How a 1993 study on air pollution changed the story

In the 1970s, London's smog had become a distant memory. The last major smog had occurred in 1962 and it appeared that the urban air pollution problems in the United Kingdom had been solved. The air pollution control unit of the Medical Research Council of St. Barthelemy Hospital in London, at the head of the world, has been closed. In the eyes of the government, he did his job. He simply did not need it anymore.

At the same time that the United Kingdom was closing its research capabilities, in the United States, Doug Dockery and his colleagues were putting in place a new type of study on the health effects of air pollution. When it was completed and published nearly twenty years later, Dockery's groundbreaking discoveries changed our perception of air pollution even more profoundly than the 1952 smog in London.

Dockery did not start as a doctor or health care professional. His first degree was in physics, and then, gradually, through meteorology and environmental science, he then went into the effects of the environment on our health. Dockery and his team worked at Boston's Harvard School of Public Health. Founded in 1913 to train public health professionals, the work of the school has impacted our lives around the world. Starting with infectious diseases, their researchers invented the iron lung to keep polio victims alive, before launching a vaccine in the 1950s, awarded the Nobel Prize. They also led the eradication of smallpox. Along with these achievements, the school can also list the work of Dockery and his team on air pollution that began with the Six Cities study.

Starting in 1974, the Six Cities study included 8,111 people randomly selected from six selected locations. These were Watertown in Massachusetts, parts of St. Louis, the city of Steubenville steel in Ohio and the less polluted cities of Portage in Wisconsin, Harriman in Tennessee and Topeka in Kansas. Participants completed questionnaires about weight, height, smoking, occupation, and medical history. Everyone had their breathing tested. Then, each year, the Dockery team sent a postcard to each person to find out if she was still dead. In the absence of response, they sent an investigator to chat with family, friends and neighbors to find out what had happened. It lasted sixteen years. During this period, 1,930 participants died. There was nothing extraordinary about it, but it was the question of who had died and, above all, where they had lived. The inhabitants of Steubenville and Saint-Louis died faster than those of Topeka and Portage. The number of smokers, the body mass index and other factors affecting the health of people were taken into account, but unexplained differences remained between cities. However, when these differences were compared to particle pollution in each city, an extraordinary pattern emerged.

Think about the laboratory experiments you did at school and the results you drew on grid paper. There would always be some flickering points that did not quite fit. You would expect that a 16-year experience contains many variables and anomalies, but the team discovered an almost linear relationship that has become one of the most famous intrigues of the science of the atmospheric pollution. It is listed below, using the original data from the Dockery team.

Because of the additional air pollution caused by traffic and the industries around them, residents of Steubenville die about 30% faster than those in Portage. And people did not just die of lung problems, but, like London's smog in 1952, heart problems. This was not, strictly speaking, the first study to show that daily exposure to modern air pollution was detrimental to our health, but other studies had been less clear.

The publication of the Six Cities study in 1993 was followed quickly by another study of death rates among a large group of US citizens monitored to control cancer development. They died so early because of the pollution by the particles that they were breathing. We suddenly realized that the impact of modern air pollution on health was more important than anyone had imagined. Even looking at the cleanest of the six cities, the effect of air pollution was always clear. Our air was to be made cleaner; cleaner than the air of Portage. A new effort was needed, not only in polluted places like the steel town of Steubenville, but everywhere.

New pollution laws would be needed to protect the health of the population and set standards for air quality in our cities. It was clear that the industry and automakers, to name just two sectors, would have to do a lot more to clean up the pollution they were causing. But, as Arie Jan Haagen-Smit had discovered more than forty years ago, legitimate interests would oppose it.

The publication of the Six Cities study in 1993 sparked controversy and debate. As for the 21st century climate change problems and acid rain problems in Europe in the 1970s, doubt was sown by those who did not like the results. How could Dockery be sure that it was particle pollution that was causing the premature death of people? People were breathing a range of air pollutants, not one. (In fairness, other pollutants were measured in the Six Cities study, but their links to mortality rates were not as clear.) The Dockery team could not measure all the possible pollutants, so what about pollutants that have not been measured? Could one of them have been the cause? The particles in each city came from very different sources and had different chemical compositions, so how could they all produce the same effect? The association is not the same as the cause; the fact that the inhabitants of the most polluted cities died earlier does not mean that air pollution actually caused their deaths *. Could the difference in mortality rate be due to certain other differences between cities; maybe it was the difference in time or the number of people who smoked? Did the researchers simply make a mistake? How could minute amounts of particles in the air cause problems for people? Was it really the mass of these particles in the air or their number? Unless the government can be absolutely sure of it, it should not unfairly hurt corporate profits. The voices pointing out that something is killing hundreds of people in these cities and that immediate action was needed in these debates. A delay would mean more people die prematurely.

One solution would be to relaunch the Six Cities study to prove it a second time. But it would take at least sixteen years, plus the time of analysis, during which the industry could continue pretty much as before. The US Congress was involved and it was decided that a separate and independent group of researchers would review the data with a fine-tooth comb and repeat the original work. In the end, in 2000, the original conclusions were confirmed. Daily pollution by the particles we breathe has been and continues to shorten our lives.

The Six Cities study precipitated another evolutionary step in the management of air. We moved from the source management approach of the 1950s to the new air pollution laws that set standards for the air itself. Standards and limits have been created in the United States and Europe, and guidelines have been established by the World Health Organization.

The impact of the Six Cities study did not stop there. Between 1990 and 1998, an additional 1,394 out of 8,111 people died. By remembering the controversy of the initial study, the researchers asked all victims to question them, weigh them and know their current state of health and smoking habits. Once again, the same linear relationship between survival and particle pollution was found, but this time the news was better. During the 1990s, steps were taken to improve air pollution. Over the entire twenty-six year study period, particulate pollution had decreased and the largest improvements had been observed in the most polluted cities. In Steubenville and Saint-Louis, particle pollution in 1998 was less than two-thirds of the level measured twenty years earlier. At the other end of the scale, Portage and Topeka showed little or no improvement. Where air pollution has improved, the survival rate has also improved. (The researchers found a similar result by checking the Six Cities survivors again in 2009.) The air cleaning worked and at least some of the adverse health effects were reversible.