Bad Ozone Reaching Critical Levels in Tehran

Concentration of bad ozone as a known secondary air pollutant is gradually reaching critical levels in Tehran, director of Tehran's Air Quality Control Company was quoted as saying.
"Bad ozone, aka ground level ozone, concentration has been recorded at unhealthy levels for all groups, especially those suffering from respiratory problems," Hossein Shahidzadeh told ISNA Wednesday.
Ozone is a natural gas with a strong odor. Environmental scientists have classified the gas into good and bad.