Variability of Ozone and Related Trace Gases Over India

Abstract

Ozone plays key roles in atmospheric chemistry, radiation balance, and air quality, including human health. In this chapter, an analysis was made to document the variability and changes in ozone and related trace gases over India. The analysis of the total ozone data up to 1996 at six sites including Ahmedabad shows increasing trend at all the sites except at Varanasi, where a decreasing trend was found (Chakrabarty et al. in J. Geophys. Res, 103:19245–19249, 1998). The rates of increase in ozone during this period were found to be 1.98, 2.33, 1.85, and 0.68 % per decade at Kodaikanal, Ahmedabad, New Delhi, and Srinagar, respectively, while rate of decrease in ozone at Varanasi is 1.02 % per decade. Ozonesonde data (1972–2001), Pune and Trivandrum, show statistically insignificant trends over Trivandrum. But the trend over Pune is close to statistical significance at 9.7 ± 6.1 % per year in the planetary boundary layer and somewhat insignificant above 600 hPa. A comparison of surface ozone observations at Ahmedabad during 1954–55 and 1991–93 show increase of 1.45 % year−1. These observations also show change in seasonal variations with maximum ozone in winter–spring during the 1950s, while maximum ozone has been in autumn–winter during the 1990s. Surface ozone observations made in Delhi show positive trends in daily maximum and daytime (1000–1700 h) ozone levels with a rate of about 1.7 (±0.7) and 1.3 (±0.6) ppbv year−1, during 1997–2004, respectively.