Concentrations and influencing factors of indoor ozone



by LORENZO CIOTTI

Concentrations and influencing factors of indoor ozone

"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." This was written in the Indoor ozone: Concentrations and influencing factors study, published on the Indoor air.

In 1785, Dutch chemist Martinus van Marum was conducting experiments involving electric sparks above water when he noticed an unusual smell, which he attributed to electrical reactions, failing to realize that he actually created ozone.

In 1839, Christian Friedrich Schönbein while conducting experiments on the slow oxidation of phosphorus and the electrolysis of water, noticed the same smell and associated it with what follows a lightning bolt in the sky.

In 1840 he isolated the molecule and called it ozone. The chemical formula O3 was determined in 1865 by the Swiss chemist Jacques-Louis Soret and was confirmed by Schönbein in 1867. Although ozone has positive effects when it is free in the atmosphere, in 1873 James Dewar and John Gray McKendrick documented some negative effects this molecule has on organisms: frogs became slower, birds breathed out of breath, and the blood of rabbits showed reduced oxygen levels after exposure to ozone-rich air.

Schönbein himself reported that chest pains, mucosal irritation and breathing difficulties occurred due to ozone inhalation and that small mammals died during his experiments. To date, the only fully established knowledge of the physiological effect of ozone is that it causes irritation and edema of the lungs and death if inhaled in a relatively high concentration for any period of time.