The modifying effect of the building envelope on population exposure to PM2.5 from outdoor sources

Abstract

A number of studies have estimated population exposure to PM2.5 by examining modeled or measured outdoor PM2.5 levels. However, few have taken into account the mediating effects of building characteristics on the ingress of PM2.5 from outdoor sources and its impact on population exposure in the indoor domestic environment. This study describes how building simulation can be used to determine the indoor concentration of outdoor-sourced pollution for different housing typologies and how the results can be mapped using building stock models and Geographical Information Systems software to demonstrate the modifying effect of dwellings on occupant exposure to PM2.5 across London. Building archetypes broadly representative of those in the Greater London Authority were simulated for pollution infiltration using EnergyPlus. In addition, the influence of occupant behavior on indoor levels of PM2.5 from outdoor sources was examined using a temperature-dependent window-opening scenario. Results demonstrate a range of I/O ratios of PM2.5 , with detached and semi-detached dwellings most vulnerable to high levels of infiltration. When the results are mapped, central London shows lower I/O ratios of PM2.5 compared with outer London, an apparent inversion of exposure most likely caused by the prevalence of flats rather than detached or semi-detached properties.

Practical implications: Population exposure to air pollution is typically evaluated using the outdoor concentration of pollutants and does not account for the fact that people in London spend over 80% of their time indoors. In this article, building simulation is used to model the infiltration of outdoor PM2.5 into the domestic indoor environment for dwellings in a London building stock model, and the results mapped. The results show the variation in relative vulnerability of dwellings to pollution infiltration, as well as an estimated absolute indoor concentration across the Greater London Authority (GLA) scaled by local outdoor levels. The practical application of this work is a better understanding of the modifying effect of the building geometry and envelope design on pollution exposure, and how the London building stock may alter exposure. The results will be used to inform population exposure to PM2.5 in future environmental epidemiological studies.

Keywords: Building stock model; EnergyPlus; Geographical information systems; Indoor air quality; PM 2.5.

Figure 1

Research area: Greater London. Areas without dwelling information are shown in gray

Figure 2

Research workflow and data inputs

Figure 3

Estimated outdoor PM_2.5 concentrations in Greater London for 2010 (DEFRA, 2011)

Figure 4

Average monthly PM_2.5 I/O ratios for the bungalow living room under scenarios 1 and 2 (modeled with trickle vents), and monthly variation in London background PM_2.5 levels (London Air, 2014)

Figure 5

The seasonal average I/O ratio of PM_2.5 pollution from outdoor sources, weighted according to room occupancy schedule and estimated frequency of trickle vents

Figure 6

Seasonal average I/O PM_2.5 ratios for dwellings across London for Scenario 1 and Scenario 2

Figure 7

Estimated absolute indoor PM_2.5 concentrations from outdoor sources, based on I/O ratio (Scenario 1) and estimated temporal and spatial variations in outdoor concentrations. The inset shows outdoor concentrations from Figure3

Figure 8

Estimated absolute indoor PM_2.5 concentrations from outdoor sources, based on I/O ratio (Scenario 2) and estimated temporal and spatial variations in outdoor concentrations. The inset shows outdoor concentrations from Figure3