Ozone (03) is a highly reactive gas composed of three oxygen atoms. It is both a natural and a man-made product that occurs in the Earth’s upper atmosphere (stratosphere) and lower atmosphere oxygen (troposphere). Depending on where it is in the atmosphere, ozone affects life on Earth in either good or bad ways. Formation of tropospheric and stratospheric ozone Tropospheric or ground-level ozone is formed primarily from photochemical reactions between two major classes of air pollutants, volatile organic compounds (VOCs) and nitrogen oxides (NOx). NOx and VOC break apart in the presence of intense sunlight and recombine into new structures, creating ozone. It is created by human activities as emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapor, and chemical solvents are some of the major sources of NOx and VOC. On the other hand, stratospheric ozone is formed naturally through the interaction of solar ultraviolet (UV) radiation with molecular oxygen (02). Solar ultraviolet radiation breaks apart one oxygen molecule (02) to produce two oxygen atoms (20) and each of these highly reactive atoms combines with an oxygen molecule to produce an ozone molecule (03). These reactions occur continually whenever solar ultraviolet radiation is present in the stratosphere. Role of tropospheric and stratospheric ozone The tropospheric ozone or bad ozone can trigger a variety of health problems including chest pain, coughing, and throat irritation. It is also a major component of urban smog, which can worsen bronchitis and emphysema, trigger asthma, and permanently damage lung tissue. Further, bad ozone also damages vegetation and ecosystems as it leads to reduced agricultural crop and commercial forest yields, reduced growth and survivability of tree seedlings, and increased susceptibility to diseases, pests, and other stresses such as harsh weather. Whereas, the stratospheric ozone absorbs a portion of UV (Ultra Violet) light called UVB from the sun, preventing it from reaching the planet’s surface. Thus, it protects from many harmful effects, including skin cancers, cataracts, and harm to some crops and marine life. But this good ozone is gradually being destroyed by man-made chemicals referred to as ozone-depleting substances (ODS), including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), etc.

Strategies to prevent the formation of tropospheric ozone.

• Fossil fuels & transport sector
  • Vapor recovery nozzles at the gasoline pumps to reduce refueling emissions.
  • Cleaner burning gasoline is reformulated through catalytic convertors to reduce VOC, NOx, etc.
  • Strict NOx emission limits for power plants and industrial combustion sources.
• Agriculture sector:
  • Apply intermittent aeration of continuously flooded rice fields.
  • Introduce selective breeding to reduce emission intensity and increase production.

• Waste management

• • Separate and treat biodegradable municipal waste, and turn it into compost or bioenergy.
  • Upgrade wastewater treatment with gas recovery and overflow control.
• Better Monitoring of Ozone mitigation initiatives such as that of long-range Transboundary Air Pollution through the implementation of the Gothenburg protocol and effective forecasting through SAFAR (System of Air Quality and Weather Forecasting).

The Government has further taken initiatives such as the National Clean Air Programme (NCAP), Graded Response Action Plan (GRAP), etc. to check ozone pollution and improve air quality. There is a need for the effective implementation of multi-faceted programs to cut NOx and VOC emissions from vehicles, industrial facilities, and electric utilities. Voluntary programs may also be started to encourage the communities to adopt practices, such as carpooling, to reduce harmful emissions.