Short chimneys and, later, tall smokestacks have dispersed emissions across our landscapes in ever-widening spheres of influence, to the point where anthropogenic air pollutants today cover broad regions in developing and developed countries across the globe. Scientific study of the impact of these emissions on plants has extended beyond the dramatic local-point source problem to current major programs investigating effects of air pollutants on regional ecosystems. Research on air pollutants and their effects on plant life has encompassed many disciplines, thousands of research reports, and many books and symposium volumes. The policy issues surrounding this topic are quite distinct from the more broadly ranging scientific issues, including the study of physiological mechanisms, population consequences, epidemiology and whole-system function. Resolving the scientific issues at all these levels will require many years and probably a new approach to the manner in which we structure scientific disciplines to tackle interdisciplinary problems.
Ozone is probably the most damaging regional-scale air pollutant.
It is a secondary pollutant formed by the action of sunlight on various products of fuel combustion, such as nitrogen oxides and hydrocarbons. Ozone currently is the only regionally dispersed air pollutant that has been shown conclusively to damage crops and forests. SO2 is a primary pollutant, in and of itself toxic. It is widespread and damages agricultural crops and forests in industrialized countries. Gaseous air pollutants impact virtually all aspects of plant growth and development, either directly or indirectly.