Abstract
This paper presents the first observational results from an Indian station on the long-term changes in surface ozone (O3)-a major environmental pollutant and green house gas-over a period of about 40years. It is based on the in situ measurements carried out during 1973-1975, 1983-1985, 1997-1998 and 2004-2014 at the tropical coastal station, Thiruvananthapuram. From 1973 to 1997, surface O3 shows a slow increase of ~ 0.1ppbyear-1 and a faster increase of 0.4ppbyear-1 afterwards till 2009 after which it showed a levelling off till 2012 followed by a minor decrease. The highest rate of increase is observed during 2005 to 2009 (2ppbyear-1), and the overall increase from 1973 to 2012 is ~ 10ppb. The increase in day time O3 (peak O3) is estimated as 0.42ppbyear-1 during 1997-2012 and 2.93ppbyear-1 during 2006-2012. Interestingly, the long-term trend in O3 showed seasonal dependence which is more pronounced during O3 peaking seasons (winter/summer). The observed trends were analysed in the light of the changes in NO2, a major outcome of anthropogenic activities and methane which has both natural and anthropogenic sources and also meteorological parameters. Surface O3 and NO x exhibited positive association, but with varying rate of increase of O3 for NO x < 4 and > 4ppb. Methane, a precursor of O3 also showed increase in tune with O3. Unlike many other high-latitude locations, meteorology plays a significant role in the long-term trends in O3 at this tropical site with water vapour abundance and strong solar irradiance which favour photochemistry. A comparison with the corresponding changes in the satellite-retrieved tropospheric column O3 (TCO) also showed an increase of 0.03DUyear-1 during 1996-2005 which enhanced to 0.12DUyear-1 after 2005. Both surface O3 and satellite-retrieved TCO were positively correlated with daily maximum temperature, increasing at the rate of 1.54ppb°C-1 and 1.9DU°C-1, respectively, on yearly basis. Surface O3 is found to be negatively correlated with water vapour content (ρv) at this tropical site, but at higher levels of ρv, O3 shows a positive trend.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
