Regional Ozone Levels Higher this Summer

Published 12:00 am Wednesday, September 14, 2011

By Kathy Chaffin
Ground-level ozone levels are higher in the region this year than they were last year. Hot, dry conditions with light winds, which were especially prevalent during the first week in June, play a significant role in ozone levels.
As of Aug. 19, there have been 23 days of reported elevated ozone levels across North Carolina and 21 ozone alert days in the Charlotte region, which includes Rowan and Cabarrus counties. Last year, the Charlotte region had only 17 days for the entire season, which runs through October.
The orange zone, the first of three elevated ozone level forecasts, indicates the air is “unhealthy for sensitive groups” such as children, the elderly and people with chronic respiratory issues. These groups are advised to stay indoors on days with elevated levels to avoid shortness of breath, wheezing and coughing.
The Mooresville Regional Office of the North Carolina Division of Air Quality, which includes Rowan, Cabarrus, Stanly, Iredell, Alexander, Catawba, Cleveland, Gaston, Lincoln, Mecklenburg and Union counties, operates ozone monitors in Rowan, Alexander, Lincoln and Union counties, and the Mecklenburg County Air Quality Program operates ozone monitors there, one on the Mecklenburg-Cabarrus line.
“There seems to be a slightly higher number of days this year,” says Charles Davis, environmental chemist for the North Carolina Division of Air Quality office in Raleigh, “but I don’t consider it to be significant because you’ll get a little fluctuation. You actually get a better feel for how things are going when you look at them long term.”
Davis says the number of ozone alert days could increase between now and Oct. 31, which marks the official end of the ozone season. Last year, there were 26 days of elevated ozone levels statewide with the last one in the season being reported on Sept. 23, according to Davis.
“It is actually pretty late in the season,” he says, “but we can have high ozone readings in September and October, and we’ve had them in April and May also. The general pattern is June, July and August.”
This year, for example, the first elevated ozone reading wasn’t reported until June 1, he says, as compared to the first elevated reading in 2010 on April 2 and two days in May.
Davis says ozone levels are considered to be elevated when they exceed the eight-hour national standard of 75 parts per billion (ppb) based on weight and micrograms per cubic meter. The highest level reported in the state so far this year was in Mecklenburg County on June 8, which reported an eight-hour average concentration of 91 parts per billion. On that same day, he says monitors in Rowan reported a concentration of 76 parts per billion.
“I think the wind direction had a big impact,” Davis says. “The wind was coming more out of the north, northeast whereas the normal summer air flow tends to be from southwest to northeast.”
The highest eight-hour average concentration in Rowan County so far this season was on June 4 with 89 parts per billion. There is no monitor in Cabarrus County, but a monitor exists on the Mecklenburg/Cabarrus line.
The national standard was lowered in 2008 to 75 ppb from 85 ppb, which was set as the standard in 1997. The EPA is proposing to drop the standard to between 60 and 70 ppb. “If the EPA drops that standard to 60,” he says, “we would have reported elevated levels across the state of North Carolina on 94 days, which is huge.”
Downward Trend in Ozone Levels over Past 10 Years
Davis says the general trend over the past 10 years has been notably declined ozone concentrations. “When I started doing this for the state about 15 years ago,” he says, “the levels and the frequencies were all much higher.”
There are several reasons ozone concentrations have dropped, he says. One is the Clean Smokestacks Act enacted by the North Carolina Legislature in 2002, which required power plants to reduce nitrogen oxide emissions.  
Davis says North Carolina residents have also become more energy conscious. “The compact fluorescent light bulb everybody uses now, seven years ago it was a weird-looking thing on the shelf,” he says. “Now everybody’s got them … so you burn less electricity and the power plants don’t have to run as hard.
“If every household across the state has 20 of them, it makes a big difference.”
Another reason that we see improvement, he says, “is the changeover of the vehicle fleet. As the older cars age out, news cars are actually coming into the population of vehicles. “The newer vehicles, especially the ones which get higher miles per gallon, have distinctly lower nitrogen oxide emissions.”
Davis says another factor in ozone levels is traffic flow. The Interstate 85 bypass that now misses Greensboro and the Interstate 40 bypass that misses Winston-Salem along with more lanes going into Charlotte keep traffic moving. “They’re not just sitting there running their engines,” he says. “So as the highway system gets better, it makes for less emissions.”
Davis says one of the biggest variables with ozone levels is the weather because the wind blows in from one direction if it rains or it’s a cloudy day. “It all impacts,” he says, “but those are the things that we’re not able to control. We are able to control the emissions.”