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The particle and vapour phases of ETS are complex mixtures of many chemicals, including known carcinogens, such as nitrosamines and benzene (WHO, 2000a). One of the commonly used indicators of environmental pollution by tobacco smoke is PM10; this has been found to be 2 to 3 times higher in houses with smokers than in other houses (Schwartz and Zeger, 1990). Nicotine concentrations of up to 10 μg/m3 have previously been found in houses with smokers (WHO, 2000a). 20 Particle concentrations (μg/m3) and exposures in eight major global environments (WHO, 2000a which cites Smith, 1996) Region Concentration Exposure (%) Total Indoor Outdoor Indoor Outdoor Urban Rural 100 80 70 40 7 2 1 0 Urban Rural 250 400 280 70 Developed 7 2 Developing 25 9 34 52 5 57 Total 86 14a 100 a) Variance in summation of individual values to total value was observed in cited reference Note: population exposures expressed as a percentage of the world total.

1 Smogs and air pollution episodes An air pollution episode is the general term applied to a period of poor air quality, sometimes lasting for several days, often extending over a large geographical area. During an air pollution episode, concentrations of all the measured pollutant substances may be increased, or only one may be affected (Environment Agency, 2000). Air pollution episodes can vary widely in terms of spatial coverage, duration, pollutants affected and incidence throughout the year (Department of Health, 2000).

On a global scale, biomass fuels (wood, crop residues, dung, grass, etc) are used in about half the world’s households for cooking and/or heating. In China, for example, it has been estimated that coal burning results in indoor particulate concentrations up to 5000 μg/m3, whereas residences in Nepal and Papua New Guinea have peak levels of >10,000 μg/m3 (WHO, 2000a cites Smith, 1996). Biomass smoke contains significant amounts of pollutants including CO, particles, hydrocarbons and to a lesser extent NOx.