Background and Objective: Urban air pollution is currently recognized as one of the most important environmental and public health challenges worldwide and is responsible for millions of premature deaths annually. Following the historical Great Smog of 1952, London has implemented comprehensive and effective policies that have resulted in substantial improvements in air quality. Given the effectiveness of these policies and the shared challenge of air pollution in the metropolitan city of Mashhad, this study aimed to analyze London's experience and propose a practical, locally adapted framework for reducing air pollution in Mashhad.

Materials and Methods: This descriptive-analytical study used population data, concentrations of air pollutants, including NO₂, PM₁₀, PM₂.₅, and O₃, and transportation-related indicators for the period 1990–2022. Data were extracted from reliable sources, including the London Air Quality Network (LAQN), Transport for London (TfL), and the Greater London Authority (GLA). Pearson's correlation test was used to assess the relationships between population growth and pollutant concentrations.

Results: The population of London increased from 6.79 million in 1990 to 9.54 million in 2022. Despite population growth, the annual NO₂ concentration at the roadside station decreased from 95 µg/m³ in 1997 to 43 µg/m³ in 2021. At the same station, PM₁₀ concentration decreased from 50 µg/m³ in 1997 to 16 µg/m³ in 2021. PM₂.₅ concentration at the North Kensington station also decreased from approximately 20 µg/m³ in 2008 to 9 µg/m³ in 2021. The Pearson correlation test revealed a strong inverse correlation between population growth and the reduction in concentrations of NO₂, PM₁₀, and PM₂.₅. In contrast, a positive correlation was observed between population growth and increased O₃ concentrations. Controlling pollutants led to a 44% reduction in NO₂ concentrations in central London.

Conclusion: London's success in reducing air pollutant concentrations despite population growth has resulted from an integrated approach involving emission-based vehicle zoning, modernization of the transportation fleet, development of green infrastructure, and promotion of active transportation. Given the structural similarities between London and Mashhad, targeted adaptation of London's experience to Iran's specific conditions could represent an effective step toward reducing air pollution and improving public health in Mashhad.

Open Access Policy: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/