As expected, Louisville's air was unhealthy yesterday. But there are discrepancies as to exactly how unhealthy.
Air Pollution Control District spokesman Tom Nord says the highest recorded reading was at the district's air monitor in New Albany. It registered 104 parts per billion of ozone in the air, which translates to a 172 on the Air Quality Index. That's a red alert–when the air is unhealthy for everyone to breathe.
But the federal government-run AIRNow website reported different data. At one point yesterday, Nord says AIRNow reported an AQI of 201 in Louisville, which is categorized in the purple range, or VERY unhealthy for everyone. Jim Bruggers of the Courier-Journal has a screenshot here.
The APCD still isn't sure why the two numbers don't line up. Nord says AIRNow gets its information directly from the APCD's air pollution monitors, and the district is checking to see why the site reported different information.
I'll update here when I hear back with an answer.
UPDATE: 3:35. Tom Nord from the Air Pollution Control District confirmed that the discrepancy lies with how AIRNow and the APCD calculate the ozone levels. The district uses an eight-hour average, which is the standard approach. But AIRNow runs a calculation to generate a “real-time” estimation of the air quality. So, both numbers are right. At the New Albany monitor, ozone levels did spike and for a time, the AQI was at 201. But overall the AQI for the eight hour period was 172. Either way, both numbers are unhealthy.
“I agree that it’s better to overstate the danger of ozone rather than understate it, but it’s a tough line to walk,” Nord wrote in an email. “Overall, I think we do our best to warn people that the air might be bad on a given day without creating undue panic or anxiety.”