Cancer and cardiovascular effects from exposure to combustion products

The key indoor air exposures leading to cancer and severe cardiovascularconsequences are radon, certain volatile organic compounds (VOCs) and incompletecombustion generated particulate matter (PM and PAHs) and carbon monoxide. Ofthese radon [1] and carbon monoxide [2] are dealt with in focused presentations, PMand VOCs are covered in the current presentation.Complete oxidation of a hydrocarbon fuel would result in only water and carbondioxide as combustion products. Combustion of even the simplest fuel, methane (over90 % of natural gas), however, is a complicated chemical process, let alonecombustion of the infinitely more complex solid fuels, coal and wood. Completeoxidation is never achieved even in the most advanced industrial scale boiler plants,which are built upon generations of engineering sciences, are equipped with advancedflue gas cleaning technologies, and employ professional operating teams using anetwork of sensors and automated feedback control systems.In comparison, the domestic combustion devices to heat, cook and entertain(fireplaces, incense, candles) represent much simpler technologies, use moreheterogeneous fuels, are operated by untrained lay persons, and are hardly everequipped with any feedback control or flue gas cleaning. Consequently the harmfulemissions per generated heat unit of small scale combustion devices are orders ofmagnitude higher than those of industrial and power generating stations (NOX is anexception). A fact that highlights the consequences of this difference is that per unitoperating time the emissions of particle phase polycyclic aromatic hydrocarbons(PAH 1) are equally large for a residential woodstove and a coal fired generatingstation with 10.000 times larger heat output.The total emissions of combustion particles to outdoor air are orders of magnitudehigher than into indoor air, but the intake fraction (iF) of the particles emitted intoindoor air that is inhaled by people, and could thus harm their health is in the order of10-2..10-3, i.e. 100 10.000 times the intake fraction of particles emitted into outdoorair [3, 4]. Therefore by far the highest exposures to combustion particles (also vapoursand gases) occur in indoor air, and originate from indoor sources.