Population: 2,172,191

Cardiovascular cases: 534,359

Rank in most ozone-polluted cities: 21

The Southern Ohio city has been stepping up its efforts to improve air quality over the past few years by launching several different programs, according to a Megan Hummel, a spokeswoman for the Southwest Ohio Air Quality Agency.It has retrofitted hundreds of old diesel engine school buses and replaced dozens more to reduce harmful emissions.The second initiative is a 24-hour hot line to report smoke, dust and odors. People can call and inspectors are available to check out problems.As part of that effort, Hummel said the city has distributed canisters to residents who can capture the condition in case it dissipates before the inspector arrives."They can turn a valve on the canister when the condition happens," said Hummel. The contents are later tested.

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