The aim of this study was to compare the radon levels at workplaces and in homes located nearby. Homes (number of 57) and partly or fully underground workrooms (number of 55) have been studied at the four workplaces in southern Finland and one workplace in northern Finland. Radon concentrations both at workplaces and in homes seemed to be at the same level in the same district. The mean radon concentration in workrooms was 406 Bq.m³, and in homes concentration was 398 Bq.m³.

This paper reports the findings of a pilot field study carried out to investigate the internal and external air pollution levels of two adjacent buildings, one naturally-ventilated and the other air-conditioned in an urban area, to investigate their relative attenuation of external pollution levels and to compare internal levels with existing air quality guidelines. Concentration levels of sulphur dioxide, nitrogen oxides, carbon monoxide and carbon dioxide were monitored.

A condition often assumed when designing a naturally ventilated building is where air enters at low level and leaves at high level due to the stack effect. It then follows that, at upper levels, the air may be relatively 'stale' since it has previously passed through the lower storeys. An analogous situation may arise when wind is blowing, in which the air entering through the windward face becomes stale as it passes through the building to the downwind sections. It is not well understood how ventilation may, in reality, be affected by this.

The effect of recirculation on the age of air is described. A new effectiveness measure called the relative air-change effectiveness is defined in such a way that the air distribution pattern in a room may be quantitatively characterized even when the age of the supply air is non-zero. This admits the evaluation of air distribution patterns in single-zone systems that recirculate air, and also multizone systems with or without recirculation.

Adequate ventilation with the "right amount of air, to the right place and at the right time" are important factors for achieving a good indoor climate. Thus it is of prime importance that the ventilation system is working properly. Using traditional methods, it is a very time consuming, and some times even impossible, task to balance ventilation systems to achieve correct air distribution. In most countries the growing concern about Indoor Air Quality has resulted in Building Codes demanding increased ventilation rates.

Air quality, air flows in buildings, and ventilation are most important topics. Good air quality is however critically dependent also on other things than ventilation, e. g. source strengths, as is well known. The theme of our conference could also lead to the assumption that there is a simple connection between ventilation and air quality. As the public tend to see ventilation systems as responsible for bad air quality, it is important to state that there is no general criterion for good air quality possible to use in practice to control ventilation processes.