Atmospheric Chemistry of Surface Ozone its Precursors Particulate Pollutants in Relation to Indicators of Climate Change in the Kullu Valley Northwestern Indian Himalaya

Abstract

Abstract newlineThe accumulation of gaseous and particulate matters on the elevated cum valley sites of Indian Himalaya has a considerable impact on Indian climate. Investigations have suggested that surface ozone, the third most important green house gas and particulate matter potentially may accelerate the seasonal warming. In view of the importance and sensitivity of gaseous and particulate pollutants aerosols over the northwestern Himalaya, the present study has its unique importance which has not been done earlier from this part of the country. Continuous measurements of surface ozone (O3) with its precursor NOx (NO+NO2) using online O3, NOx analyzers, black carbon aerosol (BCA) concentration using aethalometer and meteorological parameters using automatic wheather station (AWS) were carried out at Mohal (31.9°N, 77.12°E, 1154 m amsl), a semi-urban location in the Kullu valley in the northwestern part of the Indian Himalaya from January 2010 to December 2012. The concentration of respirable particulate matter below 10 µ (PM10) and fine particulate matter below 2.5 µ (PM2.5) in size were also measured with the help of respirable dust sampler (460 NL Envirotech) and fine dust sampler (550 APM Envirotech).The mean diurnal value of O3 showed a peak (68.6 ± 21.9 ppbv) in the late afternoon and a minimum (4.3 ± 0.8 ppbv) in the early morning hours. Seasonal variations in surface ozone show maximum concentration in the summer (61.2 ± 8.5 ppbv) followed by autumn (51.95 ± 9.5 ppbv). The hourly surface ozone concentration reaches sometime up to 126 ppbv in study site. Humans and vegetations are likely to be affected at elevated surface ozone concentration above 75 ppbv. O3 has an inverse relationship with its precursor NOx. The high NOx values were observed in the autumn (21.2 ± 5.2 ppbv) followed by winter (14.3 ± 9.5 ppbv). Seasonal variation in surface ozone and reasons for high O3 episodes during summer are associated with meteorological parameters such as the sunny weather, insolation, fire counts and