Severe haze events in the Indo-Gangetic Plain during post-monsoon: Synergetic effect of synoptic meteorology and crop residue burning emission.

In recent years, the frequent occurrence of haze events in the Indo-Gangetic Plain (IGP) during crop residue burning period has caused a serious reduction in atmospheric visibility and deteriorated air quality. The present study is carried out to investigate the haze event observed in IGP in Nov 2017 using ground-based observations, satellite data and synoptic meteorology to understand the possible factors responsible for haze formation. PM (particulate matter with aerodynamic diameter ≤ 2.5 μm) concentrations and Air Quality Index (AQI) at two sites (Agra and Delhi) situated in the central Indo-Gangetic Plain (CIGP) showed a sudden increase in PM concentrations and deteriorated air quality during 7-14 Nov. To monitor the variation of particulate matter (PM) in IGP, PM and PM (particulate matter with aerodynamic diameter ≤ 10 μm) concentrations were monitored at 22 stations in 12 cities of IGP during 1-15 Nov which also showed an increase in PM concentrations during haze event (7-14 Nov). Crop residue burning activities in north-west Indo-Gangetic Plain (NW-IGP) were observed during haze event. Synoptic weather conditions of IGP identified using geopotential height and wind at 700 hPa showed high-pressure systems and low winds in IGP favoring stagnant conditions during haze event. A detailed analysis of the variation of pollutants and meteorology was carried out at Agra. Ozone (O), carbon monoxide (CO), sulphur dioxide (SO) and nitrogen oxides (NO) showed higher concentrations during haze event along with lower temperature, low wind speed and high relative humidity. Aerosol ionic composition showed a higher contribution (~84%) of Cl, NO, SO and NH to total soluble ions suggesting secondary aerosol formation during haze event.