Consider these two facts:
One, motor vehicles account for about 45% of ozone-causing pollution, according to the City of Indianapolis' Office of Sustainability. Two, traffic in June and early July was down nearly 5% in Indiana compared to that same time last year.
So, it stands to reason that Hoosiers have endured fewer "bad air days" this year.
Except we haven't.
Despite the drop off in vehicle traffic, the number of ozone Air Quality Action Days in Indiana has not decreased this year. The number of days is actually similar to three of the four previous years.
Experts say the weather could be to blame. The heat and other weather conditions this summer — which are also necessary for ozone formation — could be outweighing the effect of decreased car traffic.
Barry Sneed, the public information officer for IDEM, said in an email this is a "modest decrease." He also stressed that weather is the main underlying factor to ozone formation.
Janet McCabe, director of the Environmental Resilience Institute at Indiana University, said the traffic decrease is “not insignificant,” but she echoed Sneed that ozone levels are also dependent on weather. She said that when there is hot, sunny and stagnant weather in late June — the peak time for ozone formation — there will likely be high ozone levels. Indiana saw three ozone action days in the second half of June this year — on June 18, 19 and 20.