We spend 90% of our time indoors, so we have to consider how a home's design and construction can affect indoor air quality. To achieve superior indoor air quality it is important to:

• remove any contaminants at the source of production;
• reduce the contaminants built into the house;
• exchange the indoor air with.fresh outdoor air.

The modern era of tuberculosis began in the mid 1980s. At that time it was realised that tuberculosis had not only ceased to decline in many developed countries, notably the USA, but was actually increasing. This forced health services to look more closely at the problem of tuberculosis. It was realised that the disease was out of control across most of the poorest regions of the world, especially Central Africa and South Asia. It was for this reason that in 1993 the WHO took the unique step of declaring tuberculosis to be a world emergency.

A series of bioaerosol measurements have been conducted at two typical offices in Hong Kong for both a 4-day and a weekly period. Both the investigated offices were installed with heating ventilation and air-conditioning (HV AC) systems coupling with air handling units and fan coil units. Measurements were performed starting from early morning by the Anderson N6 impactor.