Wildfires pollute cities with ozone

On May 23, smoke from wildfires blanketed Denver, and one location in the city exceeded 81 parts per billion (ppb) of ozone, compared to an average of about 40 parts per billion (ppb) the year before. Atmospheric chemist Susan Paulson of the University of California, Los Angeles, says the new study’s findings are important because elevated ozone levels are “relevant to certain groups, especially those with respiratory illnesses.” According to Paulson, who was not involved in the study, “It certainly shows that there will be more ozone than there otherwise would have been.”

Getting rid of ozone is not always easy

With unhealthy levels of ozone in the air, exercise and other strenuous outdoor activities should be limited to the morning and evening whenever possible. People who are exposed to breathing difficulties should stay home. The authorities also recommend against driving when ozone levels are high because exhaust fumes promote gas formation.

Brown says reducing the contribution of wildfires to ozone is a challenge for every city. Ozone production increases as the concentration of nitrogen oxides increases to a certain point. Above a certain threshold, ozone production becomes less effective. A city is considered “nitrous oxide sensitive” if it has not yet reached the maximum amount of ozone that can be produced for a given amount of nitrogen oxides. A city that exceeds this level, on the other hand, is called “saturated nitrous oxide.” This NO saturation is more common in city centres, where the majority of emissions originate.

Contrary to what one might think, a city saturated with nitrogen oxide first increases ozone levels when it responds to wildfires with fewer emissions of nitrogen oxide. In contrast, cities sensitive to nitrous oxide have an easier time reducing ozone: stricter regulations on emissions from traffic and other sources improve ozone levels.