Ozone levels across Shelby County crossed acceptable limits for the fourth time this year on June 23, causing the Alabama Department of Environmental Management (ADEM) officials to place the area back under federal control for pollution.

The announcement came less than a month after Shelby County was declared clean of harmful air pollutants.

For the past week, Jefferson and Shelby Counties have been under an air quality alert, with officials asking residents to cut back on driving.

The ADEM air quality index listed the Birmingham area as a 106 on a scale of 0-500. Such high levels of ozone concentration can be unhealthy, the index states.

&8220;Active children and adults, and people with lung disease, such as asthma, should reduce prolonged or heavy exertion outdoors.&8221;

The city of Helena, which produced the county&8217;s latest &8220;unacceptable&8221; reading on two weeks ago, has become a hotspot for high readings because air pollution tends to drift there from other areas.

Following air-quality control tests this week, Alabama officials will begin work on an 18-month plan to bring Shelby County and the surrounding area back under acceptable air quality limits