Courthouse crew

Construction crews work on the new Denton County Courthouse in Thursday’s hot weather. Denton residents huddled under high ozone Thursday and are expected to do so again Friday.

North Texans huddled under high ozone Thursday and are expected to do so again Friday.

Ozone burns the lungs and airways in the same way the sunlight burns skin. Should ozone levels get as high as state environmental officials expect on Friday, even healthy people will feel the burn.

Forecasters with the Texas Commission on Environmental Quality said the stuffy, hot weather should help push ozone to unhealthy levels in North Texas on Friday. Sunlight cooks up ground-level ozone — a superoxidant with its three oxygen atoms — from nitrogen dioxide (emissions from engines and power plants) and volatile organic compounds (naturally occurring gases from trees and emissions from oil and gas facilities).

Thanks in part to a wetter-than-normal summer, Denton and the Dallas-Fort Worth region have had fewer “bad air” days this year compared with last year. The region’s eastern counties logged 13 bad air days so far this year, compared with 26 last year.

TCEQ tallies up the bad-air days in two ways: when the average measures more than 71 parts per billion for eight hours or when the average ozone measures more than 125 ppb for one hour. Last year, one DFW monitor recorded an hour of ozone at 137 ppb. So far this year, no bad-air days have gotten that high.

All those tallies likely will change by the end of the week. On Thursday afternoon, for example, ozone levels climbed to 122 ppb by 5 p.m.

Regardless of where this week’s numbers fall out, the region still has an air quality problem.

In its annual review of national compliance with ozone and other air quality standards, the American Lung Association gives Denton and the rest of the region an “F” — the same grade the region has received since 1997.

Ozone levels have decreased over the past 22 years, primarily because of reductions in automobile emissions. Several coal plants in Texas, including Denton’s, shuttered this summer, but whether that has boosted air quality overall remains to be seen.

The Electric Reliability Council of Texas has declared power emergencies this summer, and that means TCEQ changes how it assesses each power generator’s compliance with air quality permits.

“At this time, the full extent of power generation facility activities is not known until all final reports are submitted to the agency,” TCEQ spokesman Andrew Keese wrote in an email.

In addition, the Environmental Protection Agency continues to strengthen its attainment requirements. In 2015, the compliance threshold went down from 75 ppb to 70 ppb.

Under the federal Clean Air Act, the TCEQ is required to write plans to reduce ozone in North Texas to meet those thresholds. With the current plan, the long-term ozone average is supposed to stay at or below 70 ppb at all of the region’s ozone monitors.

Currently, the region’s highest long-term average stands at 76 ppb, with the Denton monitor’s long-term average at 73 ppb.

Most scientists agree that ozone below 60 ppb is safe to breathe; however, they have not been able to persuade policymakers to lower the federal standard that far.

So what’s a breather to do?

In addition to encouraging individuals to avoid heavy exertion outdoors during peak ozone times, state environmental officials also encourage people to drive less and reduce their electricity consumption on bad-air days.

In North Texas, ozone season typically lasts through October.

PEGGY HEINKEL-WOLFE can be reached at 940-566-6881 and via Twitter at @phwolfeDRC.

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