Unusual diurnal variation in surface ozone observed after the 26 December 2004 tsunami over the rural site of Bay of Bengal, India

Abstract

Measurements of surface ozone (O₃) and nitrogen dioxide (NO₂) were studied from December 2004 to February 2005, covering the giant tsunami event on 26 December 2004 at Tranquebar (11° N, 79.9° E, 9 m) over the west coast of the Bay of Bengal, India. An unusual maximum O₃ concentration of 28 parts per billion by volume (ppbv) was observed in the morning and a minimum (16 ppbv) in the evening, indicating that pronounced chemical loss of O₃ occurred in the daytime after the tsunami over this coastal region. An increase in NO₂ concentration from 5.6 ppbv before the tsunami to 10.5 ppbv after the tsunami was observed in the daytime. The observed unusual diurnal changes in O₃ were not due to mass transport processes as the five-day back trajectories of air parcels transport before and after the tsunami remained unchanged. Similarly, meteorological and micrometeorological parameters were found to be normal before and after the tsunami. The unusual low O₃ level during the daytime was possibly due to prolonged excess emission of iodocarbons from the sea surface after the tsunami, which resulted in enhanced inorganic iodine (I _x ) concentration, leading to massive destruction of O₃. Similarly, unusually high O₃ levels during the night-time were possibly due to the intrusion of ozone-rich air after the tsunami from the free troposphere into the surface layer when the boundary layer height shrinks after midnight. The present work can be extended on a regional scale by incorporating modelling studies using recent remote sensing tools.

Acknowledgements

The authors are grateful to Prof. B.N. Goswami, Director, Indian Institute of Tropical Meteorology, Pune for his keen interest and kind support in carrying out this study. The internet-based NOAA HYSPLIT4 model is also acknowledged for tracing the back-trajectories over the study location.