Evaluating line source emission models for Indian urban environments

Abstract

Vehicular emissions have constituted a primary source of urban air pollution, with profound implications for public health and environmental quality, especially in rapidly developing countries like India. This review has chronicled the progression of mobile source emission inventory methodologies, which have transitioned from simplified Excel-based bottom-up approaches to sophisticated tools such as MOBILE, MOVES, COPERT, and IVE. Early methods have primarily utilized static emission factors combined with limited vehicle activity and road length data, resulting in poor spatial and temporal resolution and inconsistent emission estimates. Advanced inventory models have improved accuracy by incorporating modal driving cycles, vehicle-specific power calculations, and detailed fleet characteristics; however, their efficacy in developing country contexts has often been hampered by the unavailability of comprehensive local inputs, including fuel composition, vehicle kilometres travelled, and fleet age distributions. This review has highlighted significant deficiencies in model validation, emission factor localization, and integration of real-world traffic dynamics within existing emission inventories. Current inventories have largely neglected to disaggregate vehicle kilometres travelled by road type or to capture heterogeneous traffic behaviour, leading to biased spatial emission distributions and compromised policy relevance. The review has identified the Indian Vehicle Emission (IVE) model as a promising example that has improved context specificity through detailed driving cycle and terrain sensitivity, complementing established models like MOVES and COPERT. To enhance emission inventory reliability for rapidly urbanizing Indian cities, the adoption of a modular, India-specific emission framework has become essential. Such a framework should incorporate real-time vehicle counts, stratified vehicle activity by road classification, and heterogeneous traffic patterns. Implementing an India-tailored emission inventory model will greatly support urban air quality management and policy formulation, aligning with national objectives such as the National Clean Air Programme (NCAP). It will provide policymakers with precise, actionable insights to target emission hotspots, design effective interventions, and ultimately safeguard urban environmental health.