Abstract
Estimates of population air pollution exposure typically rely on the outdoor component only, and rarely account for populations spending the majority of their time indoors. Housing is an important modifier of air pollution exposure due to outdoor pollution infiltrating indoors, and the removal of indoor-sourced pollution through active or passive ventilation. Here, we describe the application of an indoor air pollution modelling tool to a spatially distributed housing stock model for England and Wales, developed from Energy Performance Certificate (EPC) data and containing information for approximately 11.5 million dwellings. First, we estimate indoor/outdoor (I/O) ratios and total indoor concentrations of outdoor air pollution for PM2.5 and NO2 for all EPC dwellings in London. The potential to estimate concentration from both indoor and outdoor sources is then demonstrated by modelling indoor background CO levels for England and Wales pre- and post-energy efficient adaptation, including heating, cooking, and smoking as internal sources. In London, we predict a median I/O ratio of 0.60 (99% CIs; 0.53–0.73) for outdoor PM2.5 and 0.41 (99%CIs; 0.34–0.59) for outdoor NO2; Pearson correlation analysis indicates a greater spatial modification of PM2.5 exposure by housing (ρ = 0.81) than NO2 (ρ = 0.88). For the demonstrative CO model, concentrations ranged from 0.4–9.9 ppm (99%CIs)(median = 3.0 ppm) in kitchens and 0.3–25.6 ppm (median = 6.4 ppm) in living rooms. Clusters of elevated indoor concentration are found in urban areas due to higher outdoor concentrations and smaller dwellings with reduced ventilation potential, with an estimated 17.6% increase in the number of living rooms and 63% increase in the number of kitchens exceeding recommended exposure levels following retrofit without additional ventilation. The model has the potential to rapidly calculate indoor pollution exposure across large housing stocks and estimate changes to exposure under different pollution or housing policy scenarios.
Highlights
Air pollution exposure is one of the largest contributors to premature mortality in the UK, with around 40,000 deaths brought forward attributable to exposure to particulate air pollution and NO2 annually (RCP, 2016)
Background annual average PM2.5 and NO2 levels for 2015 were obtained from the UK Department for Environment, Food and Rural Affairs (DEFRA) website in a 1 km × 1 km grid for London (DEFRA, 2015). These outdoor values were spatially joined to London postcode boundaries in ArcGIS, and matched to the modelled EPC dwellings; the outdoor levels were multiplied by the modelled I/O ratio of individual dwellings to estimate total indoor concentration of outdoor air pollution
The estimated indoor concentrations have a good spatial correlation with outdoor concentrations (ρ = 0.88), indicating that outdoor concentrations of NO2 may provide a reasonable estimate of relative indoor exposures to NO2 from outdoor sources
Summary
Air pollution exposure is one of the largest contributors to premature mortality in the UK, with around 40,000 deaths brought forward attributable to exposure to particulate air pollution and NO2 annually (RCP, 2016). PM2.5 and NO2 levels for 2015 were obtained from the UK Department for Environment, Food and Rural Affairs (DEFRA) website in a 1 km × 1 km grid for London (DEFRA, 2015) These outdoor values were spatially joined to London postcode boundaries in ArcGIS, and matched to the modelled EPC dwellings; the outdoor levels were multiplied by the modelled I/O ratio of individual dwellings to estimate total indoor concentration of outdoor air pollution. The metamodel was used to model the background indoor concentration from indoor sources, while local 8-hour annual maximum outdoor concentrations were extracted from modelled values (Fig. 3, see Vieno et al (2016) and references therein for model description) These were summed to estimate the maximum theoretical 8-hour concentration from both indoor and outdoor sources in dwellings
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