By most measures, Louisville’s air quality has been pretty good this summer.Typically, ozone is the pollutant that causes the problems: local pollution gets trapped in the Ohio River valley and cooks under the hot summer sun. A notoriously bad year for ozone was 2012, but since then Louisville hasn't had any days that exceeded the federal ozone standard.But this year’s Fourth of July celebrations caused problems with another type of air pollution:particulate matter, or soot, which is linked to health problems like aggravated asthma and respiratory problems.This year, for the first time since 2010, Louisville exceeded the federal 24-hour standard on July 4.The reason the city doesn’t routinely exceed the standard every Fourth of July is partially because the way the measurement is calculated. It’s a 24-hour average for particulate matter, or PM, that goes from midnight to midnight. If people don’t start shooting off fireworks until later in the evening, the pollution is effectively divided between two different days, APCD spokesman Tom Nord says.“Just by the nature of how the standard works, you’d see a spike, you could clearly see a lot of PM in the air, on our monitoring data around 9, 10, 11:00, 12:00, 1:00, 2:00,” he said. “And then it dissipates as people go to bed and they stop shooting fireworks off.”So the fact that the city hasn’t officially exceeded the standard in the past few years is sort of a technicality; the fireworks set off on the Fourth of July still increased the amount of particulate matter in the city’s air, just not enough all at once to trigger an exceedance.“We were very upfront,” Nord says, about previous years. “Obviously there was a lot of PM in the air. And if you were out there, you were breathing it. But it didn’t make an official exceedance.”But this year was different, perhaps because the cancellation of the large city-wide fireworks display at Waterfront Park caused neighborhoods to ramp up their own celebrations. All the monitors around town recorded spikes, but one was high enough to exceed the standard—theSouthwick Community Center monitorat 3621 Southern Avenue.Right now, the exceedance isn’t officially on the books. Once it’s confirmed, Nord says the Air Pollution Control District will likely ask the EPA to classify the exceedance as an “exceptional event”—it’s not something that’s routine for Louisville’s air—and if the EPA agrees the exceedance will be essentially erased from the record.
