A tracer pulse method was used to investigate the spread of airborne formaldehyde from its source into the surrounding air and the distribution of the air supply in a particleboard mill. The contaminant flow was labeled with sulfur hexafluoride, and the supply of outdoor air with nitrous oxide. The pulse responses of the injected tracer gases were interpreted in terms of the age concept. The result of improvements in the ventilation system was studied through measurements of the formaldehyde concentration and with tracer gas tests. It was found that the approach used in this paper is applicable to charting airflow patterns in a complex industrial environment.