Air quality in indoor environments is associated with our health and should be given due attention since in a vertical city many people spend more than 80% of their time indoors, such as homes, offices, schools and other common areas.

A recent study found that odour emission from air-cooling units is sometimes reported even when the air conditioning and ventilation system is clean and free of visible dust accumulation, resulting in discomfort and low productivity. The research also found that the source of the unpleasant smell is not common pollutants such as benzene, nitrogen dioxide, formaldehyde. Rather, the source of the problem is skin squames.

Dr Lai Ka-man, Associate Professor of the Department of Biology, points out that IAQ is strongly associated with air-conditioning and ventilation systems. Sick Building Syndrome, with symptoms including headache, malaise, nausea, flu and allergy that develop for no apparent reason in the occupants of a building, seems to be more prevalent nowadays. Most of the complainants report relief soon after leaving the building. Dr Lai says, "There are many potential sources affecting indoor air quality including construction materials, new furniture and photocopiers. Those materials emit pollutants and volatile organic compounds (VOCs), resulting in unpleasant smell and poor indoor air quality.

Funded by the Environment and Conservation Fund under the Government's Environmental Protection Department, Dr Lai's research was the first to show that the accumulation of skin squames which release proteins for further degradation in an air conditioning system is positively correlated to ammonia (urine-like smell) produced by bacteria, resulting in discomfort experienced by occupants and poor IAQ.

Dr Lai reveals that it is commonly believed that odour problems are due to a dirty air conditioning system, which contains accumulated dust and harbours different types of microbes. Therefore, cleaning the system repeatedly is the general practice to eliminate the odour. In fact, for effective long-term odour control, it is necessary to reduce the amount of skin squames entering the air conditioning system by replacing filters with those that capture skin squames more effectively. This is also the most effective method to improve indoor air quality.