Time-Resolved Measurements of Indoor Chemical Emissions, Deposition, and Reactions in a University Art Museum

Abstract

A 6-week study was conducted at the University of Colorado Art Museum, during which volatile organic compounds (VOCs), carbon dioxide (CO2), ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), other trace gases, and submicron aerosol were measured continuously. These measurements were then analyzed using a box model to quantify the rates of major processes that transformed the composition of the air. VOC emission factors were quantified for museum occupants and their activities. The deposition of VOCs to surfaces was quantified across a range of VOC saturation vapor concentrations (C*) and Henry’s Law constants (H) and determined to be a major sink for VOCs with C* < 108 μg m–3 and H > 102 M atm–1. The reaction rates of VOCs with O3, OH radicals, and nitrate (NO3) radicals were quantified, with unsaturated and saturated VOCs having oxidation lifetimes of >5 and >15 h, making deposition to surfaces and ventilation the dominant VOC sinks in the museum. O3 loss rates were quantified inside a museum gallery, where reactions with surfaces, NO, occupants, and NO2 accounted for 62%, 31%, 5%, and 2% of the O3 sink. The measured concentrations of acetic acid, formic acid, NO2, O3, particulate matter, sulfur dioxide, and total VOCs were below the guidelines for museums.

The atmospheric chemistry of indoor environments

“…28 These effects can be pronounced in heavily populated settings. [29][30][31][32] 3. Sources of indoor chemical constituents reactive chemistry occurring indoors.…”

“…77 As well, the photolysis of HONO can also occur to form OH, particularly when direct sunlight is present. 78,79 OH concentrations are on the order of 10 5 molecules per cm 3 in most indoor settings, 32,74,80 whereas concentrations of 10 6 -10 7 molecules per cm 3 have been reported via photolysis of HONO in sunlit air or via the use of cleaning agents close to the inlet of the OH detector. 78,81 NO 3 is formed by the reaction of NO 2 with ozone.…”

“…This was recently demonstrated, for example, in an indoor museum setting. 32 To illustrate, a molecule such as nicotine, which reacts with the OH radical at close to the gas-kinetic collision rate constant of z10 À10 cm 3 per molecule per s, 88 has a lifetime of over a day if OH is at 10 5 molecules per cm 3 . This is much longer than typical residence times and so only a small fraction will be oxidized before it is mixed outdoors.…”

“…For example, multiphase loss represented 67% of the total ozone sink in an art gallery. 32 Studies of ozone uptake have focussed on a wide range of indoor materials. 168 Known to be reactive are carpet, 169,170 clothing and fabric, [170][171][172] some green building materials, 173 human hair, cooking oil and skin oil substituents, [174][175][176][177] insulation materials, 156 and ventilation lters and ducts.…”

“…Recent advances have arisen from the application of fast-timeresponse instrumentation with low detection limits, such as on-line mass spectrometry instruments that sample gases and aerosol particles, and spectroscopic instruments that can monitor reactive intermediates. 3,21,29,32,38,56,105,121,252 It is now possible to study how the indoor environment dynamically responds to transient behavior indoors, as during window or door opening, cleaning, cooking, or changing human occupancy. Research questions include: what is the timescale for the lingering chemical effects of humans aer they leave an indoor space, or aer cooking stops?…”