Comparing methods for aggregating indoor air pollutant concentration over space and time

This paper explores the impact of different approaches to aggregating the indoor concentration of fine particulate matter (PM_2.5) in a case study home. Indoor- and outdoor-sourced PM_2.5 was modelled in CONTAM-EnergyPlus for a bungalow occupied by a family of four in Plymouth, England. Simulations were conducted assuming energy efficiency levels typical of a 1950s home and following retrofit. Pollutants were modelled at a 5-min temporal resolution in bedrooms, kitchen and living room and aggregated according to four metrics: (i) household arithmetic mean concentration, (ii) household time-weighted mean concentration, (iii) arithmetic mean of individual exposure, and (iv) household arithmetic mean exposure. Comparing the household metrics revealed differences of up to 50.0 % (3.6 μg/m³) for the pre-retrofit model, which remained largely consistent following retrofit. When comparing against individual exposure, differences were observed for all three metrics and reached 55.6% (9.1 μg/m³) for the pre-retrofit model, and 50.6% (8.7 μg/m³) for the post-retrofit model. Approaches (i) and (ii) consistently underpredicted individual exposure. Further, the differences were greatest for the time-weighted mean method, suggesting that taking into consideration the total time that each room is occupied but not when it is occupied will not necessarily provide a more accurate description of occupant exposure compared to the simple arithmetic mean. To better represent individual exposure, data on occupant presence is required.