The Rio Grande Valley had the second-worst air quality in the country on Monday morning, according to an index published by the federal government.

The Valley had an air quality index of 110, which is considered unhealthy for sensitive groups, according to AirNow.gov. Only Hamilton County, Florida, had a higher air quality index.

A index score of 101 to 150 is considered unhealthy for sensitive groups.

"Although general public is not likely to be affected at this AQI range, people with lung disease, older adults and children are at a greater risk from exposure to ozone, whereas persons with heart and lung disease, older adults and children are at greater risk from the presence of particles in the air," according to AirNow.gov.