local legislation. The United Nations Environment
Programme (UNEP) maintains a Register of International Treaties and Other Agreements in the Field
of the Environment for the interested reader (http://
www.unep.org/law/PDF/register_Int_treaties_con
tents.pdf). Specifically, the 1979 Convention on the
Long-Range Transboundary Air Pollution and its
eight associated protocols, generally named after
the cities in which they were signed (such as Aarhus, Denmark), are relevant for air quality as with
the signing of the convention air pollution is recognized as a transboundary issue. There is likewise an
international agreement regarding transboundary
haze pollution.
Air quality issues are generally on a long-term
scale; however, in urban areas, municipal authorities
need to be prepared for acute events such as those
that may be arising from an industrial accident such
as what occurred at a pesticide plant in Bhopal,
India, in December 1984 or from elevated levels of
air pollution such as experienced in London during
the “Great London Smog” of 1952. It has been
estimated that just in this single event, about
12,000 deaths could be directly attributed to the
incident [1].
As point sources such as those responsible for
the acute incidents above are addressed by policies, other man-made sources, generally the
“mobile sources” (i.e., vehicular traffic), are
becoming the new primary contributor to
degraded air quality in urban areas.
Natural sources are also an important contributor depending on the locality with dust, sea
spray, and other types of particulate matter such
as pollen as well as volatile organic compounds
emitted from plants and trees being those that
contribute often to degraded air quality.
Historically in urban areas across the world,
high levels of smoke and sulfur dioxide from
domestic burning of coal in people’s homes and
later combustion of fossil fuels in coal-fired power
plants have been the major point source of air
pollutants, and this has led to major episodes of
air pollution with resultant degraded air quality
and associated health effects, including deaths
directly attributed to the poor air quality.
Air quality in urban environments, especially
in developed countries, is nearly always a
function of vehicular traffic and the emissions
arising from vehicles. Both petrol (gasoline)and diesel-driven vehicles emit vast amounts of
pollutants. These include carbon monoxide (CO),
the oxides of nitrogen (NO x ), and volatile organic
compounds (VOCs). Particulates (PM 10 ) and
finer-sized particles (PM 2.5 ) are emitted not just
from the combustion processes in the motor but
also and more predominantly from physical processes, such as resuspension of road dust and wear
of tires, brakes, and road material.
Introduction
Air pollution is estimated by WHO to cause about
two million premature deaths (half of this is associated with outdoor and the other half with indoor
air pollution) worldwide annually [2], and this is in
addition to a variety of other adverse health effects
like asthma and other airway diseases, cardiovascular disease, different types of cancer, as well as
adverse pregnancy outcome. The most hazardous
of the ambient pollutants are generally believed to
be related to the particulate matter (PM), although
the mechanisms behind these health effects are not
yet fully understood. It is therefore still very uncertain what it is about the particles that cause these
negative health effects. Despite the uncertainties
related to the mechanism behind these effects, it
has, e.g., been estimated by WHO that reducing
ambient air concentrations of PM 10 from 70 to
20 mg/m
3 would lower the number of air qualityrelated deaths by approximately 15% [2].
People are generally most at risk in the urban
areas with respect to health effects related to air
pollution. More than half of the world’s population reside in cities, and it is here that the highest
air pollution exposure [3] and thus also most of
the associated negative health impact take place.
The projections for the next 50 years furthermore
indicate that the worldwide urban population will
be increasing by two thirds [3]. As a result of rapid
urbanization, urban air pollution has been increasing in many major cities, especially those found in
developing countries (such as in Brazil, Russia,
India, Indonesia, and China). The cost to society
of the associated health effects is very significant
196
Urban Air Quality: Sources and Concentrations
Programme (UNEP) maintains a Register of International Treaties and Other Agreements in the Field
of the Environment for the interested reader (http://
www.unep.org/law/PDF/register_Int_treaties_con
tents.pdf). Specifically, the 1979 Convention on the
Long-Range Transboundary Air Pollution and its
eight associated protocols, generally named after
the cities in which they were signed (such as Aarhus, Denmark), are relevant for air quality as with
the signing of the convention air pollution is recognized as a transboundary issue. There is likewise an
international agreement regarding transboundary
haze pollution.
Air quality issues are generally on a long-term
scale; however, in urban areas, municipal authorities
need to be prepared for acute events such as those
that may be arising from an industrial accident such
as what occurred at a pesticide plant in Bhopal,
India, in December 1984 or from elevated levels of
air pollution such as experienced in London during
the “Great London Smog” of 1952. It has been
estimated that just in this single event, about
12,000 deaths could be directly attributed to the
incident [1].
As point sources such as those responsible for
the acute incidents above are addressed by policies, other man-made sources, generally the
“mobile sources” (i.e., vehicular traffic), are
becoming the new primary contributor to
degraded air quality in urban areas.
Natural sources are also an important contributor depending on the locality with dust, sea
spray, and other types of particulate matter such
as pollen as well as volatile organic compounds
emitted from plants and trees being those that
contribute often to degraded air quality.
Historically in urban areas across the world,
high levels of smoke and sulfur dioxide from
domestic burning of coal in people’s homes and
later combustion of fossil fuels in coal-fired power
plants have been the major point source of air
pollutants, and this has led to major episodes of
air pollution with resultant degraded air quality
and associated health effects, including deaths
directly attributed to the poor air quality.
Air quality in urban environments, especially
in developed countries, is nearly always a
function of vehicular traffic and the emissions
arising from vehicles. Both petrol (gasoline)and diesel-driven vehicles emit vast amounts of
pollutants. These include carbon monoxide (CO),
the oxides of nitrogen (NO x ), and volatile organic
compounds (VOCs). Particulates (PM 10 ) and
finer-sized particles (PM 2.5 ) are emitted not just
from the combustion processes in the motor but
also and more predominantly from physical processes, such as resuspension of road dust and wear
of tires, brakes, and road material.
Introduction
Air pollution is estimated by WHO to cause about
two million premature deaths (half of this is associated with outdoor and the other half with indoor
air pollution) worldwide annually [2], and this is in
addition to a variety of other adverse health effects
like asthma and other airway diseases, cardiovascular disease, different types of cancer, as well as
adverse pregnancy outcome. The most hazardous
of the ambient pollutants are generally believed to
be related to the particulate matter (PM), although
the mechanisms behind these health effects are not
yet fully understood. It is therefore still very uncertain what it is about the particles that cause these
negative health effects. Despite the uncertainties
related to the mechanism behind these effects, it
has, e.g., been estimated by WHO that reducing
ambient air concentrations of PM 10 from 70 to
20 mg/m
3 would lower the number of air qualityrelated deaths by approximately 15% [2].
People are generally most at risk in the urban
areas with respect to health effects related to air
pollution. More than half of the world’s population reside in cities, and it is here that the highest
air pollution exposure [3] and thus also most of
the associated negative health impact take place.
The projections for the next 50 years furthermore
indicate that the worldwide urban population will
be increasing by two thirds [3]. As a result of rapid
urbanization, urban air pollution has been increasing in many major cities, especially those found in
developing countries (such as in Brazil, Russia,
India, Indonesia, and China). The cost to society
of the associated health effects is very significant
196
Urban Air Quality: Sources and Concentrations