By: Nadine Borduas-Dedekind
Dr. Nadine Borduas-Dedekind is currently a sub-group leader at ETH Zurich in Switzerland and will be joining the Department of Chemistry at UBC as an assistant professor in January 2021. The NBD group is interested in studying the molecules we breath and following them from their source to their sinks by studying their reactive transformations using online chemical ionization mass spectrometry. The NBD group also works on the organic chemistry of atmospheric aerosols and their ice nucleation ability. To find out more about the NBD group, its research and interests, visit http://www.atmoschemgroup.org.
The human nose is an impressive analytical chemistry tool. It can detect and speciate concentrations of volatile organic compounds (VOCs). The smell of crisp air when we are strolling in the forest is really just our nose detecting monoterpenes like a-pinene (Figure 1). The smell of fresh citrus fruits is limonene. And the less fresh smell of rotten eggs is hydrogen sulfide. We care about these molecules because they can have adverse health effects and they can impact atmospheric composition and ultimately climate. In atmospheric chemistry research, we want to detect and monitor these compounds to understand where they come from, where they go and what they become. To do so, we need the equivalent of a highly sophisticated human nose: online mass spectrometry.1 Historically, the atmospheric chemistry community has been using this technique to spend time outdoors, measuring VOCs and their transformation products in challenging environments both in urban and remote areas. The air we breathe is of course closely linked to our health and the air the planet breaths is intrinsically associated with the planet’s climate and biogeochemical cycles. In addition, lately, the atmospheric chemistry community has also been spending time indoors.
Figure 1: The molecules responsible for the smell of forests, such as a-pinene, oranges, such as limonene, and rotten eggs, such as hydrogen sulfide.
In general, people spent 80% of their time indoors. At home, at work and during their commute, “occupants”, as we call people in indoor air quality research, are breathing air filled with interesting VOCs, including some they themselves are emitting!2 These VOCs can partition to the walls, to the carpets, to the furniture and unfortunately to our lungs (Figure 2). They can also be circulated through ventilation or make their way outdoors through open windows.3 Exposure to some of these volatile chemicals is known to be problematic, and occupational health and safety policies exist to minimize harmful exposure. Some of these compounds are persistent and accumulate indoors, allowing them to accumulate in passive samplers for example. However, we have less information about the VOCs that are reactive towards oxidation and therefore need fast online analytical instrumentation to detect them. And why do I care so much about the fate of these indoor VOCs in our homes, our offices and labs and in cars, buses and trains? Because of green chemistry!
Figure 2: Molecules present in indoor air can originate from a variety of sources (in green), including outdoor air, plants, pets, cookware and food, cleaning products and occupants. These molecules can be emitted (E), produced in the air (P) or penetrate from outdoor flow (Fin). The fate of molecules then depends on their sinks (in red) which include chemical loss processes (L), deposition (D) and flow outdoors (Fout).
Green chemistry is often associated with wet chemistry and industrial processes minimizing waste, but green chemistry principles are even more broadly applicable. I argue that these principles are applicable to indoor air quality research, including gas phase chemistry. In indoor air, there are starting materials, such as emitted limonene from peeling an orange or chlorine from cleaning the bathroom, there are solvents, such as water, there are catalysts, such as iron in dust, there are final products, such as carbon dioxide, there are even concerns about renewable feedstocks, such as wood, coal and oil for cooking and heating. We can imagine an indoor environment as a round bottom flask with ventilation as the stirrer, indoor lighting and sunlight as the heat plate and all the VOCs as the reagents. The green chemistry principles thus apply to save energy, to use safe chemicals, to reduce waste and contamination and to reduce exposure. It’s necessary to prevent (Principle #1) waste as well as exposure. If we better understand how cleaning with bleach produces Cl2 gas, we can create inherently safer cleaning products and safer chemicals (Principles #4 and #12).4 Atmospheric chemists are experts in real-time analysis for pollution prevention (Principle #11). Our research uses online mass spectrometry and spectroscopic techniques to measure molecule concentrations change as a function of time. If we could design chemicals for everyday use whether it be for cleaning, for personal care or for cooking with known and safe degradation products (Principle #10), we could completely transform exposure science. Fate and exposure models are already providing important stepping stones towards this goal. Ultimately, the objectives of green chemistry and of indoor air chemistry overlap: to inherently use safer chemicals for accident prevention and to minimizing harmful exposure (Principle #12). Our noses could therefore smell fewer and less harmful VOCs!
1- Hunter, J. F.; Day, D. A.; Palm, B. B.; Yatavelli, R. L. N.; Chan, A. W. H.; Kaser, L.; Cappellin, L.; Hayes, P. L.; Cross, E. S.; Carrasquillo, A. J.; et al. Comprehensive Characterization of Atmospheric Organic Carbon at a Forested Site. Nature Geoscience 2017, 10 (10), 748–753. https://doi.org/10.1038/NGEO3018.
2- Weschler C. J. Roles of the Human Occupant in Indoor Chemistry. Indoor Air 2016, 26 (1), 6–24. https://doi.org/10.1111/ina.12185.
3- McDonald, B. C.; De Gouw, J. A.; Gilman, J. B.; Jathar, S. H.; Akherati, A.; Cappa, C. D.; Jimenez, J. L.; Lee-Taylor, J.; Hayes, P. L.; McKeen, S. A.; et al. Volatile Chemical Products Emerging as Largest Petrochemical Source of Urban Organic Emissions. Science 2018, 359 (6377), 760–764. https://doi.org/10.1126/science.aaq0524.
4- Wong, J. P. S.; Carslaw, N.; Zhao, R.; Zhou, S.; Abbatt, J. P. D. Observations and Impacts of Bleach Washing on Indoor Chlorine Chemistry. Indoor Air 2017, 27 (6), 1082–1090. https://doi.org/10.1111/ina.12402.