutant, ozone, into the troposphere. Boundary-layer ozone is formed photochemically in areas of intense industrial, urban or biomass burning (Note 14.G). These processes generate the gases required to form ozone, i.e. the 'precursors'. These are nitrogen monoxide, hydrocarbons, and to a lesser extent carbon monoxide. Ozone concentrations in the upper troposphere have been found to increase following the outbreak of thunderstorms over areas rich in lower-tropospheric ozone in Brazil, the Atlantic and South Africa. Some ozone is also created by the ultraviolet radiation generated by lightning flashes. So it is difficult to quantify the effect of thunderstorms on lower-tropospheric ozone.
References
(1) Thompson, A.M., W-K Yao, K.E. Pickering, J.R. Scala, and J. Simpson, 1997. Tropical deep convection and ozone formation. Bull. Amer. Meteor. Soc, 78, 1043-53.