113
quences were frequent in London until the 1970s.
During the ill-famed smog in London in
December 1952 around 4000–6000 people died.
This was the time when reducing smog was
termed London type smog which has now become
widely known. Since then, however, air in London
has become significantly cleaner as a result of
numerous measures. (It can be noted that the concentration of SO 2 has been decreasing in developed countries and cities.) This type of smog is
more typical in Asian major cities nowadays.
The second type of smog, so-called Los
Angeles type or oxidising smog (Photochemical
smog) forms in the summer due to strong solar
radiation (ultraviolet radiation has decisive role)
with pollutants involved that are emitted in vast
amount primarily by traffic. These pollutants are
nitrogen oxide and hydrocarbons that go under
complex photochemical transformations due to
UV radiation. Typical smog constituents produced by photochemical processes include ozone,
PAN (peroxyacetyl nitrate), nitric acid and hydrogen peroxide. When the concentration of PAN
exceeds 0.02 ppm vegetation is damaged within
hours, human health is threatened and the metallic and certain mineral constituents of the built
environment are corroded. Los Angeles is made
prone to the formation of photochemical smog
due to its huge vehicle traffic, sunny Mediterranean
summer and atmospheric inversions caused by
the cold Californian sea current (hence the name
of the smog type). It is not rare that smog alert has
to be ordered in the stifling summer heat. Similar
problems occur in major cities around the
Mediterranean Sea (Athens, Barcelona, Rome).
Precipitation is also more frequent above cities than in the surrounding areas; therefore, cities
get 5–10% more precipitation. Interestingly precipitation falling in the form of snow is 5% less in
cities than in their vicinity. This can be explained
by the formation of urban heat islands, i.e. if the
temperature outside a city is −1 to (−2) °C snow
will fall but at the same time snow melts in the
warmer air above the city and arrives down to the
surface as rain. In the temperate climatic zone
energy usage of cities in winter is generally
greater than in the summer and this energy excess
prolongs the frost free period by 3–8 weeks.
Even though urban climate has more precipitation than the surrounding areas, the air is drier
as shown by the decrease of relative moisture
content due to the rapid runoff of precipitation
water. Accompanied by higher air temperature
urban climate on hot summer days in the temperate climate could be similar to desert climate with
20–30% of relative moisture content. Therefore
the city centre—due to its hot and dry climate—
is also referred to as “urban desert”.
Several specifics of urban climate challenge the
biological tolerance of humans. Apart from the
already mentioned serious cases (heat stroke, heart
problems) too dry, warm and polluted air increases
the number of those having bronchitis. Temperatures
varying from place to place (overheated concrete,
asphalt—compared to the shade of parks), draughty
housing estates due to channelling, significant temperature differences within some of the buildings
cause people catching cold. Most serious health
impacts are caused by heat waves and smog catastrophes. According to estimates, urban air pollution
causes the death of 800,000 people annually
(Stephens and Stair 2007).
Chafe (2007) approaches the effects of cities
on climate and the feedback of nature on residents
from a global perspective. He considers that the
majority of greenhouse gases originate from cities
(industrial emission, residential and institutional
heating, emission of traffic); therefore, they are
dominant factors in global climate change. This
effect of cities, however, eventually intensifies
natural hazards. Due to the heat wave afflicting
Europe in 2003 the costs of climate change
amounted to 60 billion US dollars in that year,
10% more than in the previous year. Sea level rise
already threatens New Orleans while it will cause
water supply problems in Boston and New York,
amphibian houses are built in the Netherlands,
and hard work is going on to save Venice from
flooding. There are 21 coastal cities with residents
more than eight million and sea level rise is about
to cause greater or smaller problems within a few
decades. Increasing frequency of tropical cyclones
could further deepen the concerns of cities.
Another typical city problem is noise. Level of
noise inside a flat is determined by the location of
the flat within the city, their distance from busy
4.1 Changes in the Outer Boundary Zone of the Earth’s Crust
quences were frequent in London until the 1970s.
