Thunderstorm induced changes in near-surface O3, NOx and CH4 and associated boundary layer meteorology over a tropical coastal station

Abstract

The paper presents four cases of the response of near-surface O3, NOx and CH4 to thunderstorm activity at a tropical coastal site in India, occurred during pre-monsoon and post-monsoon seasons. The associated changes in boundary layer meteorology in terms of temperature, relative humidity (RH), wind and boundary layer height (BLH) are also examined. The meteorological parameters like temperature and RH respond very fast depicting changes during the initial phase of the thunderstorm activity, whereas a delayed response is observed in the wind direction (changing from the sea breeze to land breeze) and collapse of the BLH (1–1:30 h delay) at the mature phase of the activity. Associated with the thunderstorm activity, significant changes were observed in the mixing ratios of the near-surface O3, NOx and CH4. An increase in NOx (5.2–8.7 ppbv) and CH4 (36.7–134.6 ppbv) and reduction in O3 (9.9–18.8 ppbv) were recorded at the mature phase of the thunderstorm. The rise in NOx is attributed to the combined effect of thunderstorm activity and wind reversal whereas that in CH4 is attributed to the wind reversal and associated change in air mass. A post activity increase is observed in mixing ratio of O3 in all the four cases. This is attributed to the downdrafts characteristic of the dissipation phase of thunderstorm activity which brings in O3 rich upper air down.