Frequency of airborne Alternaria spores in Tucson, Arizona over a 20-year period.

Once recommended by clinicians to the allergy sufferer as a refuge due to its healthful arid climate, Tucson is now noted for its incidence of asthma which if two to three times higher than the nation as a whole. This increase in asthma incidence has been attributed in part to a 10-fold increase in atmospheric pollen over the years due to the widespread use of high pollen-producing shade and ornamental trees. Data obtained by Durham slide sampler also reveal a five-to-tenfold increase in numbers of Alternaria (Alt) spores in Tucson over the last 20 years. This may be linked to the increasing numbers of certain pollen producing plants which may serve as the substrate for the mold. Relationships appear to exist between Alternaria frequency and numerous climatic conditions such as precipitation, average monthly relative humidity, average monthly temperature and incident radiation. Because of these relationships the frequency of Alternaria may be predictable on a daily, seasonal and yearly basis.