Airborne Contaminants in Office Buildings: Some Aspects of Factors Influencing the Indoor Air Quality

Doctoral thesis, 1994

The thesis focuses on airborne contaminants in office buildings located in urban environments. The work is a contribution to a research field, the aim of which is to improve the basic knowledge needed for successful design and construction of buildings and HVAC systems, with regard to the indoor air quality. The aim of this particular study is to give information about some of the factors that can influence the indoor air quality. The report is principally based on the results presented in seven papers. The results were mainly obtained by field measurements of a variety of contaminants. The majority of the measured data were collected as time series with a time resolution of a few minutes. The impact on the indoor concentrations of contaminants originating outdoors were studied in particular. The contaminants studied are mainly: volatile organic compounds, particulate polycyclic aromatic hydrocarbons, carbon monoxide and nitrogen oxides. All of these contaminants may originate both from indoor and outdoor sources. The measurements have shown that the indoor concentrations of these contaminants may vary considerably with time. Rapid concentration changes are likely to occur in buildings located close to streets with heavy traffic, especially during the rush hours in the weekday mornings. The concentration of contaminants originating from indoor sources may also vary with time. For example, the total concentration of volatile organic compounds may be considerably higher when a building is occupied (daytime) than during periods of non- occupancy (night-time). The results indicate that neither of the three different source types: outdoor sources, intermittent indoor sources and constant indoor sources should be assumed to be negligible. Measurements aimed at characterizing the indoor air quality should be planned, taking possible concentration transients into consideration. Suggestions on the design and planning of contaminant concentration measurements are presented in this thesis. Numerical calculations valid under transient conditions are used in order to support the evaluation of the measurement results. It is demonstrated how a mass balance equation can be used to calculate the relationship between indoor and outdoor contaminant concentrations. Furthermore, by the use of the mass balance model, it is indicated that the indoor concentration of contaminants originating outdoors can be reduced considerably if the outdoor air flow rate is reduced temporarily during periods with high outdoor concentrations.