Our world is changing at an accelerating rate. The global human population has grown from 6.1 billion to 7.1 billion in the last 15 years, and is projected to reach 11.2 billion by the end of the century (United Nations, 2015b). The distribution of humans across the globe has also shifted, with more than 50 percent of the global population now living in urban areas, compared to 29 percent in 1950.1
The world’s demands have evolved with this expanding population and with advancing technologies. Energy demands are altering energy sources and extraction locations, atmospheric emissions, land use, and transportation. Industrial activity supporting increasing standards of living has altered the quantity and quality of goods transported worldwide. Changes in agricultural practices, urbanization, and other anthropogenic (human-caused) activities in response to increasing population have led to land cover and land use change around the globe, expanding not only the landscapes used for crops and livestock cultivation, but also the use of fertilizers and other techniques that improve food production. This growth in human activities and changes in their spatial distribution, along with natural disturbances such as volcanic eruptions and lightning-induced wildfires, have a substantial impact on the Earth system. As a world, we have entered a period when human activities are overriding some natural processes and leading to a discernable impact on the Earth system. In recent decades, this period has been labeled the “Anthropocene,” an era in which human activities are having irreversible impacts on the Earth system (Crutzen and Stoermer, 2000; Steffen et al., 2007).
All of these processes directly affect the atmosphere—the only environmental medium in which humans are unavoidably and continuously immersed and linked to other humans around the globe. Atmospheric motion transports anthropogenic and natural emissions around latitude bands within weeks, between the tropics and the poles within months, and between the Northern and Southern Hemispheres within a year (Jacob, 2000). Because the atmosphere mixes far more quickly than other media such as water or soil and flows unimpeded across political boundaries, emissions to
the atmosphere are rapidly distributed from one region to another, requiring global cooperation to achieve positive change. The atmosphere is a global commons that connects all life.
The composition of the atmosphere impacts society in a number of ways—from changes in weather and climate to food production and human health. Climate change is one of the greatest environmental challenges facing society today (NRC, 2011). Earth’s average surface temperature has increased by more than 1.4°F (0.8°C) over the past 100 years, and the 21st century has already experienced 15 of the 16 warmest years since 1880.2 Sea level, Arctic sea ice, and other parts of the planet are changing, including alteration of the water cycle, changes in biogeochemical cycles, and biodiversity loss (Sala et al., 2000). Recent studies establish a link between climate change and certain types of extreme weather events (NASEM, 2016), which come with high economic costs. For the period 1980–2011, it was estimated that droughts and heat waves cost the U.S. economy a total of $210 billion (Smith and Katz, 2013). The Pentagon’s strategic plan indicates that climate change, which is largely caused by changes in atmospheric composition, is an immediate leading security risk to the United States (DoD, 2014). Atmospheric chemistry plays an important role in controlling climate change; for example, aerosol particles impact climate through direct radiative forcing, by indirectly modifying clouds, and by modifying carbon uptake. Atmospheric chemistry also leads to the formation of air pollutants that are greenhouse gases, such as ozone. Society needs forecasts of those aspects of the changing climate structure that most urgently threaten human health, security, economic opportunity, social stability, and confidence in the future. Such forecasts require a far more fundamental understanding of the physical, chemical, and biological relationships intrinsic to the Earth’s climate system than is currently within the grasp of the scientific community.
Air pollution represents a serious threat to human health both in the United States and worldwide. The annual human health costs due to air pollution in the United States alone are estimated to be in the range of $71–$277 billion per year (Muller and Mendelsohn, 2007). One out of eight deaths globally is caused by air pollution (WHO, 2014), including those due to high levels of indoor air pollutants in both homes and places of work.
Lastly, future food production is vulnerable to both climate change and air pollution, with serious implications for global food security (Tai et al., 2014). Reduced production of soybeans and maize from ozone exposure during the period 1980–2011 is estimated to have caused losses of about $9 billion per year in the United States (McGrath
Climate change and other human-induced global changes contribute to a growing sense of urgency to improve overall understanding of the physical, chemical, and biological processes controlling the composition of the atmosphere and how it impacts the health of humans and ecosystems.
Atmospheric chemistry research encompasses understanding the processes controlling the chemical composition of the atmosphere through development of fundamental scientific knowledge, and applying that knowledge to improve the quality of life for humans and ecosystems. As such, the field bridges “basic” research, which addresses fundamental questions about how the world works, and “applied” research, which is motivated by a desire to answer questions of relevance to society. This marriage has been described as “use-inspired basic research” (Stokes, 1997).
