Assessment of Emission Reduction Scenarios with a Focus on the Impact of Vehicle Fleets on Tehran Air Quality: Case Study

Abstract

In recent years, the city of Tehran has frequently experienced severe air pollution episodes, and the increase in the use of vehicles has exacerbated this critical situation. It is unclear to what extent each vehicle category contributes to the production of pollution during a pollution event. For this purpose, a combination of the weather research and forecasting (WRF) and the Comprehensive Air Quality Model with Extensions (CAMx) modeling systems was used to simulate the distributions of pollutant concentrations over Tehran in a pollution episode from December 3 to 23, 2017. First, the performance of the modeling system was evaluated with respect to the simulation outputs against observations. Results showed satisfactory performance by the models in predicting meteorological parameters and pollutant concentrations. There were some discrepancies between measured and simulated pollutant levels that might have several causes, including, for example, not considering dust emissions in the system. The second step focused on the assessment of different emission scenarios to quantify the impact of each vehicle fleet in producing pollution during such severe episodes. For this reason, eight different scenarios were considered in which the emissions of each vehicle category were entirely eliminated from the corresponding scenario. The results show that the removal of passenger cars and motorcycles could have the most significant impact on PM_2.5 reduction, with a maximum drop of 32% and 30%, respectively. In addition, the NO₂ concentrations could be reduced by about 20% and 10% as a result of the removal of passenger cars and motorcycles, respectively. Finally, two traffic schemes with a main focus on the role of motorcycles on the degradation of Tehran’s air quality were also examined for the same episode.