Indoor Air Quality




Three main groups of pollutant have been distinguished as affecting indoor air quality.


According to Schieweck et al., [1] they are outdoor air pollutants, occupant-related pollutants, and building-related pollutants. Those entering a building from outside include carbon monoxide (CO), benzene (C6H6), sulphur dioxide (SO2), ozone (O3), oxides of nitrogen(NO, NO2), and particles. Pollutants mainly produced by occupants include CO2, bio-effluents and particulate matter. Those originating from the materials used in building construction, furnishing and indoor equipment are typically volatile organic compounds, and also viruses, fungi and bacteria.

The levels of such pollutants may clearly be important to the health of occupants, but are of particular concern if energy saving measures are taken which may increase the concentration of any pollutants by reducing ventilation levels. Such measures are of interest to many Community Energy groups in the UK, where domestic heating efficiency is a major concern, and the paper will be considered mainly from that viewpoint.

Two questions arise; what are the safe levels of the various pollutants, and how are they measured? The World Health Organization has provided guidelines for acceptable levels of selected indoor air pollutants. A 2005 publication [2] covered Particulate matter, Ozone, Nitrogen dioxide, and Sulphur dioxide, and 2010 guidelines [3] covered Benzene, Carbon monoxide, Nitrogen dioxide, Formaldehyde, Naphthalene, Polycyclic aromatic hydrocarbons, Radon, Trichloroethylene and Tetrachloroethylene.

Schieweck et al. point out that “Most studies have used CO2, temperature and relative humidity as indicators of thermal comfort.” They have taken their figures for CO2 levels from a 2008 German Federal Environment Agency study [4]. Since CO2 level may well be a preferred measurement in the context of energy saving through reduction of air change rates, a section from the study is quoted:
“For over 150 years, carbon dioxide has been an acknowledged indicator of indoor air quality. To estimate the air quality in mechanically ventilated buildings, DIN EN 13779 proposes four different levels of indoor carbon dioxide concentration. However, apart from the early guideline value of 1000 ppm carbon dioxide recommended by Pettenkofer in 1858, there is no actual guideline value for naturally ventilated buildings. Regarding recent intervention studies, the German Working Group on Indoor Guideline Values of the Federal Environmental Agency and the States´ Health Authorities therefore recommends the following guide values, based on health and
hygiene considerations: concentrations of indoor air carbon dioxide below 1000 ppm are regarded as harmless, those between 1000 and 2000 ppm as elevated and those above 2000 ppm as unacceptable.”

Schieweck et al. discuss sensors for measuring pollutant levels, and give the required range and detection limit for some types:

Pollutants                       Measuring range           Detection limit
                                       [mg/m3]                         [µg/m3]

Carbon monoxide         0–100                            100
Benzene                        0–200                             0.2
Nitrogen dioxide           0–500                             10
Ozone                            0–500                             20
PM10                             0–400                              1
PM2.5                            0–400                              1
PM1                               0–400                              1

Median values of pollutants measurement in a variety of sites are also given; examples of figures for CO2 are listed below together with air change rates.

AER [per hr]       CO2 [ppm]     Comment

0.2                       655                Low energy residential buildings Lithuania
2.9                     1306                Low energy school buildings France
0.6                  < 1000                Passive houses Sweden
0.5                  < 1000               Energy efficient houses France
---                         587               Retrofitted houses Finland
---                         849               Retrofitted houses Lithuania
---                       1360               Energy efficient buildings Austria
0.304                   ---                  High performance homes California
---                         914               Retrofitted homes United States

The paper goes on to discuss in detail issues relating to the suitability of sensors for domestic environments, and their use with online technology, databases and mobile devices. Present limitations are noted, for example in measuring volatile organic compounds with cheap sensors, as is the need for “miniature, battery-operated and low-power devices”, potential solutions being still under development. Other issues raised include data security, the possible benefits to elderly occupants of environmental sensors, and the need for behavioural adaption to realise the full potential of the smart home.
The paper provides extensive references to the literature.

[1] Smart homes and the control of indoor air quality by Alexandra Schieweck et al., 2018 (open access)

[2] WHO World Health Organization. Air quality guidelines - global update 2005. Copenhagen: WHO Regional Office for Europe; 2006.

[3] WHO World Health Organization. WHO guidelines for indoor air quality: selected pollutants. Copenhagen: WHO Regional Office for Europe; 2010 (open access)

[4] Umweltbundesamt. Gesundheitliche Bewertung von Kohlendioxid in der Innenraumluft. Bundesgesundheitsblatt - Gesundh – Gesundh 2008:1358–69
(open access)


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