Effect of Outside Air Ventilation Rate on VOC Concentrations in Office Buildings
The importance of adequate outdoor air ventilation in office buildings is supported by a number of studies that have investigated the association between ventilation rates and human responses (Seppanen et al., 1999). Ventilation increases above 10 liters per second (L/s) per person have been found in some studies to decrease symptom prevalence or to improve perceptions. These improvements were presumably due to reductions in the concentrations of airborne contaminants such as VOCs. Simple mass-balance models directly relate ventilation and concentrations of VOCs generated indoors. For example, at steady-state ventilation conditions, a two-fold increase in ventilation rate should reduce airborne concentrations of VOC produced by steady sources by half. However, this simple relationship is affected by a number of factors potentially affecting air mixing, VOC emission and removal rates and chemical reactions. Thus, the effectiveness of ventilation rate for controlling indoor VOC concentrations may vary widely within and among buildings.

Design of Study to Measure Effect of Ventilation Rate on VOC Concentrations in a Call Center
A study was conducted during 2000 in a call center located in the San Francisco Bay Area to investigate the effect of ventilation rate on indoor VOC concentrations and emissions (Hodgson et al., 2002). This was part of a larger investigation of ventilation rate and worker productivity (Fisk et al., 2002). The building, constructed in 1998, had two floors, an area of 4,600 m², and about 300 workers. The building was ventilated and conditioned by four air handling units (AHUs 1-1, 2-1, 2-2 and 2-3) located on the rooftop. Each AHU served a defined interior zone although there likely was considerable air mixing among zones. Equipment was added to enable manipulation and measurement of outside air ventilation rates. For the three AHUs serving the study population, three fixed damper positions were selected to provide periods of low, medium, and high ventilation rates. The positions for the low period were fixed to provide the code-minimum outside air supply rate of 76 L/s per 100 m². The positions for the medium and high periods were selected to provide about 2- and 4-times the code minimum. The dampers in AHU 2-2 were fixed in one position. Periods of ventilation were scheduled over 13 weeks in one of four modes: low, medium, high, and economizer mode. Carbon dioxide concentrations were measured in all supply and return air systems and outside air on a regular cycle. Samples for VOCs and aldehydes were collected from the return air ducts and outside air over a Tuesday workday in weeks 2, 3, 6-8, 11 and 13. VOC samples were collected on sorbent tubes and analyzed for 49 compounds using thermal desorption GC/MS. Samples for formaldehyde and acetaldehyde samples were collected on treated cartridges and analyzed by HPLC.