Maryland is "very close" to meeting all federal air quality standards, state environmental officials said Monday, but tightened regulations on ozone pollution could mean an uptick in "Code Orange" air quality days this summer.
The Environmental Protection Agency last year lowered the threshhold for what is considered an unhealthy level of ozone from 75 parts per billion to 70 parts per billion. Three of 18 ozone monitors around the state have not yet measured below the new threshold, according to the Maryland 2016 Clean Air Progress Report.
That could mean hot summer days that have, in the past, been labeled "Code Yellow" on the Air Quality Index — a "moderate" level of pollution — may now cross into "Code Orange" territory, which is considered unhealthy for sensitive groups such as children and the elderly.
Ozone is a form of oxygen that is beneficial in the upper atmosphere but a harmful pollutant at ground level. It comes from chemical reactions between vehicle and industrial emissions and sunlight.
Levels of particulate matter, the other chief air pollutant, have meanwhile been below federal standards since at least 2010, according to the report.
Maryland Department of the Environment Secretary Ben Grumbles said the state must continue to invest in improving air quality to meet the new ozone standard.
"More needs to be done, within the state and beyond in upwind states, to consistently improve and maintain Maryland's air quality," he said in a statement.
Up to 70 percent of ozone measured in Maryland comes from upwind states, officials said.
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