Atmospheric Sciences Research Spotlight

Evaluating the Impact of Maryland's Healthy Air Act

Reducing emissions of short-lived gaseous sulfur pollutants from power plants had an immediate, local benefit, but controlling longer-lasting harmful particulate matter will require regional action.

Source: Earth's Future


Many regions of the United States suffer from air pollution severe enough to harm human health. To alleviate such conditions, the state of Maryland implemented its landmark 2009 Healthy Air Act, the East Coast’s strictest power plant emissions law. The first phase reduced emissions of sulfur dioxide, a short-lived pollutant linked to respiratory illnesses, by roughly 80% compared with 2002 levels. The legislation was also expected to reduce longer-lived sulfate aerosols—tiny particles suspended in the atmosphere, then the main source of air pollution–related deaths in the United States.

Here He et al. evaluate the impacts of these dramatic emissions reductions on local and regional air quality. The researchers analyzed the trends in sulfur dioxide and sulfate aerosol pollution above Maryland and the surrounding states for two 3-year intervals, one prior to 2006–2008 and one following implementation of the legislation (2010–2012). Using aircraft, satellite, and surface measurements, the team consistently found that summertime levels of both sulfur and particulate pollution decreased across the region following implementation of the Healthy Air Act.

The researchers discovered a significant difference, however, in the degree of these reductions. Whereas atmospheric and surface sulfur dioxide concentrations decreased by about 50%, the concentrations of sulfate aerosols only declined by about 20%. The team attributes this discrepancy to the greater atmospheric lifetime of the sulfate aerosols, which persist about 5 times longer than sulfur dioxide. They argue that regional, upwind sources of sulfate aerosols play a much more important role in determining Maryland’s air quality than comparable sources of sulfur dioxide, whose atmospheric lifetime of about a day is comparable to the transport time across state borders.

Although local emissions regulations like Maryland’s Healthy Air Act are effective at improving air quality for short-lived pollutants, substantial reductions in longer-lived pollutants like harmful particles will require regional controls across state and international borders, according to the researchers. (Earth’s Future, doi:10.1002/2015EF000330, 2016)

—Terri Cook, Freelance Writer

Citation: Cook, T. (2016), Evaluating the impact of Maryland’s Healthy Air Act, Eos, 97, doi:10.1029/2016EO051979. Published on 12 May 2016.

© 2016. The authors. CC BY-NC-ND 3.0