What’s next for air quality in the United States?

Tracey Holloway
University of Wisconsin, USA

Whether you remember the 1970s, or – like me – have seen hazy skylines in movies like Rocky, you may notice something has changed. The U.S., like many other industrialized countries, has drastically cleaner air today than in decades past.

Figure 1
Figure 1: (above) Philadelphia, Pennsylvania as seen in the movie Rocky, released in 1976, image from United Artists; (below) Birmingham, Alabama, July 1972, photo by Leroy Woodson, National Archives, Records of the Environmental Protection Agency

A layer of haze used to be a common part of city life. While occasional bad air days still occur throughout the U.S., on most days, in most cities, the air is clear and and for the most part healthy. If you could breathe that ‘70s air, you would feel the difference in your lungs, your eyes, and your life expectancy.

Airborne concentrations of carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead have decreased 60-93% between 1980-2013. The frequency of high ozone “smog” days has plummeted.  Particles in the air, considered most damaging to human health, have gone down by a third just between 2000-2013. These benefits have all been achieved – remarkably – while our population has grown, the U.S. economy has soared, energy use has risen, and the miles we drive have almost tripled since 1970. Figure 2 shows these trends from 1970-2013.

The massive clean-up in U.S. air pollution was brought about by the Clean Air Act, subsequent Figure 1bamendments, and built-in mechanisms to review and update air standards, known as the National Ambient Air Quality Standards (NAAQS, pronounced “nacks”). In the U.S., we have a layered system of air pollution control, where the federal government sets air pollution limits to protect public health, while states and industries are charged with lowering emissions to meet these goals. For example, states operate permitting systems, where industries and power plants apply to expand and build new facilities. There are also industry-wide standards on technologies, markets for trading sulfur and nitrogen oxide emissions among power plants, and county-specific requirements on vehicle emission testing.

The U.S. air quality management system has been remarkably effective at yielding health benefits to the U.S., but is it also expensive. According to a 2014 Draft Report from the White House, about half the costs of all unfunded federal regulations are due to regulations from the Environmental Protection Agency (EPA). By far the most costly environmental rules are those aimed at air quality. The cost of implementing air rules totals about $50 billion each year.

Still, the benefits are huge. When economists put dollar values on lives saved or extended, hospital visits avoided, work and school days not missed – the payback on the U.S. investment in clean air is about $10 for every $1 we spend. According to that White House report, air rules account for 98-99% of the monetized benefits of all EPA regulations.

Figure 2
Figure 2: Comparison of trends in economy, vehicle miles traveled, population, energy, carbon emissions, and emissions of criteria pollutants. From EPA http://www.epa.gov/airtrends/images/y70_13.png

As the air gets cleaner, health researchers evaluate how mortality and morbidity patterns are changing. In some cases, new research finds new health risks, even at lower air pollution levels. As a result, EPA air standards have generally been getting stricter over the past 40 years, even as U.S. air gets cleaner and cleaner. A new standard was announced for the fine particulate matter NAAQS in 2012 and the ozone NAAQS was lowered in 2008 as part of previous review cycles. These cycles continue based on mandates under the Clean Air Act and these NAAQS could be lowered again in the future.

On October 1, 2015, the EPA will announce the outcome of the current review of the ozone NAAQS. For reference, the current U.S. standard is 75 parts per billion (ppb) and the 2015 Canadian standard is 63 ppb. Depending on whether the EPA changes the ozone standard, and – if changed – how tight it is set, the number of U.S. counties in or out of attainment may change.

Compliance with the NAAQS is primarily determined by measurements from ground-based monitors – instruments recording pollution levels across the U.S. In the case of ozone, the NAAQS level is set based on the maximum 8-hour average, often spanning late morning through the afternoon. Ozone is chemically produced in the presence of sunlight, so concentrations peak during the afternoon, reaching the highest levels on hot, sunny days.

Figure 3, from collaborators of mine at the Lake Michigan Air Directors Consortium (LADCO), shows the 2011-2013 average of the 4th highest maximum daily 8-hour ozone value, also known as the “design value” for ozone over this three-year period. Across the region, 2012 was a particularly hot summer. As a result, 2011-2013 shows more design values above the 75 ppb threshold than occurred during 2008-2010 or 2009-2011, the years used by EPA to finalize non-attainment with the current ozone NAAQS. With summer temperatures projected to increase in future years, it may become more difficult to meet ozone targets.

Figure 3
Figure 3: Presented to National Air Monitoring Conference, Atlanta, Aug. 2014 Donna Kenski, Ph.D. Lake Michigan Air Directors Consortium Rosemont, IL

U.S. success in air pollution control may be attributed to technology improvements such as catalytic converters, particulate filters, and stack scrubbers. These end-of-pipe treatments have been effective in reducing gas- and aerosol-phase emissions of health-damaging pollutants. But this approach may not carry us through the decades ahead. To control carbon dioxide, the next major challenge for U.S. air quality, there are significantly fewer end-of-pipe solutions.

