Air pollution causes more deaths than smoking and almost double the number of deaths researchers had previously thought, according to a new study published on Tuesday.

Published in the European Heart Journal, the report found that 8.8 million people died because of air pollution in 2015, despite previous estimates projecting only 4.5 million deaths.

“To put this into perspective, this means that air pollution causes more extra deaths a year than tobacco smoking, which the World Health Organization (WHO) estimates was responsible for an extra 7.2 million deaths in 2015. Smoking is avoidable but air pollution is not,” Professor Thomas Münzel of the Department of Cardiology of the University Medical Centre Mainz in Germany and co-author of the study said in a statement.

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“The number of deaths from cardiovascular disease that can be attributed to air pollution is much higher than expected. In Europe alone, the excess number of deaths is nearly 800,000 a year and each of these deaths represents an average reduction in life expectancy of more than 2 years,” he added.

It is evident that air pollution is connected to cardiovascular disease and respiratory disease, Münzel said. He added that air pollution increases oxidative stress and damages blood vessels, leading to increased blood pressure, diabetes, stroke, heart attacks and heart failure.

In their research, Münzel and his colleagues found air pollution caused twice as many deaths from cardiovascular diseases as from respiratory diseases.

Researchers used a model that simulated atmospheric chemical processes and how they interact with natural and man-made sources like energy generation, industry, traffic and agriculture, a new release stated.

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They used data from that model and applied it to a newer model of global exposure and death rates. They also compared that data with information on population density, geographical locations, ages, risk factors for several diseases and causes of death from the WHO.

Their focus was primarily on levels of fine particulate matter in the air and ozone.

Researchers didn’t only look globally. They also looked specifically at Europe and the 28 countries in the European Union.

Globally, they found air pollution causes 120 extra deaths every year per 100,000 people.

In E.U. states and Europe, the rates were even higher. E.U. states saw an extra 129 deaths per 100,000 people and in Europe air pollution caused an extra 133 deaths per 100,000 people.

Münzel and his colleagues have urged governments to work to reduce air pollution based on the findings of their study.