Pollution does not occur only outdoors. The World Health Organization (WHO) recently recognized that indoor air is more polluted than outdoor air. Worldwide, it attributes 4.3 million deaths a year to indoor air pollution, compared with 3 million to outdoor air pollution. The two overlap, of course, since 30% of the latter enters buildings, making it difficult to strike the right balance between insulation and ventilation. Indoor pollutants come from our lifestyles, building materials and furniture, and combustion and cooking appliances.
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Coal in the big cities
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In France, wood heating accounts for 42% of average emissions of particles smaller than 2.5 micrometers (known as PM2.5), three times the share produced by road transport (14%). According to the French Agency for Ecological Transition, depending on the age and type of equipment, heating a home with wood for one day emits, on average, as many particles as a diesel car traveling 3,500 kilometers. Moreover, large district heating networks, such as the one in Paris, run primarily on... fuel oil and coal.
Once emitted, air pollution is subject to weather conditions and prevailing winds, and varies according to known factors—green spaces, bodies of water, terrain and major roads—or unknown ones (no one can really explain why Porte d’Auteuil is five times more polluted than the Paris region on average).