Instead, carbon control necessitates large-scale changes to our energy system, especially electricity production, transportation, and the built environment. As it adapts to meet both carbon and air quality goals, the U.S. energy system will be shaped by policies at the local, state, and national scales. Where current air quality management occurs primarily through interactions between state-level resource management agencies and the federal EPA, effective control of health-damaging and greenhouse gas emissions will require the engagement of new stakeholder communities.

Municipalities, for example, have mechanisms to reduce energy consumption and associated emissions that are unique to the local scale, such as many building codes, urban development plans, or transit system design. These policy and technology options have not typically been integrated with state-level air quality management planning. In a similar way, other agencies may play a larger role in air quality management as energy systems change.

Fortunately, integration of climate and air quality planning can also yield big benefits, including pollution control cost reduction. By including the value of air quality and health benefits in carbon policies we reduce the cost of carbon mitigation, and we may even save money on air pollution control. There are three broad approaches to reduce emissions from energy use: 1) reduce energy consumption; 2) reduce fuel burned to meet energy demands; or 3) reduce the emissions per unit fuel combusted. For the most part, technology solutions applied to control emissions of health-damaging air pollutants fall into this third category – where emissions are addressed without energy or fuel reductions. Carbon emissions are trickier to control with this technology approach. Except for (expensive) carbon capture and storage, the only way to reduce carbon without reducing fuel use is to switch to lower carbon fuels like natural gas or biofuels. Unlike reactive gases and particles, there are no technological solutions to emit less carbon from the same amount of a particular fuel.

Carbon reductions are, however, a natural outcome of energy reductions and fuel efficiencies. These same measures typically reduce emissions of other regulated pollutants, including those that are already costing billions of dollars to control. As such, energy efficient technologies, or policies that reduce consumption hold the potential for a quadruple-win: reduced carbon, reduced need for expensive end-of-pipe air pollution controls, reduced energy expenses, and healthier people.

While better integration of energy and emission strategies makes sense, the linkages between cause and effect are not obvious. The air quality management community already uses a complex suite of computer models to evaluate how emission changes will lead to air quality outcomes. As we consider the role of behavior, fuel choice, and energy policies, the scope of model and evaluation methods will need to expand. For example, transportation models are needed to link rush-hour traffic and congestion mitigation with air emissions. Similarly, energy dispatch models are need to calculate where, when, and how much emissions will change as a function of demand, fuel costs, and renewables. Fortunately, we are not starting from scratch. There are already tools that are widely used by the transportation, energy, and other industry and regulated communities – they just need to be better integrated with air quality assessment and research.

The U.S. air quality system also has the potential for big benefits from new data sources. Increasingly satellites are able to “see” health- and climate-relevant air pollution from space. Figure 4 shows how satellites can detect reductions in nitrogen dioxide, emitted primarily from vehicles, power plants, and industry. Nitrogen dioxide is regulated with the NAAQS, and it is a key precursor in ground-level ozone and certain types of fine particulate matter. So, an understanding if sources and trends bears direct relevance to air pollution control. Besides nitrogen dioxide, satellites can detect particulate matter, carbon monoxide, sulfur dioxide, formaldehyde (another precursor to ozone), and climate gases including methane and carbon dioxide.

These eyes in the sky offer an opportunity for assessing air emission patterns and trends, evaluating models, understanding air chemistry, and deciding where to site ground-based monitors. Over the past few years, I have worked with a team of NASA-funded researchers, the NASA Air Quality Applied Sciences Team (AQAST), to better link satellite data with air quality management. It has been exciting to be part of the effort to link satellites in space with health and energy issues here on earth.

A lot has changed since 1970, when the Clean Air Act was first passed. Back then we did not have an understanding of air quality as a multi-scale issue. We did not yet see climate change occurring, or have policies in place for carbon control. Computer modeling of energy and atmospheric processes was just beginning. And, the idea of satellites seeing invisible gases near Earth’s surface would have been science fiction.

Figure 4
Figure 4:Nitrogen dioxide as seen from space by NASA’s Ozone Monitoring Instrument (OMI), aboard the Aura satellite. http://airquality.gsfc.nasa.gov

Air quality in the U.S. is a success story, but the story is not over. We are turning a corner in the science, engineering, policy, and law of air quality.  Whatever the next chapter holds, it is likely to create healthier communities, lower-carbon energy systems, and new connections among problem-solvers across energy and environmental fields.

Postscript: These issues, and others, are the basis of the 2015 Energy Summit at the University of Wisconsin—Madison: Air and Energy, The Path Ahead for U.S. States. The Energy Summit is open to the public on October 13, 2015, hosted by the Wisconsin Energy Institute, and chaired by Dr. Holloway. Information and webcasts will be available here: https://energy.wisc.edu/events/2015-energy-summit

Tracey 2

Dr. Tracey Holloway is Professor at the Nelson Institute for Environmental Studies at the University of Wisconsin – Madison, USA.  She is also inaugural Public Engagement Fellow of the Alan I. Leshner Leadership Institute for Public Engagement with Science for 2016-17.

Header Image:  San Diego, California.  Credit: Author


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