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Modeling Matters

EPA scientists are developing advanced models to monitor pollution exchanges between air, water, and land.

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Historically, people have considered air, water, and land as separate systems, leading to divided research and management efforts. The Clean Air Act and the Clean Water Act, for example, provide distinct mandates for how the EPA sets regulations to safeguard these critical resources and to protect human health.

But, of course, air, water, and land are intricately linked: there is constant exchange between them across multiple scales—including the exchange and deposition of pollution. While EPA scientists have long used models to better understand how chemical constituents cycle through air and other systems separately, they are now tackling the challenge of linking them into connected, cross-media models that better reflect the complexity of real world conditions.

"To understand how the atmosphere moves the stuff that is put into it, scientists use models—collections of equations built from what we know," writes EPA research scientist Tanya Otte in her blog post titled Modeling Matters.

The world is interconnected and we need to start modeling it as such. While we couldn't do it before because of a lack of computer power and sophisticated modeling capability, we are closer than ever. Now is the time. - Dr. Robin Dennis, EPA Scientist

Dr. Robin Dennis, a senior scientist in EPA's Atmospheric Modeling and Analysis Division, is leading a team of Agency researchers and outside experts to develop a prototype set of models linking air, water, and terrestrial systems. These models will then be connected to a combined health and welfare benefits mapping tool, allowing policymakers to be more effective in maximizing the benefits and minimizing the costs of the environmental regulations they put into place.

"The world is interconnected and we need to start modeling it as such. While we couldn't do it before because of a lack of computer power and sophisticated modeling capability, we are closer than ever. Now is the time," says Dennis.

Making the Connection: Nitrogen as a Multimedia Pollutant

One focus area for new modeling research is excess reactive nitrogen pollution, one of the country's most widespread and challenging environmental problems. Reactive nitrogen is natural and, in moderation, helps plants grow. But agricultural and industrial activity has gradually added more and more reactive nitrogen into the nitrogen cycle, beyond what ecosystems can handle.

Excess reactive nitrogen in soil, water bodies, coastlines, and the atmosphere is contributing to a host of environmental and human health effects, including acid rain, smog, particulate matter, coastal dead zones, harmful algal blooms, contaminated water, stratospheric ozone depletion, and global climate change.

For Dennis and his team, the ultimate goal is to track nitrogen—and other pollutants like sulfur oxides (SOx) and mercury—with a multimedia, one-environment modeling system. A model of this complexity is years away, but the team has started to build it in stages. The key pieces they are working on include:

  1. reducing uncertainty in atmospheric deposition models (how pollution moves between air and ground);
  2. connecting meteorology (atmosphere, weather) and hydrology (water systems) models to connect the hydrosphere for advanced climate and land-use change analysis; and
  3. expanding the capabilities of the atmospheric modeling system to better link to the ecosystem models.

This last piece—linking to ecosystems and "ecosystem services"—is the most challenging. The ecosystem models concern many things we care about in addition to clean air: water quality, water resources, biodiversity, and the health of our communities. As these prototype linkages become more developed, policymakers will be better able to zero-in on multiple pollution sources and problem areas and avoid unintended consequences as they craft solutions. By 2016, researchers hope to incorporate the effects of climate change at the regional level.

Improving the MARKAL model to Support Energy Decisions

EPA scientists are also improving existing models. A team of EPA scientists is developing databases of U.S. energy production to advance the capability of the MARKet ALlocation (MARKAL) model. This model, created in the late 1970s by the Brookhaven National Lab, identifies the complex tradeoffs involved in choosing between energy sources.

EPA's team uses MARKAL to compare how different energy use scenarios—such as the expanded use of electric vehicles, biofuels, hydrogen fuel-cell vehicles, large-scale batteries, and solar power—could affect air pollution, greenhouse gas emissions, and water use.

"Electric vehicles are a good example of how our choices in producing and using energy are all interrelated," explains EPA scientist Rebecca Dodder, a member of the MARKAL research team. "We can use MARKAL to examine different ways that these choices could play out, gaining important insights about their environmental implications."

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