On hot days, when the air is heavy and stagnant, nitrogen oxide molecules released from cars and industrial sources react with volatile organic compounds to produce ozone.
In large quantities, the chemical reaction can have dire consequences.
Ozone causes muscles in the airways to constrict, trapping air in small sacks in the lungs called alveoli. That constriction can lead to shortness of breath or wheezing and can be particularly dangerous to small children, the elderly or people who already have respiratory problems.
But ozone has become less and less of a problem in North Carolina over the past several years, and recent numbers indicate the state has recently reached an important milestone: the fewest ozone days in a single season since the state began monitoring for the gas in the 1970s.
North Carolina experienced four unhealthy ozone days during the 2017 ozone season, which lasted this year from March through the end of October.
Ozone days occur when the concentration of ozone in the atmosphere is higher than the 70 parts-per-billion standard set by the U.S. Environmental Protection Agency, a standard that was changed from 75 ppb to 70 ppb in 2015.
“It shows really great collaboration with citizens who are trying to be mindful of how they drive, with companies that are being very careful about their air emissions — the pollutants that they’re letting out,” said Jill Lucas, the public information officer with the N.C. Department of Environmental Quality’s air quality division. “It’s really good news for North Carolina because we used to have a lot more high ozone days, unhealthy ozone days, and now they’re pretty uncommon.”
The unhealthy days occurred May 16 in Mecklenburg and Guilford counties, July 20-21 in Mecklenburg County and Sept. 28 in Union County.
The state has also been officially designated as in “attainment” by the EPA, which means the federal government has verified that the state is in compliance with the 2015 ozone standards.
The rating represents an improvement over where the state was in the early 2000s. Back then, about one-third of North Carolina counties were considered “nonattainment” for ozone, and the state used to see orange alerts or worse for upward of 100 days out of the year. Since 2000, the number of days per year at or above a code orange and red designation have steadily decreased.
The EPA measures air quality using an index from 0 to 500, with certain ranges corresponding to particular colors. For example, an air quality index between 0 and 50 is green and means air quality is considered satisfactory. Maroon is on the far end of the spectrum, representing an AQI between 301 and 500; in that range, the entire population is likely to be negatively impacted by the air quality.
Kevin Lance, the field services program manager for the Western North Carolina Regional Air Quality Agency, says the last time Buncombe County had orange days was in 2012. In that year, the county had two. Ozone levels have been at code green or code yellow ever since.
Bill Eaker, senior environmental planner for the Land of Sky Regional Council, can say confidently that air quality in North Carolina has improved significantly over the last 15 years.
“And in the Asheville area,” he says, “we’ve gone from teetering on violating the federal ozone standard, becoming a nonattainment area … to where we are today where air quality has improved — both ozone and particulate matter.”
The Land of Sky Regional Council is a support agency that offers assistance to local governments on a diverse slate of issues. Air quality is one of them.
Eaker says a number of factors have contributed to the decrease in the ozone over the years. “Probably the most significant factor has been the switch from coal to natural gas at a number of coal-fired power plants,” he says. “Not only in North Carolina but in the Southeast.”
In North Carolina, Eaker says this change came about thanks in part to a piece of state legislation called the Clean Smokestacks Act, which forced the state’s 14 coal-fired power plant sites to significantly reduce their emissions.
The state’s Division of Air Quality and three local programs — including the WNC Regional Air Quality Agency — regulate industrial air pollution.
“We have approximately 70 facilities that are required to have air permits,” says Ashley Featherstone, permitting program manager for the WNC Regional Air Quality Agency. “Permits are written to include all applicable regulations. We go out and inspect the facilities to determine compliance.”
If a facility is not following pollution regulations, Featherstone says the agency works to bring them into compliance.
“Generally, that would include issuing a notice of violation and in some cases, a civil penalty or fine is required to be paid,” Featherstone explains. “The facility would need to pay the fine and show us what they intended to do to come back into compliance.”
The transition to low-emission, fuel-efficient vehicles, a switch that has been driven in part by federal fuel efficiency standards, has also had a major impact on ozone levels across the nation. “Especially at the heavy-duty sector,” Eaker says. “Diesel engines have gotten much cleaner than they were 15, 20 years ago.”
At a more grassroots level, Lance says ordinary people can do small things to help control the amount of ozone they release into the atmosphere, particularly during the heat of the summer. This can include limiting car travel, keeping the thermostat set a little bit higher and waiting until after the peak heat of the day to mow the lawn.
The indicators for ozone might be improving, but clean air activists are pushing to bring attention to other air quality concerns.
There are 34 ozone monitors operated across North Carolina. The WNC Regional Air Quality Agency operates one ozone monitor at Bent Creek as well as three PM2.5 monitors in Buncombe County.
PM2.5 refers to the cocktail of infinitesimally small particles in the air, both solid and liquid, that have a diameter of less than 2.5 microns, which is about thirty times thinner than a human hair. Like ozone, PM2.5 molecules pose a serious health risk.
“It’s small enough that it makes it through a lot of your defense systems for things that you breathe in,” said Calvin Cupini, program manager of citizen science for Clean Air Carolina. “It’ll make it past the mucus membranes. It’ll get into the lungs, and it’s actually small enough to exist in those little gas exchange chambers called the alveoli.”
Cupini says PM2.5 is most commonly associated with heart attacks and strokes, but it’s also linked with asthma and can be detrimental to lung function.
North Carolina has monitors in locations across the state that track PM2.5, but Cupini says there aren’t many and the total number has actually been decreasing, hovering now at around 23.
“We have some fiscal conservatives that find a way to justify taking them down,” Cupini said. “They are expensive, they are pretty maintenance-heavy, but we just don’t feel like that’s the right practice.”
That’s where the AirKeepers Citizen Science Program comes in. The initiative, launched by Clean Air Carolina in Charlotte in 2016, encourages students, teachers and members of the general public to become involved in monitoring local levels of PM2.5 using small, portable sensors.
Cupini relayed this information during a presentation at the Collider in downtown Asheville on Nov. 8. Clean Air Carolina hopes to put several of these small monitors in various locations around Asheville. “23 monitors just doesn’t cover the heterogeneity of the entire state,” he said.