Smog increased slightly in Maryland last year amid hot weather, missing a recently tightened federal air quality standard. But state officials said the air was nevertheless healthier than it has been during muggy summers in the early 2010s.
The Maryland Clean Air report found that ozone levels were slightly higher in 2016 than in 2015, while fine particles and sulfur dioxide pollutants held steady.
But officials said the number of days and hours when air conditions were considered unhealthy decreased relative to previous warm years. They credited state efforts to rein in power plant emissions and promote clean cars, but said more must be done to keep pollution from blowing in from other states.
"We're making clean air progress with strong partnerships and steady investments, but more is needed regionally and nationally to sustain our pace and protect our health," Maryland Department of the Environment Secretary Ben Grumbles said in a statement. "Marylanders' hearts, lungs and waterways will benefit from smart actions at home and in upwind states to keep improving our air quality."
Ozone levels around Baltimore were better than in the Philadelphia region but worse than in Washington, D.C., according to the report.
Ozone is created when nitrogen oxide pollutants from vehicle and industrial exhaust interact with organic compounds in the sunlight. Ozone pollution can trigger the EPA to issue "Code Orange" or "Code Red" air quality alerts on hot summer days with little wind.
Summer 2016 was the third-hottest on record in Maryland, and the fifth-hottest on record for the contiguous United States, according to the National Centers for Environmental Information.
Maryland officials are pressing the EPA to step in to reduce pollution that blows into the state on hot days. They petitioned the agency in November to require 19 coal power plants to do more to cut their emissions on those days.
David Smedick, leader of the Sierra Club's "Beyond Coal" campaign in Maryland, said more hot days, and thus more ozone, "are what we need to be preparing for moving forward." The environmental group is urging Gov. Larry Hogan to support strengthening of a carbon-capping partnership for power plants across the Northeast.
Smedick also emphasized that air quality remains unhealthy around the H.A. Wagner Generating Station in Pasadena, which the EPA last year said is not meeting federal standards for sulfur dioxide pollution.
State officials said they are preparing a plan for EPA showing how they will bring the air around the coal plant to healthy levels.