Air quality improvements from a transport modal change in the São Paulo megacity

Air quality and urban mobility are complex socioenvironmental issues faced by megacities, particularly those in the Global South. Investments in efficient and inclusive public transport networks, as well as encouraging active transport modals, can mitigate both traffic congestion and air pollution, leading to improved quality of life. Few studies have integrated the potential effects of a well-developed rail network in influencing modal choice - from motorised to active transport - and their impacts on pollutant emission and air quality through dynamic air quality models. In the megacity of São Paulo, the expansion of the subway system has not achieved the planned targets, as intended by state government plans. This induces the question "What would have happened to air pollution if planned stations had been properly implemented?" which this paper aims to answer, through the increased adoption of cycling or walking to and from railway stations. We applied the WRF-Chem air quality model to model the effects of railway development in a megacity, focusing on criteria pollutants. Results show that the more investments there are in public transport, by expanding the metro system, the more expressive are the decreases in air pollution, and the farther these benefits spread out spatially. More intense reductions in pollutant concentrations are predicted to occur near the new stations' buffers, but citizens living far from the metro stations will also benefit from these improvements. Additionally, modal change from car to walking/cycling and subway in all trips within a radius of 1.3 km centered in existing and planned stations is expected to result in a decrease of 11.7 % in CO₂eq vehicular emissions. Therefore, improvements in public transportation could help improving environmental and social justice, leading to better air quality and transport accessibility, decreasing public health problems and costs, while helping cities reach their GEE emissions reduction targets.