Air Quality and Climate Connections

John D. Bachmann

The spread of the industrial revolution from Britain to the rest of Europe and North America in the nineteenth century began a massive, albeit inadvertent, experiment in planetary geo-engineering that continues to this day. In terms of atmospheric modifications, the key drivers were the shift in the dominant source of energy from biofuels and hydropower to the increasing consumption of fossil fuels required to power expanding industries and provide heat for the growing urban populations needed to support them (Keay, 2007). The early results of this ‘experiment’ were obvious in industrialized urban areas, especially those using coal for residential heating (Brimblecome, 1978; Melosi, 1980). These cities experienced episodes of sky-darkening smoke and fog that by the time of the London event of 1952 were found to produce marked increases in deaths and illnesses (Bell and Davis, 2007). Just a few years earlier, a new kind of eye burning smog of unknown origin had been found in Los Angeles (SCAQMD, 1997). These events led to governmental programs to reduce air pollution in the U.S. and Europe. They also prompted new monitoring and research programs in air pollution-related atmospheric and health-effects sciences and development of new technologies for reducing air pollution (Bachmann, 2007).

Research programs began to unravel complex atmospheric chemistry that transformed gases into particles and photochemical oxidants (Haagen-Smitt, 1952), which, together with advances in health sciences, broadened the pollutants and sources of concern beyond smoke. The focus on urban air quality, along with societal demands for cleaner air and more convenient heating sources, produced remarkable successes that were accelerated in the United States with the passage of the Clean Air Act (CAA) of 1970 (Bachmann, 2007).

By the mid-twentieth century, scientists were also working on the more subtle consequences of the continuing ‘experiment.’ In addition to launching the space race, the International Geophysical Year (IGY) (1957-58) funded the establishment of Charles Keeling’s base in Mauna Loa, which has provided a continuing record of atmospheric carbon dioxide (CO₂) since 1958 (Harris, 2010; Hofmann et al., 2009). The World Meteorological Organization coordinated worldwide atmospheric measurements for the IGY and began work on the Global Ozone Observing System and. by the late 1960s, the Background Air Pollution Monitoring Network; these were later merged into the Global Atmospheric Watch (WMO, 2014). By the end of the decade, scientists were trying to explain the curious trends in global temperatures, which rose through the 1940s and then began a continuing decline (Peterson et al., 2008). The possibility of growing CO₂ being partly responsible for the increase was recognized, but inconsistent with the decline. The 1969 criteria document for particulate matter (PHS, 1969, p. 42) noted “the observed increase in turbidity of the past few decades may play a role in the reported decrease in worldwide air temperature since 1940 by increasing the planetary albedo.” Despite some significant crosscutting work on global tropospheric chemistry (e.g. Levy, 1971), research on climate was, however, often separated from that driven by concerns over ‘dirty air.’

In the early 1970s, air pollution scientists began to take notice of more disturbing trends in rural locations. Surprisingly, rural sites were becoming more polluted as evidenced by increasing sulfates and turbidity and declining visibility in the eastern U.S. (Charlson et al., 1967; Frank, 1974; Miller et al., 1972). In the 1970s and 80s, both Europe and the United States recognized the emergence of regional-scale air pollution issues, including acid rain, regional haze, fine particles, and ozone (O₃) smog that were the result of increased regional emissions and long-range transport of air pollution (EPA, 1975; NRC, 1975; Wolff et al., 1977; Eliassen, 1978). The next two decades brought increasing evidence that such regional-scale air pollution was contributing to significant effects on public health and welfare. It was not until the 1990 CAA Amendments that U.S. policy-makers took serious steps to address the growing scientific evidence on the regional component of air pollution. The emerging scientific evidence prompted a “rethinking” of conventional air pollution policies, particularly concerning O₃ and acid rain (NRC, 1991; Bachmann, 2007). The realization that natural sources contributed significant amounts of volatile organic compounds on a regional scale meant that the focus of regional O₃ control needed to be weighted heavily toward anthropogenic sources of nitrogen oxides and not on reducing non-methane hydrocarbons, which are often the limiting precursor in more polluted urban areas.

The major reductions of emissions that were initiated by air pollution programs in the developed nations by the mid-1970s also provided a natural experiment for climate scientists. In the intervening years, continued advances in monitoring (Katz, 1980; Chow, 1995; WMO, 2014), satellite technology (Hoff and Christopher, 2009), and especially atmospheric modeling (Hidy, 1984; Seinfeld, 1988) made it easier to examine the linkages between air pollution and climate. New health research led to tighter air quality guidelines raising the importance of international transport of air pollution (Vedal, 1997; Pope and Dockery, 2006; Bachmann, 2007; Park et al., 2006; Fiore et al., 2009). By the late 1990s, these continuing scientific developments and insights had progressed to the point where the scientific and policy communities that had been focused on conventional air pollution and those studying global phenomena needed to be more closely coordinated (Jacob et al., 1999; Hansen et al., 2000; Jacobson, 2001). Work on understanding the climatic effects of globally important air pollutants, such as O₃, methane (CH₄), and aerosols like black carbon and sulfates, has expanded since (Hansen, 2002; Fiore et al., 2015), revealing both concerns and opportunities for air pollution and climate mitigation programs.

