The effect of proximity to major roads on indoor air quality in typical Australian dwellings

An Indoor Air Quality Study of residential dwellings was carried out in Melbourne, Australia, and a subset of the data was analysed to investigate the effect of proximity to major roads on indoor air quality (IAQ). Seven-day measurements of PM10, NO2, benzene, toluene, ethylbenzene and xylenes, along with continuous CO and PM2.5 measurements were utilised. The measurements were made indoors and outdoors in 27 dwellings; 15 Near Road (<50 m from a major road) and 12 Far Road (>300 m from a major road). Dwellings were sampled for one week each in Winter/Spring 2008 and Summer/Autumn 2009, over an eight month period. Analysis of 7-day measurements showed that NO2 and toluene were elevated at the 5% significance level both indoors and outdoors at Near Road Dwellings compared to Far Road Dwellings. Indoor/Outdoor (I/O) ratios of NO2 and toluene were not significantly different between Near and Far Road dwellings giving no evidence of any anomalous dominant indoor source for NO2 and toluene in Near Road dwellings. Indoor NO2 was significantly correlated to gas stovetop and oven use in both Near and Far Road dwellings. In the absence of gas cooking, indoor NO2 was elevated in Near Road dwellings relative to Far Road dwellings by approximately 4 ppb and this can be attributed to infiltration of outdoor air. I/O ratios for NO2 were <1 for Near and Far Road dwellings, indicating that outdoor NO2, and hence roadway emissions can potentially contribute a significant proportion to the indoor NO2 concentration. Mean toluene I/O ratios were >2 indicating that indoor sources dominate with minor contribution from outdoors. Hence the relative contribution of roadways to indoor NO2 is potentially greater than the relative contribution of roadways to indoor toluene. Findings elsewhere suggest that a similar outdoor enhancement of traffic related NO2 (∼5 ppb) increases risk of lung cancer and childhood asthma (Brauer et al., 2000 and Nyberg et al., 2000). A simple conceptual model indicated spatial and temporal variance in the concentrations was the biggest limitation in detecting roadway influence outside Near Road dwellings for PM10, PM2.5 and NO2 while measurement uncertainty was also important for CO.

► Elevated indoor NO2 and toluene at Near Road dwellings attributed to road emissions.
► Road emissions contribute a significant proportion to indoor NO2 concentrations.
► Road emissions contribute a minor proportion to the indoor toluene concentrations.
► Elevated NO2 in Near Road dwellings likely to result in adverse health effects.
► Conceptual model explores spatial, temporal variance in background concentrations.