Air Pollution's Invisible Toll
Years before Janice Nolen began keeping tabs on the nation’s air quality for the American Lung Association, her mother used to tell her about air pollution in her native Nashville that was so bad that people brought an extra shirt to work so they’d have a clean one to change into.
By 1993, those days seemed to be in the past. The major amendments to the U.S. Clean Air Act that passed in 1970 had been at work for decades, and the air was visibly cleaner. So it was a shock to Nolen —today the Lung Association’s assistant vice president of national policy and advocacy—when Harvard School of Public Health researchers highlighted still deadly air pollution in the small city of Harriman, Tennessee that was taking years from people’s lives.
“It was not one of those places you’d think of as having a pollution problem,” Nolen said. Nolen, who joined the Lung Association the year after the study was published and who authors its annual State of the Air report, has followed the far-reaching effects of the Harvard Six Cities Study, including a new suite of U.S. air pollution regulations that has seen the nation’s air grow cleaner, political controversy over those regulations that continues today, and a new generation of studies investigating avenues opened by Six Cities’ findings.
“It’s a landmark, no question about it,” Nolen said of the Harvard study. “[It has] just absolutely been fundamental to the work we’ve been doing over the last 20 years to reduce particle pollution across the country…Because of this work showing an association, it was easier to convince people that this wasn’t just an arbitrary health effect, it was lives lost.”
The Six Cities Study documented the health effects of air pollution over nearly two decades in Harriman; St. Louis, Missouri; Watertown, Massachusetts; Steubenville, Ohio; Portage, Wisconsin; and Topeka, Kansas. It broke new ground by highlighting for the first time the danger from the smallest particles, no bigger than 2.5 microns in diameter—one fourth the size in the air pollution standards at the time. It linked pollution from those particles not only to ill health, as other studies had before, but directly to deaths, which were 26 percent higher in the most polluted city—Steubenville—than in the least.
The nature of those deaths was a surprise as well. The biggest cause was not respiratory disease, as seemed logical, but rather stroke, heart attack, and other coronary conditions.
Perhaps most important for federal regulatory officials, Six Cities also illustrated that some 23 years after the modern regulatory scheme was adopted in the Clean Air Act amendments of 1970, air pollution was still killing thousands of Americans annually.
“We were surprised by this very strong unexpected effect on mortality,” said Douglas Dockery, chair of the Harvard School of Public Health’s Department of Environmental Health. Dockery, a faculty associate of the Harvard University Center for the Environment (HUCE), joined Six Cities as a graduate student in the 1970s and later became the study’s principal investigator. “There’d been lots of papers on respiratory illness and asthma and chronic obstructive pulmonary disease and lung function and so forth, but it was the mortality paper that got the most attention and really galvanized the political debate.
“When you think about the routes of exposure, you expect a respiratory problem and the biggest effect to be on the lungs,” Dockery continued. “It has become apparent that the lungs and heart are so intimately connected that if air pollution is straining the lungs, it puts a strain on the heart also. The most important effects we see are cardiovascular.”
From killer smoke to concerted action
Six Cities got its start in 1974, four years after the Clean Air Act of 1970 and at a time when public pressure was building and action was already beginning to clean up skies over the U.S. That pressure resulted from a shift in the public’s attitude toward air pollution and economic development. But in the early decades of the 20th century, a different kind of pressure was on: to innovate and modernize. Ever bigger factories churned out new products resulting from wave after wave of innovation. New cars packed the roads, adding their own emissions to the air. Radios and televisions, washing machines, and a dizzying array of goods were demanded by the burgeoning consumer society. The fumes that poured from smokestacks, darkening the skies, made people cough and wheeze, but many just shrugged at their ailments, believing their sniffles were the cost of progress.
It soon became apparent, however, that progress’ price wasn’t just ill health, but potentially life itself. In 1948, an atmospheric inversion over the industrial town of Donora, Pennsylvania trapped emissions from steel and zinc smelters over the town for days. Twenty people died and some 6,000—nearly half the population—had severe respiratory problems, including chest pains and shortness of breath.
A few years later, in 1952, a December fog settled over London, the still air brewing toxic emissions into a deadly stew, causing the worst air pollution disaster on record. Some 4,000 deaths were immediately attributed to the episode and its aftermath. A 2004 analysis examined excess deaths later that winter and put the number several times higher, at about 12,000.
