Ozone O3

Ground-level ozone is one of the major components of photochemical smog and a key health risk linked to breathing problems, asthma, reduced lung function and respiratory diseases. It is a secondary pollutant, meaning that it is not directly emitted. Instead, it is produced when carbon monoxide (CO), methane, or other volatile organic compounds (VOCs) are oxidized in the presence of nitrogen oxides (NOx) and sunlight. In addition to their role as ozone precursors, CO, VOCs and NOx are dangerous air pollutants themselves. Major sources of NOx and VOCs include emissions from motor vehicle exhaust, industrial facilities, and chemical solvents. Major sources of methane include waste and the fossil fuel and agricultural industry. Aside from its health impacts, tropospheric ozone is a short-lived climate pollutant and one of the most important greenhouse gases.



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