This year marks the 45th annual Air and Waste Management Association (A&WMA) Critical Review (CR). Understandably, most of these reviews have dealt with air quality related topics, and more recently, waste management. In the first 32 years of the program, only one focused on climate change (Firor and Jacobson, 1993). This is now the fifth such CR in the last 13 years, and the first to examine the links between climate change and air quality. This reflects the fact that climate change is widely recognized as one of the most serious challenges facing society now and for the foreseeable future. Because the U.S. and other developed countries have made such great strides in improving air quality, however, the magnitude of the continuing threat posed by air pollution around the globe is less well appreciated. The most recent World Health Organization estimates of the global burden of disease found that each year, up to 7 million premature deaths—or one out of every 8 deaths—can be linked to ambient and household exposures to air pollution, making it the number one environmental threat to public health globally (Burnett et al., 2014; WHO, 2014).

This year’s timely CR examines the rapidly growing body of scientific information underlying our understanding of the many linkages connecting air quality and climate change (Fiore et al., 2015). More than a compendium of studies, the authors discuss what is known and not known about key relationships and scenarios, and focus on results that ultimately may have relevance to present and future policy choices for both areas. The CR begins with a separate examination of the effects of air pollution on climate and the effects of climate on air pollution. The major air pollutant classes of interest are O₃ and precursors (including CH₄) and particulate matter (PM) and its components and precursors. Here the reader is introduced to key concepts and tools used in evaluating the relative contribution of various pollutants and source categories to climatic and air quality effects. The authors discuss the ‘Representative Concentration Pathway’ (RCP) scenarios that the Intergovernmental Panel on Climate Change (IPCC) relied on in charting alternative climate futures, ranging from no climate policy to massive CO₂ reductions. They note that all four RCP scenarios include the somewhat optimistic assumption that large reductions in O₃ and PM related air pollution emissions will occur over the next 100 years. They also note that air program reductions in sulfur oxide emissions and resulting ‘cooling sulfate particles’ may already have accelerated warming by ‘unmasking’ the effects of CO₂.

The authors’ analysis of climate effects on air quality suggests that the projected climate ‘penalty’ of a no-climate-policy scenario on air quality depends greatly on the extent of regional air pollution control strategies, but also on what happens to global CH₄ emissions. The authors move to an examination of the potential role that reducing various short-lived air pollutants might have in a more holistic strategy for climate, concluding that for climate, reducing emissions of certain air pollutants might serve a useful supplemental role in limiting near-term warming. But there is overwhelming agreement among researchers that preventing the multiple serious effects associated with long-term warming requires a substantial commitment to reducing CO₂.

Dr. Arlene Fiore is an Associate Professor in the Department of Earth and Environmental Sciences at Columbia University and Lamont-Doherty Earth Observatory and is eminently qualified to lead this review. Since her Ph.D. thesis at Harvard on regional air pollution and climate (Fiore, 2003), she has been among the leaders in this cross-cutting discipline. She has published over 80 peer-reviewed papers and was selected to be a lead author for Chapter 11 of the 2013 IPCC report. In 2011, the American Geophysical Union awarded her the prestigious James B. Macelwane Medal. Vaishali Naik is a Scientist in the Atmospheric Chemistry & Climate Group at NOAA’s Geophysical Fluid Dynamics Laboratory and was a contributing author to Chapter 11 of the IPCC report. She earned her Ph.D. in atmospheric sciences from the University of Illinois in 2003. Eric M. Leibensperger is an assistant professor in the Center for Earth and Environmental Science at the State University of New York at Plattsburgh. Eric completed his B.A. in Chemistry and Physics at Ithaca College and then earned his S.M. and Ph.D. in Applied Physics from Harvard University.

A&WMA members and their guests are invited to read, attend, and comment on the 2015 Critical Review at the A&WMA’s 108th Annual Conference & Exhibition to be held in Raleigh, NC. The presentation of the review and the discussants commentary is planned for Tuesday morning, June 23, 9:00–11:45 a.m., in Ballroom BC on the fourth floor of the Raleigh Convention Center. The invited discussants include John Bachmann, Principal of Vision Air Consulting; Jason West, Associate Professor Department of Environmental Sciences and Engineering, University of North Carolina; Howard Feldman, senior director of regulatory and scientific affairs at the American Petroleum Institute; and David McCabe, Staff Scientist, Clean Air Task Force, a non-profit environmental organization.

The discussants will provide different views on the authors’ evaluations, conclusions, and recommendations regarding approaches to a more holistic approach to climate and air quality. They may agree with or challenge the authors about their evaluation of the literature. Comments also will be solicited from the floor and from written submissions to the Critical Review Committee Chair. The Chair will synthesize these comments for publication in the November issue of the Journal of the Air & Waste Management Association (JA&WMA). Members are encouraged to suggest topics for future reviews and seek membership on the Critical Review Committee to participate actively in this important element of A&WMA science reporting. If you are interested in joining the committee, please inquire with the chair at [email protected].

2015 Critical Review Committee

Michael T. Kleinman, Chair

A. Gwen Eklund, Immediate Past Chair (2013–2014)

George Hidy, Past Chair (2009–2012)

Judith Chow, Past Chair (2001–2008)

John Watson, Past Chair (1994–2000)

Sam L. Altshuler

Prakash Doraiswamy

Marcel Halberstadt

Naresh Kumar

Luis Diaz-Robles

Peter Mueller

Eric Stevenson

Abhilash Vijayan

Patricia A. Brush, Technical Council Liaison

John Bachmann, 2015 Local Host Committee Liaison