Tracing Back Pollution, pt.1: The Most Evil

In this and the next post, I will look at the sources of pollutants – to be more specific, the anthropogenic emissions. This figure by Zhao, Zhang and Nielson (2012) (cited in Greenpeace, 2012) illustrates China’s air pollutants emission inventory by sectors in 2010:

Source: Greenpeace, 2012.

It is evident that industry and power plants emitted most of the SO₂ and NO_X. As for particulate matter emissions, the proportion of residential and commercial sources was higher than that of power generation, while industry remained the largest source. As mentioned before, particulate matter does not refer to a single substance like SO_2, but rather a complex mixture of particles from a wide range of sources. We differentiate between directly emitted primary particles (via fuel combustion) and secondary particles, which are produced by reactions of primary gases. Hence, the chemical composition and source apportionment of particulate matter is essential. Huang et al. (2014) investigated PM_2.5 during the severe haze events in January 2013 in four cities. Their results are summarised in this figure:

Source: Huang et al., 2014.

Organic matter was the main component of PM_2.5 in all four cities, followed by sulfate (8–18%), nitrate (7–14%) and ammonium (5–10%). Sulfate, nitrate and ammonium derive from the oxidation of SO₂, NO_X and NH₃ respectively. Organic matter (OM) can be either primary or secondary; secondary OM derives from oxidation of volatile organic compounds, which can be of either biogenic or anthropogenic origin. Overall, secondary particles contributed 44-71% of OM and 30-70% of total PM_2.5 (Huang et al., 2014). 

The large proportion of secondary particles reflects the significance of their precursor gases, above all SO₂ and NO_X, which then brings us back to their main sources: power plants and industry.

Source: U.S. Energy Information Administration, 2015.

The figure above demonstrates that coal-fired thermal power plants made up 63% of China’s installed electricity capacity in 2013. Hydropower was the second largest source of electricity generation (22%), while thermal power plants that burn natural gas or oil were less significant (4% and 2% respectively). China’s energy mix is due to its resource structure. According to World Energy Council (2013, cited in U.S. Energy Information Administration,2015), China held an approx. 126 billion short tons of proven coal reserves in 2011, which is the third largest in the world and an equivalent to 13% of the total global coal reserve. By comparison, China held 24.6 billion barrels of proven oil reserves and 164 trillion cubic feet of natural gas reserves by 2014 (Oil & Gas Journal, 2015, cited in cited in U.S. Energy Information Administration,2015), both of which did not make it to top 10 reserves in the world. Furthermore, coal is cheaper and more accessible. As a result, China is the world’s largest producer and consumer of coal, accounting for 46% of global production and 49% of global consumption—almost as much as the rest of the world combined:

Source: U.S. Energy Information Administration, 2015.

Coal is also widely consumed in energy intensive heavy industry, especially the production of iron and steel and cement. In 2014, about 49% of the world’s crude steel (World Steel Association,2015) and 57% of cement was produced in China (The European Cement Association,2015). Coal-fired industrial boilers are less efficient and thus emit more pollutants than coal-fired power plants (Greenpeace, 2012).

In summary, China’s industrialisation relies heavily on its extensive coal resource. However, coal is considered the dirtiest fossil fuel, for its extraction, processing, transportation and combustion all cause environmental damage. Coal combustion is not only the biggest source of anthropogenic CO₂ emissions; it also releases many harmful by-products. According to Greenpeace (2010), it is responsible for 75% of China’s total SO₂, 85% of NO₂, 80% of NO and 70% of the total suspended particulate emission. Coal is the biggest source of air pollution in China.