Even as public concern was mounting over industrial pollution in the East, another problem arose in the clear skies of Los Angeles. Though little coal was burned in L.A., residents were periodically afflicted by an eye-burning haze, first noticed in 1943. Investigations found a new kind of pollution, ozone, which was not emitted directly from smokestacks, but instead was produced in the atmosphere by the reaction of auto exhaust, industrial emissions, and sunshine, trapped and simmering in the Los Angeles basin.
Frank Speizer, professor of environmental science at the Harvard School of Public Health, Kass distinguished professor of medicine at Harvard Medical School (HMS), and principal investigator of the Six Cities Study, worked on early air pollution studies in the 1950s in Los Angeles. He recalls being halted at a stop sign and someone banging on the window and asking when something was going to be done about the air pollution.
Though momentum toward change was slowly building, effective action was still decades away, at least in part because so little was actually known about how air pollution affected health.
As a student in Los Angeles in the late 1950s, Speizer worked on an early study of ozone pollution’s effects on lung function of patients at a veterans hospital. He spoke of the crude measures they used to gather data at the time.
“You could see the mountain or you could not see the mountain,” said Speizer, a HUCE faculty associate. “It actually turned out to be a very good measure, but that’s how qualitative it was.”
Early federal legislation included the Clean Air Act of 1963, amendments in 1966, initial restrictions on auto exhaust in 1965, additional legislation in 1967, and the Clean Air Act of 1970, which established the regulatory structures in effect today.
Despite the legislation, change was slow. Michael McElroy, Harvard’s Butler professor of environmental studies and faculty associate of HUCE, remembers growing up in Belfast in the 1940s and 1950s and how the white handkerchief he put in his pocket each morning became black by the end of the day from his repeated blowing. By the time he visited Pittsburgh in the 1960s, the problem hadn’t changed.
“The problems of that time were pretty obvious. The air was dirty,” McElroy said. “That was sort of the situation in many of the industrial cities of the world. I grew up in Belfast, Northern Ireland and that is the environment I experienced. I visited Pittsburgh in the ’60s, and Pittsburgh was just as bad as Belfast was when I left. You sort of became used to it.”
By the early 1970s, significant action was being taken, but Speizer said that the science underpinning many of the new standards was still wanting. These were the early days of the field of epidemiology, which would provide some answers, and, though some studies pointed the way, others ran into problems of quality control and data analysis, Speizer said.
Speizer told of how carbon monoxide limits in Boston’s Sumner Tunnel were established at the time, among officials at a restaurant over dinner, with guesswork playing an uncomfortably large role in the process.
“Nobody knew what levels to set, that was the problem,” Speizer said. “We knew carbon monoxide was bad for you—there were studies done in the ’20s that showed cognitive decline and acute poisoning. But the question was what should the level be in the Sumner Tunnel for workers and drivers?”
From Steubenville to Topeka
Shortly after the 1970 Clean Air Act, Speizer and Ben Ferris, both professors at HSPH, appeared before a federal commission investigating the health impacts of burning coal. Commissioners asked how the two would go about assessing those impacts. In response, Speizer drafted a document detailing a study of sulfur dioxide and total suspended particles, which would later be refined to examine particles of different sizes. Shortly after, the two were asked to submit the proposal, which would become the Six Cities Study, for funding.
The first city to be enrolled in Six Cities was nearby Watertown in 1974. Watertown was selected because of its proximity so that the researchers could work out kinks in their procedures before the study spread to more distant locations. Harriman, Tennessee and St. Louis were enrolled in 1975. Steubenville, Ohio—the most polluted city—was enrolled in 1976, along with Portage, Wisconsin, which had the cleanest air. Topeka, Kansas, which rivaled Portage for cleanliness, was the last to join, in 1977.
The study enrolled 8,111 adults between age 25 and 74 who were followed up annually, as well as some 14,000 children in grades one through four, who were followed through high school. Researchers set up instruments in each city and gathered air quality data. After conducting initial physical examinations and detailed questionnaires, researchers returned every third year and tracked down participants, taking basic health measurements and asking about smoking habits, health history, and occupational history. In the years between, researchers sent annual post cards that served to alert researchers when a study participant died, after which researchers tracked down cause-of-death information.
