- Fine particles are thought to pose a risk to health, especially for vulnerable groups such as children with asthma. These children are also known to be affected by meteorological and seasonal changes. We assessed the association between air pollution and lung function via peak expiratory flow (PEF), controlling for seasonal changes, meteorological conditions and personal physiological, clinical and sociodemographic measurements, in a panel of schoolchildren with asthma living near two power plants in Israel. Two hundred and eighty-five children with confirmed asthma performed PEF tests and completed a respiratory symptoms diary twice a day. Particulate matter <10 microm in diameter (PM10), particulate matter <2.5 microm in diameter (PM2.5) and meteorological conditions were measured at six fixed stations. Data were analysed using time series analysis-generalized linear model and generalized estimating equations. The models were built under the assumption that any health outcome belongs to a multivariate hierarchical system and depends on meteorological, geophysical and sociocultural variables and pollution factors. No significant differences were found in the demographic (age, gender, mean parental education level, parental smoking habits, place of birth and housing density), physiological (body mass index) and clinical factors (illness severity) between the communities participating in the study. A significant direct effect of PM2.5 on the PEF was found in Ashdod (P=0.000). In Sderot, this effect was through an interaction between PM10 and the sequential day of the year (P=0.000). The main conclusion of this study is that children with asthma are at risk from air pollution and geophysical conditions. Policy makers should take these results into consideration when setting thresholds for environmental protection.