Air pollution in cities with unplanned urban growth, a case study of Toluca Valley: trends and health impacts compared with Mexico City

Abstract

Unplanned urban growth is occurring in many cities in developing countries and is associated with social and environmental problems. The Metropolitan Area of Toluca Valley (MATV) began its disorganized expansion since the 1960s, and according to the IQAir platform, it has been the city with the worst air quality in Mexico, in terms of PM₂.₅, since 2019. Materials and methods: Tenyear (2011-2021) monitoring databases of air criteria pollutants (ACP) from six MATV monitoring stations were processed to establish spatiotemporal variations and to estimate the mortality proportion attributable to PM₂.₅ exposure using AirQ+ software. The evolution of ACP concentrations and the PM₂.₅ mortality proportion between the MATV and Mexico City were compared. The COVID-19 lockdown impact on ACP was also assessed. Results: PM₂.₅ and PM₁₀ are the main ACP that worsen air quality in MATV and exceed the WHO Air Quality Guidelines (AQG) almost the entire year, risking public health. The estimated mortality proportion associated with PM₂.₅ exposure in 2019 for MATV was 11.97% (7.98-15.55) as for Mexico City, 6.95% (4.59-9.1). MATV presented higher levels of ACP and lower reduction percentages than Mexico City Metropolitan Area over the ten-year period. PM and O₃ patterns are very similar between cities, suggesting that air pollution is shared. The COVID-19 lockdown in 2020 caused a reduction of all ACP concentrations except for O₃. Conclusions: MATV case study provides a reference scenario of the impact of unplanned urban growth on public health and the need for the government to develop solutions to improve urban mobility and environmental surveillance.