More than 3 million people a year are killed prematurely by outdoor air pollution, according to a landmark new study, more than malaria and HIV/Aids combined.
Wood and coal burning for heating homes and cooking is the biggest cause, especially in Asia, but the research reveals a remarkably heavy toll from farming emissions in Europe and the US, where it is the leading cause of deaths.
The report warns that, unless action is taken, the number of deaths – already equivalent to six deaths every minute – will double by 2050. “This projection should sound alarm bells for public health agencies around the world,” said environmental health expert Professor Michael Jerrett, at the University of California and who was not involved in the research.
Most air pollution deaths are caused by tiny particles that can be inhaled deep into the lungs. These cause heart attacks and strokes, which account for three-quarters of the 3.3 million annual deaths, with lung cancer and respiratory diseases responsible for the rest. The work did not include the effect of indoor air pollution, from cooking fires for example, which is estimated to cause an additional 3.4 million deaths a year.
The new work, published in the journal Nature, is the first study to single out different outdoor air pollution sources and estimate the number of premature deaths they each cause, considering road traffic, fossil fuel power stations and other sources. The researchers used a detailed computer model of the global atmosphere to assess the impact of air pollution on different populations, including new information on how pollution affects people in China and India.
A third of all premature deaths were the result of using smoky fuels such as wood and coal for heating homes or cooking and using dirty diesel generators for electricity, all well-known hazards. This domestic energy use causes half the 645,000 annual deaths in India and a third of the 1.4 million annual deaths in China.
But the research found that agricultural emissions of ammonia had a “remarkable” impact, according to Professor Jos Lelieveld, at the Max Planck Institute for Chemistry in Germany, who led the research. A fifth of all global deaths resulted from these emissions, which come mainly from cattle, chickens and pigs and from the over-use of fertiliser.
The ammonia reacts with fumes from traffic and industry to produce tiny particles and is the largest cause of air pollution deaths in the eastern US, Japan and in Europe. “For London, agriculture is the main source,” said Lelieveld. Across the UK, 48% of the premature deaths were ultimately the result of agricultural pollution.
Traffic pollution was still important in developed countries, causing a fifth of deaths, despite crackdowns on dirty vehicles. It only caused 5% of deaths across the globe as a whole, but this is likely to rise as more cars take to the road in developing countries.
Air pollution from power stations, mainly coal-burning plants, was significant globally, causing one in seven deaths. It is the biggest single factor in the US, causing a third of the 55,000 annual deaths, compared to 16% in the UK.
Natural air pollution, mostly dust in arid regions, caused almost a fifth of global air pollution deaths. This source is a major factor in some dry countries, accounting for 92% of deaths in Egypt and 81% in Iran.
“The overlap of high pollution and large populations takes a huge toll on public health, but little [was] known about the pollution sources that are responsible for premature deaths,” said Jerrett. “The results are surprising and potentially important for protecting public health globally.”
Currently it is assumed that all particulates are equally toxic. But if those from fuel burning are more toxic, as some scientists suspect, the proportion of premature deaths attributable to farming emissions would be lower. Even so, Jerrett said, “the finding is highly valuable … because agriculture has generally not been seen as a major source of air pollution or premature death, and because it suggests that much more attention needs to be paid to agricultural sources, by both scientists and policymakers.”
Dr Oliver Wild, an atmospheric scientist at Lancaster University in the UK said: “The study really brings home the need for air quality controls to avoid these additional deaths, particularly in heavily populated parts of Asia.”