The IVAIRE Study: Inter- and Intra-Seasonal Variations in VOC's Measured in Canadian Homes with Asthmatic Children during a Intervention Field Study

Abstract

A randomized intervention study was done to measure the impact of improved ventilation on indoor air quality (IAQ) and the respiratory health of asthmatic children in Québec City. The intervention involved the installation of a Heat or Energy Recovery Ventilator while a comprehensive suite of environmental parameters were used to characterize the IAQ. The IAQ measurements were taken during three separate periods both before and after the intervention. The winter measurements, used to correlate ventilation rates with IAQ and respiratory health, were taken twice to account for intra-seasonal variations in IAQ while the single summer measurement was taken to determine the inter-seasonal variations. A cohort of 111 asthmatic children were enrolled for the pre-intervention phase of which 83 were selected to participate in the subsequent intervention phase because their homes were found to be under-ventilated (air exchange rate <0.30 h-1). The children were then randomized into an intervention (n=43) and control (n=40) group for the second year (post-intervention phase) of the study. This paper presents the variations in the VOC’s measured within the same season, between seasons (winter, summer), along with the year-over-year variations within the same season. A statistically significant seasonal variability was observed for relative humidity, NO2, VOC’s and aldehydes. The aromatic and aliphatic hydrocarbons were most elevated in winter, up to 2x higher, and were the most strongly impacted by the ventilation intervention. The aldehydes, oxygenated VOC’s, and NO2, all had higher summertime concentrations despite the median air exchange rate being almost twice as high during summer. A possible explanation could be that the increased temperature and humidity encountered in summer would promote the release of aldehydes from hydrolysis reactions and off-gassing from construction and consumer products and that ambient formaldehyde is generally higher in summer.