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Published on November 1st, 2017 | by James Ayre


3 Urban Form Metrics Strongly Tied To Air Pollution Levels

November 1st, 2017 by  

The alteration of the urban form of cities — and thus the alteration of motor vehicle use patterns — could be used as a means of reducing local air pollution levels, according to a new study from researchers at the University of Washington and the University of Minnesota.

Image by City of Vancouver Archives (some rights reserved)

The findings are the result of an analysis of satellite-based measurements of urban form and nitrogen dioxide levels (a proxy for traffic related pollution), across 1,274 cities worldwide.

So, what are the findings exactly? Three urban form metrics in particular — contiguity (ratio of the largest contiguous polygon of built-up area to the total built-up area for a given city), circularity (quantifying the relative closeness of the built-up area to the geographic center), and vegetation levels — were determined to be in a statistically significant relationship with urban NO2 levels. The 3 metrics, when taken together, apparently exert a pronounced effect on local air pollution levels.

To use Christchurch, New Zealand, as an example — if the urban form of that city matched that of Indio-Cathedral City, California, then models used by the researchers show that local NO2 concentrations would be around 60% higher than they are now.

Interestingly, the combined effect of the urban form metrics on small cities is greater than it is on larger cities.

Green Car Congress provides an overview of the study findings:

  • Higher population had the largest effect; i.e., higher populations are associated with worsened air quality.
  • Increased urban contiguity, circularity, and vegetation metrics are significantly associated with lower urban NO2 concentrations.
  • The impervious surface metric has a non-significant effect on urban NO2.
  • Although the magnitude of the effect size of the three significant urban form metrics are small relative to population, their combined effect could be large.
  • Meteorology and country-level income play an important role in describing differences in urban NO2 concentrations among cities; income, solar insolation, and precipitation together describe 52% of the variation in urban NO2 concentration.

The new research is detailed in a paper published in the ACS journal Environmental Science & Technology.


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About the Author

James Ayre's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy.

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