Fine particulate matter in the air of China’s cities

Recent months have seen a growth in the awareness among China’s urban residents of fine particulate matter suspended in the air. Atmospheric pollution is nothing new to the Chinese. If you lived in northern China like Beijing twenty years or more ago, you would be plagued by coal dust in the winter and desert sand in the spring. The coal dust was so thick that it coated shelves and furniture in apartments. After a foggy morning, the dust dropping out from the fog would form a layer on the side-walks which would be swept away by the street cleaners. Spring storms would blow in dust from Mongolia and north-west China and bring air traffic to a stop. 


Since that time, coal-fired district heating systems have been converted to natural gas, many small coal-fired power stations have been closed and new, cleaner ones have been built outside the major cities. A number of large steel plants have been transferred to other locations. The spring dust storms still come, but a massive programme of tree planting seems to have reduced their intensity.


Fine particulate matter


But suddenly a new and less visible form of pollution has been making the headlines: the so-called PM2.5. This is particulate matter with a diameter of less than 2.5 microns or 2.5 millionths of a metre. Popular interest was stirred by the revelation that the government had not been reporting information on PM2.5, but had only been reporting data on concentrations of PM10 which is a much coarser dust with a diameter of less than 10 microns.  The concentration of PM10 in Beijing had indeed been falling for several years, at least until 2008. In contrast the concentrations of PM2.5 have been rising since the late 1990s. The health effects of PM2.5 are well known and include a range of respiratory and heart problems. The small size of these particle means that they penetrate deeper into the lung than the coarser PM10 particles and are therefore more dangerous. In cities with consistently high concentrations, mortality rates are significantly increased.


The problem of PM2.5 started to emerge into public view in 2010 when data released by the US Embassy in Beijing contradicted  official statements. In the autumn of 2011 the measurements publicised by the Embassy showed that the air quality was hazardous on some days. Meanwhile Beijing municipal government was not revealing quantitative data, but was just declaring that the pollution was ‘moderate’ or ‘slight’. A few residents acquired monitors allowing them to measure PM2.5 themselves. Public pressure eventually grew to a level at which the Beijing government was forced to release the PM2.5 data it collects starting in January 2012.


No easy solutions


Recent information published in the newspapers, on internet sites and in scientific journals is revealing the scale of the problem in China as well as the scale of the challenge facing the government if it wishes to address this problem.


A recent study from satellite data (and therefore not necessarily absolutely precise) shows that most of China’s provinces have average PM2.5 concentrations in excess of 30 micrograms per cubic metre. This compares to a standard set by the World Health Organisation of 10 micrograms per cubic metre and a standard of 15 micrograms per cubic metre in the USA. Average concentrations in Shandong and Henan Provinces are in excess of 50 micrograms per cubic metre.


Studies on the ground are much more accurate. Those in Beijing have shown that the annual average concentration of PM2.5 between 2005 and 2008 was higher than 60 micrograms per cubic metre, with weekly values often reaching 100 micrograms per cubic metre. In comparison cities like London and New York have mean values of 10-20 micrograms per cubic metre, depending on location, and peaks of up to 40 micrograms per cubic metre. It is hardly surprising to read reports that Beijing’s lung cancer rates have increase by 60% in the last ten years.


These studies have also tried to identify the sources of these fine particles. The common belief is that they come from the burning of coal and from motor vehicles. If it was this simple, the solution would appear to be relatively straightforward. Power stations and steel plants would need use the necessary technology to stop these particles escaping or else the plants should be closed, and the number of conventional motor vehicles should be reduced. For many years China has been fitting coal-fired power stations with electrostatic precipitators to capture these fine particles, but other heavy industrial plants appear not to have been subject to these measures.  This is not just an issue for plants near Beijing, since much of the city’s PM2.5 from coal is blown in from Shanxi Province. Since the beginning of 2011, the Beijing municipal government has put in place measures to constrain the growth of motor vehicle numbers, but not to reduce the numbers. Any moves to encourage electric vehicles would merely transfer to pollution problem out of Beijing to those regions where additional electricity has to be generated, mainly from coal.


But coal and vehicles are not the sole sources of PM2.5 in Beijing. The spring storms bring in fine dust from the north-west, but this effect is seasonal. The other major sources are industrial dust of different types and the dust from vehicles using paved roads, including asphalt, tyres and brakes. PM2.5 dust has also been traced to construction sites, landfill waste dumps, waste incineration plants, bare fields in the winter, unpaved roads, and the burning of biomass. These results are just for Beijing, and cities in different parts of China will show different concentrations and different sources of PM2.5, depending on such factors as the proportion of coal in the fuel mix, the proximity to deserts, the vegetation cover in winter, and the number of motor vehicles.


These scientific studies show that the problem of PM2.5 in China’s cities will not be easy to address. Appropriate industrial and transport policies will make a significant difference, but even these will take a great effort. The management of waste, of construction and of biomass will add substantial complexity to the task. Further, this is not just a matter for city governments, for these fine particles can travel a long way in the wind. Managing PM2.5 is an issue for national and provincial governments.


Print Friendly, PDF & Email