Long-term trends in tropospheric ozone over the Indian tropical region

We report a statistical regression model analysis of long-term linear trends in the ozonesonde vertical profiles in the troposphere for the period 1972-2001 from the three tropical stations in tropical India. An analysis of tropospheric column ozone (TCO) data derived from ozonesonde and Nimbus7/Earth Probe -total ozone mapping spectrometer (TOMS) during the period 1979-2002 has also been done. There are no statistically significant trends over Trivandrum (8.3°N, 76.6°E, 61 m) but significant positive trend (within 2-sigma error) are found to occur in the lower troposphere over Pune (18.3°N, 73.5°E, 559 m) and throughout the entire troposphere over a heavily air-polluted urban center Delhi (28.4° N, 77.1° E, 216 m). However, over the last decade, variations in tropospheric ozone have become statistically insignificant even over Delhi in spite of increasing surface NOx concentrations. The TCO obtained by ozonesonde as well as TOMS satellite data over Trivandrum do not reveal any statistically significant trend