Asthma cause, nitrogen dioxide

Given the central role of inflammation in the cause and persistence of asthma, it is plausible that enhancement of airway inflammation is a mechanism by which particle exposure may worsen asthma. More specifically, it will be important to determine whether atmospheric pollutant exposure further shifts the cellular inflammatory response in the airways to favor a Th2 lymphocyte response, with an increase in susceptibility to allergic sensitization or responsiveness. Recent studies in humans (39) and in animal models of allergy (40) suggest that exposure to relatively low concentrations of nitrogen dioxide increases responsiveness to allergen exposure. Other possible mechanisms include direct injury to epithelial cells, increases in reflex bronchoconstriction, or increased nonspecific airway responsiveness. 

The main ingredient in industrial smog is sulfur dioxide. Laboratory experiments have shown that sulfur dioxide increases aerosol formation, particularly in the presence of mixtures of hydrocarbons and nitrogen oxides. For example, mixtures of 3 parts per million (ppm) hydrocarbons, 1 ppm NOg, and 0.5 ppm SO2 at 50% relative humidity form aerosols that have sulfuric acid (HgSO ) as a major product. Breathing a sulfuric acid aerosol is very harmful, especially to people suffering from respiratory diseases such as asthma or emphysema. At a concentration of 5 ppm for 1 hour, this kind of aerosol can cause constriction of bronchial tubes. A level of 10 ppm for 1 hour can cause severe breathing distress. 

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