Is remaining indoors an effective way of reducing exposure to fine particulate matter during biomass burning events?

Smoke from the bushfires currently burning across southern Australia has sent air pollution warnings sky rocketing in many cities and regional centres. Remaining indoors with windows and doors closed is a common recommendation by health authorities to minimize exposures to peak concentrations of fine particles during smoke plume events. But how effective is this strategy? Fabienne Reisen and Jenny Powell from CSIRO’s Atmospheric, Composition and Chemistry Group, along with colleagues from EPA Victoria, University of Tasmania and the Australian Catholic University addressed this very question in a paper published last year in the Journal of Air and Waste Water Management.

In a small study involving the simultaneous week-long indoor and outdoor measurements of PM_2.5 at 21 residences in regional areas of Victoria, Australia, they found that during smoke plume events, remaining indoors protected residents from peak outdoor PM_2.5 concentrations. However, the level of protection was highly variable, with indoor levels ranging from 12% to 76% below outdoor concentrations. Housing stock (e.g., age of the house) and ventilation (e.g., having windows/doors open or closed) played a significant role in the infiltration of outdoor PM_2.5 indoors. The results also showed that leaving windows and doors closed once the smoke plume abates trapped PM_2.5 indoors and increased indoor exposure to PM_2.5

Full details of this study can be found at  https://www.tandfonline.com/doi/full/10.1080/10962247.2019.1567623?src=recsys