Five years surface ozone behaviour in a semi-rural location at Mohal-Kullu in the north-western Himalaya, India

Abstract

Surface ozone is one of the most important Green House Gases (GHGs). Five years (2011–2015) measurements of surface ozone (O3) and one of its precursors- oxides of nitrogen (NOx) were carried out at a semi-rural location, Mohal (77.12°E, 31.91°N, 1154 m amsl) in the north-western Indian Himalaya. The concentration of O3, NO, NO2 and NOx was measured maximum 74.6 ± 23.2 ppb in 2013, 27.5 ± 7.5 ppb in 2013, 51.8 ± 13.2 ppb in 2013, and 60.8 ± 13.2 ppb in 2012, respectively. Seasonally, O3 concentration was highest during summer while lowest in monsoon. The O3 concentration shows unimodal peak while its precursors show bimodal peaks. A reasonable decrease in percent change was found in terms of O3 (-13), NO2 (-6), and NOx (-3) due to imposing regulations imposed by local government in compliance with the order of Hon’ble National Green Tribunal (NGT) of the country in 2015. However, NO (9) is increasing due to vehicular activities in the nearby area which is one of the famous tourist spots. Washout effect due to increasing rainfall by 8% might have also affected O3 concentrations. Biomass burning for heating and cooking purposes and forest fire for tender livestock forage and transported gaseous pollutants from the Middle East countries and Indo-Gangetic Plain (IGP) could be major contributors of surface ozone and its precursors. HYSPLIT air-mass back trajectories drawn for external ozone sources showed the maximum air masses reached the study location either with the western desert countries or IGP polluted regions.