Surface ozone measurements at tropical rural coastal station Tranquebar, India

Abstract

Abstract Surface ozone (O3) has been measured at Tranquebar (11°N, 79.9°E), a tropical rural coastal site on the east coast (the Bay of Bengal) of southeast India, during the period from May 1997 to October 2000. The measurements have shown that there exists a significant diurnal cycle/oscillation of average O3 with a maximum concentrations (33±4 ppbv) in the afternoon and average minimum O3 concentrations (11±2 ppbv) at sunrise with 1σ standard deviation. Further, O3 measurements have also shown that average higher concentrations (23±9 ppbv) in May and lower concentrations (17±7 ppbv) in October at this site. The reason for this high O3 in May (low O3 in October) is mainly due to active (inactive) photochemical production mechanism along with favourable (unfavourable) meteorological conditions and the related increasing (decreasing) precursors concentration. The increase in O3 is attributed to the increase in NOx and other O3 precursor emissions by different sources in the proximity of this site. The daytime and nighttime average O3 concentration are 30±3 and 13±2 ppbv with 1σ standard deviation. It is important to note here that, average O3 concentration (21±8 ppbv) in January at Tranquebar appears to be quite low as compared to the O3 concentration over the inland sites, whereas average O3 concentration (23±9 ppbv) in May is more or less in the same range.