The air quality levels in both Trumbull and Mahoning counties are safe, the Trumbull County Emergency Management Agency director said U.S. Environmental Protection Agency monitoring shows.

EMA Director John Hickey said both counties’ air quality was tested Monday night. The U.S. EPA tested for phosgene, hydrogen chloride and multiple volatile organic compounds (VOCs). These are chemicals and compounds that could have been created by the train derailment and subsequent controlled burn in East Palestine.

Hickey also said the air quality is continuing to be monitored at the site of the derailment by aircraft and ground vehicles. He said safe levels were reported at the site on Monday.

The Ohio EPA, U.S. EPA and the Mahoning County hazardous material (HAZMAT) agency are the professionals, Hickey said, and he is just reporting their results.

On Monday night, an odor was reported in some local areas thought to be due to the controlled burn, especially in southern Mahoning County. According to Tuesday’s update from the U.S. EPA, the reason is that byproducts of the controlled burn have a low odor threshold, which means people can smell the contaminants at a much lower level than what is considered hazardous.

When the odor became apparent, Trumbull and Mahoning County EMAs recommended people stay inside and keep doors and windows shut. Hickey said this was strictly a precaution to give the EPA time to do testing.

“There was no thought that anything could be wrong. Mahoning County was experiencing some problems,” Hickey said of the smell. “So, I did what I could do to keep people safe. That’s all I want to do.”

A Tuesday update provided by the U.S. EPA states that during Monday’s controlled burn of rail cars containing vinyl chloride, air monitoring detected particulate matter resulting from the fire.

But, in the hours following, no chemical contaminants of concern, like phosgene, hydrogen chloride and VOCs, were detected.

The Air Quality Index (AQI) measures particulate matter and ozone in the atmosphere. AQI levels are measured from zero to 500 and are divided into six categories, each of which corresponds with different health concerns, according to Air Now, a U.S. government resource on air quality.

“Green” or “good” air quality corresponds with values zero to 50 and means that air pollution poses little or no risk. The next category up is “yellow” or “moderate.” This corresponds with the values 51 to 100 and means the air quality is acceptable, but there may be a risk for some, especially those who are “unusually sensitive” to air pollution, according to Air Now.

Throughout the past week, the AQI in the Youngstown area averaged in the “good” category every day. On Feb. 1, the AQI was 43; on Feb. 2, the AQI was 49; on Feb. 3, the day of the derailment, the AQI was 14; on Feb. 4, the AQI was 26; on Feb. 5, the AQI was 19; and on Feb. 6, the day of the controlled burn, the AQI was 32.

While particulate matter can have harmful effects on one’s health, it cannot be erased from the atmosphere, according to Air Now. Particulate matter sources range from construction sites, unpaved roads, fields or fires. But, most particle s form in the atmosphere as a result of reactions of chemicals emitted from power plants and automobiles.