Outdoor visibility can be influenced by various factors, including weather and pollution. The presence of atmospheric particles and gases can absorb or scatter light, reducing outdoor visibility. Pollution from sources like wildfires or industrial emissions can significantly impact visibility by introducing additional particles and absorbing gases. Changing angles of sunlight and other factors also affect outdoor visibility. Air pollution effects related to visibility include phenomena like "brown clouds" caused by light scattering and absorption.
The factors that affect visibility outdoors can be complex. We often associate outdoor visibility simply with the weather, which can be the case, of course, but it can also be strongly affected by pollution.
Visibility can be defined in different ways. It could simply be how far we can see, or, alternatively, it could be how clearly we can see, or how we can differentiate objects at a distance, or even if we can see the same colors at different times.
When we look at an object what happens is that sunlight illuminates the object and the reflected light or photons can make their way to our eyes which then generate the image for us (very crudely speaking). So how can pollution or atmosphere impact this?
Well, the visual information (light) that comes from the object that we are looking at, can interact with atmospheric particles and gases. They can absorb or scatter that light. As a consequence less light arrives at our eye and we have loss of visual information or “visibility”.
The absorption depends on the nature of gases or molecules and so, yes, the more absorbing gases and particles we have, the “less” visual information comes to us and the poorer our visibility.
The same applies to particles which will scatter away the light. Now scattering of light by particles and gases is also responsible for what we might call “pollution,” light or garbage visual information in our light path. In this case we see photons of light which do not come from what we are looking at but are stray light that gets into our eye and hence blurs in a sense the information we see. All this leads to a decrease in overall visibility.
How does this relate to pollution? Well more particles and absorbing gases - pollution - means less visibility and so there is a direct link between visibility and pollution. Sources of pollution, such as wildfires, industrial emissions, or even natural dust storms, could be many hundreds or even thousands of kilometers away from the places it is serving to impact visibility.
There are, however, a lot of other additional factors at play too. A simple example is the changing illumination of an object or landscape through the angle of the sun - this changes through the day, and, therefore, so does our perception of exactly the same view - visibility, colors, distance etc.
Despite this, we can still confidently state that in many cases, air pollution changes all aspects of visibility.
A nice pollution example is the phenomenon of a “brown cloud”, in this example from Phoenix, which is the result of pollution and a combination of light scattering by particles (providing a white haze) in conjunction with absorption by particles such as Soot and light absorption by gases such as nitrogen oxides from vehicles (brown color).
A natural example you might see in forested areas is caused by the emission of volatile compounds by trees (which are responsible for their beautiful smell). These compounds can get oxidized in the air and form particles. These particles, if there are enough, can be a source of haze of forested areas caused by light scattering by the particles (in a sense pollution) from the trees. The famous example would be the great Smokey Mountains in the US where a great deal of haze is due to these particles.