Ozone O3

Ozone (O3), is not emitted directly into the atmosphere, but is a secondary pollutant produced by reaction between nitrogen dioxide (NO2), hydrocarbons and sunlight. Whereas nitrogen oxide (NO) destroys ozone acting as a local sink. For this reason, ozone levels are not as high in urban areas (where high levels of NO are emitted from vehicles) as in rural areas. Ozone levels are usually highest in rural areas, particularly in hot, still, sunny weather conditions giving rise to “summur smog”



Time-weighted average

80 - 120 µg/Nm3 (ppm)

Averaging time

1 hour - 8 hour

Time –weighted average Averaging Time Number of allowable exceedances
120 ppb 1-hour 2 times per 30 days
80 ppb 8-hour 2 times per 7 days
Number of allowable exceedances

2 times per 7 days