Long Term Variation in the Vertical Distribution of Tropospheric Ozone in India

The seasonal, interannual and decadal variance in tropospheric ozone levels has been examined at three Indian cities: New Delhi, Pune and Thiruvananthapuram over the period from 1970 -2009 using ozonesonde data.It is observed that the tropospheric ozone levels have not changed monotonically in a single direction over these years and the observed changes in ozone levels is a mixture of countervailing signals from both natural and anthropogenic factors.In general, the ozone concentration in the lower troposphere at all these stations is high during winter, decreases throughout summer reaching a minimum during monsoon and increases thereafter during post monsoon.For most part of the year, the ozone concentration in the lower troposphere is highest at Delhi followed by Pune and lowest at Thiruvananthapuram, while in the middle and upper troposphere it is highest at Delhi followed by Thiruvananthapuram and lowest at Pune.Linear trend of ozone partial pressure at different altitudes indicates that the maximum decreasing trend occurs around 10-13 km altitude.This altitude is observed to increase with increase in latitude.