Effect of ozone, thunderstorms and other weather conditions on the respiratory function of asthmatics

There is concern that exposure to the air pollutant ozone may adversely affect respiratory function. Ozone is formed photochemically by the action of sunlight on pre-cursor pollutants and peak concentrations usually occur during spells of hot sunny weather in summer. There is also evidence that summer thunderstorms may exacerbate asthma. In order to investigate the possible effects of ozone and summer weather conditions on asthma a panel of 29 patients was recruited from outpatients from a hospital asthma clinic in Norfolk. Daily morning peak-flow measurements (pre-medication) were analysed for June, July and August 1994. For each subject the daily measurements were expressed as the percentage of their best peak-flow and the average for the whole panel was then calculated. Daily ozone measurements from the national air pollution monitoring site at Sibton and data on weather conditions in Norwich were also collected. Multiple regression analysis was used to examine the association between daily peak flow, ozone and a number of weather variables, including the occurrence of thunderstorms, with lags of up to 5 days. A significant positive association (p<0.001) was found between peak flow and temperature over the previous 3 days. Peak flow was significantly negatively associated with the number of days with thunder in the previous 5 days (p=<0.001), the number of days with poor ozone (at or above 90 ppb) in the last 3 days (p<0.001) and the number of days with rain in the last 4 days (p<0.001). These 4 variables explained 48% of the variance in daily peak flow. The model estimate is that each day of poor ozone is associated with a change in peak flow (as % of best) of -1.07 (95% c.i. -1.52, -0.63) and each day with thunder -0.70 (95% c.i. -0.98, -0.43). During the summer period studied there was therefore evidence of small, but statistically significant adverse effects of ozone, thunderstorms and wet weather on the respiratory function of asthmatics in Norfolk