Real-time Indoor PM2.5 Monitoring in an Urban Cohort: Implications for Exposure Disparities and Source Control.

Chu MT, Gillooly SE, Levy JI, Vallarino J, Reyna LN, Cedeño Laurent JG, Coull BA, Adamkiewicz G. Real-time Indoor PM2.5 Monitoring in an Urban Cohort: Implications for Exposure Disparities and Source Control. Environ Res. 2020 Dec 1:110561. doi: 10.1016/j.envres.2020.110561.

When people think about air pollution, they often focus on concentrations outdoors. But what about inside our homes? The air in our homes can be affected by the outdoor environment (air from outside that enters our home) and by activities inside. A recent CRESSH publication (MyDzung Chu et al.) reports on these questions: How much of our indoor air quality is driven by indoor versus outdoor sources of air pollution? What are the primary drivers of indoor air pollution? And do these answers differ across homes, and in particular, by socioeconomic factors such as homeownership status?

Specifically, Chu et al. examined “fine particulate matter”, which is also known as PM2.5 and includes particles smaller than 2.5 microns in diameter. These smaller particles are particularly damaging to health, as they are easily inhaled, can penetrate deep in our lungs, and cause a range of health problems including asthma, cardiovascular disease, and more.

The CRESSH study team, in partnership with GreenRoots, Inc, in Chelsea, MA, recruited 72 households in Chelsea, MA, a densely-populated and diverse city just northeast of Boston. When possible, each household was visited twice by researchers, once in the heating season (November – May) and once in the non-heating season (June – October). Each home hosted a small air quality monitor for one week in each season, which captured indoor environmental measurements, including real-time concentrations of PM2.5. The study team also collected a range of other information about the home, including a visual inspection, resident surveys about demographic and building characteristics, and daily activity diaries about resident activities that may contribute to indoor PM2.5 concentrations (e.g., AC use or window opening, cooking, use of a stove vent/range hood, and the use of candles, incense, and air fresheners). Indoor and outdoor air sensors were also used to help determine air exchange rates in the unit, which can influence the levels of air pollution indoors from both indoor and outdoor sources.

Chu et al. found that the amount of PM2.5 measured in indoor air was driven by indoor source activities and behaviors (over 77% on average), rather than by outdoor air pollution. These activities were primarily cooking, smoking, and use of stove range hood (which could indicate more intense cooking periods or ineffectiveness of the range hood). Furthermore, the authors found significantly higher levels of indoor PM2.5 concentrations among rental (i.e., tenant-occupied) and multi-family households compared to owner-occupied, single-family households. Indoor sources in households occupied by renters contributed up to 95% of concentrations seen during peak periods.  (There were no study participants who rented and lived in single-family homes, consistent with the predominantly multi-family tenant-occupied housing stock in Chelsea, MA). Although both renter and owner-occupied households reported cooking activity, renter and multifamily households were more likely to live in smaller units and denser apartment buildings, which could contribute to their greater indoor concentrations. In addition, these apartment units tended to be older with higher air exchange rates, in general, which could allow for greater infiltration from the outdoors and from neighboring units. Smoking and second-hand smoke exposure were more frequently reported among renters, who also reported more air freshener use, which can contribute its own indoor air quality challenges. The higher levels of indoor air pollution and prevalence of indoor sources contributors among renter households have important implications for addressing racial/ethnic and socioeconomic disparities, given that renter households were also more likely to be non-English speakers, non-White, and with less education than owner-occupied households.

While the types of housing stock and ambient air pollution levels may vary across the country, the role of indoor sources and building factors in shaping indoor air pollution concentrations is generalizable to all communities. Building-wide improvements designed to address ventilation and eliminate PM2.5 sources (such as implementing smoke-free building policies, improving the effectiveness of stove vents/range hoods) could help reduce PM2.5 exposure in the home. Targeted behavioral-level interventions, such as increasing ventilation practices while cooking (e.g. window opening, stove vent/range hood use), reducing use of chemical air fresheners, and engaging in smoking cessation programs), could be paired with landlord-tenant education and financial and housing assistance for low-income tenants. Multi-level interventions such as these would not only help to improve the health of all residents, but would also address racial/ethnic and socioeconomic disparities in air pollution exposure and alleviate existing health inequities.