It has been known since the 17th century that air pollution can cause serious damage to vegetation, causing both visible blemishes on foliage and/or reductions in growth and crop yield. Research into this topic started in the late 19th century, initially in Germany, but followed rapidly by the UK, USA, Canada and elsewhere. Initially interest was centred on the traditional pollutants in the form of coal smoke and SO2, later it was realised that there were other phytotoxic pollutants present in the atmosphere. Thus in the period after World War II interest shifted to photochemical oxidants, particularly O3, formed as secondary pollutants resulting from complex atmospheric chemical reactions involving nitrogen oxides and volatile organic compounds under conditions of high temperature and sunlight. The recognition of O3 as a widespread pollutant, particularly in rural areas, occurred first in California, then elsewhere in North America, followed by Europe and Japan in the 1970s and much more recently in some parts of the developing world, although in the latter case the severity of the problem is largely unrecognised. Subsequently other pollutants became recognised as of major importance, notably NO2 and NH3 and their products. Widespread problems are not restricted to O3, because acid rain and total nitrogen deposition are known to cause large scale problems of acidification and eutrophication, respectively.

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