Measurement of indoor relative humidity using a passive sampler for water vapour.

As part of the energy and indoor climate survey recently carried out in Sweden (the ELIE study) a simple, inexpensive but reliable passive sampler for estimating monthly averages of relative humidity has been developed. The diffusion sampler consists of a 5 ml plastic tube prepared with lithium chloride monohydrate as trapping medium. After necessary calibration of this particular design of sampler the relative humidity can be calculated from the weight change of the sampler, the time of sampling and the average temperature during this period. The estimated accuracy of the method is better than ± 2% RH up to 65% RH.