The increase in tropospheric ozone has been identified to be a serious and critical cause of concern world over. Inter-Governmental Panel for climate change (IPCC) and World Meteorological Organization (WMO) assessment reports have predicted large increases in tropospheric ozone (O3) resulting from the emissions of O3 precursors. Ground level concentrations of O3 have been increasing steadily since the industrial revolution. Ozone concentration has risen by 1-2% per year in the industrialized countries of the northern hemisphere. Most of the countries of western Europe, eastern and mid-western region of USA and eastern Asia are found to show the highest background concentrations of O3. Most developing countries are facing increasingly severe air pollution problems due to recent emphasis on economic liberalization leading to rapid increases in industrialization and urbanization. Tropospheric O3 is one of the secondary air pollutants, predominantly formed by photochemical reactions involving precursors like nitrogen oxides (NOx) and volatile organic compounds (VOCs) generated by anthropogenic activities. In polluted air masses, production of Nitrogen dioxide (NO2) takes place by reaction of NO with HO2 and RO2 and then photolysis of NO2 in the presence of strong solar radiation (l< 424nm) releases atomic oxygen, which combines with molecular Oxygen (O2) to form O3. In the free troposphere, O3 formation also depends on photochemical reaction of methane, carbon monoxide and non-methane organic compounds with O2. Tropospheric O3 concentration also depends upon the stratospheric-tropospheric exchange processes.

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