Black Carbon Aerosol Concentration in Five Cities and Its Scaling with City Population

A question of importance for urban planning and attainment of air quality standards is how pollutant concentrations scale with city population. This study uses measurements of light absorption and light scattering coefficients as proxies for primary (i.e., black carbon aerosols) and total pollutant concentration to start addressing the relationship between per capita air pollutant concentration and city population. Analyses of aerosol light scattering and absorption measurements in suburban Mexico City, Mexico; Las Vegas, Nevada; Reno, Nevada; Beijing, China; and Delhi, India, suggest that common air pollutant concentrations scale approximately as the square root of the urban population, which is consistent with a simple 2D box model. This simple scaling relationship for per capita air pollution concentration might be useful both as a guide for comparing cities as well as for preparing for future projections of increased urbanization, especially for cities having more than 10 million inhabitants.