HOUSTON (CN) — A bipolar frenemy that protects you from skin cancer but damages your lungs and makes you sluggish when exercising outside on hot summer days, ozone is oxygen’s enigmatic cousin.
Discovered in lab experiments in the 1800s, ozone, O3, is a gas made of three oxygen atoms, rather than two.
It’s mostly a friend. Ninety percent of the ozone in the atmosphere is in the stratosphere, 6 to 31 miles above the earth’s surface, forming the ozone layer that protects humans from the sun’s ultraviolet radiation.
Its dark side is found in the remaining 10 percent, which forms in the troposphere — from the earth’s surface to 6 to 10 miles above it — when nitrogen dioxide and volatile organic compounds such as benzene, emitted by cars and factories, cook in sunlight on hot summer days.
In sprawling Sunbelt cities such as Houston, where carpooling and mass transit are almost sacrilege, and the population is exploding with people taking advantage of the relatively low cost of living and healthy job market, bringing more vehicles and gridlock, conditions are ripe for bad ozone, also known as smog.
Ozone’s wrath is fickle.
“Ozone is partially due to high temperatures, hot days, calm winds,” said Neil Carman, clean air director for the Sierra Club’s Lone Star Chapter.
“When the winds die to almost nothing, you’ll see peak ozone levels forming. Also clear skies. So it’s a combination of warm temperatures, clear skies, calm winds and a lot of precursors, the volatile organic compounds, the nitrogen oxides.”
Carman keeps daily tabs on some of Texas’ nearly 120 ozone monitors. He said ozone is typically a problem in Houston from April to October, and the peak hours are from 10 a.m. to 6 p.m., with two rush-hour driven spikes, after the morning and evening commutes.
Due to its three oxygen atoms, ozone is unstable, meaning it is much more sensitive to meteorological changes than oxygen.
“Oxygen is stable, but ozone is not. So, for example, if the wind picks up from being calm to like suddenly there’s a breeze coming in from the Gulf of Mexico, 10 to 15 mph, the ozone is instantly breaking down,” Carman said.
“You see it in the monitors. The ozone levels fall. Or if the sunlight is blocked by clouds coming in from the Gulf, the ozone levels will quickly, almost instantly, drop.”
Through Tuesday this week, there have been 15 “ozone-action days” issued for Houston this year, according to Andrew Keese, spokesman for the Texas Commission on Environmental Quality.
The TCEQ advises “sensitive groups” — children, the elderly and people with breathing problems — to limit outdoor activities on such days.
But what are the risks for healthy younger adults?
Dr. Richard Castriotta, Director of Pulmonary and Sleep Medicine at McGovern Medical School at The University of Texas Health Science Center in Houston, said that unlike other air pollutants, ozone is a molecule, so it’s too small to be filtered by masks, and can evade the body’s natural defenses.
“A lot of the other pollutants will get trapped up in our nose and in the back of our throats in mucus membranes before they get down into the lower levels of the lungs,” Castriotta said.
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