Particles from forest fires have a measurable impact on public health not only locally, but also in areas hundreds of kilometres away from the combustion source. Plumes from combustion sites also affect concentrations of pollutants other than the particles found near fire sites, such as carbon monoxide and atmospheric ozone. Concentrations of pollutants (e.g.: ozone) that contribute to urban smog can also increase downwind of and at a great distance from these sites.