QUANTIFYING THE SPATIAL AND TEMPORAL VARIATION OF THE AIR QUALITY HEALTH INDEX IN HALIFAX, NOVA SCOTIA
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The AQHI, currently used by the Canadian government, is a multi-pollutant public health information tool that is based upon extensive Canadian epidemiological evidence. As the AQHI is a relatively new metric, there is little published information about the accuracy, and behaviour of this metric both spatially and temporally. The goal of this work was to provide more information to the scientific community on the spatial and temporal behaviour of the AQHI in the Halifax, Nova Scotia region. Sampling was conducted in both the winter and summer of 2009, at 50 sites distributed around the city and at the central NAPS site in downtown Halifax. Statistical analysis was conducted using daily calculated AQHI values. AQHI values in the region were predominantly in the 1 to 3 range on the AQHI scale which corresponds to very good air quality. The Government reported AQHI was found to be significantly different from the 50 sample site s AQHI values for both summer and winter (P=<0.001 for both seasons). The Government reported AQHI was significantly higher (P=0.05) than the AQHI calculated for the 50 sampling sites. Analysis identified that more than 50% of the daily AQHI index values were reported differently than the local sites, most commonly over predicted by one AQHI index point. Analysis also indicated a temporal trend of disagreement between the reported and sampled AQHI values. It was observed that during periods when the AQHI was higher, there was greater disagreement between that reported and the sample site AQHI value. This finding raises some concern regarding the behaviour of the AQHI in both larger cities and over the next decade as Halifax increases in size. The miss-reporting of AQHI values also raises some concern for epidemiological work, if the AQHI is used as an exposure metric it could over estimate exposure to air pollution. However, the AQHI is a useful scientific measure having a number of advantages, first it is a multi pollutant measure based on sound epidemiological evidence linking a mixture of three major air pollutant metrics to health effects and second that it has been distilled into a form that is readily understood by the public. This project has been successful in providing more information to the scientific community on the spatial and temporal variation of the AQHI in the Halifax region. It has been able to identify both seasonal and temporal variation, reinforced the understanding of pollutant behaviour and has begun to provide information on the behaviour of the AQHI on small urban scales and provide valuable information for both researchers and policy makers on the AQHI from a public health context.