QUANTITIVE STUDY ON VISIBILITY EFFECT IN ROAD TUNNELS

摘要

The term “visibility” is generally used synonymously with “visual range”, meaning the farthest distance at which an object can be clearly discerned. Meteorological visibility refers to transparency of air: in dark, meteorological visibility is still the same as in daylight for the same air. It can be reduced by the absorption and scattering of light by both gases and particles. With more and more serious air polluted globally, visibility has been attached more attention as the most straightforward measure of visual air quality, some countries and area use “visibility” as an indicator of atmosphere pollution. Visibility is a driving force in normal operation in road tunnels, however, theoretical research on tunnel visibility is scarce. Based on law of Beer-Lambert, the correlation between visibility in tunnels and extinction coefficient is clarified firstly. Accordingly to Mie theory, light absorption and scattering from gaseous and particle matters are analyzed, and atmospheric extinction coefficient linear equation is presented logically. In view of emission characters in road tunnels, road tunnel extinction coefficient equation is derived finally. This equation can be used as ventilation calculation as well as analysis factors sensitivity of fine mass, coarse mass and NO2 in road tunnels, and also provides foundation for the management of ventilation operation in tunnels.