Indoor ozone: Concentrations and influencing factors

Abstract

Because people spend most of their time indoors, much of their exposure to ozone occurs in buildings, which are partially protective against outdoor ozone. Measurements in approximately 2000 indoor environments (residences, schools, and offices) show a central tendency for average indoor ozone concentration of 4-6 ppb and an indoor to outdoor concentration ratio of about 25%. Considerable variability in this ratio exists among buildings, as influenced by seven building-associated factors: ozone removal in mechanical ventilation systems, ozone penetration through the building envelope, air-change rates, ozone loss rate on fixed indoor surfaces, ozone loss rate on human occupants, ozone loss by homogeneous reaction with nitrogen oxides, and ozone loss by reaction with gas-phase organics. Among these, the most important are air-change rates, ozone loss rate on fixed indoor surfaces, and, in densely occupied spaces, ozone loss rate on human occupants. Although most indoor ozone originates outdoors and enters with ventilation air, indoor emission sources can materially increase indoor ozone concentrations. Mitigation technologies to reduce indoor ozone concentrations are available or are being investigated. The most mature of these technologies, activated carbon filtration of mechanical ventilation supply air, shows a high modeled health-benefit to cost ratio when applied in densely occupied spaces.

Emission Rates of Volatile Organic Compounds from Humans

“…This is understandable given the relatively high steady-state ozone concentration in our chamber (∼37 ppb) compared to other indoor environments. 60 In an occupied cinema, 4-OPA was not detected and the ER of 6-MHO was lower than that in our study without ozone. 16 The authors attributed the low ER to limited indoor ozone due to low outside ozone in the inner city.…”

Ozone Initiates Human-Derived Emission of Nanocluster Aerosols

“…68 It should be noted that indoor ozone levels are strongly dependent on outdoor ozone concentrations, ventilation, and indoor ozone sources/sinks 69,70 and thus vary in indoor environments. 71,72 Future research on the influence of ozone concentration on human-derived NCA emissions is warranted.…”

“…The ∼40 ppb ozone level in the occupied chamber has been measured in buildings with high ventilation rates during ozone pollution episodes . It should be noted that indoor ozone levels are strongly dependent on outdoor ozone concentrations, ventilation, and indoor ozone sources/sinks , and thus vary in indoor environments. , Future research on the influence of ozone concentration on human-derived NCA emissions is warranted.…”

The human oxidation field

“…The fourth case investigates the spatial gradient using the conditions applied in the third case but with lower indoor O 3 concentration (5 ppb). This is the median reported O 3 indoor concentration from a number of residences, schools, and offices during occupancy ( 28 ). As shown in Fig.…”