Four-year assessment of ambient particulate matter and trace gases in the Delhi-NCR region of India

A key challenge in controlling Delhi's air quality is a lack of clear understanding of the impacts of emissions from the surrounding National Capital Region (NCR). Our objectives are to understand the limitations of publicly available data, its utility to determine pollution sources across Delhi-NCR and establish seasonal profiles of chemically active trace gases. We obtained the spatiotemporal characteristics of daily-averaged particulate matter (PM₁₀ and PM_2.5) and trace gases (NO_X, O₃, SO₂, and CO) within a network of 12 air quality monitoring stations located over 2000 km² across Delhi-NCR from January 2014 to December 2017. The highest concentrations of pollutants, except O₃, were found at Anand Vihar compared with lowest at Panchkula. A high homogeneity in PM_2.5 was observed among Delhi sites as opposed to a high spatial divergence between Delhi and NCR sites. The bivariate polar plots and k-means clustering showed that PM_2.5 and PM₁₀ concentrations are dominated by local sources for all monitoring sites across Delhi-NCR. A consequence of the dominance of local source contributions to measured concentrations, except to one site remote from Delhi, is that it is not possible to evaluate the influence of regional pollution transport upon PM concentrations measured at sites within Delhi and the NCR from concentration measurements alone.