Airborne Particles Leave Lungs Susceptible To Ozone

Epidemiological studies have demonstrated that airborne particles cause lung problems, but scientists haven't known how. Agustín J. Colussi and colleagues at Caltech now have found that particles wreak havoc on the lungs' natural protection against damaging ozone (Proc. Natl. Acad. Sci. USA 2008, 105, 7365). Ascorbic acid (vitamin C) in lung fluid usually scavenges inhaled ozone and breaks it into harmless by-products. The researchers used mass spectrometry to show that when droplets of ascorbic acid meet ozone gas under acidic conditions, ascorbic acid turns ozone into potentially harmful secondary ozonides such as ascorbic ozonide. Inhaling fine particles (less than 2.5 µm) can lower the pH of lung fluid and thus might trigger the production of ozonides, they suggest. Most airborne particles also carry iron, which can cause ozonides to turn into cytotoxic radicals, they note. The researchers suggest that it is the combination of ascorbic acid, ozone, low lung pH, and iron that causes an acute inflammatory response in the lungs when airborne particles are inhaled.