Perceived air quality, Sick Building Syndrome (SBS) symptoms and productivity were studied in a normally furnished office space (108 m 3 ) ventilated with an outdoor airflow of 3, 10 or 30 L/s per person, corresponding to an air change rate of 0.6, 2 or 6 h ª1 . The temperature of 22 aeC, the relative humidity of 40% and all other environmental parameters remained unchanged. Five groups of six female subjects were each exposed to the three ventilation rates, one group and one ventilation rate at a time. Each exposure lasted 4.6 h and took place in the afternoon. Subjects were unaware of the intervention and remained thermally neutral by adjusting their clothing. They assessed perceived air quality and SBS symptoms at intervals, and performed simulated normal office work. Increasing ventilation decreased the percentage of subjects dissatisfied with the air quality (PϽ0.002) and the intensity of odour (PϽ0.02), and increased the perceived freshness of air (PϽ0.05). It also decreased the sensation of dryness of mouth and throat (PϽ0.0006), eased difficulty in thinking clearly (PϽ0.001) and made subjects feel generally better (PϽ0.0001). The performance of four simulated office tasks improved monotonically with increasing ventilation rates, and the effect reached formal significance in the case of text-typing (PϽ0.03). For each twofold increase in ventilation rate, performance improved on average by 1.7%. This study shows the benefits for health, comfort and productivity of ventilation at rates well above the minimum levels prescribed in existing standards and guidelines. It confirms the results of a previous study in the same office when the indoor air quality was improved by decreasing the pollution load while the ventilation remained unchanged.Key words Perceived air quality; IAQ; SBS symptoms; Productivity; Ventilation; Outdoor air change rate; Office. Practical ImplicationsGood indoor air quality is beneficial for health, comfort and productivity. It is therefore advisable to ventilate indoor environments at rates above the minimum levels prescribed in present standards and guidelines. Reducing costs and conserving energy by maintaining modest levels of ventilation can easily result in a net loss if productivity is decreased. Increasing ventilation rates above minimum levels can raise productivity and will, in many cases, pay for itself while decreasing the intensity of SBS symptoms and improving perceived air quality. Intelligent use of energy recovery can often minimize energy consumption caused by increased ventilation. As an alternative or supplement to increased ventilation, it will often be beneficial for indoor air quality to eliminate or reduce sources of indoor air pollution or to supply ventilation air close to the breathing zone of the occupants.

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Sensory responses to clean air and air polluted by five building materials under different combinations of temperature and humidity in the ranges 18‐28°C and 30‐70%RH were studied in the laboratory. A specially designed test system was built and a set of experiments was designed to observe separately the impact of temperature and humidity on the perception of air quality/odour intensity, and on the emission of pollutants from the materials. This paper reports on the impact on perception. The odour intensity of air did not change significantly with temperature and humidity; however, a strong and significant impact of temperature and humidity on the perception of air quality was found. The air was perceived as less acceptable with increasing temperature and humidity. This impact decreased with an increasing level of air pollution. Significant linear correlations were found between acceptability and enthalpy of the air at all pollution levels tested, and a linear model was established to describe the dependence of perceived air quality on temperature and humidity at different pollution levels.

Perceived air quality, Sick Building Syndrome (SBS) symptoms and productivity were studied in an existing office in which the air pollution level could be modified by introducing or removing a pollution source. This reversible intervention allowed the space to be classified as either non-low-polluting or low-polluting, as specified in the new European design criteria for the indoor environment CEN CR 1752 (1998). The pollution source was a 20-year-old used carpet which was introduced on a rack behind a screen so that it was invisible to the occupants. Five groups of six female subjects each were exposed to the conditions in the office twice, once with the pollution source present and once with the pollution source absent, each exposure being 265 min in the afternoon, one group at a time. They assessed the perceived air quality and SBS symptoms while performing simulated office work. The subject-rated acceptability of the perceived air quality in the office corresponded to 22% dissatisfied when the pollution source was present, and to 15% dissatisfied when the pollution source was absent. In the former condition there was a significantly increased prevalence of headaches (P = 0.04) and significantly lower levels of reported effort (p = 0.02) during the text typing and calculation tasks, both of which required a sustained level of concentration. In the text typing task, subjects worked significantly more slowly when the pollution source was present in the office (P = 0.003), typing 6.5% less text than when the pollution source was absent from the office Reducing the pollution load on indoor air proved to be an effective means of improving the comfort, health and productivity of building occupants.