Air Pollution and Asthma

Air pollution is detrimental to all persons, but it is especially bad for persons who have asthma. Air pollutants may cause acute asthma attacks. Additionally, some air pollutants may actually increase nonspecific airway reactivity, inducing an asthmatic state. Also, various pollutants have been found to decrease ciliary motion, increase mucus production, inhibit phagocytosis, cause epithelial injury, and increase the number of acute respiratory illnesses. Epidemiologic studies have documented a number of air pollution disasters and have shown that severe air pollution causes significant health effects, especially in persons who has lung disease. For example, in the Meuse river valley of Belgium in December 1930, industrial emissions were trapped by an atmospheric thermal inversion. Thousands became ill, and 60 died. In Donora, Pennsylvania, in October 1948, industrial emissions were similarly trapped by a thermal inversion. Six thousand of 14,000 residents became ill; the death rate increased from two expected to 20 during the period. In London in December 1952, soft coal was widely used for heating. An inversion trapped the pollutants produced by coal burning and industrial processes and caused 4000 excess deaths in 5 days. In December 1962, 750 deaths were attributed to another inversion in London. In all of these disasters, air pollution affected most severely the elderly and those who were already ill with heart and lung disease. More than one pollutant was responsible for the disasters, but the sulfur oxide-particulate complex is most often implicated as a causative factor. Lesser levels of air pollution than those that caused the disasters may induce or exacerbate asthma, but because many environmental factors operate simultaneously, the causality is less clear. Thus, Cohen and others found that the frequency of asthma attacks related weakly to concentrations of ambient sulfur dioxide and particulates, but the relationship of asthmatic attacks to ambient temperature variations was stronger. Kahn found that high levels of ozone correlate with the number, duration, and severity of asthma attacks, but found that this factor is only one of many in the complex etiology of asthma attacks. Whittemore and Korn found that persons with asthma living in the Los Angeles area tend to have more attacks on days with high oxidant and particulate pollution. After World War II, Tokyo-Yokohama asthma was described. Many American military personnel and their dependents in Tokyo and Yokohama developed recurrent bronchoconstriction that appeared to be related to the level of air pollution. When afflicted persons left the area, they tended to get better. The relationship between air pollution and asthma was obscured, however, by the fact that almost all affected patients were moderate to heavy smokers. Thus, because many environmental factors alter airway function, it is often difficult to correlate symptoms or lung function with the concentration of one particular pollutant or with a particular combination of pollutants. To avoid this problem, controlled human studies have been performed to detect the effect of single pollutants on asthma. The specific effects of sulfur dioxide (SO2), ozone (O3), and nitrogen dioxide ( N O 2 on asthma are discussed in the remainder of this article.