China’s inhabitants increasingly face exposure to air pollution. So far, there are very limited studies that address either the cause or the consequences within the pollution levels observed in China. Breathing in fine dust, especially Particular Matter 2.5 (PM2.5), has a proven impact on respiratory function and overall health.
Whereas the WHO considers values below 25 microgram/cubic meter (ug/m3) safe, Beijing experienced, on average, 231 ug/m3 PM2.5 in the second week of January 2013. In September 2014, a consortium of researchers from China, Hong Kong, Italy and Switserland published an extensive report in Nature, on their analysis of the early 2013 pollution haze in China. The study cites a high number of Chinese reports and studies, including one showing an increased hospital visit that exactly overlaps during intense pollution periods.
The results show that the pollution was strongly driven by emissions of so-called secondary aerosol precursors. Reduction in such emissions would clearly benefit the air quality; estimated was that these contribute to 30 to 77% of the particular matter concentrations in Beijing, Shanghai, Guangzhou and Xi’an.
Secondary aerosol precursors are released after burning fossil fuel or biomass. These are not particles that are released as matter directly into the air, such as ash, but are formed after conversion of (organic) compounds in chemical reactions to form sulfates, ammonium compounds, etc.
The Chinese government has published its goal to reduce particulate matter-based air pollution by 25% compared to 2012 levels. The authors of the study note that this could be achieved by reducing secondary aerosol emissions.