VOC Concentrations Versus Outside Air Flow Rate in Call Center
The In-Out concentrations of six VOCs variously identified with a range of sources are plotted in Figure 1 versus normalized airflow rate. Only steady state data is included. The concentrations of isopropanol and 2-butoxyethanol, two compounds with likely cleaning product sources, showed little relationship with ventilation. Formaldehyde concentrations also were not apparently associated with ventilation as the concentrations in the zones served by AHUs 2-2 and 2-3 were nearly identical and constant throughout the study. Formaldehyde concentrations in the zones served by AHUs 1-1 and 2-1 were mostly higher possibly indicating a localized source; but, they were not associated with ventilation. Concentrations of acetaldehyde, hexanal, ethanol and isoprene (last two compounds not shown in the figure) in zones served by AHUs 1-1, 2-1 and 2-3 exhibited trends of higher concentrations at lower flow rates to varying degrees. The concentrations of d-limonene, commonly used as an air freshener, were not strongly associated with ventilation.

Figure 1. Indoor minus outdoor concentrations of 6 VOCs variously identified with a range of sources in a call center. Concentrations were measured in four air handling unit (AHU) zones on 7 days at varying AHU airflow rates. (LBNL-49535)
 

Implications for Control of VOC Concentrations in Office Buildings
Differences in the concentrations of most of the abundant VOCs in the building on the 7 days of sampling could not be directly predicted by differences in ventilation rates on those days. Temporal and spatial variations in cleaning products likely obscured the relationship between concentration and ventilation for solvents. For other compounds, it is likely that effective emission rates increased with ventilation due to their re-emission from sinks. Oxidation reactions driven by ozone also may have altered the relationship between ventilation and concentrations of some reactive and product compounds. These results emphasize the importance of source control for limiting the concentrations of VOCs in office buildings. Examples of control procedures include use of low emitting materials to finish and furnish interiors, use of low-emitting cleaning products, avoidance of products containing highly reactive chemicals, and scheduling of maintenance and janitorial activities at times when building occupancy is low.