Development of an Integrated Modeling Framework for Visibility and Air Quality Forecasting in Delhi

Abstract Rapid urbanization has subjected the megacities of developing countries to various environmental stresses. Delhi, a major Indian megacity, faces increasing urban stress leading to reduction in air quality and visibility. These challenges necessitate an integrated modeling framework to mitigate adverse environmental impacts on public health. Therefore, we have developed an advanced version of the high-resolution Delhi Model with Chemistry and aerosol framework (DM-Chem) at the National Centre for Medium Range Weather Forecasting (NCMRWF) under the Weather and Climate Science for Service Partnership India (WCSSP India) project. This collaborative initiative between India and the United Kingdom aims to provide real-time forecasts of visibility and fine particulate matter (PM 2.5 ) for Delhi and neighboring regions during the winter season. The DM-Chem framework is unique due to its detailed urban canopy scheme and realistic aerosol representation, making it well suited for city-scale forecasts. It is designed to predict extreme fog and pollution events in the winter season. Here, we discuss the major physical parameterization improvements for the model, along with its skill and deficiencies in predicting extreme events. Notably, irrigation effects on surrounding agricultural areas have significantly improved fog and visibility forecasts, but have degraded the wind forecasts. We demonstrate the applicability of this modeling framework to study aerosol–radiation interaction during fog holes and discuss its potential to be applied or adapted to other megacities worldwide. Significance Statement The capital city Delhi and, in general, many metropolitan cities of India often report high levels of particulate matter pollution especially during wintertime, often accompanied by episodes of dense fog. Air quality and visibility forecasting for an urban region is dependent upon many key model inputs other than emissions and meteorology. Realistic representation of the (i) city’s local urban morphology, (ii) surface aerosols, and (iii) soil conditions impacted by irrigation activities has been found to significantly influence air quality and visibility prediction in Delhi and surrounding areas. This work aimed at providing a reliable air quality and visibility forecast for Delhi, which is crucial to minimize both health and economic losses.