Micro-fine airborne pollutants: probably the most significant long-term pollution-related risk for city dwellers
Particles of partly combusted fuels and soot at the smallest size range (less than 2.5 microns, often called PM2.5 in measurement studies) come mainly from diesel engines and coal burning, also from cigarette smoke if you are (or live with) a smoker. They are probably the biggest health risk for residents of large cities worldwide today and should be a major concern for city dwellers in China. The main sources of these particles are ageing trucks and buses with poorly adjusted diesel engines. The soot particles are clearly visible in the black smoke from the exhaust. Industrial operations are another source.
The pollution index that the US Embassy in Beijing issues hourly is a measurement of PM2.5, defined as the total weight of particles of 2.5 microgrammes or less. The majority of these particles as measured by weight are in the 0.1 - 2.5 micron size range. There are also some particles in the 0.01 - 0.1 micron size range, but these are a small part of the total pollution by weight.
The health effects of PM2.5 particles are now recognized by healthcare professionals, and they are a worldwide risk for city-dwellers. For example, this from a clinician writing in the Medical Journal of Australia recently:
“In Sydney, Melbourne, Brisbane and Perth, air pollution causes an estimated 1611 premature deaths every year, with more than 3000 estimated for Australia as a whole. The most serious health problems relate to fine particles (PM2.5), emitted predominantly by diesel-powered vehicles and woodheaters.”
Bear in mind that Australian cities have relatively low levels of air pollution compared with Beijing and Shanghai!
The health risks of micro-fine soot particles stem from their ability to penetrate the lungs and pass into the bloodstream. This is the reason they are associated with cardiovascular disease (diseases of the heart and blood circulation) as well as lung disease. There are many research papers addressing this issue published and available online: the references below are a selection. There are further references related to China and Beijing-specific issues on our Beijing Air Quality page.
References and links for further reading
In addition to these references, many more studies can be found indexed online at Air Pollution Research News.