Photochemical smog is a
unique type of air pollution which is caused by
reactions between sunlight and pollutants like hydrocarbons and nitrogen dioxide.
Although photochemical smog is often invisible, it can be extremely harmful,
leading to irritations of the respiratory tract and eyes. In regions of the
world with high concentrations of photochemical smog, elevated rates of death
and respiratory illnesses have been observed.
Smog itself is simply airborne pollution which may
obscure vision and cause various health conditions. It is caused by small
particles of material which become concentrated in the air for a variety of
reasons. Commonly, smog is caused by an inversion, in which cool air presses
down on a column of warm air, forcing the air to remain stationary. Inversions
are notorious in Southern California, where smog can sometimes get so severe
that people are warned to stay indoors.
Some of the particulate matter in the air
can oxidize very readily when exposed to the UV spectrum. Nitrogen dioxide and
various hydrocarbons produced through combustion will interact with sunlight to
break down into hazardous chemicals. It doesn't have to be sunny for
photochemical smog to form; UV light can also penetrate clouds. The pollutants
released through human activity in this situation are known as “primary
pollutants,” and they include sulfur dioxide, carbon monoxide,
and other volatile organic compounds. When these compounds interact with the
sun, they form “secondary pollutants” like ozone and
additional hydrocarbons.
While
ozone is an excellent thing in the upper atmosphere, since it protects the
delicate environment of the Earth, it is not desired at ground level. Ozone can
be extremely irritating to the respiratory tract, leading to fits of coughing
and various medical conditions if exposure is prolonged. The mixture of
hazardous pollutants formed by the reaction between UV rays and smog can travel
on the wind to rural areas, meaning the photochemical smog does not just impact
big cities.
Some measures have been taken around the
world to reduce photochemical smog. Light emissions regulations
on vehicles and factories are one such step; many factories must use scrubbers
and treatment systems before releasing air from their manufacturing facilities,
for example. The use of harmful chemicals is also restricted in some regions of
the world, since these chemicals can create photochemical smog. Government
agencies also monitor air quality through testing, citing companies which
violate the law and issuing warnings when smog levels are dangerous.
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