CO and opacity detection
Introduction
Opacity, referring to the air that surrounds us, is the opposite of visibility. The atmosphere is said to be opaque when, as a result of the amount of solid particles in suspension it contains, it makes clear and defined visibility of more or less distant objects difficult.
In certain populous cities such as London, Tokyo, Beijing or Mexico, it frequently happens that the opacity of the air is great: it has a large amount of particles in suspension, in such a way that they affect, or may affect, the health of its inhabitants. Humanity has always highlighted the quality of the air we breathe and the harmful effects on health of breathing highly polluted air. In 1943, nearly 4,000 people died in England due to smog.[1] The word smog comes from the contraction and union of the two English words "smoke" with "fog".
Without reaching these disastrous effects, millions of people have experienced them on their own bodies and that one scholar on the subject describes like this: "...if you have experienced an unfavorable case of smog, you will never forget it. You can't see in the distance, you have difficulty breathing. And the air you breathe doesn't feel good. Your eyes and throat become irritated. Food and plants are seriously damaged. The paint on your house is affected..."[2].
This article does not refer to this phenomenon but more specifically to "visibility in vehicle traffic tunnels", the effects on the ease or difficulty that the driver has in differentiating objects, signs, other more or less distant vehicles, etc., due to the risk that driving in an atmosphere with a high degree of opacity entails, this risk being maximized by the fact that, when occurring in a tunnel, access is, in the best of cases, by two roads but sometimes by only one. Panic greatly increases the adverse effects of an accident inside a tunnel. It is precisely this type of opacity of the atmosphere inside tunnels, and the devices to measure it, that this article refers to.
In tunnels with vehicle traffic, whether urban or interurban, opacity and the concentration of carbon monoxide (CO) are totally linked since all internal combustion vehicles generate, in greater or lesser quantities, solid particles and CO.[3].
Opacity and carbon monoxide CO
opacity and CO concentration are the two easily measured parameters that determine the quality of the air inside a tunnel. As the percentage of Otto cycle (gasoline) vehicles with a catalyst increases, the measurement of nitrous oxides may become more relevant, making it necessary to also consider this parameter. With fluid traffic, the most important parameter is usually opacity. Consequently, the mechanical ventilation of the tunnel must be carried out in this case depending on the opacity. To guarantee adequate visibility inside the tunnel, which will allow other vehicles and possible obstacles to be recognized, good visibility inside the tunnel is of fundamental importance. Only with correct visibility can the vehicle driver react sufficiently in advance to, for example, an obstacle or traffic accident.