Estimating the influence of feasible interventions on potential decrease in PM2.5 concentrations in Delhi-NCR using a one-way nested regional and urban air quality modelling framework

PM_2.5 in Delhi is always related to alarmingly high premature mortality, and thus has become one of the biggest challenges which require immediate attention. Rapid urbanisation, industrialization and rising vehicle numbers have led to elevated concentrations of air pollutants in the city. The pollutants transported from neighbouring states have made the situation further complex. To control PM_2.5 concentrations government of India formulated and implements a Graded Response Action Plan (GRAP). However, it is pertinent to validate such air quality management plan which includes feasible interventions to effectively counter the increasing PM_2.5 and its associated effects. In this study, a one-way nested regional air quality model (WRF-CMAQ) along with an urban air quality model (USEPA'S AERMOD) with very fine scale emissions were used to identify the hotspots and estimate the potential decrease in concentrations using different feasible interventions during winter months of 2019. Analysis shows that the model meets the USEPA's criteria performance for PM_2.5 in 25 out of 31 observation stations. Unpaved road dust, industries and on-road vehicles are three major sources of PM_2.5 concentrations in the city. Several interventions were simulated to estimate the potential reduction in PM_2.5 concentrations during winter. For example, in the best feasible intervention, seven major emission hotspots which are influenced by industry, unpaved roads and heavy-duty vehicles were identified. Sensitivity analysis indicated that a domain wide reduction of 20% emissions from all sources along with 25% reduction in emissions from industries, unpaved road dust and heavy-duty vehicles in the seven emission hotspot regions can reduce PM_2.5 concentrations by approximately 18% in entire Delhi-NCR.