Letters Section Editor: Stephen J. Lurie, MD, PhD, Senior Editor.
In Reply: While we concur with Mr Donnay that
carbon monoxide has adverse effects on respiratory health in its own right,
we disagree with his assertion that carbon monoxide confounds the association
between ozone and asthma. Carbon monoxide in the urban environment is mainly
produced by motor vehicle emissions, and it is often regarded as a surrogate
for exposure to such other such emissions collectively. These motor vehicle
emissions also contain not only nitric oxide, which becomes NO2,
but particulate emissions (including ultrafine particles), and many different
organic and inorganic species. Because levels of all of these pollutants are
usually strongly intercorrelated (which is not surprising considering their
shared source-origin in urban areas), it has not always proved possible to
statistically assign some measure of "responsibility" to them individually
when a strong association has been shown to exist between them all and some
adverse health outcome over time.
Thurston GD, Bates DV. Ozone and Asthma—Reply. JAMA. 2004;291(4):423-424. doi:10.1001/jama.291.4.423-b