by Paul Ehrlich (Clean Air Issues Coordinator; phehrlich-nj@outlook.com)
In the article Tips on Coping with Air Pollution on this website I pointed out that air pollution is very local. For example, living one hundred yards from a major road can make a difference in health risk. A new scientific report demonstrates that pollution is hyperlocal. Apte et al. (Environ. Sci. Technol., 51, 6999 [2017]) used specially-equipped Google Street View vehicles to repeatedly measure three important pollutants on the streets of Oakland CA. Within a single block, pollution could vary up to eight-fold.
How does this affect life-style choices – besides choosing a place to live? Environmentalists have long urged that commuting by bicycle would reduce a community’s air pollution. But would the biker benefit? This is presently under study. Some good news regarding the hyperlocality of air pollution is that bicycle commuters can benefit by carefully choosing their routes, times of day, etc. Municipal officials (with the help of Google and others) could assist all who use city streets and sidewalks – by providing high-resolution maps of pollutants. They could also remediate the health consequences of pollution hot spots by tweaking traffic routes or rules. Separating bicycle lanes from motor vehicle traffic by traffic islands, especially islands with bushes and trees, should also help. Some organizations are already contributing to this effort: the Rails-to-Trails Conservancy promotes conversion of abandoned railroad lines to bicycle and walking trails, many of which are well separated from major roads.
The pollutants measured by the Google vehicles are the smog-formers: participants in temperature-dependent chemical reactions that produce ozone. Since urban areas are warmer than surrounding suburban and rural areas, pollution risk to bikers will be greater there, especially during the summer. A typical temperature difference is 5⁰ F. So, if the temperature could be lowered it would not only help make it more pleasant to commute by bike it would also make it healthier. Of course, it would also help mitigate climate change. The ozone-forming chemical reactions are so complex that there is no easy way to estimate the ozone reduction, especially since it depends on knowing precisely the concentrations of the various pollutants. The expected increase in regional ozone concentrations due to global warming, called the “ozone-climate penalty” or the “climate penalty factor,” has been estimated by climate scientists. The good news is that reduction of nitrogen oxide emissions has caused the climate penalty factor to decrease in the eastern U.S. (Rasmussen et al, Environ Sci Technol, 47, 14258 [2013]).
There are many ways that urban temperatures can be lowered, including more trees and switching to renewable energy and electric vehicles. Additional efforts include, for example, New York City’s Cool Roofs Program: “a City initiative that provides local jobseekers with training and work experience installing energy-saving reflective rooftops.” The Heat Island Group of the Lawrence Berkeley National Laboratory recently released a report on “cool pavements” which showed that one method of increasing the solar reflectance of streets can significantly reduce global warming over a fifty year life cycle.
The author thanks Dick Colby, newsletter editor of the Sierra Club NJ Chapter, for editorial assistance.