Modelling seasonal influences on reactive indoor air pollution chemistry for residential environs in the southern hemisphere

In the developed world people spend over 80% of their time indoors. The quality of the air indoors is therefore very important for population health. Indoor air quality may be affected by the photochemical degradation of primary indoor air pollutants. These indoor reactions need to be understood because they lead to secondary pollutant formation, which may have potentially serious and often unknown health implications. A highly detailed computational model study for UK homes proposed that free radical driven chemical degradation of constituents of indoor air contribute significantly to the formation of secondary air pollutants. Furthermore that the reaction pathways for indoor radical formation are different to those of outdoors, being highly dependent on the levels of ozone (O3) and reactive monoterpenes (MTs) present (Carslaw 2007). The study presented here was undertaken to investigate indoor air chemistry of residential properties in Perth, (WA) across two seasons. Observational measurement data from these houses were then used to constrain a near explicit chemical model for indoor environs in the southern hemisphere (SH). This, like Carslaw (2007) is based upon the Master Chemical Mechanism (MCM) (http://mcm.leeds.ac.uk/MCM), as the model framework. Data were collected from 88 homes over two seasons. The southern hemisphere indoor-air box model was developed based on an extended MCM framework. This was developed to be a more refined and reflective model and to extend what has previously been reported on in the literature. Indoor volatile organic compound (VOC) emission rates were modified to reflect the typical air exchange rate expected for the type of houses sampled. Representative outdoor O3 and NOx profiles were generated using air quality monitoring station (AQMS) data over the sampling period. Output data from this model were evaluated to investigate the seasonal changes in the indoor air chemistry. Here we observed subtle changes in the indoor air chemistry, as a consequence of house functioning (heating and air exchange) resulting from the changing outdoor climate conditions. As this is a baseline model, ongoing sensitivity testing over the range of observations made will give a greater understanding of the influence of reactive indoor air chemistry in comparison to models that consider physical processes alone. This is the first detailed indoor air study in Perth, WA, combining measurements of O3, NO2, VOC and meteorological parameters in this geographic location to then constrain a complex and highly explicit indoor air model.