Study: Air pollution kills 3.3 million worldwide, may double

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WASHINGTON (AP) — Air pollution is killing 3.3 million people a year worldwide, according to a new study that includes this surprise: Farming plays a large role in smog and soot deaths in industrial nations.

Scientists in Germany, Cyprus, Saudi Arabia and Harvard University calculated the most detailed estimates yet of the toll of air pollution, looking at what caused it. The study also projects that if trends don't change, the yearly death total will double to about 6.6 million a year by 2050.

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The study, published Wednesday in the journal Nature, used health statistics and computer models. About three quarters of the deaths are from strokes and heart attacks, said lead author Jos Lelieveld at the Max Planck Institute for Chemistry in Germany.

The findings are similar to other less detailed pollution death estimates, outside experts said.

"About 6 percent of all global deaths each occur prematurely due to exposure to ambient air pollution. This number is higher than most experts would have expected, say, 10 years ago," said Jason West, a University of North Carolina environmental sciences professor who wasn't part of the study but praised it.

Air pollution kills more than HIV and malaria combined, Lelieveld said.

With nearly 1.4 million deaths a year, China has the most air pollution fatalities, followed by India with 645,000 and Pakistan with 110,000.

Click through to see more of the staggering pollution in China:

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Study: Air pollution kills 3.3 million worldwide, may double
CHENGDU, CHINA - JUNE 30: Apartment buildings rise into the smog filled skyline June 30, 2015 in Chengdu, China. First inhabited more than 4 thousand years ago, Chengdu now has more than 14 million people living in its metropolitan area. It is China's 5th most populous city and the provincial capital of Sichuan Province in southwest China. The city is is struggling to maintain its ancient cultural identity, while becoming a modern major tech and industrial center. (Photo by John Moore/Getty Images)
BEIJING, CHINA - MARCH 03: A delegate wearing the mask walks to the Great Hall of the People during severe pollution before the opening of the 2nd session of the 12th Chinese People's Political Consultative Conference (CPPCC) on March 3, 2014 in Beijing, China. Air pollution has become a big concern during the Chinese People's Political Consultative Conference. Over 2,000 members of the 12th National Committee of the Chinese People's Political Consultative, a political advisory body, are attending the annual session, during which they will discuss the development of China. (Photo by Feng Li/Getty Images)
This picture taken on June 23, 2015 shows vehicles running in smog covered streets in Beijing. China's cities are often hit by heavy pollution, blamed on coal-burning by power stations and industry, as well as vehicle use. The issue has become a major source of popular discontent with the Communist Party, leading the government to vow to reduce the proportion of energy derived from fossil fuels. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
In this Tuesday, June 9, 2015 photo, Indian policemen wear masks as they control traffic in New Delhi, India. Never mind lowering the rate of death from air pollution in India and China. Just keeping those rates steady will demand urgent action to clear the skies, according to a new report published Tuesday, June 16, 2015. (AP Photo/Altaf Qadri)
This picture taken on June 23, 2015 shows a cyclist wearing a mask in Beijing covered by heavy smog. China's cities are often hit by heavy pollution, blamed on coal-burning by power stations and industry, as well as vehicle use. The issue has become a major source of popular discontent with the Communist Party, leading the government to vow to reduce the proportion of energy derived from fossil fuels. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
A Chinese woman wearing a facemask walks in front of the Forbidden City on a hazy day in Beijing on June 23, 2015. AFP PHOTO / FRED DUFOUR (Photo credit should read FRED DUFOUR/AFP/Getty Images)
In this Friday, March 8, 2013 Chinese paramilitary policemen march across Tiananmen Square on a hazy day in Beijing, China. Facing public outrage over smog-choked cities and filthy rivers, China's leaders are promising to clean up its neglected environment, a pledge that sets up a clash with political pressures to keep economic growth strong. (AP Photo/Andy Wong)
A golfer plays on the court on a hazy day at Pine Valley Golf Club on the outskirts of Beijing, China, Sunday, Oct. 6, 2013. Fog and pollution descended on northern China on Sunday, forcing international golf and tennis players to play in hazardous smog and leading to flight cancellations and road closures as millions of Chinese headed home from a national holiday. (AP Photo/Alexander F. Yuan)
Residents cross an overhead bridge during a hazy day in Beijing, China, Thursday, Jan. 31, 2013. Endless lines of slow-moving cars emerge like apparitions and disappear into the gloom of the thick smog that has shrouded Beijing for weeks and reduced its skyline to blurry gray shapes. With more than 12 million cars sold in China last year, motor vehicles have emerged as the chief culprit for the throat-choking air pollution in big cities especially Beijing.(AP Photo/Ng Han Guan)
Vehicles crawl along a major road in Beijing, China, Thursday, Jan. 31, 2013. Endless lines of slow-moving cars emerge like apparitions and disappear into the gloom of the thick smog that has shrouded Beijing for weeks and reduced its skyline to blurry gray shapes. With more than 12 million cars sold in China last year, motor vehicles have emerged as the chief culprit for the throat-choking air pollution in big cities especially Beijing.(AP Photo/Ng Han Guan)
A China Eastern Airlines plane, bottom, is seen taxiing as the Beijing Capital International Airport is shrouded by pollution haze in Beijing Monday, March 24, 2014. (AP Photo/Andy Wong)
Air China passenger planes taxi at the Beijing Capital International Airport shrouded by pollution haze in Beijing Monday, March 24, 2014. (AP Photo/Andy Wong)
Chinese people wearing face masks walk against the capital city skyline shrouded by a haze of pollution in Beijing Monday, March 3, 2014. (AP Photo/Andy Wong)
Chinese women wearing masks cross the road near the headquarters of the China Central Television headquarters during a hazy day in Beijing, China, Wednesday, Feb. 26, 2014. Beijing remained cloaked in hazardous white pollution hiding much of its skyline Wednesday, despite the announced closures or production cuts at 147 of the city's industrial plants. (AP Photo/Ng Han Guan)