“We were in Steubenville, a steelmaking community, and periodically they’d have bad air pollution episodes,” Dockery recalled. “We set up the study to monitor the kids, measure lung function, and then, when the air pollution was going to get bad, re-tested some kids. We measured lung function before, during and after air pollution events. We could see their lung volumes dropped during these events.
“It was the first study I was involved in that directly showed the effect of air pollution with objective physiological measures,” Dockery said. “We were taking these clinical measures into the field and providing objective measures of the health of the kids. That was one of the innovations of the study.”
Another innovation was provided by John Spengler, today the Yamaguchi professor of environmental health and human habitation at HSPH, who joined Six Cities as a postdoctoral fellow shortly after it began and designed instruments to measure particles of different sizes. This allowed the study to shift from the crude measure of total suspended particles to measuring and analyzing particles of different sizes, which would be key in the landmark 1993 paper.
Called an “impactor,” the device sucked air through a nozzle and directed it around an impactor sheet and then through a filter paper. By tuning the air flow, the greater momentum of the larger, heavier particles would cause them to hit the impactor sheet, where they could be measured, while the lighter, smaller particles remained entrained in the air flow and collected on filter paper deeper inside the instrument. Developed together with an aerosol physicist from the University of Minnesota and a research team at the U.S. Environmental Protection Agency (EPA), the instrument could be tuned by changing the size of the opening and the speed of the air flow, to separate particles of different sizes, which could then be measured and analyzed.
Particles larger than 10 microns were gathered, along with particles smaller than 10 and smaller than 2.5 microns. Once the samples were gathered, Spengler said, they could be sent to the EPA lab, where they were analyzed for metals.
“That was a big advance, because from the metals, we could tell the sources [of the emissions],” said Spengler, today a faculty associate at the Harvard University Center for the Environment. “Vanadium and nickel were from oil, sulfur and selenium were from coal, Earth crustals and iron were from steel plants.”
In addition to the hundreds of research papers spawned by the study itself, the instruments themselves have also had an enduring impact, Spengler said, and have been duplicated and used around the world. The work also launched two generations of academic careers—Spengler tallied four professorships resulting from the first generation of research, including his own, and several among the numerous fellows who worked under those faculty members’ auspices.
The study’s most far-reaching effects, however, stemmed from that 1993 mortality paper, published in December in the New England Journal of Medicine.
The results were shocking enough—even to the researchers—that Speizer, the paper’s senior author, refused to submit them for publication until they had been validated. The difference in mortality between the cleanest and most polluted cities was much larger than anticipated, equivalent to two or three years’ life expectancy, Dockery said. That’s equal to what would be anticipated nationally if all cancers were cured.
“It was totally unexpected that air pollution, and at these modest levels, was having such a dramatic effect,” Dockery said. “That really changed the whole discussion.”
The researchers looked around for datasets that they could use to validate their results and found health statistics from across the country in an enormous study of 1.2 million people gathered by the American Cancer Society. Researchers examined the mortality data from roughly 500,000 of that study’s subjects who lived in 151 cities for which there was also air pollution data.
It was only after researchers saw similar results that they submitted the Six Cities paper.
Government officials took notice, prodded by an American Lung Association lawsuit that demanded that the EPA review air pollution standards on the schedule required by law. In 1997, the EPA approved new particulate standards based on Six Cities and the American Cancer Society data. The new standards restricted levels of 2.5 micron particles in the air.
Most of these particles, it turned out, are not caused by the initial burning that leads to industrial emissions, but are rather formed in reactions in the atmosphere between chemicals released by burning—mainly sulfur dioxide but also nitrogen oxides.
Unlike larger particles that become ensnared in nose hairs and caught on the walls of the upper respiratory tract and spit out, these tiny particles—made of a variety of compounds—can be inhaled deep into the lungs, where they land on the delicate lung tissue separating air from blood and do their damage.
The result, as highlighted in Six Cities, is indeed respiratory symptoms—higher asthma rates, poor lung function, slowed lung growth among the young—but also heart attacks, strokes and death.
The new standards forced additional restrictions on industrial emissions of 2.5 micron particles—called PM (particulate matter) 2.5—and have been under assault by industry and their political allies ever since.
That assault has taken various forms. A few years after the new standards went into effect, Congress asked for a detailed review of the Six Cities and American Cancer Society studies. After examining the data, a team of U.S. and Canadian researchers led by Daniel Krewski at the McLaughlin Centre for Population Health Risk Assessment in Ottawa reported in 2003 that they were in “almost complete agreement” with the original study’s conclusions.
