Carbon monoxide is an odorless, invisible gas that reduces the ability of blood to carry vital oxygen. Persons with heart conditions are at special risk when exposed to elevated levels. Visual impairment, reduced coordination and mental confusion are all associated with exposure. High exposure can poison, even cause death in healthy persons.

Carbon monoxide is especially dangerous inside homes and buildings. In heavily traveled and congested urban areas, carbon monoxide levels can be elevated. Extended exercise such as running and cycling in these areas may not be advisable.

Carbon monoxide is emitted from automobiles and from oxygen starved fires such as a smoldering pile of leaves or dampened-down fireplaces.

Widespread leaf burning and storm related disaster burning of large quantities of brush and downed trees can impact local carbon monoxide levels. This can be magnified during thermal inversions.