Gifted Chemistry IB
1997 March 19
in pollutants in the atmosphere over the last three centuries. Before 1950, the
conditions, the smoke and sulfur dioxide produced from the burning of coal can
combine with fog to create industrial smog. In high concentrations, industrial
smog can be extremely toxic to humans and other living organisms. London is
world famous for its episodes of industrial smog. The most famous London smog
event occurred in December, 1952 when five days of calm foggy weather created a
fossil fuels, nuclear power, and hydroelectricity instead of coal has greatly
reduced the occurrence of industrial smog. However, the burning of fossil fuels
like gasoline can create another atmospheric pollution problem known as
photochemical smog. Photochemical smog is a condition that develops when primary
pollutants (oxides of nitrogen and volatile organic compounds created from
mixture of hundreds of different and hazardous chemicals known as secondary
pollutants. Development of photochemical smog is typically associated with
One way in which the production of photochemical smog is initiated is through
many sources of photochemical smog, including vehicle engines (the number one
cause of photochemical smog), industrial emissions, and area sources (the loss
thinners, and natural gas leakage).
which is released through the vehicle exhaust along with a high concentration of
hydrocarbons. The absorption of solar radiation by the nitrogen dioxide results
in the formation of ozone (O3). Ozone reacts with many different hydrocarbons to
produce a brownish-yellow gaseous cloud which may contain numerous chemical
compounds, the combination of which, we call photochemical smog.
Both types of smog can greatly reduce visibility. Even more importantly, they
concentrations of pollutants that are trapped near the surface by a temperature
inversion. Many of the components which make up these smogs are not only
respiratory irritants, but are also known carcinogens.
There are many conditions for the development of photochemical smog:
1. A source of nitrogen oxides and volatile organic compounds.
2. The time of day is a very important factor in the amount of photochemical
? Early morning traffic increases the emissions of both nitrogen oxides (NOx)
? Later in the morning, traffic dies down and the nitrogen oxides and
volatile organic compounds begin to react forming nitrogen dioxide, increasing
? As the sunlight becomes more intense later in the day, nitrogen dioxide is
broken down and its by-products form increasing concentrations of ozone.
organic compounds (VOCs) to produce toxic chemicals.
? As the sun goes down, the production of ozone is halted. The ozone that
remains in the atmosphere is then consumed by several different reactions.
smog. These conditions include :
? Precipitation can alleviate photochemical smog as the pollutants are washed
out of the atmosphere with the rainfall.
problems may arise in distant areas that receive the pollution.
? Temperature inversions can enhance the severity of a photochemical smog
episode. Normally, during the day the air near the surface is heated and as it
warms it rises, carrying the pollutants with it to higher elevations. However,
if a temperature inversion develops pollutants can be trapped near the Earth’s
surface. Temperature inversions cause the reduction of atmospheric mixing and
therefore reduce the vertical dispersion of pollutants. Inversions can last from
a few days to several weeks.
4. Topography is another important factor influencing how severe a smog event
can become. Communities situated in valleys are more susceptible to
the air flow, allowing for pollutant concentrations to rise. In addition,
valleys are sensitive to photochemical smog because relatively strong
temperature inversions can frequently develop in these areas.
A possible solution to the problem of photochemical smog is to enforce stricter
U.S. My point is that you can go from one country to another, and notice the
differences between the two levels of photochemical smog. If the world were to
enforce the same legal smog levels, we wouldn?t have to worry about
concentrations of smog in some places more than others.
Another possible solution is to come up with a cleaner burning fuel for
are not in mass production, therefore, leaving the world to rely on
gasoline/diesel as the primary source for power. If the world were to accept
production, we would have lower levels of the photochemical pollutants
“Photochemical Smog and the Okanagan Valley”
Photochemical smog can be a significant pollution problem in the Okanagan Valley.
The Okanagan meets all the requirements necessary for the production of
photochemical smog, especially during the summer months. During this time period
there is an abundance of sunlight, temperatures are very warm, and temperature
inversions are common and can last for many days. The Okanagan Valley also has
some very significant sources of nitrogen oxides and volatile organic compounds,
1. High emissions of nitrogen oxides and volatile organic compounds primarily
2. The release of large amounts of nitrogen oxides and volatile organic
contributes to the creation of photochemical smog creation in two ways: the
burning of slash from logging; and, the burning of woodchip wastes in wood
burning of prunings and other organic wastes.
The idea that the Okanagan is immune to the big city problems of photochemical
ozone has shown that the values between here and the Lower Mainland are quite
comparable. In addition, research over a 4 year period (1985-1989) has shown
that ozone levels can at times be higher over the Okanagan Valley than the Lower
Mainland of British Columbia by almost 49 %.
“The Photochemical Problem in Perth”
The Perth Photochemical Smog Study, a joint effort of Western Power Corporation
and the Department of Environmental Protection (DEP), was undertaken to
determine, for the first time, the extent to which photochemical smog had become
a problem in Perth.
Measurements of photochemical smog in Perth’s air began in 1989, at a single
site in the suburb of Caversham, 15 kilometers north-east of the city center.
Despite the common perception that Perth is a windy city and therefore not prone
to air pollution, the first summer of measurements revealed that the city was
sometimes subjected to smog levels which approached or exceeded the guidelines
recommended by the National Health and Medical Research Council of Australia
Power Corporation) sought to extend the capacity of the gas turbine power
station it operated at Pinjar, some 40 kilometers north of the Perth central
business district. In view of the Caversham data, the Environmental Protection
Authority expressed concern that increasing the NOx emissions at Pinjar could
contribute to Perth’s emerging photochemical smog problem which, at that stage,
was poorly defined.
A consequent condition on the development at Pinjar was that SECWA undertake a
study of the formation and distribution of photochemical smog in Perth, a
particular outcome of which would be to determine the effect of the Pinjar power
station’s emissions on smog in the region.
the Perth Photochemical Smog Study (PPSS) was developed as a jointly operated
and managed project, funded by SECWA and with DEP contributing facilities and
The primary objective of the Perth Photochemical Smog Study was to measure, for
the first time, the magnitude and distribution of photochemical smog
concentrations experienced in the Perth region and to assess these against
Australian and international standards, with consideration given to health and
other environmental effects.
the distribution of Perth’s smog. The Perth region experiences photochemical
smog during the warmer months of each year. On average, during the three year
peak hourly ozone concentration exceeded 80 parts per billion (ppb) somewhere
over the Perth region.
1. Cope, M.C. and Ischtwan, J., 1995, “Perth Photochemical Smog Study, Airshed
Modelling Component”, EPA of Victoria, August 1995.
2. Minderly, Calvin 1995, “Photochemical Smog and the Okanagan Valley”,
3. Pidwirny, Michael, Gow, Tracy, et al. “Photochemical Smog”, Microsoft
4. Woodward, A.J., Calder, I., McMichael, A.J., Pisaniello, D., Scicchitano, R.,