Particulate matter (PM), also being referred to as particles and aerosols, are present in the air we breathe in different microenvironments, including indoors and outdoors. The sum of all PM we inhale in different microenvironments constitutes our total PM inhalation exposure. To identify the microenvironments contributing the most to the cumulative exposure, we must quantify both the time spent in a microenvironment and the PM concentrations in that microenvironment. Previous studies have reported that people spend about 90% of time indoors and pollutants from an indoor source can be trapped for an extended time owing to tightening building envelopes.
The ongoing coronavirus pandemic has forced people to spend even more time in their residences. A recent study attributed more than half of the total exposure (including different microenvironments and outdoors) to PM2.5 in residences. With already well-established impacts of PM on human health, it is critical to study sources, transport, transformation, and the fate of PM in residences.
We recently conducted the HOMEChem campaign to comprehensively characterize indoor air pollutants, both gaseous and particulate, while performing prescribed activities such as cooking and cleaning in a test house. We deployed a range of particle sizers to measure real-time particle PM size distributions in the size range 1 nm – 20 µm. Cooking activities were identified as the single largest source of indoor PM on a mass basis per activity. During cooking, we measured PM2.5 concentrations exceeding 250 μg m-3 and these observed short-lived peak concentrations were similar to those in the world’s most polluted cities. Sub-100 nm or ultrafine particles (UFP) dominate number concentrations. Usually, UFPs do not contribute much to PM2.5 mass concentration but we observed mass concentrations of UFPs as high as 100 μg m-3 on the Thanksgiving Day experiments.
In the absence of any indoor sources, indoor PM concentrations were lower than that outdoors indicating the test house building envelope provides protection against the pollutants of the outdoor origin. However, we found PM2.5 exposures over the duration of cooking to be either lower or comparable to that during the post-cooking decay phase highlight that the building envelope also traps the pollutants of indoor origin. Modeled total lung deposition demonstrated similar trends as the concentrations but the fate of PM within the respiratory system varied. For example, on Layered Day experiments, about 20% of the total PM deposited in the alveolar region which is the deepest part of our respiratory system. For the Thanksgiving Day experiments, the alveolar region accounted for about 50% of the total depositions.
Apart from PM generated during high-temperature cooking processes, we also observed PM formation and growth during room temperature activities. New particles formed and grew up to 30 nm following the post-dinner mopping with a bleach solution on the Layered Day experiments. Interestingly, no new particle formation was observed in association with any of the bleach mopping events during the two Sequential Cleaning experiments or during the Layered Day in which bleach mopping was preceded by lasagna instead of chili cooking. We hypothesize that residual gas-phase emissions associated with chili cooking and bleach cleaning participated in the physicochemical processes leading to new particle formation
Read our recent publication on PM measurements at HOMEChem for more details:
Sameer Patel, Sumit Sankhyan, Erin K. Boedicker, Peter F. DeCarlo, Delphine K. Farmer, Allen H. Goldstein, Erin F. Katz, William W Nazaroff, Yilin Tian, Joonas Vanhanen, and Marina E. Vance. “Indoor particulate matter during HOMEChem: Concentrations, size distributions, and exposures.” Environmental Science & Technology 2020, 54, 12, 7107–7116