“WE SHOULD GET out of here,” says air pollution chemist Eben Cross. At 7 a.m. on this cold November day the wind blows steadily through the Massachusetts Institute of Technology’s Cambridge campus, cutting through our thin jackets. But Cross isn’t afraid of the cold. He worries about the air we’re breathing—especially considering the six fire trucks directly ahead, idling in the dim morning light.
“We’re getting hammered right now,” Cross says, shouting over the hum of the engines. He’s taken his gloves off to manipulate the display panel on his pollution monitor. The acrid smell of diesel is unmistakable. “Anytime you can smell it, you are in a regime that is very polluted,” he says. “In many ways your nose is a better mass spectrometer than any device on the market.”
Cross’ monitor measures the presence of microscopic particles suspended in the air. Earlier, in his home, the device reported average concentrations of between 10,000 and 100,000 airborne particles per cubic centimeter of air (the latter after he burned some toast). Now it detects millions. The massive size of the fire trucks’ engines, combined with their inefficient combustion in cold weather, means that the air reaching us is replete with fine and ultrafine particles—specks of waste at least 36 times finer than a grain of sand, often riddled with toxic combinations of sulfate, nitrate and ammonium ions, hydrocarbons, and heavy metals. Though we have long known that these tiny particles cause and exacerbate respiratory problems—like asthma and infections and cancers of the lungs—they are also suspected to contribute to adiverse range of disorders, from heart disease to obesity. And now cutting-edge research suggests that these particles play a role in some of humanity’s most terrifying and mysterious illnesses: degenerative brain diseases.
While coarse pollution particles seldom make it past our upper lungs, fine and ultrafine particles can travel from our nostrils along neural pathways directly into our brains. Once there, they can wreak a special havoc that appears to kick off or accelerate the downward spiral of degenerative diseases like Alzheimer’s and Parkinson’s. While much of the research is still preliminary, the findings so far are compelling. Autopsies of the brains of people who lived in highly contaminated areas have turned up traces of pollution and corresponding brain trauma. And among those still living, epidemiologists have recorded elevated rates of brain disease and accelerated mental decline.
All of this is especially scary when you consider how many people are at risk. Alzheimer’s and Parkinson’s already afflict 50 million people worldwide and about 6 million in the United States. In 2015, nearly 1 in 5 Medicare dollarswill be spent on Alzheimer’s; this disease and other types of dementia will cost the United States $226 billion. By 2050, experts predict, that cost will rise to $1.1 trillion—the baby boomers are only now entering the phase of life when degenerative diseases usually emerge. Because boomers were born before the improvements of the Clean Air Act, passed in 1970, they likely have had a greater lifetime exposure to air pollution than any other generation before or after them.
But although American air today is the cleanest it has been in four decades, pollution is still a major public health problem. According to estimates from the American Lung Association, more than 46 million Americans—about 15 percent of the US population—are chronically exposed to levels of particle pollution that exceed Environmental Protection Agency (EPA) standards, with a further 44.1 million plagued by periodic unhealthy exposures on bad air days or, as in parts of California, seasonal air pollution spikes. Meanwhile, in some Chinese and Indian cities, air pollution levels are routinely three to six times higher than World Health Organization standards. A recent study in the peer-reviewed journal Environmental Health and Technology estimated that we could avoid two million deaths globally by cleaning up the world’s air.
Researchers have struggled for decades to pinpoint the risk factors that, in addition to genetics, can contribute to a person’s likelihood of developing Alzheimer’s and Parkinson’s diseases; theories have ranged from viral infection to aluminum exposure to high-fat diets, but none of these has withstood scientific scrutiny. The research implicating air pollution is in its early stages, and many questions remain unanswered—for example, it’s unclear whether particle pollution initiates degenerative disease or merely accelerates it. Still, the evidence so far suggests that pollution could be the most pervasive potential cause of brain disease that scientists have ever discovered. We’re not “beyond a doubt,” says Michelle Block, a neurobiologist at the Indiana University School of Medicine, but “everything we do says this is probably happening.”