Evolution and mitigation of vehicular emissions due to India's Bharat Stage Emission Standards – A case study from Delhi

Abstract

Vehicular emissions are the major contributors of particulate matter and ozone pollution, which has a greater negative impact on human health, climate and vegetation. Bharat Stage emission standards (BSES) are implemented in India to reduce vehicular emissions and there are several stages of BS norms (BS–I, BS-II, BS-III, BS-IV and BS-VI) proposed since 2000. Currently BS-VI emission norms are implemented nationwide from 2020 onwards. The BS standards came into force in prior advance in Delhi region compared to the other cities. Hence, the current study presents an introspection of the impact of several stages of BS norms in reducing the vehicular emissions in Delhi. The impact is studied through the survival fraction of the vehicles in use with different norms, the fleet average emission factors and the fuel consumption for the years 2012–2022. The analysis shows that the emissions from light-duty vehicles (LDV) are significantly higher than the emissions from heavy-duty vehicles (HDV). In the 2017–2022 age group, the PM2.5 and VOC emissions showed a gradual decrease when compared to the 2012–2017 age group, whereas the CO, NOx, PM10 and BC emissions were fluctuating. Overall, in the case of LDV, except for NOx, all the emissions are controlled as an impact of different stages of BS norms and in the case of HDV almost all the pollutants are regulated. The NOx emissions show a positive correlation with vehicular population and the correlation has not changed with the different norms. Though the NOx emission limits are regulated tightly at each stage of the norms, the increase in NOx emissions is unavoidable. This is due to the discrepancy between real-world conditions and laboratory testing. Enforcing BS-VI standards is expected to eliminate this discrepancy and the advanced aftertreatment technologies adopted in BS-VI engines should interact in a balanced way such that the control of one pollutant should minimize the emission of other pollutants.