Analysis of the aerosol and the ozone observations at a southwest peninsular coastal station using microtops sunphotometer

Abstract

This study analyses the variations of aerosol optical depth, total column ozone and water vapour, measured by a Microtops-II (MICRO-processor based Total Ozone Portable Spectrometer) ozonometer/sunphotometer over a coastal station in southwest peninsular India, Kochi. Observations of ozone and aerosols are analysed for a period, May 2012 to May 2013. Satellite data sets available over the region are also analysed, and a comparison is made with the in situ data. Sunphotometer measured 1020 nm aerosol optical depth (AOD) shows a temporal variability with an increase in AOD during the summer (high value of 0.35 in May 2012) and fewer values near 0.2 during the winter and the post-monsoon seasons. Satellite observations also show a similar pattern of variability with high AOD during the summer. Water vapour is maximum (near 3.5 cm) during the pre-monsoon and the summer monsoon and minimum (below 2 cm in January 2013) during the winter. Ozone shows seasonal variability with a minimum concentration during the winter (230 Dobson Unit (DU) in January 2013) and maximum (280 DU in May 2012) during the summer. OMI (Ozone measuring Instrument) onboard Aura satellite overestimates the column ozone by 10 DU in comparison with the Microtops ozonometer. However, the sunphotometer and satellite observations show a similar pattern of temporal variability with a small difference in magnitude during certain months. The zonal ozone distribution shows a seasonal variability with a reverse gradient between the summer and the winter.