A few of you might have seen the MNDOT signs “refuel after dusk” on Memorial Day. KARE 11 viewer Steve Hurt sure did, and posted this request on our Facebook page.
"Can Sven please explain the MNDOT sign yesterday that read 'refuel after dusk- poor air quality'?"
He can, and did. Here is Sven's response.
You may have also associated this (the refuel after dusk sign) with the air quality alert across much of Minnesota and you’d be right. How on earth are the two related? We know our cars put off pollution but on hot, sunny days with calm winds we’re particularly concerned about ozone.
When you pump gas volatile organic compounds in the gas (VOCs) are released and when the extreme heat and strong sun interact with them, one of the results is ozone. Ozone is hard on our breathing- especially vulnerable populations like the elderly and those with asthma or other breathing issues. There is also particulate pollution that gets trapped on 90 and 100 degree days, but ground-level ozone increases dramatically on hot, sunny days.
Ozone is good when it’s in the stratosphere, miles above us. In fact, the chemical reaction that takes place between the sun and ozone (3 oxygen atoms) absorbs ultraviolet energy that would otherwise have negative consequences here on earth’s surface. Oxygen (2 oxygen atoms) is, of course, what we need, and constitutes about 20% of our air we breathe. CFCs (chlorofluorocarbons) in the 1970s and 1980s contained chlorine which interacted with ozone to deplete it by bonding with oxygen atoms thereby decreasing ozone and creating ozone ‘holes’ that have since mostly recovered. That serves as a sure sign that when humanity decides to mitigate a problem we’ve created in our atmosphere we CAN have a positive impact.