China's particulate pollutionIn a new study published in Environmental Health Perspectives, Chinese researchers shed light on which components of PM2.5 pollution do the most damage to health. Previous work has shown that exposure to PM2.5s (particles less than 2.5 microns in size) are linked to heart and lung problems and to excess mortality. But it has not been known just what compounds in the PM2.5s do the most damage.

China's particulate pollution is one of the highest concentrations of PM2.5 pollution in the world, but the impact that air pollution exposures have on the health of the Chinese population is not well understood. A team led by Haidong Kan of Fudan University in Shanghai studied PM2.5 pollution in Xi’an, which is one of China’s most polluted cities. It is the largest city in northwestern China and has a population of over 8 million. The researchers looked at mortality data for residents of the inner urban area and at daily levels of PM2.5. They also measured levels of PM2.5 components like organic carbon, elemental carbon, ions including nitrate and sulfate, as well as a number of elements including nickel and chlorine.

During the study period, the average daily concentration of PM2.5 was 182.2 micrograms per cubic metre – which is way above the World Health Organization’s recommended upper limit of 10 micrograms per cubic metre. In Beijing, which gets a lot of bad press about its pollution, the corresponding levels are ‘only’ 122 micrograms per cubic metre.

Taking the pollution measurements with mortality data showed that there was a significant link between exposure to PM2.5 and daily mortality. On a ‘bad air’ day people were more likely to die of heart disease, lung disease or, indeed, of any cause. Digging deeper into the data, the researchers showed that the following components of PM2.5s were linked to increased mortality:

  • organic carbon
  • elemental carbon
  • sulphate ion
  • ammonium ion
  • nitrate ion
  • chloride ion
  • chlorine
  • nickel

The researchers note that these specific components of PM2.5s are associated with the burning of fossil fuels (mainly coal, heavy oil) in Xi’an. They note that this is the first study to link the health of the population of a developing country to specific components of PM2.5s. These new findings are consistent with the famous Six Cities study which showed the link between PM2.5s and mortality in the United States urban environment. Pollution is a global issue and a major public health problem, particularly where the combustion of fossil fuels is inadequately controlled. The study should push the Chinese authorities into setting out tighter environmental legislation to protect the health of its citizens. The announcement that they are publishing PM2.5 daily data may be a good start but, clearly, much more needs to be done.