Fundamental atmospheric chemistry research focuses on natural processes and human activities, and how they control the chemical composition of Earth’s atmosphere. Ultimately, the research addresses processes that control the local, regional, and global distributions of atmospheric chemical composition—chemical inputs to, transport and transformations within, and removal from the atmosphere. Because the atmosphere includes a wide range of temporal and spatial scales and many different chemical species whose concentrations can be affected by emissions, transport, reactions, removal, and other meteorological variables, a combination of approaches is essential. These include laboratory and theory studies to elucidate processes on a molecular scale, field observations that provide atmospheric composition, and models that integrate the current understanding from laboratory, theory, and field studies and provide a mechanism for assessing different future alternative scenarios.
These approaches are mutually synergistic, with a discovery in one area often leading to new advances in many others, and each has its challenges. Laboratory studies provide controlled conditions to evaluate individual chemical pathways and provide molecular properties required for atmospheric measurements. Theory provides support for interpretation of laboratory results and can provide predictions that can then be tested by experiments. Challenges include the large number of different species and phases involved—gas, liquid, and solid, as well as interfaces and partitioning between the phases. An additional challenge involves developing a wide range of approaches for laboratory studies that encompass single reactions to complex systems that
simulate conditions like the real atmosphere, or can be reliably extrapolated to atmospheric conditions, providing a bridge to field measurements and modeling studies.
Field studies of atmospheric composition provide discoveries in previously unexplored environments, test the knowledge of atmospheric chemistry through intensive field campaigns involving simultaneous measurements of many different species, and discern meaningful trends when time scales are sufficiently long. Challenges include the need to study chemical processes as they happen, recognizing that most of the atmosphere’s volume is decoupled from the surface of the Earth and human emissions. This requires simultaneous measurements of a multitude of atmospheric constituents at low concentrations, which relies on sensitive and specific instrumentation as well as observing platforms that can carry these instruments to measurement locations that can be difficult to access.
Models integrate the knowledge from laboratory, theory, and field studies to predict atmospheric chemistry and composition across a range of temporal and spatial scales, an integral part of simulating the complex Earth system. These models are also central to testing the relative importance and synergies between mechanisms and processes identified in the laboratory and field for controlling the regional and global distributions of atmospheric species. Challenges include developing models that cover the wide ranges of temporal and spatial scales, while accurately capturing processes from the molecular and sub-second scales on which chemical processes occur, to the global and decadal scales relevant to describe societal impacts.
The pioneers who settled the frontier of atmospheric chemistry were trained in a range of disciplines. Today’s atmospheric chemists are from an equally rich range of backgrounds, including chemistry, physics, mathematics, statistics, biology, meteorology, oceanography, engineering, and environmental science. These diverse backgrounds and skills are required to tackle the problem-centered, use-inspired challenge of developing a predictive capability for the changing atmosphere.
Choices made by society change the chemical composition of the atmosphere, which in turn affects societally important issues such as air quality, climate and weather, water resources, human health, agriculture, and ecosystems. These impacts feed back into societal choices, for example, a choice to move out of highly polluted areas or change behavior that drives emissions. Development of a more comprehensive understanding of societal challenges and their possible solutions is a complex problem spanning
responses in human behavior and the natural world. This endeavor has led to the rise of “big science” that requires coordinated and focused interdisciplinary efforts.
Minimizing negative impacts, maximizing standards of living, and avoiding unintended negative consequences requires a comprehensive understanding of the systems and feedbacks involved in the atmosphere. Well-guided research in atmospheric chemistry can improve this understanding. Finding solutions for problems such as the ozone hole, acid deposition, and polluted urban regions air in the United States all followed a similar pattern (see Chapter 2). Beginning with a sufficient understanding of the atmospheric system, societal impacts of particular human activities were identified, the gaps in scientific understanding were defined, and fundamental research was conducted to fill the gaps. The core contribution of atmospheric chemistry research was the creation of a predictive framework that integrated the physical understanding of atmospheric chemistry with the outcomes of potential policies. This research was then synthesized for policy makers to provide a scientific basis for informed choices (see Box 1.1). As one example of quality of life improvement following policy changes, decreasing concentrations of chemical pollutants in the atmosphere (including nitrogen dioxide, ozone, and particulate matter) in the 1990s and 2000s have been associated with significantly lower rates of childhood bronchitis (Berhane et al., 2016).
