Research Library

Atmospheric chemists Jos Lelieveld and colleagues describe how hydroxyl (OH) radicals start the photochemical reactions that oxidize most gases in the lower atmosphere, turning them into products that rain and surface deposition remove more easily. Through this self-cleansing process, thousands of megatons of natural and human-made gases are removed from the troposphere each year.

Lelieveld et al., Atmospheric Chemistry and Physics 4:2337–2344 (2004)

The University of Rochester’s atmospheric chemistry group describes the hydroxyl radical as the main atmospheric oxidant and lists carbon monoxide among the pollutants it removes. The same chemistry is used to reconstruct past hydroxyl levels: radiocarbon monoxide (¹⁴CO) is produced naturally in the atmosphere by cosmic rays and removed by OH, so its record tracks how much hydroxyl the atmosphere held.

University of Rochester — The Hydroxyl Radical (OH) →

A meta-analysis of 49 studies found that indoor VOC exposure has a medium-sized effect on lung health, including the onset of asthma (effect size about 0.37) and wheezing (about 0.26). Most of the studies came from high-income countries, where people spend much of their time indoors.

Alford & Kumar, Int. J. Environ. Res. Public Health 18(4):1578 (2021)

A review of 20 studies found limited evidence of direct links between building airtightness and indoor air quality overall. Tighter buildings tended to have higher CO2 levels, and there was some evidence of higher VOC and formaldehyde levels, though several studies found no clear relationship. Where outdoor pollution is high, airtightness reduced the entry of outdoor contaminants. In short, airtightness tends to help against pollution from outside and worsen pollution from sources inside the home.

Kempton, Daly, Kokogiannakis & Dewsbury, Journal of Building Engineering 57:104798 (2022)

The EPA reports that concentrations of many VOCs are consistently higher indoors, up to ten times higher, than outdoors. Its TEAM study found about a dozen common organic pollutants at 2 to 5 times higher levels inside homes than outside, whether the homes were in rural or highly industrial areas. Sources include paints, solvents, cleaners, disinfectants, air fresheners, building materials and furnishings. Benzene, one indoor VOC, is a known human carcinogen.

U.S. EPA, Volatile Organic Compounds' Impact on Indoor Air Quality

The EPA reports concentrations of many VOCs consistently higher indoors — up to ten times higher — than outdoors. Its TEAM study found about a dozen common organic pollutants at two to five times higher levels inside homes than outside, regardless of whether the homes were rural or in highly industrial areas, and notes that elevated concentrations can persist long after the activity that caused them.

EPA — Volatile Organic Compounds’ Impact on Indoor Air Quality →

Direct measurements in a school classroom in Marseille found hydroxyl concentrations up to 1.8 × 10⁶ molecules per cubic centimeter — the same order of magnitude as outdoor urban air. Before this work, the possibility of photolytic hydroxyl formation indoors had been ignored. The hydroxyls measured were naturally occurring, from sunlight entering the room, not produced by a device.

Gómez Alvarez et al., PNAS, 2013 →

Atkinson and Arey’s review in Chemical Reviews sets out the atmospheric degradation pathways for volatile organic compounds. Reaction with the hydroxyl radical is the dominant daytime removal route for most of them.

Atkinson & Arey, Chemical Reviews, 2003 →

Human lung cells were exposed to particles alone, then to the same particles after contact with gas-phase VOCs. The VOC-modified particles caused significantly more damage and inflammation than the original particles, demonstrating that a non-toxic phase can become toxic through interaction with gases.

Ebersviller et al., Atmospheric Chemistry and Physics, 2012 →

Korea Conformity Laboratories exposed a WellisAir unit to single compounds and measured the reduction: toluene 99.5% in 2 hours, ammonia 80.0% in 4 hours, formaldehyde 65.0% in 4 hours.

This is a third-party laboratory test on the product, not a peer-reviewed study.

Korea Conformity Laboratories, test report 026961

CRESCA, the food safety and control research center at the Polytechnic University of Catalonia, measured total VOCs down 94.3% and formaldehyde down 93.4% after 30 minutes of exposure to a WellisAir unit.

The two laboratories' formaldehyde results differ because the exposures differ — 93.4% at 30 minutes here, 65.0% at 4 hours at Korea Conformity Laboratories. Both are published. This is a third-party laboratory test on the product, not a peer-reviewed study.

CRESCA, Universitat Politècnica de Catalunya, test report 20190930