Evaluation on four sampling schemes for assessing indoor air quality

Continuous sampling is one of the common approaches for assessing indoor pollutant level. It is believed that the longer the measurement time, the higher the accuracy and confidence level of the measurement can be achieved. In 2003, the Hong Kong Environmental Protection Department (HKEPD) launched an Indoor Air Quality (IAQ) certification scheme to promote an acceptable IAQ in workplaces. However, measurement efforts and uncertainties associated with the sampling method have not been addressed. Alternative sampling schemes taking shorter measurements in the sampling period were proposed in some circumstances. In this study, the average carbon dioxide (CO₂) concentration of a workplace is selected as an indicator of the indoor air quality to investigate the probable errors and measurement efforts in four sampling schemes, regarding the sampling period: in Scheme A, it is from a continuous sampling throughout the measurement; in Scheme B, it is from two sampling periods of two equal sessions of the measurement; in Scheme C, it is from two structural sampling periods of the two sessions; and in Scheme D, the average concentration is from four sampling periods in four equal sessions of the measurement. In particular, a year-round indoor CO₂ concentration at 17 locations in a typical office in Hong Kong was used to evaluate the probable errors using these four sampling schemes. At certain confidence levels, the required measurement times of the alternative sampling schemes (Schemes B, C, D) were evaluated and compared with that of an 8-hour continuous one (Scheme A). It was found that Scheme C would offer a reduction of measurement effort up to 30%. It is recommended to specify the uncertainties and efforts of measurement in future codes, and to consider these sampling schemes in determining practical strategies for IAQ measurement.