P.S. Hui

Feasibility study of an express assessment protocol for the indoor air quality of air-conditioned offices

It is costly to sample all major toxic pollutants in community air. Sampling should be conducted based on an assessment strategy and monitoring planning. Assessment methods that rely on monitoring some representative pollutants have been proposed variously at different times. In Hong Kong, the Environmental Protection Department (HKEPD) launched an Indoor Air Quality (IAQ) certification scheme to grade the IAQ in workplaces as “Excellent” or “Good” by measuring the levels of 12 indoor environmental parameters, i.e. 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), temperature (T), relative humidity (RH) and air velocity (V). The present study proposes an Express Assessment Protocol (EAP) to quantify IAQ problems by assessing the “dominant” contributors to unacceptable IAQ prior to any detailed assessment for benchmark purposes. To aid this, a comprehensive measurement of the 12 stated indoor environmental parameters was performed in some Hong Kong offices. The results were used to identify the dominant contributors and assess the performance of the proposed protocol in identifying the associated IAQ problems in an office environment. Comparing the results with the parameter measurements in the certification scheme they showed that for the “Excellent” IAQ level, 96% (94 to 98% for 95% confidence interval (CI)) of the “unacceptable” offices (414 samples) could be identified from the measurements of TVOC, RSP and HCHO; while those that achieved the “Good” level, 93% (90 to 97% for 95% CI) of them (201 samples) could be identified from the measurements of TVOC, ABC, RH, HCHO and O3. The EAP would be a useful tool for policymakers, building owners and professionals to quantify IAQ problems in offices and to make improved decisions based on resources and manpower management for efficient mitigation actions.

A New Sampling Approach for Assessing Indoor Air Quality

Continuous sampling has been widely adopted for assessing indoor pollutant level. It is believed that the longer the measurement time, the higher the accuracy and improved error rate of the measured average pollutant concentration can be achieved. This study proposes an alternative sampling scheme in which the average pollutant concentration is obtained from two short sampling periods in two sampling sessions when a building was occupied. Two indoor pollutant concentration databases for a 1-year continuous measurement of carbon dioxide (CO2) and radon concentration in a typical openplan office building in Hong Kong were used to investigate the probable errors of the proposed scheme regarding the sampling period. The results showed that these errors deviated from a long-term average value and correlated with the required measurement time. At certain confidence levels, the potential reductions in measurement time of the proposed sampling scheme would be up to 30% and 50% for CO2 and radon, respectively, as compared with an 8-h continuous one.

Using Carbon Dioxide Concentration to Assess Indoor Air Quality in Offices

Carbon dioxide (CO2) concentration is commonly used as a surrogate indicator for assessing indoor air quality (IAQ) and ventilation efficiency. The measurement and analysis of average indoor CO2 concentration is useful to understand the performance of a ventilation system. However, uncertainties due to the ventilation rate effectiveness as well as the initial state, build-up, fluctuation, and decay of indoor CO2 concentration from occupant load variation have not been addressed in many measurements; considerable measurement efforts are obligatory. This study, taking the long-term CO2 measurement and occupant profile of a typical open-plan office building as reference, has developed a database to examine the probable errors of an alternative sampling scheme for assessing indoor CO2 level in which the average pollutant concentration is obtained from two short sampling periods in two sampling sessions when the building is occupied. The results show that the assessed CO2 level deviates from the long-term average and the probable errors correlate with the required measurement time and occupant load profile. At certain confidence levels, the potential reductions in measurement time of the alternative scheme, as compared with an 8-h continuous one, will be up to 30%, some 20% less than the reduction of measurement time for assessing indoor radon level.