The study’s political opponents haven’t given up, however. As recently as last fall, congressional Republicans subpoenaed the Six Cities data, much of which is protected by the confidentiality restrictions that guard all human studies, in an effort to bring to light what they term “secret science” underpinning emissions standards.
Dockery, who received the subpoena, declined comment. But Spengler pointed out that the science has not only proven sound, the cleaner air has been shown to save the U.S. economy far more than it cost, with one study estimating that the economic benefits of improved health for millions of Americans—in reduced sick days and extended working lives—outweigh the cost of air pollution controls by 18 to 1.
“You’d think it’d be asked and answered,” Spengler said. “In spite of all that, the pressure’s still on.”
Though primary data collection ceased in 1991, Six Cities continues to inform. Mortality statistics are still collected, using the federal government’s National Death Index, and in 2006, HSPH Associate Professor Francine Laden was the lead author of a paper that again confirmed the association between air pollution and mortality, albeit using a happier trend. Her analysis showed that mortality fell along with levels of the 2.5 micron particles, with three percent fewer deaths for every microgram reduction in a cubic meter of air. The observed reduction equaled approximately 75,000 lives each year in the U.S., Laden said.
In 2012, an extended follow-up of Six Cities by Laden, Dockery, Johanna Lepeule, a visiting scientist at HSPH, and Joel Schwartz, HSPH professor of environmental epidemiology, confirmed the initial findings with 11 years of additional data. Specifically, they found that every 10 microgram increase of PM-2.5 per cubic meter of air was associated with a 14 percent increased risk of death from all causes, a 26 percent increased risk of death from cardiovascular causes, and a 37 percent increased risk of death from lung cancer.
Though the nation’s air has gotten cleaner in the years since the new particle pollution standards were implemented in 1997, work remains to be done, according to the American Lung Association’s annual State of the Air report.
“It [the particle pollution standards] saves lives, but we’re not where we need to be. Last year’s report showed we still have 140 million people who lived in areas that were unhealthy. Part of that is understanding better what unhealthy is, and that’s what studies like the Six Cities Study helped us to see,” Nolen said. “It wasn’t just [removing] the soot—the worst of the haze was invisible soot—we had to get cleaner and cleaner and cleaner…We haven’t solved the problem by any means, but it’s less burdensome on people’s health.”
An eye on Asia
In many places around the world, the lessons from Six Cities remain to be applied. Some 3.7 million people died in 2012 from outdoor air pollution—more than 80 percent in low- and middle-income countries, according to a March 2014 report by the World Health Organization (WHO), and millions more died from indoor air pollution, much of it generated by smoky indoor cookstoves. As it once was in industrialized nations, the stench from burning forests and coal-fueled plants is still thought to be the price of progress in many places, progress that national leaders are loath to curb. The result is that some 20 years after the Six Cities Study dramatically highlighted the danger, air pollution is the world’s single largest environmental health risk, according to the WHO report.
Harvard researchers are working with collaborators at universities around the world to both understand air pollution’s local dynamics and explore approaches that would help millions breathe easier.
The choking smog that wreathes China’s major cities is the focus of Harvard’s China Project, begun by Mike McElroy in the early 1990s. Despite his boyhood in industrial Belfast, McElroy recalls being nearly bowled over by the choking smells experienced during an early trip, in 1995, to Chongqing, a city of about 20 million on the Yangtze River.
“We arrived late at night. I’ve experienced air pollution in my life, but this was 95 to 100 degrees at night, people were working in the streets, pouring tar, with no shirts on,” McElroy said. “The place just smelled awful, awful, awful.”
McElroy was later escorted to one of the city’s iron and steel factories by an environmental official.
“I have never seen anything like this in my life,” McElroy said. “There were coal trains coming through that place continually dumping off the coal, just an astounding flow of coal. There were high smoke stacks and one in the middle, about a quarter mile back. It was like standing behind a jet plane taking off, like a supersonic blast. You could see the dirty smoke coming out of these stacks.
“I turned to my guide and asked, ‘Is this place consistent with clean air standards your ministry is imposing? He smiled and said, ‘Of course not. If this place had to meet international standards, it would have to be closed down.’”
