The Success of Maryland’s Healthy Air Act

Pollution levels in Maryland plummeted this year in response to the COVID-19 pandemic. Even before the widespread shutdown, hot summer days in Maryland rarely receive code red and purple designations for unhealthy air quality like they did a decade ago. The reason: Maryland’s Healthy Air Act.

Aerial photograph of Baltimore from a June 2018 research flight. Photo credit: Sarah Benish

The Maryland Department of the Environment (MDE) implemented the Healthy Air Act in 2009 to require major reductions in atmospheric pollutants—such as nitrogen oxide, sulfur dioxide, and mercury emissions—from large coal burning power plants. The legislation also required Maryland to become a member of the Regional Greenhouse Gas Initiative, a market-based program to reduce greenhouse gas emissions in the energy sector. Atmospheric pollutants, including carbon dioxide, contribute to global warming.

The Healthy Air Act dramatically improved air quality in Maryland. University of Maryland atmospheric scientists involved in the Regional Atmospheric Measurement Modeling and Prediction Program, or RAMMPP, have integrated air quality forecasting, measurements and chemical transport models to generate a more informed understanding of the factors controlling air quality in the region and is a key component in improving the state’s air quality.

“Results from the RAMMPP greatly helped Maryland to attain its air quality with providing scientific evidence for the State Implementation Plan,” explains Hao He, an assistant research professor in atmospheric and oceanic science at UMD. The State Implementation Plan is a state plan for complying with the federal Clean Air Act.

Local sulfur dioxide emissions fell by approximately 90 percent after implementation of the Healthy Air Act in 2010. In 2012, aircraft results from RAMMPP indicated a decrease of approximately 40 percent in column sulfur dioxide and a decrease of approximately 20 percent in aerosol loading over Maryland. Satellites measure air pollutants by looking down through the atmosphere, producing a column of measurements that do not necessarily reflect concentrations at the surface. Aircraft observations from RAMMPP were converted to column amounts in order to directly compare with satellite data. Satellite data from the Ozone Monitoring Instrument of sulfur dioxide and particulate matter showed similar downward trends. These results were published by researchers including He in 2016 in the journal Earth’s Future.

Airborne observations of air pollution play an important role in informing air pollution regulations in Maryland.

As the toughest power plant emission law on the East Coast, Maryland’s Healthy Air Act focused on reducing emissions from the state’s largest and oldest coal-burning power plants. According to MDE’s 2017 Clean Air Progress Report, Maryland power plants invested $2.6 billion in air pollution controls.

Among the measures taken by Maryland coal-fired power plants, many installed flue gas desulfurization technology to “scrub” sulfur dioxide from their exhaust. Scrubbers use chemicals inside the stack, such as limestone or magnesium oxide, to react with sulfur dioxide in the flue gas, thereby removing it from the exhaust. Power plants also reduced pollution by switching to low-sulfur fuel and by burning natural gas for electricity instead of coal.

 “Scrubbers for sulfur dioxide were mandated and a specific time was set. When that time came, the scrubbers had to be in place and ready to turn on. This happened efficiently,” explains Russell Dickerson, a professor in the UMD Department of Atmospheric and Oceanic Science.

Despite improvements in Maryland air quality due to the Healthy Air Act, the state sued the U.S. Environmental Protection Agency over pollution originating from neighboring upwind states. “Maryland has made significant progress in improving our air quality in recent years, and that progress is in jeopardy due to a lack of action by the EPA,” said Maryland Governor Larry Hogan when announcing the lawsuit. Seventy percent of Maryland’s ozone pollution comes from upwind regions, according to Maryland officials.

“The particulate matter pollution is regional due to long-range transport of air pollutants from upwind states such as Pennsylvania and Ohio,” He explained.  “Regional control measures are needed to improve Maryland particulate matter pollution.”

Continued air quality research informing state decision makers is necessary to best protect the health of all Marylanders. While the pandemic has reduced the threat of air pollution in many areas, the complex interactions between pollution and the coronavirus requires further investigation. The MSTEHP fellowship could play an important role in helping address the direction of future air quality research and subsequent recommended policies for the state.

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