Global intraurban intake fractions for primary air pollutants from vehicles and other distributed sources

Abstract

We model intraurban intake fraction (iF) values for distributed ground-level emissions in all 3646 global cities with more than 100,000 inhabitants, encompassing a total population of 2.0 billion. For conserved primary pollutants, population-weighted median, mean, and interquartile range iF values are 26, 39, and 14-52 ppm, respectively, where 1 ppm signifies 1 g inhaled/t emitted. The global mean urban iF reported here is roughly twice as large as previous estimates for cities in the United States and Europe. Intake fractions vary among cities owing to differences in population size, population density, and meteorology. Sorting by size, population-weighted mean iF values are 65, 35, and 15 ppm, respectively, for cities with populations larger than 3, 0.6-3, and 0.1-0.6 million. The 20 worldwide megacities (each >10 million people) have a population-weighted mean iF of 83 ppm. Mean intraurban iF values are greatest in Asia and lowest in land-rich high-income regions. Country-average iF values vary by a factor of 3 among the 10 nations with the largest urban populations.

Figure 1

Population-weighted distribution of intraurban intake fraction by city size (small, medium, large) and region (labels on horizontal axis; see Table 2 and the map in Figure SI.7 (Supporting Information) for definitions of the abbreviations). For cities of similar size, iF is generally higher in Asia (e.g., EAP, SCA, and SEA) and lower in high-income regions (e.g., EUJ and LRD). See Table SI.3 (Supporting Information) for a tabulation of the results.

Figure 2

Map of intraurban intake fraction for cities in the Americas (upper panel) and Asia (lower panel). Values of iF are denoted by symbol area. City colors correspond with Figure 1 and indicate population size bins. Intake fractions for selected cities are labeled. Stars designate megacities (population >10 million, 11 on Asia map, 3 on Americas map). The same scale applies to both maps. The Supporting Information provides maps for other continents.