Construction workers walk into a work site during a hazy day in Beijing, China, Wednesday, Feb. 26, 2014. Beijing remained cloaked in hazardous white pollution hiding much of its skyline Wednesday, despite the announced closures or production cuts at 147 of the city's industrial plants. Chinese characters at bottom left reads "China dream, my dream" at right reads "China, Go!" (AP Photo/Ng Han Guan)
A farmer shovels in a field near electric pylons in heavy haze on a severely polluted day in Shijiazhuang, in northern China's Hebei province, Wednesday, Feb. 26, 2014. (AP Photo/Alexander F. Yuan)
Women walk up an overpass near a highway during a hazy day in Beijing, China, Wednesday, Feb. 26, 2014. Beijing remained cloaked in hazardous white pollution hiding much of its skyline Wednesday, despite the announced closures or production cuts at 147 of the city's industrial plants. (AP Photo/Ng Han Guan)
A man wears a mask during a hazy day in Beijing, China, Wednesday, Feb. 26, 2014. Beijing remained cloaked in hazardous white pollution hiding much of its skyline Wednesday, despite the announced closures or production cuts at 147 of the city's industrial plants. (AP Photo/Ng Han Guan)
A man and a car travelling on a road are obscured in heavy haze on a severely polluted day in Pingshan county of Shijiazhuang, in northern China's Hebei province, Wednesday, Feb. 26, 2014. Chinese President Xi Jinping braved Beijing's choking smog Tuesday, making an unannounced visit to a trendy alley and sitting with residents in his latest public relations effort to be seen as a man of the people. (AP Photo/Alexander F. Yuan)
Men wearing masks walk near a road during a day of heavy pollution in Beijing, China, Sunday, Feb. 23, 2014. (AP Photo/Ng Han Guan)
Cars clog in the traffic in Beijing's Central Business District on a hazy day, Friday, Feb. 21, 2014. A rare air pollution alert issued Friday in Beijing prompted health advisories and bans on barbeques, fireworks and demolition work, but fell short of the strictest measures which would include ordering half the city’s cars off the streets. (AP Photo/Alexander F. Yuan)
A tourist wearing a protective mask stands by as a couple look at buildings in Pudong across the Huangpu River shrouded in heavy haze, at the Bund in Shanghai, China, Friday, Dec. 20, 2013. Shanghai’s environmental protection bureau issued a “yellow” pollution warning this afternoon and said it was taking “emergency emission reduction” measures and recommended that children, the elderly and people suffering from heart disease or lung disease should stay indoors and cease outdoor exercises. (AP Photo/Eugene Hoshiko)
A tourist with a protective mask watches the buildings at the Bund under heavy haze in Shanghai, China, Monday, Dec. 9, 2013. The dirty air that has gripped Shanghai and its neighboring provinces for days is attributed to coal burning, car exhaust, factory pollution and weather patterns, and is a stark reminder that pollution is a serious challenge in China. (AP Photo/Eugene Hoshiko)
A couple in protective masks walk under haze in Shanghai, China, Friday, Dec. 6, 2013. Shanghai authorities ordered schoolchildren indoors and halted all construction Friday as China's financial hub suffered one its worst bouts of air pollution, bringing visibility down to a few dozen meters and obscuring the city's spectacular skyline. (AP Photo/Eugene Hoshiko)
Houses and buildings are covered with heavy haze in Shanghai, China, Wednesday, Dec. 4, 2013. China, one of the most visited countries in the world, has seen sharply fewer tourists this year - with worsening air pollution partly to blame. (AP Photo/Eugene Hoshiko)
Houses and buildings are covered with haze in Shanghai, China, Wednesday, Dec. 4, 2013. China, one of the most visited countries in the world, has seen sharply fewer tourists this year - with worsening air pollution partly to blame. (AP Photo/Eugene Hoshiko)
Houses and buildings are covered with haze in Shanghai, China, Wednesday, Dec. 4, 2013. China, one of the most visited countries in the world, has seen sharply fewer tourists this year - with worsening air pollution partly to blame. (AP Photo/Eugene Hoshiko)
This picture taken on March 29, 2014 shows residents breathing 'mountain air' from blue bags in a square in Zhengzhou in central China's Henan province, reportedly brought in from 190 kms away by a Henan-based travel company as part of a promotional event. Premature deaths and health problems from air pollution cost China as much as 300 billion USD a year, an official joint report by the World Bank and the Development Research Center of the State Council said on March 25, calling for a new urbanisation model for the world's second-largest economy. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
BEIJING, CHINA - APRIL 09: People with mask walk in Nanluoguxiang on April 9, 2014 in Beijing, China. China is vowing to ammend its procedures to curb pollution as smog in some areas of China have registered over 20 times the level considered safe by the World Health Organization (WHO) (Photo by Xiao Lu Chu/Getty Images)
This picture taken on March 29, 2014 shows residents breathing 'mountain air' from blue bags in a square in Zhengzhou in central China's Henan province, reportedly brought in from 190 kms away by a Henan-based travel company as part of a promotional event. Premature deaths and health problems from air pollution cost China as much as 300 billion USD a year, an official joint report by the World Bank and the Development Research Center of the State Council said on March 25, calling for a new urbanisation model for the world's second-largest economy. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
This picture taken on March 26, 2014 shows a girl wearing a mask in Beijing as environmental authorities issued a 'yellow' smog alert for the capital. Chinese companies have offered up a fresh idea to help pollution-weary travellers while cashing in on public concerns over dirty air at the same time -- smog insurance. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
BEIJING, CHINA - MARCH 26: The people wear face mask walking on the road in smog in Beijing, China, on March 26, 2014. Chinese authorities suggest that old people and those who are sensitive should not get out from their house. Symbolic buildings of Beijing cannot seen due to the air pollution. (Photo by Ali Ihsan Cam/Anadolu Agency/Getty Images)
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The United States, with 54,905 deaths in 2010 from soot and smog, ranks seventh highest for air pollution deaths. What's unusual is that the study says that agriculture caused 16,221 of those deaths, second only to 16,929 deaths blamed on power plants.

