I have a doctor friend, a lifelong germaphobe, who always holds his breath whenever someone walking toward him sneezes, then lets it out after the fellow has passed him by.
Now I find myself doing the same thing when a diesel vehicle comes along. My hypochondriacal tic began last week, when Volkswagen admitted that it had fitted 11 million diesel cars worldwide with engine-control software that cheats on the standard emissions test. The software clamps down on emissions when it senses that the car is running on a laboratory’s dynamometer, then lets the engine rip when the car is back on the open road.
Here the critical pollutants were nitrous oxides, or NOx. But diesel engines also make a lot of carbon particulates, which are caught in special traps. Even so, a lot of them get out, and like NOx, they’re bad for your lungs. Diesels predominate in European cities, so they’d have been the major source of both pollutants there even if their engine algorithms were honest.
It turns out my breath-holding is almost reasonable. A study presented at the European Respiratory Society's International Congress, in Amsterdam, finds that even a single diesel vehicle can create a brief spike in local particulates—and that these spikes are common on busy avenues but not on quiet back streets.
Lee Koh, a researcher at the Blizard Institute at Queen Mary University, in London, carried a monitor while walking along the two kinds of routes in London during the evening rush hour. Though the busy streets had only slightly higher average particulate levels, they alone showed local spikes. “For example, when you stop to cross a busy road and so you are subject to a higher level of pollution compared to when walking away from the traffic,” she said in a statement that accompanied her presentation.
Some spikes reached above 10,000 nanograms of carbon per cubic meter, which is three times the average rush-hour level in London, one of the most particulate-choked cities in Western Europe.
To avoid those plumes of diesel exhaust, Koh planned her walks with an app called Walkit. It’s just the thing for walkers as they wait for the day when diesel emissions controls use their own considerable brainpower excusively for good—and not for evil.
Philip E. Ross is a senior editor at IEEE Spectrum. His interests include transportation, energy storage, AI, and the economic aspects of technology. He has a master's degree in international affairs from Columbia University and another, in journalism, from the University of Michigan.