Developing a new passive tracer gas test for air change rate measurement

Ventilation is critical in interpreting indoor air quality (IAQ), yet few IAQ assessments report ventilation rates; even when they do, the measurement method is often not fully described. Most ventilation assessments use a tracer gas test (TGT) to measure total air change rate. In a TGT, the indoor air is marked with an easily identifiable gas (tracer) so that the air change rate can be inferred by monitoring the tracer’s injection rate and concentration. Passive sampling (adsorptive/absorptive samplers) is mostly preferred to monitor tracer concentration for its simplicity, practicality and affordability. Such samplers are commercialized by a range of companies and are widely used in IAQ studies to assess pollutants levels. Currently used passive TGTs present some limitations: inadequate tracer gas, disconnection from IAQ analysis (providing ventilation rates in a different time-scale than the pollutant concentrations) and possible bias arising from the perfect-mixing assumption. Thus, this paper proposes a new approach on the passive TGT method, which uses as tracer a suitable gas that can be co-captured and co-analysed using commercial passive samplers employed in common IAQ studies and which includes a more careful planning phase to account for imperfect mixing. A literature review was carried out in pursuit of such a gas. Considering that the most relevant compounds in IAQ studies are volatile organic compounds (VOCs), which are sampled separately from inorganic pollutants, the gases considered as possible tracers were the VOCs capable of being captured by the samplers commercialized by Radiello®, 3M and Gradko. They are composed by activated charcoal, which captures all VOCs in the targeted molar mass range by adsorption. The info-sheets for these samplers were consulted. Two options for alternative tracer gas are currently under consideration: 2-butoxyethyl acetate (EGBEA) and deuterated decane. Both present low-reactivity, usually negligible background indoor concentration, generally low toxicity and no links to chronic health effects. A preliminary field test was carried out in order to check EGBEA’s measurability, and results showed insignificant background EGBEA concentration and good measurability by the Radiello® sampler. Two test chambers were also performed: TCP1 and TCP2. TCP1 tested a first option of tracer source for EGBEA; TCP2 tested a second option of source for EGBEA and decane (as proxy for deuterated decane). Results from both showed that the used sources yielded emission rates higher than targeted, but the concentration curves obtained for EGBEA in TCP1 and decane in TCP2 suggest emission rates stability. Future work includes further chamber testing in pursuit of an adequate source design and computer simulations using CONTAM software coupled to CFD to study the effects of source/samplers positioning on the accuracy of the resulting air change rate calculations.