Indoor PM _2.5 exposure in London's domestic stock: Modelling current and future exposures following energy efficient refurbishment

Simulations using CONTAM (a validated multi-zone indoor air quality (IAQ) model) are employed to predict indoor exposure to PM _2.5 in London dwellings in both the present day housing stock and the same stock following energy efficient refurbishments to meet greenhouse gas emissions reduction targets for 2050. We modelled interventions that would contribute to the achievement of these targets by reducing the permeability of the dwellings to 3 m ³ m ^-2 h ^-1 at 50 Pa, combined with the introduction of mechanical ventilation and heat recovery (MVHR) systems. It is assumed that the current mean outdoor PM _2.5 concentration of 13 μg m ^-3 decreased to 9 μg m ^-3 by 2050 due to emission control policies. Our primary finding was that installation of (assumed perfectly functioning) MVHR systems with permeability reduction are associated with appreciable reductions in PM _2.5 exposure in both smoking and non-smoking dwellings. Modelling of the future scenario for non-smoking dwellings show a reduction in annual average indoor exposure to PM _2.5 of 18.8 μg m ^-3 (from 28.4 to 9.6 μg m ^-3) for a typical household member. Also of interest is that a larger reduction of 42.6 μg m ^-3 (from 60.5 to 17.9 μg m ^-3) was shown for members exposed primarily to cooking-related particle emissions in the kitchen (cooks). Reductions in envelope permeability without mechanical ventilation produced increases in indoor PM _2.5 concentrations; 5.4 μg m ^-3 for typical household members and 9.8 μg m ^-3 for cooks. These estimates of changes in PM _2.5 exposure are sensitive to assumptions about occupant behaviour, ventilation system usage and the distributions of input variables (±72% for non-smoking and ±107% in smoking residences). However, if realised, they would result in significant health benefits.