In the early twentieth century, people fled over-crowded cities for suburbs, or at least lower-density areas of the city, in part because of the poor environmental quality. While water quality in cities has significantly improved, and sewers are sanitary, and horses no longer befoul our streets, today still, air quality in cities is usually worse than in lower density areas.

Recent research by University of Minnesota colleagues reports:

Results: The proportion of physically active individuals was higher in high- versus low-walkability neighborhoods (24.9% vs. 12.5%); however, only a small proportion of the population was physically active, and between-neighborhood variability in estimated IHD mortality attributable to physical inactivity was modest (7 fewer IHD deaths/100,000/year in high- vs. low-walkability neighborhoods). Between-neighborhood differences in estimated IHD mortality from air pollution were comparable in magnitude (9 more IHD deaths/100,000/year for PM2.5 and 3 fewer IHD deaths for O3 in high- vs. low-walkability neighborhoods), suggesting that population health benefits from increased physical activity in high-walkability neighborhoods may be offset by adverse effects of air pollution exposure.

Over the coming decades however, hybrid-electric and electric vehicles are likely to be more common, if not the only vehicles allowed on city streets. The smell of the city will change. EV cities will be less polluted and much nicer, and thus more attractive than earlier polluted cities, or cities without such vehicle-type regulation. It will come a time that not only will cities be better for the global environment, resulting in less overall carbon emissions than lower density areas with greater distances and fewer shared walls, but they will be as good (if not better) for the individuals residing in them, with less overall pollution per capita and perhaps lower pollution intake than suburban areas.