Tropospheric Ozone And Food Productivity

Ozone is life threatening if found to be increasing near the earth’s surface as it is toxic to life when inhaled. Ozone not only damages airways, but also reduces crop yields as well if it increases beyond the threshold levels. Worries are mounting as India marks a rate of increase of around 1 percent each year. Anthropogenic sources of emissions are responsible for increase in surface ozone, which needs urgent control in the near future.

- Gufran Beig & Suvarna Tikle

The discovery of ozone (O3) in the troposphere was first made in the 1840’s. Consequently, an intensive study about its distribution was made in the latter part of the nineteenth century due to its supposed health giving properties as a germicide (Schönbein, 1840). The first classical explanation of ozone in the troposphere was that it was made in the stratosphere by direct photolysis of oxygen at wavelengths less than 242 nanometer.

Stratosphere is a layer above the earth’s surface, between approximately 15 and 50 km. It was believed that once the ozone is formed, it is transported downward from the stratosphere to the troposphere, to be ultimately destroyed in contact with the earth’s surface, particularly land surfaces. Although it became known that there was a direct source of ozone in the troposphere in photochemical smogs (first discovered in Los Angeles in the 1940s) it was not understood to be significant on a global scale.

This classical view of the origin of ozone in the troposphere underwent a complete turnaround during the course of time. It is now well documented that ozone is produced in two regions of the earth’s atmosphere. Most ozone—about 85-90 percent, resides in the stratosphere, commonly known as the ‘ozone layer’. The remaining ozone is in the lower regions of the atmosphere—the troposphere, which extends from the earth’s surface up to about 8 km near the poles and ~18 km near the equator. Ozone from both these regions have the same chemical composition (three oxygen atoms), but their effects on humans and other living things are very different. Based on their location ozone can either protect or harm life on earth. Low lying ozone is a pollutant and a key component of smog, a familiar problem in cities around the world. Higher than usual amounts of surface ozone is now increasingly being observed in rural areas as well.