Not really a smart answer. You mentioned toxic gases with PROVEN harmful effects. Now, I want you to learn a bit, please read on...
From:
http://emedicine.medscape.com/article/832708-overview
"Oxides of nitrogen
Inhalation of nitric oxide causes the formation of methemoglobin. Inhalation of nitrogen dioxide results in the formation of nitrite, which leads to a fall in blood pressure, production of methemoglobin, and cellular hypoxia. Inhalation of high concentrations causes rapid death without the formation of pulmonary edema. Milder yet still severe exposures may result in death with production of yellow frothy fluid in the nasal passages, mouth, and trachea and marked pulmonary edema. The symptoms following the inhalation of NOx are mostly due to nitrogen dioxide.
[...]
Sulfur trioxide
Since FS is an intermediate used to produce sulfuric acid upon its reaction with moisture, the resulting toxicity is that of an acidic irritation to mucosal membranes and even skin. The corrosive effect of acid on mucosa and keratinized skin causes significant irritations and chemical burns."
Sulfur dioxide also forms acid in presence of moisture.
They talk about NOx concentration >1.5 ppm.
From:
http://www.inspectapedia.com/hazmat/CO2gashaz.htm
"Outdoors the typical carbon dioxide CO2 level in air is 300 ppm to 400 ppm.
[...]
Toxic levels of carbon dioxide: at levels above 5%, concentration CO2 is directly toxic. [At lower levels we may be seeing effects of a reduction in the relative amount of oxygen rather than direct toxicity of CO2.]"
That means 50000ppm.
See the difference?
CO2 is not considered a toxic gas.