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Analytical challenges and opportunities for indoor air chemistry field studies Delphine Farmer Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.9b00277 • Publication Date (Web): 21 Feb 2019 Downloaded from http://pubs.acs.org on February 25, 2019
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Analytical Chemistry
Analytical Challenges And Opportunities For Indoor Air Chemistry Field Studies Delphine K. Farmer Department of Chemistry, Colorado State University, Fort Collins, CO 80523
[email protected] SUMMARY Despite the vast time humans spend indoors, indoor air is far less well chemically characterized than the outdoor atmosphere. Advanced instrumentation for measurement of reactive trace gases, particles and surfaces is enabling a renaissance in indoor chemistry; this article highlights the challenges and opportunities for analytical chemistry in the built environment. INTRODUCTION Indoor air chemistry is an emerging field focused on the composition and chemical evolution of air in buildings, including surface-air exchange, multiphase chemistry and gas phase chemistry.1-4 We spend 90% of our lives indoors, where we breathe air that, while influenced by outdoor air, is quite different in composition and driving chemical processes from traditional outdoor atmospheric chemistry. Indoor air is a growing topic of interest for public health, but measuring the air composition of the built environment provides an intriguing set of challenges for analytical instrumentation. Indoor chemists avoid many pitfalls experienced in outdoor atmospheric chemistry (e.g. varying temperature and relative humidity; aircraft measurement requirements of tolerance to vibration and pressure fluctuations), but face other challenges. Indoor air is the result of infiltration of outdoor air; rapid ventilation; indoor sources (e.g. emissions from surfaces and events, such as cooking or cleaning, as well as human and animal occupants); chemical reactions in the gas, particle and surface phases; and deposition processes. Concentrations of oxidants and photon fluxes are lower indoors, but organic compounds are often higher.5-6 The scope of organic molecules detected in the indoor environment is staggering.7 Variable air exchange rates coupled to large emission sources and high surface area-to-volume ratios mean that the concentrations of gases and particles can change rapidly, on the order of seconds to minutes for orders of magnitude concentration changes!8-9 The timescales for oxidation chemistry are radically different indoors from out: where OH is considered important to the lifetime of atmospheric toluene, the resulting ~2 day lifetime is negligible given typical air exchange rates in American homes (0.5-1 hr-1), meaning that the volume of air within a house is ‘turned over’ or replaced in 1-2 hours. Dry deposition to surfaces is an important loss mechanism indoors, but wet deposition (removal by precipitation) is not. Indoor air includes many of the compounds breathed outdoors - mostly N2, Ar, and O2, but also trace gases and particles. Particles, often referred to as aerosols, are liquids or solids suspended in the air. Particles range in size from ~10-9 m (1 nm), where they are arguably clusters of gases rather than defined solids or liquids, to ~10-4 m (100 μm) for mineral dust and biological matter such as skin flakes. Both size and chemical composition of particles influences human health, with ultrafine (
