Comparison of concentrations of inorganic and organic compounds occurring inside and outside closed rooms

Although many people spend more than two thirds of their day indoors, most epidemiological studies on the health effects of air pollutants have up to now only been based on ambient air quality measurements. Using data from the literature, information is collected on the indoor-outdoor relationship of pollutant concentrations in order to estimate in which cases data on ambient air quality have to be completed by the results of indoor air measurements during epidemiological studies. For air pollutants like sulphur dioxide, nitrogen dioxide, carbon monoxide, suspended particulate matter, polycyclic aromatic hydrocarbons and nitrosamines the long-term average concentrations found indoors exceed those found outdoors only when tobacco smoke or other visible sources, e.g. gas appliances, are present in the room. A table is given which shows average indoor-outdoor ratios for the different cases. A number of organic substances, however, can be expected to be encountered in much higher concentrations indoors than outdoors. One of the main reasons for this is the use of a great variety of organic substances in modern building materials and household products. During the application of one or more of the multiple consumer products offered nowadays it is not unusual that the indoor air for several hours may show concentrations of organic substances which exceed those found in ambient air by a factor of more than 50.