Global Modeling of Intake Fractions due for Urban Vehicle Emissions

Apte JS, Bombrun E, Marshall JD, Nazaroff WW, 2012. Global intraurban intake fraction for air pollutants from vehicles and other distributed sources. Accepted, Environmental Science & Technology, DOI: 10.1021/es204021h.

Among key sources of outdoor air pollution, urban motor vehicles have especially high iF, since they emit at ground level in close proximity to populations. Previous studies have demonstrated that iF for primary urban vehicle emissions varies among cities owing to differences in urban form and meteorology. However, the vast majority of existing iF data are available only for cities in high income regions (e.g., North America, Europe).

To understand gobal patterns of iF for urban vehicle emissions, we modeled iF for primary, distributed ground-level air pollutant emissions in 3,646 worldwide urban areas. This dataset includes nearly all cities with year-2000 population ≥ 100,000, with a combined total of > 2 billion inhabitants. The analysis employed a scalable single-compartment Eulerian model, which we configured for each city using global meteorological and demographic datasets.

The analysis shows that the global average intraurban iF for vehicle emissions of primary, conserved pollutants (39 ppm) is roughly twice as large as the mean iF in US cities (21 ppm) and in other "land-rich" high income countries (16 ppm). The intraurban iF is high in rapidly motorizing countries such as China and India (mean iF ~ 44 and 51 ppm). We found very high iF for the 11 "megacities" in Asia, such as Beijing, New Delhi, and Dhaka (mean iF: 110 ppm, range: 67 - 260 ppm).

A policy implication of this research is that efforts to reduce vehicle emissions in high-iF cities (such as many cities in Asia) may yield especially high population exposure benefits per unit of mitigation.

See more at Joshua Apte's homepage.