Mitigating Occupant Exposure to PM2.5s Emitted by Cooking in High Occupancy Dwellings Using Natural Ventilation Strategies

The long term exposure to fine particulate matter with a diameter of ≤2.5 μm (PM2.5) is linked to numerous health problems, including chronic respiratory and cardiovascular diseases, and cancer. In dwellings, a primary emission source of PM2.5 is cooking, an activity conducted several times per day in most households. People spend over 90% of their time indoors and more time in their homes than any other type of building. Therefore, they are at risk of exposure to elevated levels of PM2.5 emitted by cooking if these particles are not removed at source. This is particularly important in dwellings with a high occupancy density where cooking periods are longer than average. In the UK, overcrowding is a significant issue with 1.1 million (5%) of the 23.4m households in England and Wales considered to be overcrowded. This issue affects families the most because more than 66% of overcrowded households have dependent children. Here, the consequences of PM2.5 exposure could be significant for two key reasons: (i) children breathe greater volumes of air relative to their body mass than adults, and (ii) their tissue and organs are still growing.
This paper uses theoretical and semi-empirical modelling approaches to investigate the concentrations of PM2.5s emitted by cooking in UK dwellings of high occupancy density. Firstly, the effects of increasing the rate of PM2.5 emission from cooking in proportion to occupancy density are investigated in an archetypal dwelling located in London where there is evidence of elevated levels of overcrowding that can lead to and poor indoor air quality. It is assumed that the number of cooking activities increases with the number of occupants and that they are consecutive, thus increasing the cooking period while keeping the emission rate constant. The results predict that the average weighted PM2.5 concentration emitted by cooking is approximately constant as the number of occupants increases. Although academically interesting, this highlights the need to identify realistic cooking schedules. Therefore a second approach records IAQ parameters and occupant behaviour over a 12-day period in a high occupancy student house in Nottingham. These data inform a pollutant transport model that predicts temporal variations of PM2.5 concentrations attributable to cooking. The observed occupant behaviour is predicted to lead to daily weighted concentrations well in excess of the WHO limit. To mitigate the exposure risk, it is found that kitchen windows should be left open for a minimum of 20 minutes after cooking to reduce pollutant concentration to safe levels.