The modifying effect of the building envelope on population exposure to PM_2.5from 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.

Understanding and mitigating overheating and indoor PM2.5 risks using coupled temperature and indoor air quality models

“…Dwelling permeability was estimated as per Taylor et al 16 An estimate of dwelling infiltration rates was made for each entry in the EHS, following the methodology outlined in SAP, 22 and using variables contained within the EHS database. An estimate of the dwelling permeabilities was then made by converting the infiltration rates to permeabilities, using the volume and surface areas of each EHS entry.…”

“…16 In both cases, windows remained closed if outdoor temperatures were above indoor temperatures. During cooking, additional purpose-provided ventilation in the form of extract fans was modelled in the kitchen, and was assumed to occur according to the requirements of Approved Document F of the UK Building Regulations.…”

“…The methodology used for the building simulation in EnergyPlus 8.0 is as per Taylor et al 16 Readers are referred to this paper for a more detailed discussion of the modelling work and parameters used. Briefly, simulations were run for each archetype at four different orientations, outdoor, indoor cooking and indoor smoking 32 Previous studies have used a static criterion of 5% of occupied hours over 25 C and 1% over 28 C for overheating in living rooms, and 5% of occupied hours above 24 C and 1% above 26 C for bedrooms.…”

“…However, these dwelling types may also face an increased risk of overheating, meaning that under increasingly warm weather conditions, this trend may be reversed as occupants in overheated dwellings may open their windows more frequently. 16 In addition, the lower air change rate in the dwelling may mean that occupants have a greater exposure to pollutants from indoor sources.…”

“…17 In particular, this paper builds on previous work focused on overheating risk 18 and indoor pollution from outdoor sources 16 in the London housing stock, by expanding the methodology to explore these risk factors in a nationally representative building stock under increasingly warm climates, different retrofit levels and with the inclusion of indoor pollution sources. Simulations were run in the dynamic thermal simulation tool EnergyPlus 8.0 using the integrated generic contaminant model to examine the indoor levels of PM 2.5 caused by the infiltration of ambient outdoor PM 2.5 into the indoor environment, and PM 2.5 produced indoors through cooking and smoking.…”