Airway Reactivity to Sulfate and Sulfuric Acid Aerosols in Normal and Asthmatic Subjects

Recent epidemiologic studies have emphasized a relationship between alteration in lung function, respiratory symptoms in asthmatics, and elevated levels of sulfate air pollutants. In asthmatics, it has been reported that 1) the more acidic sulfate aerosols, sulfuric acid (H₂SO₄) and ammonium bisulfate (NH₄HSO₄), provoked the greatest changes in lung function and 2) a definite exposure-response relationship exists for H₂SO₄ inhalation. To determine if sulfate aerosol exposure caused increased reactivity to a known bronchoconstrictor, normal and asthmatic subjects inhaled subthreshold doses of carbachol after the following sulfates: H₂SO₄, NH4HSO4, and sodium bisulfate. A NaCI aerosol served as a control. Exposure times averaged 16 minutes with sulfate concentrations ranging from 100 μ/m³ to 1000 jtg/m₃. In normal subjects, prior inhalation of either 1000 yug/m₃ H₂SO₄ or NH4HSO4 significantly potentiated (P < 0.05) the bronchoconstrictor action of carbachol on airway conductance compared to NaCI and carbachol or carbachol alone by t-tests. For the asthmatic group, prior inhalation of either 1000/tg/m₃ H₂SO₄ or NH₄HSO₄ (P < 0.05), or 450 μ/m³ H₂SO₄ (P < 0.05) similarly enhanced the carbachol bronchoconstrictor effect compared to NaCI and carbachol. At the low 100 μ/m³, no sulfates altered the effects of carbachol on pulmonary function. Although mean changes between the sulfate groups did not attain significance by an analysis of variance, it was found that the bronchoconstrictor action of carbachol was potentiated by the sulfate aerosols more or less in relation to their acidity.     

AN IRRIGATION SCHEDULING MODEL WHICH INCORPORATES RAINFALL PREDICTIONS1

ABSTRACT In humid areas appreciable amounts of rainfall complicate irrigation scheduling. This rainfall tends to give supplemental water application a low priority. As a result irrigation may be delayed until there is not enough time to cover the crop area before some drought damage occurs. To improve the management of irrigation systems, a scheduling model has been developed. The model's water application decisions incorporate climatological records, soil-plant data, current pan evaporation and rainfall, the number of fields to be irrigated, and 5-day weather forecasts. The model updates the soil moisture conditions, predicts impending water depletion, and if supplemental water is needed both the field priority and amount to be applied is indicated for each of the next 5 days. Errors introduced through the use of forecasts and long-term pan evaporation records have been slight because of the tri-weekly updating. Also natural rains which restore the root zone to maximum water holding capacity prevent long-term bias.