Surface ozone measurements over Himalayan region and Delhi, North India

Measurement of surface ozone concentration has been made at two Himalayan stations, Mohal (during 19-26 May 1999 and 20-25 May 2000) and Kothi (during 27 May - 1 June 1999 and during 27-31 May 2000) and at Delhi (during 2-5 June 2000). The study reveals that the average concentration of ozone at Mohal was 19.1 ppb during May 1999 and 26.1 ppb during May 2000. At Kothi, the average concentrations were 42.7 ppb and 23.0 ppb, respectively, and it was 38.3 ppb at Delhi. Diurnal variation of ozone at Mohal indicated the dominance of photochemical production mechanisms in both the years. Lack of diurnal signal was seen at Kothi over the period of observation in 1999 which suggests that there may be transport of ozone in the region from upper level of the atmosphere. During observational period in 2000, a weak diurnal variation of O 3 was observed. It suggests that apart from photochemical production of ozone, some other mechanisms also contribute considerably to the observed O 3 concentration. At Delhi also, the diurnal variation showed the influence of temperature on O 3 production. Variation of O 3 concentration with O 3 concentration at previous hour, temperature, relative humidity at previous hour and wind speed at individual locations and years showed a good degree of association of O 3 with these parameters