During the ill-famed smog in London in
December 1952 around 4000–6000 people died.
This was the time when reducing smog was
termed London type smog which has now become
widely known. Since then, however, air in London
has become significantly cleaner as a result of
numerous measures. (It can be noted that the concentration of SO 2 has been decreasing in developed countries and cities.) This type of smog is
more typical in Asian major cities nowadays.
The second type of smog, so-called Los
Angeles type or oxidising smog (Photochemical
smog) forms in the summer due to strong solar
radiation (ultraviolet radiation has decisive role)
with pollutants involved that are emitted in vast
amount primarily by traffic. These pollutants are
nitrogen oxide and hydrocarbons that go under
complex photochemical transformations due to
UV radiation. Typical smog constituents produced by photochemical processes include ozone,
PAN (peroxyacetyl nitrate), nitric acid and hydrogen peroxide. When the concentration of PAN
exceeds 0.02 ppm vegetation is damaged within
hours, human health is threatened and the metallic and certain mineral constituents of the built
environment are corroded. Los Angeles is made
prone to the formation of photochemical smog
due to its huge vehicle traffic, sunny Mediterranean
summer and atmospheric inversions caused by
the cold Californian sea current (hence the name
of the smog type). It is not rare that smog alert has
to be ordered in the stifling summer heat. Similar
problems occur in major cities around the
Mediterranean Sea (Athens, Barcelona, Rome).
Precipitation is also more frequent above cities than in the surrounding areas; therefore, cities
get 5–10% more precipitation. Interestingly precipitation falling in the form of snow is 5% less in
cities than in their vicinity. This can be explained
by the formation of urban heat islands, i.e. if the
temperature outside a city is −1 to (−2) °C snow
will fall but at the same time snow melts in the
warmer air above the city and arrives down to the
surface as rain. In the temperate climatic zone
energy usage of cities in winter is generally
greater than in the summer and this energy excess
prolongs the frost free period by 3–8 weeks.
Even though urban climate has more precipitation than the surrounding areas, the air is drier
as shown by the decrease of relative moisture
content due to the rapid runoff of precipitation
water. Accompanied by higher air temperature
urban climate on hot summer days in the temperate climate could be similar to desert climate with
20–30% of relative moisture content. Therefore
the city centre—due to its hot and dry climate—
is also referred to as “urban desert”.
Several specifics of urban climate challenge the
biological tolerance of humans. Apart from the
already mentioned serious cases (heat stroke, heart
problems) too dry, warm and polluted air increases
the number of those having bronchitis. Temperatures
varying from place to place (overheated concrete,
asphalt—compared to the shade of parks), draughty
housing estates due to channelling, significant temperature differences within some of the buildings
cause people catching cold. Most serious health
impacts are caused by heat waves and smog catastrophes. According to estimates, urban air pollution
causes the death of 800,000 people annually
(Stephens and Stair 2007).
Chafe (2007) approaches the effects of cities
on climate and the feedback of nature on residents
from a global perspective. He considers that the
majority of greenhouse gases originate from cities
(industrial emission, residential and institutional
heating, emission of traffic); therefore, they are
dominant factors in global climate change. This
effect of cities, however, eventually intensifies
natural hazards. Due to the heat wave afflicting
Europe in 2003 the costs of climate change
amounted to 60 billion US dollars in that year,
10% more than in the previous year. Sea level rise
already threatens New Orleans while it will cause
water supply problems in Boston and New York,
amphibian houses are built in the Netherlands,
and hard work is going on to save Venice from
flooding. There are 21 coastal cities with residents
more than eight million and sea level rise is about
to cause greater or smaller problems within a few
decades. Increasing frequency of tropical cyclones
could further deepen the concerns of cities.
Another typical city problem is noise. Level of
noise inside a flat is determined by the location of
the flat within the city, their distance from busy
4.1 Changes in the Outer Boundary Zone of the Earth’s Crust