outdoor air quality

The quality of indoor air in buildings depends on many factors. Some of these factors have internal sources, and some have external sources. The internal loads of the room include those generated by people: CO2 and moisture emissions from breathing, heat emissions from room equipment: volitale organic compaunds VOC. External sources are, for example, particulate matter present in the air, which is the result of emissions from cars and the burning of fossil fuels. The scientific literature states that car traffic can contribute a large share.

Ventilation systems assume that the outdoor air quality is better than the indoor air quality at al times as they use outdoor air to dilute pollutants emitted by humans, activities, the building itself and other objects. However, the outdoor air quality is not always as clean as assumed. Traffic, industry and agriculture can pollute the outdoor air making the outdoor air also a source of certain unhealthy pollutants indoors. This challenges the before stated assumption as in this case less ventilation would lower this source of pollution to the indoor environment.

Outdoor air change qualifies the air that enters into the buildings. The outdoor air moves freely along the urban mesh favoured by the wind forces and stresses. Buildings, trees and other constructions alter the natural air flow pattern inside the cities, creating stagnated air masses in those wind-protected regions. Some outdoor spaces such as light shafts and confined light shafts inhibit the correct exchange of the stagnated air with fresh air coming from the outskirts and suburban areas. 

A total of 20 toxic, carcinogenic, or mutagenic organic compounds were measured in the air and drinking water of 355 residents of Bayonne and Elizabeth. New Jersey, in the fall of 1981. The participants were selected from over 10,000 residents screened by a probability sampling technique to represent 128,000 persons (over the age of seven) who live in the two neighboring cities. Over one hμndred geographic areas throughout the two Cities were selected for monitoring. Each participant carried a personal sampler with him during his normal daily activities for two consecutive 12-h periods.

The monitoring of air pollution and health levels was carried out in coal burning districts and the districts with central heating in Chengde City. The air pollution levels in winter and summer were compared in coal burning districts and the districts with central heating, indoors and outdoors, in kitchens and bedrooms, before and after the central heating system was used. The health levels of residents who lived in coal burning districts and in the districts with central heating were compared.

Forty years ago, smoke and sulphur dioxide pollution from domestic coal burning caused an air pollution episode that led to the premature deaths of 4,000 Londoners. These so-called smogs have been all but eliminated by a combination of measures of which the most important were the Clean Air Acts of 1956 and 1968, the move away from domestic coal burning for home heating and the centralisation of electricity generation in large power stations away from towns and cities. Largely because of pollution emissions from motor traffic, urban air quality is once more causing public concern.

The new proposal for ventilation requirements in the National Building Code of Finland is on public review. The structure of the proposal is different from the existing ventilation code. Minimum requirements for acceptable indoor climate will be given to a wider extent than before, eg new requirements for indoor air temperature and purity are proposed. Also the quality of outdoor air should be taken into account in design of ventilation. Health aspects are also considered, based on today's international knowledge of indoor air quality and human health.