Health Canada has released new Residential Indoor Air Quality Guidelines for both ozone and carbon monoxide, which replace guidance provided in 1987. The maximum recommended residential exposure limit for carbon monoxide is now 11.5 mg/m3 or 10 ppm for a 24 hour period, and 28.6 mg/m3 or 25 ppm over a one hour period. The new exposure limit for ozone is 40 ug/m3 or 20 ppb over an 8 hour period.