Introductory lecture: air quality inmegacities

Abstract

Urbanization is an ongoing global phenomenon as more and more people are movingfrom rural to urban areas for better employment opportunities and a higher standard ofliving, leading to the growth of megacities, broadly defined as urban agglomeration withmore than 10 million inhabitants. Intense activities in megacities induce high levels of airpollutants in the atmosphere that harm human health, cause regional haze and aciddeposition, damage crops, influence air quality in regions far from the megacitysources, and contribute to climate change. Since the Great London Smog and thefirstrecognized episode of Los Angeles photochemical smog seventy years ago, substantialprogress has been made in improving the scientific understanding of air pollution and indeveloping emissions reduction technologies. However, much remains to beunderstood about the complex processes of atmospheric oxidation mechanisms; theformation and evolution of secondary particles, especially those containing organicspecies; and the influence of emerging emissions sources and changing climate on airquality and health. While air quality has substantially improved in megacities indeveloped regions and some in the developing regions, many still suffer from severe airpollution. Strong regional and international collaboration in data collection andassessment will be beneficial in strengthening the capacity. This article provides anoverview of the sources of emissions in megacities, atmospheric physicochemicalprocesses, air quality trends and management in a few megacities, and the impacts onhealth and climate. The challenges and opportunities facing megacities due tolockdown during the COVID-19 pandemic is also discussed