In the U.S. Northeast, all of Europe, Russia, Japan and South Korea, agriculture is the No. 1 cause of the soot and smog deaths, according to the study. Worldwide, agriculture is the No. 2 cause with 664,100 deaths, behind the more than 1 million deaths from in-home heating and cooking done with wood and other biofuels in developing world.

The problem with farms is ammonia from fertilizer and animal waste, Lelieveld said. That ammonia then combines with sulfates from coal-fired power plants and nitrates from car exhaust to form the soot particles that are the big air pollution killers, he said. In London, for example, the pollution from traffic takes time to be converted into soot, and then it is mixed with ammonia and transported downwind to the next city, he said.

"We were very surprised, but in the end it makes sense," Lelieveld said. He said the scientists had assumed that traffic and power plants would be the biggest cause of deadly soot and smog.

Agricultural emissions are becoming increasingly important but are not regulated, said Allen Robinson, an engineering professor at Carnegie Mellon University, who wasn't part of the study but praised it.

Ammonia air pollution from farms can be reduced "at relatively low costs," Robinson said. "Maybe this will help bring more attention to the issue."

In the central United States, the main cause of soot and smog premature deaths is power plants; in much of the West, it's traffic emissions.

Jason West and other outside scientists did dispute the study's projections that deaths would double by 2050. That's based on no change in air pollution. West and others said it's likely that some places, such as China, will dramatically cut their air pollution by 2050.

And Lelieveld said that if the world reduces a different air pollutant — carbon dioxide, the main gas causing global warming — soot and smog levels will be reduced as well, in a "win-win situation in both directions."

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