Assessment Parameters

Brief:

Maintaining acceptable indoor air quality (IAQ) for a healthy environment is of primary concern, policymakers have developed different strategies to address the performance of it based on proper assessment methodologies and monitoring plans. It could be cost prohibitive to sample all toxic pollutants in a building. In search of a more manageable number of parameters for cost-effective IAQ assessment in Hong Kong context, we investigated the probable correlations among the 12 indoor environmental parameters listed in the IAQ certification scheme of the Hong Kong Environment Protection Department (HKEPD) in some Hong Kong offices. These 12 parameters consists of 9 indoor air pollutants: carbon dioxide (CO₂), carbon monoxide (CO), respirable suspended particulates (RSP), nitrogen dioxide (NO₂), ozone (O₃), formaldehyde (HCHO), total volatile organic compounds (TVOC), radon (Rn), airborne bacteria count (ABC); and 3 thermal comfort parameters: temperature (T), relative humidity (RH) and air velocity (V).

Two approaches have been considered: (1) we assume all the assessment parameters are, in some degree, dependent from each other or other parameters; (2) we assume they are independent instead ...

Approach (1): The relative importance of the correlations derived, from largest to smallest loadings, was ABC, Rn, CO, RH, RSP, CO₂, TVOC, O₃, T, V, NO₂ and HCHO. Together with the mathematical expressions derived, an alternative sampling protocol for IAQ assessment with the three ‘most representative and independent’ parameters namely RSP, CO₂ and TVOC measured in an office environment was proposed. The model validity was verified with on site measurements from 43 other offices in Hong Kong. This simplified protocol provides an easy tool for performing IAQ monitoring in workplaces and will be useful for determining appropriate mitigation measures to finally honor the certification scheme in a cost-effective way.

Approach (2): By assessing only a number of ‘dominant’ contributors of an unsatisfactory IAQ prior to any detailed IAQ. Comparing with the parameter measurements in the certification scheme, these results showed that, for the ‘Excellent’ IAQ level, 96% (94% to 98% for 95% confidence interval) of the ‘unsatisfactory'offices could be identified from the measurements of TVOC, RSP and HCHO; while for the ‘Good’ level, 93% (90% to 97% for 95% confidence interval) of them (201 samples) could be identified from the measurements of TVOC, ABC, RH, HCHO and O₃.

IAQ Index and screening

We investigated the feasibility of a screening process for presumptive detection of IAQ problems of an unaccessed indoor environment, using both the approaches.

(1) The three of the nine listed common air pollutants were selected as the ‘representative’ pollutants for the overall ‘satisfactory IAQ’ and used to determine an ‘IAQ index’, calculated from the average fractional dose to certain exposure limits of the 3 representative pollutants.

(2) The ‘IAQ index’, correlated with an event of unsatisfactory IAQ regarding the ‘failure’ due to other unmeasured air pollutant levels in the IAQ assessments; which the IAQ index is defined as the average fractional dose to certain exposure limits from the assessed top dominant contributors identified from a regional database of IAQ assessment results for workplaces.

The accuracy of the proposed assessment protocol was tested with a regional IAQ database developed from IAQ measurements of common air pollutants in air-conditioned offices of Hong Kong. It is reported that the application of the screening process in the IAQ assessment would improve the overall assessment performance without additional measurement parameters. The proposed screening approaches would be a useful source of reference in setting up any IAQ assessment policies.

We have found this IAQ index give good correlations to the quality-of-life of COPD patient's. Click for more information.

IAQ benchmarks

To streamline the assessment of office IAQ performance and offer incentive for maintaining better IAQ, we have proposed and investigated the feasibility of a simple IAQ benchmark using the IAQ indicator, i.e. the IAQ index. This benchmark adopted a 5-star rating system which assigns 1 star to the top 10% samples in the highest levels of the three pollutants, 2 stars to the next 22.5%, 3 stars to the next 35%, 4 stars to the next 22.5% and 5 stars to the bottom 10%. Taking an existing IAQ certification scheme as reference, this proposed benchmarking system was proved to be feasible to distinguish offices with different IAQ labels, and illustrate the performance of office IAQ with different star ratings. Therefore, the proposed simple method can help promote better IAQ and serve as a screening assessment for IAQ in air-conditioned offices of Hong Kong.

Further information:

Hui PS, Wong LT, Mui KW, 2006. Feasibility study of an express assessment protocol for the indoor air quality of air-conditioned offices, Indoor and Built Environment 15(4) 373-378.

Wong LT, Mui KW, Hui PS, 2006. A statistical model for characterizing common air pollutants in air-conditioned offices, Atmospheric Environment 40(23) 4246-4257.

Wong LT, Mui KW, Hui PS, 2007. Screening for indoor air quality of air-conditioned offices, Indoor and Built Environment 16(5) 438-443.

Mui KW, Wong LT, Hui PS, 2009. Screening strategies of an indoor air quality express assessment protocol (EAP) for air-conditioned offices, Indoor and Built Environment 18(1) 77-82.

Hui PS, Wong LT, Mui KW, 2009. Indoor air quality benchmarking for air conditioned offices, Clean-Soil, Air, Water 37(6) 481-486.