Pollution levels and the effect of air pollution on asthma hospitalisations modified by synoptic weather type and aeroallergens

Pollution levels and the effect of air pollution on human health can be modified by synoptic weather type and aeroallergens. We investigated the effect modification of aeroallergens on the association between CO, O3, NO2, SO2, PM10 and PM2.5 and asthma hospitalisation rates in seven synoptic weather types using single air pollutant models, adjusted for the effect of aeroallergens and stratified by synoptic weather type, with pooled relative risk estimates for asthma hospitalisation in ten Canadian cities. Aeroallergens significantly modified the relative risk in 19 pollutant-weather type combinations, reducing the size and variance for each single pollutant model. Aeroallergens did not significantly modify relative risk for any pollutant in the DT or MT weather types, or for PM10 in any weather type. There is an interactive effect between aeroallergens and CO, O3, NO2, SO2, and PM2.5, on asthma hospitalisations that differs under specific synoptic weather types.