Indoor Air Quality Businesses can help improve the internal environment for their employees, including  indoor air quality. It is generally influenced by outdoor concentrations, indoor  sources, the rate of exchange between indoor and outdoor air, and the  characteristics and furnishings of buildings. Indoor air quality will vary by geographic location, season and time of day. Indoor  pollution sources could include cigarette smoke, combustion products arising from  gas appliances, emissions from furnishings and furniture, and heating, ventilation  and air conditioning systems. By improving ventilation and buying tested materials (in terms of emissions  potential), organisations can help minimise staff exposure to pollutants, especially  during refurbishment. Reducing moisture in the air can reduce microbial problems.  People working in air-conditioned buildings have consistently reported higher rates  of sickness than those working in buildings that are naturally ventilated or that have  mechanical systems of ventilation supplying ducted air without cooling or  humidifying. Organisations should ensure their heating, ventilation and air  conditioning systems are well maintained and any filters replaced regularly. The emissions and energy efficiency of equipment such as computers, photocopiers  and printers should be considered during purchasing. The EU Eco-label covers  products such as personal computers, laptops, refrigerators, lightbulbs, copying and  graphic paper, and cleaners. Better cleanliness in the workspace can improve indoor air quality, particularly the  'deep' cleaning of soft furnishings and reduction of surfaces that collect dust such as  excessive shelving (these result in elimination of dust mites and their by-products).  Obvious sources of pollutants like photocopiers and fax machines can be grouped  away from work stations and dealt with by local extract ventilation.