Why Do Heat Waves Make Ozone Pollution So Much Worse?

This mu’fucka’ is hot.
This mu’fucka’ is hot.
Photo: Getty

Boy, is it hot? The gnarly heat wave we’ve been dealing with since last week isn’t quite over yet—and it doesn’t just cause us to sweat and complain. Events like these usually bring awful ozone pollution, too. And that’s stuff people need to worry about, especially as they’re outside enjoying their Fourth of July.


With the sun beating down hard, heat indexes are reaching well into the 100s across the U.S. this week. That’s resulted in cities declaring Ozone Action Days across the nation, which only happens when the air quality reaches unhealthy levels. On Monday, 72 cities declared an action day, according to Weather Underground. These advisories are continuing through the July 4th holiday in at least five cities across the Northeast and Midwest.

Ozone is a gas that, in our upper atmosphere, protects life on Earth from harmful ultraviolet rays. Near the ground, it’s a pollutant that forms from nitrogen oxides and volatile organic compounds. These chemicals spew out of vehicle exhaust and refineries, and they react to form ozone in the presence of sunlight.

“Like most chemical reactions, that chemical reaction comes faster in warmer temperatures,” explained Jeff Masters, a meteorologist with Weather Underground, to Earther. “So you’re going to crank out the ozone the hotter the temperature is
. That’s why ozone is a summer problem.”

At high enough levels—above, say, 70 parts per billion—ozone pollution can cause muscles in the lungs to contract and increase the chance of lung infections. Although the summertime pollution is especially dangerous for vulnerable individuals (those with asthma, the elderly, and children) risks can be present even for healthy people, per the Environmental Protection Agency.

This week, ground-level ozone pollution is bad. In fact, an air monitor in southeastern New York saw its air quality enter the purple range with respect to ozone on Monday, Masters said. That’s the highest tier on the Air Quality Index (AQI) and means everyone is at risk from the air. AQIs that combine ozone and particulate matter are registering more moderate levels in the northeast today, except for Philadelphia, where the air quality is currently unhealthy.

Unfortunately, ozone pollution events like we’ve seen this week may be a sign of our times. And not just because the heat isn’t going away. The emissions aren’t either.


Under the EPA Administrator Scott Pruitt, emissions regulations are dwindling. Those regulations are what will ultimately keep the air safe from ground-level ozone. And from the greenhouse gases that warm the atmosphere, resulting in more hot days that are likely going to exacerbate ozone pollution.

Until things cool down, maybe keep your morning runs off the streets and head to the safety of the treadmill at your air-conditioned gym instead. If you’re enjoying a gluttonous Fourth of July barbecue, maybe take that hot dog indoors?


Yessenia Funes is climate editor at Atmos Magazine. She loves Earther forever.


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This is good earther, Yessenia.

In Pruitt’s defence, he might be confusing UV/ozone for water/wastewater treatment and ground-level ozone coupled with UV light from the sun. He didn’t get his job at the EPA from a career in photo-oxidation of skin cells and/or water/wastewater contaminants. He’s a lawyer from the oilpatch for crying out loud. Good christian federalists don’t move up O&G supply chain by getting lost in the technical details weeds. Especially weeds of science centered around environmental shit. God put all that oil and gas there for a reason.

Pruitt might be thinking about solutions instead of problems here. Git ‘r done environmentalism. For instance, there’s a big problem with fugitive methane (and other hydrocarbons) from oil and gas operations extending from the wellhead all the way to the end use. This was made more apparent lately as discussed previously on Earther.

Ruining the stratospheric ozone layer by releasing more ozone depleting chemicals such as refrigerants will allow for more UV light to penetrate down on us humans at the ground level. With more UV light intensity and more reactant ozone available for almost complete oxidation of things like skin cells on our bodies at ground level, more treatment of fugitive methane will occur (co-something or other). Photo oxidation isn’t necessarily compound specific.

Thusly, by Pruitt gutting environmental regulations on ground-surface ozone, he will fix the entire fugitive methane problem and allow for O&G to carry on without all those pesky federal regulations encumbering states’ rights and MAGA. Oil companies without those job killing burdensome enviro regs will have more money for its’ foundations philanthropy and greenwashing. Pruitt’s just doing the lord’s work here.