Smog can be considered
part of civilization. The word is well known in many
languages and is nearly always used to describe an
environmental problem linked to industrial development:
The word combines the two
concepts 'smoke' and 'fog.' Among Spanish-speakers,
it is often pronounced 'esmog,' and there are those
who have imitated the English fusion of words, turning
'niebla' (fog) and 'humo' (smoke) into 'neblumo'.
Smog collects over those
cities with greatest gas emissions, taking the form
of an opaque haze, generally dark in color. In the
20th Century, there were days recorded in which it
appeared to be nighttime in the middle of the afternoon.
In London, there were
times when city buses had to keep their headlights
on during the day because the sun was eclipsed by
the mixture of smoke and fog, which also proved to
be fatal. The British capital set some sad records,
as the lethal smog killed 600 people in 1948, some
3,000 in 1952, 1,000 more in 1956 and 750 in 1962.
Smog is a chemical mixture
of gases. Nitrogen oxides (NOx), volatile organic
compounds (VOC), sulfur dioxide, acid aerosols and
gases, as well as dust particles, combine to form
the haze we see above cities.
The gases originate from
industry, automobiles and even from homes, as a result
of various combustion processes.
The reaction of these
compounds with solar light produces what is known
as photochemical smog, whose principal characteristic
is the presence of ozone at ground level, a compound
that can lead to several kinds of health problems.
You can begin your search
for further information about smog at the following
Columbia Encyclopedia's definition
chronology of environmental history
problems related to ozone