The China Project, based in Harvard’s School of Engineering and Applied Sciences, today provides a focus for faculty and fellows from across Harvard and partner institutions in China who are interested in China’s energy, economy, and atmospheric environment. It works to understand what is happening in China’s skies from an interdisciplinary point of view, encompassing atmospheric chemistry, economics, and human health, and suggesting viable solutions. A book published in November, Clearer Skies over China, brings together economists and natural, applied, and health scientists from the U.S. and China to examine a successful Chinese effort to regulate sulfur dioxide and explores the potential impact of a carbon tax. McElroy’s own research, meanwhile, has focused on the potential for renewable alternatives to burning dirty coal. In fact, in a 2009 study of China’s wind power potential, McElroy found that China could potentially meet all of its power needs through wind alone.
Air that is unhealthy to breathe is just half of the Asian giant’s air pollution concerns. In recent years, it surpassed the United States to become the world’s biggest emitter of carbon dioxide, the greenhouse gas largely responsible for human-caused climate change.
If there is a silver lining for China’s air pollution problems, McElroy said, it is that actions to improve air quality will also address climate change, since both have roots in burning coal for power. Despite the Chinese government’s efforts to improve air quality, McElroy said he believes that significant change may depend on breakthrough innovations pioneered in the industrialized West.
An ill wind over Singapore
One day in late September 2013, an interdisciplinary group of researchers gathered in a conference room on the third floor of Harvard’s Hoffman Laboratory. On a screen at the front of the room played a time lapse clip showing the intensity of smoke from burning forests in Sumatra blowing across the narrow Strait of Malacca toward Singapore, with darker colors representing higher aerosol concentrations. A black plume representing the worst smoke appeared, lengthened, and reached across the strait as the date crawled toward the smoke’s peak, on June 21, the day Singapore’s air quality dipped to the worst levels in its history.
“They experienced a pollution standards index of 401, which is higher than has ever been recorded in history in the region,” said Samuel Myers, a research scientist at the HSPH and HUCE faculty associate. “The episode…probably is associated with a 10 percent to 30 percent increase in all-cause mortality. There were billions of dollars lost in morbidity and mortality.”
A team led by Myers has embarked on a project to understand burning on the Indonesian island of Sumatra, its health impacts on nearby cities, and to create computer-generated scenarios to help policymakers make informed decisions on whether, where, and when to burn.
That the fires have a health impact is beyond doubt. In addition to the data from Six Cities and subsequent studies, HSPH’s Spengler was an eyewitness to the effects while attending meetings at the University of Singapore when the fires reached their peak.
Though the fires were more than a hundred miles away, Spengler said breathing in the meeting room was labored and voices gravelly.
“You would swear the building was on fire. It had that wood-burning smell, it penetrated into buildings,” Spengler said. “Even across the quad, you just saw this veil of smoke that started to obscure the buildings on the other side. And forget about seeing the city.”
Despite the smoke’s dramatic effect, the fact that Sumatra was burning was not unusual. Subsistence farmers burn forests each year to clear land for their home gardens and burn scrub on previously cleared land to make room for crops. Larger farms burn too, clearing bigger tracts for cash crops, while industrial plantations burn forests to make room for oil palm trees.
“The public health costs of those fires are staggering,” Daniel Jacob, McCoy Family professor of atmospheric chemistry and environmental engineering and HUCE faculty associate, said later. “When you look at the kind of particulate levels Singapore was exposed to in June of this year, this is a smog that takes years from your lifetime.”
Jacob is part of the Myers-led study of Sumatra’s burning. The project also involves Senior Research Fellow in Chemistry-Climate Interactions Loretta Mickley, Professor of Environmental Epidemiology Joel Schwartz, and colleagues from Ruth DeFries’ lab at Columbia University. Using satellite imagery, newly developed analytical tools, and publicly available data, this interdisciplinary group is applying the expertise from atmospheric science, public health, and ecology and environmental biology in order to understand what’s happening in Sumatra. They’re looking at everything from the economic drivers of burning practices to the health impacts on city residents downwind.
“Our goal in using these new tools is to really characterize this system so we fully understand how certain kinds of land cover are associated with certain kinds of fires and how these fires are associated with certain kinds of emissions—and how those emissions are transported in predictable ways to reach specific concentrations of pollutants at the population level,” Myers said. “Then, what we really want to do is understand how land management decisions being made today will alter exposures in the future.”
