Influence of precursors and meteorology on ambient ozone over Indian western Himalayas

The surface ozone, oxides of nitrogen (NOx), and carbon monoxide (CO) were measured from 2015 to 2016 at a mountain site of the Indian western Himalayan region to study the temporal variability of ozone and the influence of precursor gases and meteorological parameters. Ozone showed anti-correlation with NOx and CO, indicating its photochemical origin. Significant variabilities were recorded in the annual mean values of these species during 2015 & 2016. The NO x showed ~60% fall in the mean annual concentration in 2016 compared to 2015, while a 17% increase in CO concentration and a 27% fall in mean ozone level were recorded in 2016. The observed variabilities could be due to change in wind speed, as a ~ 50% drop was recorded in the mean wind speed in 2016. The cluster analysis showed that the site received maximum air masses from the southeast to northwest directions where point sources are also located. The influence of biomass burning in Indo-Gangetic Plains (IGP) region, along with strong valley to mountain wind flow was also observed. The high values of NO x and CO observed in 2015 may be attributed to industrial activities and meteorology in this region.