Thermal Environmental Interference with Airborne Bacteria and Fungi Levels in Air-Conditioned Offices

Indoor airborne bacteria and fungi levels can be selected as indicators of a healthy indoor environment. This study investigated the relationships between the airborne bacteria levels, fungi levels, and thermal environmental parameters, i.e., air temperature and relative humidity, in some offices with a Mechanical Ventilation and Air-Conditioning (MVAC) system operating. A total of 101 samples were collected from two typical Hong Kong air-conditioned office premises. There was evidence that the operation of the MVAC system would have significant influence on both of the indoor airborne bacteria and fungi levels. The results showed that no significant difference in airborne bacteria and fungi levels was observed between offices having similar thermal environments ( p > 0.05). However, significantly higher airborne bacteria and fungi levels were found in the same office during non-office hours when the air-conditioning system was shut down ( p<0.03). It was also reported that the airborne bacteria and fungi levels would be correlated with the thermal environmental parameters in some offices ( p<0.0001).

An Epistemic Indoor Air Quality Assessment Protocol for Air-Conditioned Offices

Long-term measurement could be the best approach to determine the average pollutant concentration of an indoor environment for decisions on mitigation measures. This approach requires considerable measurement effort for accurate results and hence indoor air quality (IAQ) assessment methods that need less effort have been developed. This study proposes an epistemic approach for assessing an acceptable office IAQ against certain indoor air pollutant exposure limits. Together with the prior understanding of failure rates of IAQ determined from a number of extensive survey studies, a sample test result of pollutant levels and the uncertainties of different sampling schemes, the probability of satisfactory IAQ for an assessed air-conditioned office could be quantified. In particular, assessment of an acceptable IAQ for some air-conditioned offices in Hong Kong was demonstrated by taking CO2 as an example pollutant. Accuracy of the failure rates was improved by the application of sampling correction factors and Bayesian statistics. The probabilities of an acceptable office IAQ were evaluated against a CO2 level limit. This approach would be useful for IAQ assessment in some air-conditioned offices.

Epistemic evaluation of policy influence on workplace indoor air quality of Hong Kong in 1996—2005

Long-term measurement results of indoor air quality (IAQ) over a general community can be used to evaluate the effectiveness of mitigation measures for IAQ improvement of premises. However, this approach requires considerable measurement efforts and thus the complete data sets are not available in many circumstances. This study proposes an epistemic approach in estimating the probable influences of an IAQ policy for Hong Kong offices, using the regional IAQ measurement databases of offices in 1996, 1998—2001 and 2004—2005. After the implementation of the IAQ policy in 1997—1999, measurement results of IAQ in offices were collected and were used to quantify the IAQ improvement for Hong Kong offices. It is noted that IAQ dissatisfaction due to air pollutants predominated by indoor emissions of volatile organic compounds (VOCs) might need additional attentions for an effective IAQ improvement programme. Practical application: This study provides updated information on the forecasts of IAQ in air-conditioned offices of Hong Kong due to the influence of the IAQ policy implemented in 1997—1999. It is a useful source of reference for policymakers and decision makers in evaluating an indoor air pollution control policy for air-conditioned offices.

An Assessment of Airborne Fungi Exposure Risk Level in Air-conditioned Offices:

The exposure to airborne fungi has not been included in many regular indoor air quality (IAQ) assessments of air-conditioned (A/C) offices. This study examined the feasibility of using a proposed relative index of fungal exposure (RIFE) as a quantitative measure to specify the enclosure effect of an indoor environment in 82 Hong Kong A/C offices. The airborne fungi count ranged from 2 to 92CFU·m -3. Yeast, Aspergillus, Cladosporium, and Penicillium were reported as dominant in the offices. The RIFE of Yeast, Aspergillus, and Penicillium were 1.26, 1.21, and 1.02, respectively, and it would confirm a higher indoor exposure risk relative to that of outdoors. The RIFE of the common outdoor fungi Cladosporium was 0.48. This study presents a useful index for IAQ assessment regarding relative risk exposure of airborne fungi in A/C offices.

