Consider air quality when planning your commute.
It’s clear that how we choose to commute affects our air quality. But does our mode of transit determine how many pollutants reach us? What’s a health-conscious commuter to do? Dr. Robert Chaney, professor of health sciences at BYU, wanted to find out.
For a study published in the academic journal PLOS One last November, Chaney and his coauthors asked 15 participants to travel along a busy road near downtown Salt Lake City. They traveled via six modes of transit: electric light rail, diesel bus, car with windows open, car with windows closed and air conditioning on, bicycle, or on foot. While commuting, the participants wore personal air monitors that measured the concentrations of fine particulate matter (PM2.5) from the air around their heads every second. All the participants followed the same route for almost two miles along North Temple, just south of the fairgrounds, during rush hour traffic.
Although the study took place in August, fine particulate matter creates extra problems in the winter, causing smog—the hazy air common during inversions. Smaller than 2.5 micrometers (0.0001 inches) across, these particles can stay aloft for weeks and are associated with a variety of health problems, including coughing, aggravated asthma, heart disease and cancer. Fine particulate matter is formed from chemical compounds released during combustion. According to the Utah Department of Public Health, 57% of the fine particulate matter in the Wasatch Front comes from vehicle exhaust.
The inhaled dose
Chaney and his coauthors found the highest concentrations of fine particulate matter in buses and cars with open windows and the lowest in cars with closed windows. But they knew that how many pollutants get into your lungs also depends on how quickly you’re breathing and how long you’re outside. Incorporating these factors, the researchers estimated how much fine particulate matter reached commuters’ lungs, which is called the inhaled dose. Pedestrians had the highest inhaled dose of any of the commuters because they took the longest time to travel along the route. Cyclists inhaled the second highest dose, while commuters in cars with closed windows had the least pollutants reach their lungs.
Chaney’s results are consistent with previous findings. Nicholas Good and his coauthors, for example, also found less fine particulate matter inside cars than around cyclists, although they reported more carbon monoxide in cars. Published in the Journal of Exposure Science and Environmental Epidemiology in 2016, their study tracked the air quality experienced by 45 commuters traveling by bicycle or car in Fort Collins, Colorado.
One author of the Fort Collins study, John Volckens, points to an inherent problem when you look at as small a group of people as those included in the Salt Lake study: These findings cannot be generalized to other areas, times of day or times of the year (a point also noted by Chaney in his paper).
So what’s a conscientious commuter to do?
Chaney recommends that when you need to drive your car, keep your windows closed and set your heating (or air-conditioning) system to recirculate the air within the car. This way, if your car is a newer model, like those in the study, you may be able to achieve cleaner air inside than outside your car.
But certainly don’t stop cycling or walking in good to moderate air qualities. These forms of transport, unlike cars, obviously don’t make the problem worse by adding more pollutants to the air. Chaney notes that cycling and walking are also great forms of exercise that lower your risk for chronic diseases like obesity, heart disease, and cancer. Volckens says of his personal commuting, “I gave up my parking pass this year; I almost strictly bike to work.”
In fact, in our sedentary society, the benefits from regular exercise probably outweigh the risks from higher exposure to air pollution in all but very poor air quality. Although this hasn’t been directly studied, a 2016 review by Thomas Gotschi and others in Transport Reviews estimates that the risks from air pollution operate on a different scale than the benefits of regular exercise from cycling: While air pollution may shorten the average cyclist’s life by 0.8 to 40 days, the regular exercise of cycling may lengthen it by 90 to 425 days.
The air quality index, displayed on most weather forecasting apps and websites, reports the level of ambient pollution on any given day, and may be helpful when planning your commute. But to avoid the higher-than-ambient concentrations of pollutants near busy roads, Chaney suggests choosing routes along lower-traffic roads when possible. Volckens adds that timing your commute to avoid peak traffic flow (when your schedule allows) will also reduce your exposure to pollutants.
City-wide solutions include structural, technological and land-use changes. Cycling, walking and other forms of active commuting need to be safe, healthy and normalized ways to get around. While most cities tack bike lanes onto existing roadways, Volckens says this is a problem because it “puts bicyclists right next to one of the largest sources of air pollution in the country, which is motor vehicles.”
One alternative is to install off-road paths, such as Salt Lake’s S-Line Greenway. This is easier said than done: It’s not clear how much space is required between paths and roads to achieve health benefits; acquiring the land for such routes is usually somewhere between daunting and impossible; and the paths are only useful if they are located where commuters need to travel. However, future development projects should incorporate separate bike paths instead of on-road bike lanes.
Where physically separating paths from roads is impossible, some cities are getting creative. Volckens was interested in an idea implemented in Amsterdam, where certain roads are closed to vehicles during peak traffic times, temporarily creating cleaner-air corridors just for cyclists and walkers to enjoy.
What’s up with UTA
An eventual shift to electric vehicles will eliminate the largest source of fine particulate matter in the Wasatch Front. Salt Lake’s TRAX light rail train system is powered by electricity, and the city’s official website states that there are 28 smart charging ports for electric vehicles, making electric car ownership more feasible for some residents.
Buses help reduce the numbers of cars on the road, thereby reducing pollutants. But diesel buses often self-pollute, meaning that their own exhaust leaks back into the bus; switching from diesel to electric buses protects bus passengers’ lungs in addition to improving ambient air quality. Carl Arky with the Utah Transit Authority (UTA) says that of the 510 buses serving the greater Salt Lake area, 30 are hybrid electric models and 47 are powered by natural gas. Arky adds that the UTA plans to introduce five electric buses in 2018, saving 2,400 diesel gallon equivalents and their associated pollutants per bus.
These are steps in the right direction, but Salt Lake lags behind the rest of the United States when it comes to clean transport. The American Public Transportation Association’s handbook states that as of January 2015, 2% of US buses were powered by electricity and 17.8% were hybrid electric models. The UTA will still have fewer than 1% electric-powered and 5.9% hybrid buses, a startling discrepancy given that Salt Lake’s winter air quality is often worse than that of larger metropolitan areas.
Solving Salt Lake’s air quality problem requires hard work and creativity. But for clean air under a brilliantly blue winter sky, it will be well worth the effort.
Faith Rudebusch is a biologist and the author of the edible gardening blog, SlateMountaingarden.com. She lives in Pocatello, Idaho.