Air pollution is known to be detrimental to health.

However, the risk associated with lower pollution levels – outside of towns and cities, for example – has rarely been studied.

A new, large-scale study shows that even “safe” levels can reduce lifespan.

Over the past few decades, as global air pollution levels have risen, their effects on human health have become a major focus of research.

have repeatedly shown that air pollution can increase the risk of various illnesses and premature death.

However, these previous studies have focused primarily on urban settings, in which air pollution is generally higher.

Information on the effects of air pollution levels below those set by the National Ambient Air Quality Standards (NAAQS) is sparse.

A study, published today in The New England Journal of Medicine examines the interaction between levels of air pollution and mortality in unprecedented detail.

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Investigating pollution and longevity

The study was carried out by researchers from the Harvard T.H. Chan School of Public Health in Boston.

It used the largest data set of any study of its type.

In total, information from almost 61 million people from the United States, all over the age of 60, was collated across a 7-year period.

This accounts for around 97 percent of all people aged 65 or over in the country. It represents “460 million person-years of follow-up.”

By estimating the air pollution levels in every single square kilometer of the United States and by examining the Medicare claims of millions of people, the team developed the clearest picture available of the relationship between air pollution and longevity.

In particular, they concentrated on levels of fine particulate matter and ozone. Fine particulate matter to solid particles mixed with water, suspended in the air, that measure under 2.5 micrometers in diameter.

These particles, such as those produced by vehicles, can easily be inhaled, causing to both the lungs and body parts further afield.

Ozone is formed when pollutants – emitted by cars, refineries, power plants, or other sources – react chemically in the presence of sunlight.

The researchers created a detailed map of regional pollution by using data from an exposure prediction model.

Doctoral student Qian Di and senior study author Joel Schwartz, a professor of environmental epidemiology, worked together to design this model.

The model utilizes satellite data and air pollution computer simulations. By using this method, they could chart the effects of any level of pollution at any point in the United States.

Read more: Children’s lungs benefit from less air pollution »

Pollution affects everyone but not equally

In a nutshell, the data showed that long-term exposure to fine particulate matter and ozone increases the risk of premature death.

This is still the case at levels below those set out in the NAAQS, established by the U.S. Environmental Protection Agency (EPA).

An increase of 10 micrograms per cubic meter in fine particulate matter was associated with an increase in all-cause mortality of 7.3 percent.

The results also showed that certain groups of the population were more at risk of early death due to fine particulate matter than others.

These groups included men, black people, and those in lower socioeconomic groups.

“This is a study of unprecedented statistical power because of the massive size of the study population,” said Francesca Dominici, a professor of biostatistics at the Chan School of Public Health. “These findings suggest that lowering the NAAQS for fine particulate matter will produce important public health benefits, especially among self-identified racial minorities and people with low incomes.”

Aside from estimating the damage caused by air pollution, the team calculated the potential benefits to human life of reducing levels.

They found that if levels of fine particulate matter could be lowered by just 1 microgram per cubic meter, nationwide, around 12,000 lives could be saved per year.

Additionally, if the level of ozone could be reduced by just 1 part per billion, an estimated 1,900 lives might be saved each year.

Although these changes seem miniscule to produce such drastic improvements in health, they equate to wide-scale changes in regulatory policy.