Expert Commentary

China, cookstoves and highways: Effects of black carbon on human health

2014 study in Proceedings of the National Academy of Sciences examining the health impacts of particulate matter and black carbon from burning biomass, fossil fuels and other sources.

During the 2014 Beijing marathon, one of China’s biggest sports events, many runners wore facemasks to protect themselves from the omnipresent smog. According to a March 2014 report, among the 74 Chinese cities the central government monitors, only three had air quality that met the official minimum standards — and this after the widely reported “airpocalypse” of 2013. In response, the Chinese government has announced plans to spend $275 billion between 2013 and 2017 to address the problem, and there is some evidence that air quality is improving marginally. In November, China and the United States reached a deal to cut carbon dioxide emissions, with China pledging to cap its emissions by 2030.

China’s efforts to reduce air pollution largely focus on limiting the emissions of particulate matter (PM). As a component of PM2.5, black carbon (BC) results from the incomplete combustion of fossil fuels and biomass. Commonly known as soot, BC is the second-greatest contributor to global warming after carbon dioxide. BC also poses risks to human health, including cardiovascular disease, respiratory disease and premature death. In 2010, about half of the Chinese population still relied on burning biomass for cooking, exposing household members to BC in their daily lives. A 2014 study in the Proceedings of the National Academy of Sciences (PNAS) found that BC emissions from the North China Plain could be two to three times higher than previously estimated. Aggravating the problem is the growth in automotive traffic in China: The number of highway vehicles is expected to double in the next decade, and particulate matter from automotive traffic has been demonstrated to have significant negative impacts on health.

A 2014 study published in PNAS, Highway Proximity and Black Carbon from Cookstoves as a Risk Factor for Higher Blood Pressure in Rural China,” examines the health impacts of PM components from different sources, including burning biomass and fossil fuels. The researchers — from McGill University, University of Minnesota, University of Chinese Academy of Sciences, University of Wisconsin-Madison and Imperial College London — sought to evaluate how exposure to black carbon is associated with rural Chinese women’s blood pressure and how highway proximity affects that association.

The study involved 280 women living in northwestern Yunnan, an area where biomass is frequently used for cooking. Data collected included blood pressure, distance from major roads, and daily exposure to BC and hopane markers (indications of motor-vehicle emissions).

The study’s findings include:

  • The effect of BC exposure on blood pressure was more than twice as strong as that of PM2.5 mass and water-soluble organic mass for rural Chinese women.
  • BC’s health effect on blood pressure was about three times greater for women who lived close to highways. However, highway proximity independently did not have a significant impact on blood pressure.
  • The combined effect of BC exposure and distance to a highway was significant on the village level. Women who lived in villages next to a highway experienced the strongest effects, while women who lived in villages the farthest away were not affected.
  • Those living closest to a highway were exposed to air with significantly higher levels of hopane markers (4.6 μg/m3) — the technical unit of measurement is micrograms per cubic meter — which are traced to motor-vehicle exhaust, than women who lived in the village the farthest away from a highway (1.1 μg/m3), and, as a reference, U.S. workers in trucking terminals (1.9 μg/m3).
  • These women’s average exposure to PM2.5 was 55 μg/m3 in summer and 117 μg/m3 in winter, exceeding the WHO’s standard of 25 μg/m3 by more than two and four times, respectively.
  • These women’s average exposure to BC was 5.2 μg/m3; higher than the daytime BC level in Beijing, Mexico City and some Brazilian cities, ranging from 1.9 to 4.8 μg/m3.

Because of BC’s negative effects on human health and contribution to climate change, the researchers conclude that the Chinese government should consider shifting its target from reducing particular matter in general to specifically lowering black carbon emissions. The authors state that “as motorized transport and subsequent traffic emissions increase throughout China, air pollution policies and mitigation efforts that focus on BC control might have the largest benefits for climate and human health.”

Related research: A 2013 study published in the Proceedings of the National Academy of Sciences (PNAS), “Coal and Public Health: Scientific Evidence from the U.S. and China,” looks at the relationship between coal consumption and mortality in China.


Keywords: pollution, health, climate change, China, carbon black

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