Though the project’s primary focus is improving human health, it also serves an underlying conservation cause, Myers said. It’s not a coincidence that major health effects from burning forests are being felt in a part of the world undergoing rapid deforestation. Those forests are home to a significant part of the world’s biodiversity and include many species found no place else. In part, the project is intended to help policymakers understand the hard-to-quantify costs associated with the benefits provided by intact forests—clean water, a home for wildlife, and a purer “airshed,” as Myers terms it—compared with the costs and benefits if the forests are burned and converted to other uses.
“What’s happened [since 1985] is that essentially half of Sumatra has been burned down,” Myers said. “And the predictions are that by 2100, Southeast Asia could lose three-quarters of its forests, up to 42 percent of its biodiversity, including over half the mammals, amphibians and reptiles. Oh, and over half of the mammals, amphibians and reptiles are endemic and don’t exist in other places. That’s the conservation challenge.”
Because there are few ground-based monitoring stations in the region, most of the data are coming from satellite readings, from which Jacob’s group is working to extract as much information as possible. Once they get the data, they’re plugging it into their global climate model, which they’re using in zoomed mode to examine the region more closely.
Among other things, they want to characterize the size and optical properties of particles in the smoke so they can better interpret satellite observations, Jacob said.
“To be able to interpret satellite properly in a part of the world where the interpretation is really complicated because there’s a lot of clouds and there’s an archipelago of land and ocean—all this makes it difficult to see the particles from space,” Jacob said. “So this is something we’re working on, to see what kind of information we can get from the satellite. In the end, I think this will be key to be able to monitor the problem in the future.”
An important element in their calculations is understanding how particles change during transport, Mickley said. For example, the particles attract compounds that make them more soluble in water. This affects their transport by allowing them to rain out more readily.
“When they’re first emitted, they’re not soluble in water,” said Mickley, also an HUCE faculty associate. “As different chemicals coat them, they become more soluble, more vulnerable to raining out along the way. So a chemistry model can tell you some of this information.”
Researchers are also sorting out how to handle ozone, Jacob said. Ozone is generated by the fires but may not have the same health impact as fine particles.
“It’s a toxic gas, the number one pollutant in the U.S.,” Jacob said. “It’s produced in the fire plume, but we don’t really understand the mechanism by which it is produced. We don’t have observations from the ground, so that means our models are pretty uncertain.”
Together, the researchers are seeking to develop computer models that can generate a series of different scenarios that could be used as tools for policymakers in the region. The scenarios will project the ultimate impact of a “business-as-usual” approach to the forests, of varying levels of development, and of a “green vision” where greater emphasis is placed on conservation and in which the improved health of the region’s residents is considered.
Such a prediction tool has drawn initial interest from Singapore’s government and should enable policymakers to fully evaluate the costs, including human health, versus the economic benefits of new oil palm plantations, for example. And, if policymakers let plantations move ahead, the work could help determine where they should be located to minimize human health impacts.
“If we want to plan our fires, let’s plan them in regions that don’t affect the big cities,” Mickley said. “This is a nice tool for policymakers who want to put in rice paddies or oil palms.”
Though much work remains until such a tool is in policymakers hands, the group’s preliminary work has already suggested a geographical focus for action. The peat forests of southeastern Sumatra, where a lot of burning is going on now, are the source of a lot of the smoke that hits Singapore. Indonesian government officials have made it clear they won’t curb development, but perhaps land could be cleared on the western part of the island instead, to spare Singapore. Another tack could be taken by Singapore’s government, since many of the companies operating in Sumatra are based in Singapore. Perhaps a tax would encourage the companies to clean up their act.
“We want to quantify for the first time ever, what are the public health implications of land management decisions in Southeast Asia,” Myers said. “To date those health implications have always been a vague externality: If you grow more palm oil, maybe more people will die, but we don’t know how many or where. We want to quantify that. “We want to…produce a tool to allow policymakers in the region to calculate and argue that conservation strategies will have important public health dividends, and make that case in a scientific way,” he said.
Ultimately, Myers said, such a tool could also be used elsewhere, since there are many other places around the world that, like Sumatra, are experiencing rapid deforestation and health-destroying air pollution. By providing policy-informing tools that illuminate both the value of conservation and of improved health, the researchers’ work could help more places achieve clean air goals whose roots can be traced back to findings in the Six Cities Study.
By Alvin Powell
This article originally appeared in the Environment@Harvard newsletter, Volume 6 Issue 1.