METEOROLOGIST JEFF HABY
Visibility is the distance that an object in the distance can be clearly discerned. Visibility is measured in miles or fractions of a
mile (such as division into 1/4ths of a mile) or in kilometers or fractions of a kilometer. There are several reasons why visibility
may be limited.
The visibility can be very high, such as being able to see through the atmosphere or at distances that are 10s of miles. Thus, the air
components of Nitrogen, Oxygen and Argon by themselves do not reduce visibility nearly as much as other factors. Several factors
that reduce visibility will be explained below.
Fog: This is one of the primary reasons that visibility is reduced. Fog is a cloud on the ground. Just like clouds restrict being able
to see the sky, fog restricts visibility in all directions. Fog is composed of cloud droplets consisting of small spheres of water
vapor. Drizzle will commonly occur with fog, especially dense fog. Dense fog can reduce visibility to less than a 1/4th of a
mile. It is one of the main transportation hazards.
Smoke and emissions: Emissions from cars and factories can add particles to the air that restricts visibility. Burn sites and forest fires
will also add particulates to the air that reduces visibility. These add more significantly to reducing visibility when the relative
humidity is high since they act as great condensation nuclei for moisture to condense onto. This makes the particles larger and
restrict visibility even more.
Smog: Smog is a term that combines smoke and fog. “Sm”oke + f”og” = smog. Smoke, salt from the oceans, haze and pollution particles are
great condensation nuclei for moisture. When combined together, visibility can be severely limited. It can also
produce a whitish looking sky.
Other restrictions to visibility include: Precipitation, blowing dust, and blowing snow