To the Editor: There should be no contradiction in recommending that people enjoy recreational exercise when air pollution is low but nonetheless walk/cycle for transport.1 I cycle home after 5 pm, when pollution increases to health-hazardous levels (Box), but it is astounding to see people out jogging in such unhealthy air.

Cycling for transport is undoubtedly better than driving. Despite dangers from pollution and busy roads, commuter-cyclists have 40% lower mortality than drivers.2 Nonetheless, cycling in diesel fumes at concentrations typically present on busy roads causes significant damage to blood vessels,3 and should be avoided if there is a choice.

This concept is no harder to understand than the concept that moderate intake of mono- and polyunsaturated fats is beneficial but excessive saturated fat intake is bad. Regrettably, this distinction was once considered so complicated that people were told simply to reduce all fat consumption.

Until people understand the hazards of air pollution, controls will remain inadequate. 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.4 Winter measurements in Liverpool, Sydney, follow a similar temporal distribution to those in Armidale, in regional New South Wales (Box), suggesting that both regional and metropolitan residents should jog at lunchtime in winter, rather than after work.

A recent review estimated that health costs of PM2.5 emissions in urban Australia range from $100 to $300 per kilogram of particles. A typical woodheater (emitting 20 kg of these particles every winter) therefore generates $2000–$6000 in health costs — considerably more than switching to non-polluting heating.4 Older (pre-1990) diesel cars and utilities emit about 0.75 g PM2.5 particles per kilometre (13.8 kg per 20 000 km), generating estimated annual health costs of $1380–$4140. This exceeds the cost of converting to liquid petroleum gas or retrofitting a particle trap/oxidation catalyst.

When PM2.5 pollution was reduced in Dublin by banning non-smokeless coal in 1990, there were 2154 fewer deaths in the first 6 years of the ban than the previous 6 years (15.5% fewer respiratory and 10.3% fewer cardiovascular deaths/year).1

Euro II emission limits for new diesel-powered vehicles became mandatory in 1996/97 in Europe (and in 2002/03 in Australia). Simple, cost-effective measures for reducing the major sources of urban PM2.5 pollution — including converting or retrofitting diesel-powered vehicles that exceed Euro II limits, phasing out woodheaters and strongly discouraging stubble-burning in areas where it increases smoke pollution in rural towns1 — would significantly reduce pollution-related illness. It would also allow cyclists, pedestrians and joggers to exercise whenever desired, with fewer worries about air quality.