Sampling Scheme
Brief:
In Hong Kong, the Environmental Protection Department (HKEPD) has launched an IAQ certification scheme to promote an acceptable IAQ in workplaces. For the practical measurement, an 8-h continuous monitoring is proposed for the assessment purpose. Some alternative measurement schemes were proposed: Scheme A is to obtain an exposure concentration over a sampling period in an occupied period; Scheme B is to obtain an exposure concentration in two sampling periods from two sessions of the occupied period; and for Scheme C, the exposure concentration in two structural sampling periods from two sessions of the occupied period. However, the uncertainties and measurement efforts associated with the method have not been detailed.
We have investiaged the probable errors and measurement efforts in measuring example indoor air pollutant exposure concentration by some sampling schemes of various sampling periods. In particular, a 1-year measurement of indoor radon concentration in a typical office building has been used as basis to evaluate the probable errors between the long-term average and those obtained by the measurement schemes. By taking account the built-up or decay characteristics of the monitoring parameter(s), at a certain confidence level, the results show that the measurement time required could be reduced significantly, when compared with the existing monitoring practice of 8-h continuous monitoring.
It is recommended to specify the measurement uncertainty and effort in future codes, and sampling schemes could be considered in determining the practical strategies for IAQ parameter measurements.
A smpling scheme of shorted measurement period will increase the measurement uncertainty. We find that the Bayesian analysis could help to improve the assessment quality.
Further information:
Radon as an example ...
Mui KW, Wong LT, 2004. Evaluation on different sampling schemes for assessing indoor radon level in Hong Kong, Atmospheric Environment 38(39) 6711-6723.
CO2 as an example ...
Wong LT, Mui KW, 2007. Evaluation on four sampling schemes for assessing indoor air quality, Building and Environment 42(3) 1119-1125.
Hui PS, Wong LT, Mui KW, 2008. Using carbon dioxide concentration to assess indoor air quality in offices, Indoor Built Environment 17(3) 213-219.