Ozonization, oxidant enriched atmosphere

Following fires in which endotracheal tubes became ignited by surgical lasers or electrocautery in atmospheres enriched by oxygen and/or nitrous oxide, the flammability of PVC, silicone rubber and red rubber tubes in enriched atmospheres was studied [1], Ozonised oxygen was reacted with hydrogen at low pressure to generate hydroxyl radicals. Pressure in the apparatus was maintained by a vacuum pump protected from ozone by a tube of heated silver foil. On two occasions there was an explosion in the plastic vent pipe from the vacuum pump. The vent gas should have been outside explosive limits and the exact cause is not clear the editor suspects peroxide formation. 

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

Ozone is also a better-oxygen-atom-transfer reagent in the atmosphere because UV light results in the formation of 02 and O atoms, which react with halides. The role of metals in the catalysis of iodide oxidation is also more likely in the atmosphere because of the enrichment of iodide relative to the other halides in rainwater and aerosols (13). 

The irritation of air enriched solely with NO or NO2 did not produce photo-oxidants this only occurred when hydrocarbons were also present in the polluted urban atmosphere. This leads to a build-up of tropospheric ozone, and hence to faster rates of photoinitiation through photodissociation of ozone, and then to a further build-up of ozone, and so on. Besides ozone, which is toxic at low concentrations (0.1-1 ppmv), other intermediates responsible for adverse effects include aldehydes and organic nitrates, such as peroxyacetyl nitrate (PAN). 

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