Human Response to One Hour Pollutant Exposure (Turco, p194)
Symptom
Concentration
Parts per million by mass
Pollutant
Airway resistance, headaches      (long term lead to premature aging of lung tissue)
1.0 ppmm
General nose and throat irritation
0.3 ppmm
Nose and throat irritation in sensitive people
0.1 ppmm
Odor threshold (sweet)
0.02 ppmm
O3