PM0.1 particles from aircraft may increase risk of vascular diseaseBMJ 2013; 347 doi: https://doi.org/10.1136/bmj.f6783 (Published 19 November 2013) Cite this as: BMJ 2013;347:f6783
- Joel C Corbin, atmospheric scientist1
Hansell and colleagues reported an association between exposure to aircraft noise and increased risks of stroke, coronary heart disease, and cardiovascular disease in areas close to Heathrow airport.1 They considered several confounding variables, including air pollution. However, air pollution was represented by PM10—the mass concentration of suspended particles smaller than 10 μm—which does not reflect air pollution from aircraft.
Aircraft emit PM0.1 particles, which are so low in mass that variations in PM0.1 or even PM2.5 do not correlate well with those of PM10.2 3 Yet PM0.1 particles can penetrate deeper into the lungs and translocate more easily into the bloodstream than PM10,4 5 so they may have led to the reported increased risks of vascular disease.
Unlike noise, which dissipates immediately, PM0.1 emissions persist for hours. When emitted at low altitude, PM0.1 would reach ground level within tens of minutes owing to turbulent mixing. Over the following hours, PM0.1 would coagulate into PM2.5 particles and persist in the air for several days.3 These PM2.5 particles have adverse health effects but are not equivalent to PM0.14—for example, their larger size means reduced lung penetration. Therefore the PM0.1 coagulation lifetime of hours is comparable to Hansell and colleagues’ 8-16 hour averaging periods, and the reported association between vascular health risks and aircraft activity may have reflected exposure to aircraft emitted PM0.1 particles.
The authors probably used PM10 data because data on other pollutants were not available. Even when available, such data may reflect ground traffic rather than aircraft activity. Thus the aircraft-activity data they used to estimate noise exposure might have been the best available proxy for aircraft PM0.1 pollution. The distinction between noise and PM0.1 is important for policy makers: noise disperses immediately, but PM0.1 particles may have diluted effects over a longer period and wider area.
Cite this as: BMJ 2013;347:f6783
Competing interests: None declared.
Full response at: www.bmj.com/content/347/bmj.f5432/rr/667230.