Hot weather but one factor in ozone level

Cars, industrial emissions, humidity said to play roles

Arkansas and Memphis officials will continue to monitor air quality on high-temperature days this summer, they said, but it’s difficult to predict whether air quality will be an issue if hot weather persists.

The Health Department for Shelby County, Tenn., declared the air in the Memphis metropolitan area, which extends into Arkansas, “unhealthy for the general public” June 10 when temperatures reached the low 90s. The department issued two “Code Orange” advisories for the metropolitan area last week and another for a portion of the area Saturday.

Code Orange means that air quality is unhealthy for “sensitive groups,” such as people with respiratory impairments or the elderly.

But as temperatures soared even higher this week, the county had not issued any more advisories, said Elizabeth Hart, spokesman for the Shelby County Health Department.

“In the world of public health, you just don’t know from day to day what might happen,” she said.

The U.S. Climate Prediction Center’s forecast through mid-August shows above-average temperatures across most of the country, including central Arkansas and Memphis. The chances of higher-than-normal or lower-than-normal temperatures in Northwest Arkansas are about equal.

“It’s looking like it might be a hot summer, so we’ll be following that very carefully,” said Stuart Spencer, Office of Air Quality associate director for the Arkansas Department of Environmental Quality.

Both agencies are tasked with issuing ozone advisories, which tend to happen more often in the summer.

Hot weather is one of the contributing factors to the creation of ground-level ozone, also referred to as smog. Ozone that occurs higher in the atmosphere, commonly called the ozone layer, filters out some ultraviolet radiation and is considered beneficial.

More sunlight and fewer clouds also can contribute to the creation of ground-level ozone, Hart said.

So do wind directions and wind speeds, humidity and the number of cars on the road, Environmental Quality officials said. High humidity can curb ozone levels. Winds blowing in from high ozone areas like Memphis can contribute to higher ozone levels.

The department monitors the Little Rock and Springdale metropolitan areas, which have not issued any advisories this ozone season, which runs from May 1 through Sept. 30.

Ozone levels in the air on Friday morning were 35 parts per billion in Little Rock and 36 parts per billion in Springdale, both far below the levels set by the U.S. Environmental Protection Agency for issuing health advisories to residents.

The levels of fine particulates in the two areas were high enough that the Department of Environmental Quality labeled the air quality indexes as “moderate” or “yellow,” which mean “unusually sensitive people should consider limiting prolonged outdoor exertion.” The levels are not considered generally unhealthy.

Fine particles can be found in smoke and haze and can be emitted directly during fires or form when emissions from power plants, industry or vehicles react in the air, according to the EPA.

Last October, the EPA made its ground-level ozone standard more strict, tightening it from 75 to 70 parts per billion starting in 2017. The trucking-heavy Memphis area has struggled with air quality for years but was recently released from air quality nonattainment status by the EPA.

The metro Memphis area recorded an air-quality measurement of 89 parts per billion of ozone June 10.

Upcoming Events