For those living with the threat to life and property from wildfires, Colorado State University scientists have some more bad news: Wildfire smoke seems to elevate levels of ozone, a nasty air pollutant with proven adverse health effects. The influence of wildfire smoke on ozone levels during summer months in the United States is not well understood. CSU atmospheric science researchers took a comprehensive, multi-year look at this secondary, insidious effect of raging wildfires. Published in Environmental Science and Technology, the new study quantifies what wildfire smoke does to ozone levels over a nearly 10-year span, integrating data from hundreds of monitoring sites dotting the country.

Across the U.S., ozone levels were higher on smoky days than on smoke-free days, according to the study led by Steven Brey, a graduate student working with Emily Fischer, assistant professor of atmospheric science in CSU's College of Engineering. According to Brey's analysis, a number of urban areas had smoke present during 10 percent to 20 percent of days when the standard Environmental Protection Agency ozone levels of 70 parts per billion (ppb) were exceeded. The EPA reset the ozone standard down from 75 ppb late last year, making it more stringent.

Ozone is one of six "criteria pollutants" monitored by the EPA, and its adverse effects particularly on the young, elderly and people with asthma are well documented. "Good up high; bad nearby" is the EPA's description of ozone - the ozone layer of the Earth's atmosphere protects us from UV radiation from space, but down where we breathe, it damages lungs and destroys crops and ecosystems.

Typically, the effect of smoke on ozone levels is studied on a "plume-by-plume basis," Fischer explained. "A wildfire will be burning and someone will take an aircraft, like the NSF/NCAR C-130 or the NASA DC-8, fly around in it, and take measurements. What Steve did was take ground-level data ... to look nationwide, not just at one fire or one plume, but every ground site from 2005 to 2014."