Respiratory health researches have for years suspected a relationship between raised levels of particulate matter (defined as airborne particles smaller than 2.5 micrograms) and cardiac arrest.

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The latter include health-damaging and smog-forming airborne pollutants like hydrocarbons, nitrogen oxide, particulate matter, carbon monoxide and formaldehyde, as well as greenhouse gases that contribute to climate change, like carbon dioxide, nitrous oxide, methane and other compounds.

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