WashU researcher brings new insights into indoor air quality monitoring

Winter is a love-hate season. As temperatures drop, we can expect to spend more time indoors in the weeks before spring, making monitoring and improving indoor air quality important. Poor indoor air quality can lead to various health issues, such as headaches and asthma. Therefore, managing indoor air quality effectively is an essential step for everyone living indoors to maintain overall health, especially for those with asthma.

Volatile organic compounds (VOCs) are chemicals that have high vapor pressure, meaning they exist as gases in the air we breathe. They are commonly found indoors. Some indoor sources of VOCs include but are not limited to cooking, cleaning products and building materials. Chemicals from these sources can easily evaporate into the air, impacting indoor air quality.

Jenna Ditto, assistant professor of energy, environmental & chemical engineering in the McKelvey School of Engineering at Washington University in St. Louis, examined the complexities of accurately measuring and identifying VOCs in indoor environments. environments in research published Dec.18, 2024, in Environmental Science: Processes & Impacts. The study was conducted at the National Institute of Standards and Technology as a part of the Chemical Assessment of Surfaces and Air study.

“VOCs indoors are important to characterize so we can better understand their chemical transformations and also our exposure to them, including any associated health effects linked to that exposure,” Ditto said. “We generally care about studying two important features of these VOCs: their chemical composition and dynamics—meaning how their identities and amounts in the air change with time. Together, this information helps us assess how these VOCs evolve indoors and what that means for the quality of the air we breathe.”

To understand this, Ditto's team combines gas chromatography (GC) and proton transfer reaction mass spectrometry (PTR-MS). Each technique has its strengths and can overcome the limitations of the other. In this study, the team combined GC and PTR-MS into one instrument.  PTR-MS offers rapid data collection, but it struggles to identify between chemicals with the same molecular formula (like isomers), leading to challenges in accurately quantifying individual VOCs. On the other hand, GC allows for the separation and detailed analysis of individual compounds, providing the precision necessary to identify and quantify VOCs that share the same molecular formula.

Ditto's research also shows how indoor and outdoor air quality are connected. "Indoor chemicals eventually make their way outside, and vice versa," Ditto said. For example, a chemical called isoprene, found in human breath and trees, shows a PTR-MS signal in indoor air that includes both “true” isoprene and confounding artifacts from other chemicals like aldehydes, which are released during cooking. By using the combined GC and PTR-MS technique, Ditto’s team could distinguish between “true” isoprene and these aldehyde fragments, enabling more accurate predictions of how these chemicals behave in the atmosphere and their potential health and climate impacts.

Looking ahead, Ditto's lab is using PTR-MS to measure the dynamics of various major indoor pollutant sources. By incorporating their GC and PTR-MS findings, they aim to better interpret these new results and gain deeper insights into how indoor pollutants behave over time.

Ditto J, Huynh H, Yu J, Link M, Poppendieck D, Claflin M, Vance M, Farmer D, Chan A, Abbatt J. Speciating volatile organic compounds in indoor air: using in-situ GC to interpret real-time PTR-MS signals. Environmental Science: Processes & Impacts, Dec.18, 2024. DOI: https://doi.org/10.1039/d4em00602j

This research was supported by the Canada Research Chairs program (CRC-2019-00028) and the Alfred P. Sloan Foundation (G-2019-11404, G-2020-13929).

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