Ozone is found in two regions of the Earth's atmosphere - at ground level and in the upper regions of the atmosphere. Both types of ozone have the same chemical composition (O3). While upper atmospheric ozone protects the earth from the sun's harmful rays, ground level ozone is the main component of photochemical smog. Troposheric, or ground level ozone, is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC). Ozone is likely to reach unhealthy levels on hot sunny days in urban environments. Ozone can also be transported long distances by wind. For this reason, even rural areas can experience high ozone levels. This book mainly presents the observational studies on diurnal and seasonal variation of surface ozone and its precursors at semi-arid rural site, Anantapur (India). The measured data has been compared and validated with satellite data products.