Fungi - An indoor air quality assessment parameter for air-conditioned offices

Representative assessment parameters are proposed for indoor air quality (IAQ) audit in various strategies and guidelines.1 In Hong Kong, assessment of indoor airborne fungi is not incorporated in many IAQ audits of air-conditioned offices, although the exposure to airborne fungi could cause a variety of adverse health effects. An IAQ assessment for a local office will audit 12 parameters, including air temperature, relative humidity, air velocity, carbon dioxide, carbon monoxide, respirable suspended particulates, nitrogen dioxide, ozone, formaldehyde, total volatile organic compounds, radon, and airborne bacteria. This paper reviews recent studies of the indoor airborne fungi levels and IAQ assessments in some air-conditioned offices of Hong Kong and evaluates the contribution of the airborne fungi to an unsatisfactory IAQ in the environment. The unsatisfactory rates regarding the assessment parameters were evaluated using the Monte Carlo simulations with measured data in Hong Kong Offices. In particular, the impact of selecting representative IAQ assessment parameters was examined against an express assessment protocol (EAP), which assessed some dominant contributors of unsatisfactory IAQ.2 The results reported that the three top ranked contributors for unsatisfactory IAQ were total volatile organic compounds (TVOC), indoor airborne fungi count (AFC) and airborne bacteria count (ABC) for air-conditioned offices of Hong Kong. Practical applications: This study has shown that the assessments of airborne fungi levels in office environment is an important issue and further investigations for the airborne fungi in the IAQ audits were thus recommended. The results of this study could be a useful source of reference for policymakers in evaluation of an effective IAQ assessment protocol with some representative IAQ assessment parameters.

Bayesian Assessments for Acceptable Airborne Bacteria Levels in Air-Conditioned Spaces:

The level of indoor airborne bacteria is usually selected as a reference to identify the cleanliness of a Heating, Ventilating and Air-Conditioning system. This study proposes an epistemic approach for assessing acceptance of air-conditioned spaces against certain acceptable airborne bacteria levels. From the thermal environmental conditions and a sample test of the airborne bacteria level, the assessment model can give a rapid estimation of the probability of an unsatisfactory indoor environment. An office having a higher risk of unsatisfactory Indoor Air Quality (IAQ) would require a lower sample test value to fulfill the IAQ acceptance at certain confidence level. The model parameters were determined from databases of 529 air-conditioned spaces in Hong Kong, with airborne bacteria levels ranging from 41 to 2304 CFU · m-3, air temperatures from 13.4 to 27.8°C and relative humidities from 29 to 88%. This model would be useful to policymakers for making a fast response to the microbiological pollutant problem while avoiding an inappropriate level of reliance on the results.

Formaldehyde exposure risk in air-conditioned offices of Hong Kong

Formaldehyde (HCHO) is a carcinogenic toxicant commonly present in an air-conditioned office environment. This study examines the lifetime exposure risk of HCHO in air-conditioned offices of Hong Kong under various indoor environmental conditions. Using the regional indoor air quality assessment results of 511 Hong Kong offices recorded from 1996 to 2005, together with the mathematical correlations among HCHO exposure concentration, ventilation and thermal environment verified at 43 other local air-conditioned offices, the exposure risk in terms of loss of life expectancy (USEPA standard) was predicted for an office environment preset at certain air temperature and atmospheric carbon dioxide (CO 2) level. It was reported that the average increment of HCHO exposure risk was 2% for every 1°C increment in the air temperature range of 22.5—25.5°C, or 2.5% for every 10 ppm increment in the CO2 concentration range of 800—1000 ppm. This study presents useful information on HCHO exposure risk evaluation for air-conditioned offices associated with various policies on indoor air temperature and ventilation demands. Practical applications: This study outlines an approach to lifetime exposure risk assessment for HCHO inhaled in air-conditioned offices of Hong Kong under various indoor environmental conditions. In a typical office environment, the findings demonstrated that the average increment of HCHO exposure risk was 2% for every 1°C increment in air temperature or 2.5% for every 10 ppm increment in CO 2 concentration.