Society would benefit from further development of the ability to accurately predict the impact of human choices on the atmosphere. A predictive framework must synthesize atmospheric chemistry research results with information from physical and ecological, technological, and social science fields related to a specific societal problem. Attaining such a predictive capability requires an understanding of the Earth system developed from laboratory and theoretical studies of fundamental atmospheric chemistry and physics, instruments and atmospheric observations to establish atmospheric constituents and processes, and computational models to integrate understanding. This integration allows attribution of causes of an observed societal impact to particular societal choices, such as linking stratospheric ozone depletion with the use of chlorofluorocarbons (CFCs), acid deposition with burning high-sulfur coal, or air quality impairment due to emissions from fossil fuel combustion. Evaluation of these models with observations is critical because uncertainties affect predictions in the causal chain from human activity to impact, and thus the associated costs and benefits of actions. Assessment of complex models is then required to evaluate their fidelity and completeness, as well as to develop simplified response functions that capture key relationships and sensitivities and facilitate integration into analyses that cover many facets of physical, economic, and human systems.
The predictive framework must be able to replicate immediate societal impacts with high fidelity and also predict the responses to alternative scenarios beyond the range of immediate observations. The framework has predictability when it is able to simulate with confidence not only what is, but also what will be. A predictive framework also needs to represent the observed extremes of a societal impact, as well as slowly evolving societal choices. If there is political motivation, predictions enabled by a robust framework can lead to the development of societal and technological solutions, as well as adaptation or mitigation strategies. Examples can be found within each of the success stories described in Chapter 2. Establishing an effective predictive capability is an ultimate goal of atmospheric chemistry research.
It has been more than 30 years since the last comprehensive report to examine the field of atmospheric chemistry (Global Tropospheric Chemistry: A Plan for Action [NRC, 1984a]) was published. That report led to increased emphasis on understanding the global character and extent of natural and human perturbations to the global troposphere. Since the 1984 report, the analytical capabilities and tools used to measure the composition of the atmosphere have improved substantially in terms of sensitivity, timescale, and chemical complexity. These advances allow scientists to ask new and detailed questions that probe the chemistry of the atmosphere, and design and perform studies that support the development of predictive models. At the same time, dramatic advances in computational resources have enabled the development of more complex and comprehensive model descriptions of atmospheric chemistry within the Earth system. These models, informed by new laboratory, theory, and observational studies, can provide better predictions of the rapidly changing future atmosphere to inform policy choices, potentially protecting human health and well-being in the face of global change. In light of the rapid changes to the Earth system combined with impressive scientific advancements of the past few decades, it is clear that the next decade of research will be pivotal for advancing the understanding of atmospheric chemistry and its role in human welfare.
At the request of the U.S. National Science Foundation (NSF), the National Academies of Sciences, Engineering, and Medicine established the Committee on the Future of Atmosphere Chemistry Research. The Committee was charged with identifying priority areas of research for the next decade that will advance the basic science of atmospheric chemistry, developing a compelling strategy for the future of atmospheric chemistry research, and identifying where additional investments in research infrastructure could best advance scientific understanding. See Box 1.2 for the Committee’s
Statement of Task and Appendix A for the list of Committee members. The report was developed for the NSF’s Atmospheric Chemistry Program, which “supports research to measure and model the concentration and distribution of gases and aerosols in the lower and middle atmosphere.”3 However, the results presented will be of interest to other agencies and programs that support atmospheric chemistry research.
In addressing its task, the Committee considered the past contributions and future priorities for atmospheric chemistry research to examine natural processes and human-derived changes over time—from yesterday, through today, and continuing to tomorrow. The Committee gathered extensive input from the atmospheric chemistry community—including scientists working in academia, government, and the private sector—in a series of open public forums and incorporated that input into the results presented here (see Appendix B for a description of the community input gathering process).
This report focuses on activities that the NSF Atmospheric Chemistry Program might best support, within the broader context of atmospheric chemistry research as supported by other agencies both nationally and internationally. The report was written with a variety of audiences in mind, from funding agencies to researchers to policy makers, and as such, the technical level varies. In Chapter 2, the Committee demonstrates how atmospheric chemistry has historically played a central role in building basic scientific understanding and applying that knowledge for the benefit of society. Chapter 3 reviews the fundamental principles underlying atmospheric chemistry research at a higher technical level using recent advances over the past decade. Chapter 4 identifies key areas where atmospheric chemistry needs to contribute to societally relevant challenges, and Chapter 5 identifies priorities for a comprehensive U.S. research program in atmospheric chemistry to advance the most relevant basic and applied science over the coming decade. The grand challenge of predicting and ameliorating societal impacts requires integration with research domains beyond atmospheric chemistry. While this report addresses the Statement of Task by focusing on potential contributions of atmospheric chemistry research, Chapter 5 also identifies areas in which cross-disciplinary integration is likely to lead to major advances. Chapter 6 reviews broad trends in laboratory, field, satellite, and modeling studies within atmospheric chemistry and provides recommendations for improved research infrastructure and approaches to better address the priorities outlined in Chapter 5.
This page intentionally left blank.