the dimming and that the aerosol direct and indirect effect was the predominant cause for the
trend. The period from 1990 to the present
shows a reversal of the trend into a brightening
trend [95]. The dimming effect appeared to have
been masking, or suppressing, greenhouse
warming with reduced or even negative trends
on global temperatures over the period as greenhouse gases continued to accumulate. As the
trend reversed from dimming to brightening,
rapid temperature rises became evident since
the mid-1980s. Since the mid-1980s, the decadal
rise in temperature has been +0.38
C per decade
(Fig. 19), significantly higher than any other
period since the preindustrial era [96]. The
brightening has been associated with reduced
aerosol pollution since the 1980s as developed
countries implemented policies to clean up air
pollution.
Aerosols and Air Pollution
Aerosol is one atmospheric constituent regarded as
an air pollutant. In Air Quality communities, aerosol
particles are termed particulate matter (PM). Aerosol
air pollution is typically measured as the total mass
less than a particular cutoff size (e.g., 10 mm for
PM 10 , 2.5 mm for PM 2.5 , and 1 mm for PM 1 ). Air
quality is regulated in terms of exposure to a particular PM standard. Air pollution has been a serious
problem since the eighteenth century with the invention of the steam engine which increased the amount
of coal burning. Prior to that, air pollution was still a
problem due to wood and coal burning although not
as severe. In 1905, the term “smog” was coined and
it described the combination of smoke and fog that
was visible in many industrialized cities. London
experienced the most frequent and severe smog
events resulting in many “excess” deaths. The
worst of these occurred in December 1952 when
there were 4,000 excess deaths during the Londontype event. During this period, smoke mass concentrations reached 4,460 mg m
À3
. This is to be compared with a current EU yearly exposure of
25 mg m
À3 for PM 2.5 and 50 mg m
À3 sustained
over 24 h 35 times in 1 year for PM 10 . The events
typically occur in winter and during high pressure
weather systems.
High pressure systems generally are accompanied by colder temperatures resulting in increased
coal burning. In addition to the colder temperatures are stable atmospheric boundary layers,
which suppress the dispersion of pollution. Further exasperating the situation are very stable
surface-mixing layers 100–200 m deep, which
trap the pollution and confine the pollution to a
thick layer close to the ground.
+0.38 [+0.06 to +0.70]
Mainland Europe
1950
−1.0
1.0
2.0
0.0
T diff 1961–1990 (°C)
1960
1970
1980
1990
2000
−0.07 [−0.29 to +0.15]
+0.19 [+0.09 to +0.29] °C dec
−1
Aerosol in Global Atmosphere, Fig. 19 Temperature
rise over mainland Europe since 1950. Annual temperature
differences for the period 1950–2005 with respect to the
1961–1990 climatological mean for mainland Europe
(45_–55_N; 5_–15_E). Linear regression lines and decadal
trends with 95% confidence interval show the temperature
decline from 1950 to 1980 (green), and the temperature rise
to be twice as large for the period 1981–2005 (blue) than
for the whole period 1950–2005 (red). (Copyright American Geophysical Union 2009. Reprinted from [96])
270
Aerosol in Global Atmosphere
trend. The period from 1990 to the present
shows a reversal of the trend into a brightening
trend [95]. The dimming effect appeared to have
been masking, or suppressing, greenhouse
warming with reduced or even negative trends
on global temperatures over the period as greenhouse gases continued to accumulate. As the
trend reversed from dimming to brightening,
rapid temperature rises became evident since
the mid-1980s. Since the mid-1980s, the decadal
rise in temperature has been +0.38
C per decade
(Fig. 19), significantly higher than any other
period since the preindustrial era [96]. The
brightening has been associated with reduced
aerosol pollution since the 1980s as developed
countries implemented policies to clean up air
pollution.
Aerosols and Air Pollution
Aerosol is one atmospheric constituent regarded as
an air pollutant. In Air Quality communities, aerosol
particles are termed particulate matter (PM). Aerosol
air pollution is typically measured as the total mass
less than a particular cutoff size (e.g., 10 mm for
PM 10 , 2.5 mm for PM 2.5 , and 1 mm for PM 1 ). Air
quality is regulated in terms of exposure to a particular PM standard. Air pollution has been a serious
problem since the eighteenth century with the invention of the steam engine which increased the amount
of coal burning. Prior to that, air pollution was still a
problem due to wood and coal burning although not
as severe. In 1905, the term “smog” was coined and
it described the combination of smoke and fog that
was visible in many industrialized cities. London
experienced the most frequent and severe smog
events resulting in many “excess” deaths. The
worst of these occurred in December 1952 when
there were 4,000 excess deaths during the Londontype event. During this period, smoke mass concentrations reached 4,460 mg m
À3
. This is to be compared with a current EU yearly exposure of
25 mg m
À3 for PM 2.5 and 50 mg m
À3 sustained
over 24 h 35 times in 1 year for PM 10 . The events
typically occur in winter and during high pressure
weather systems.
High pressure systems generally are accompanied by colder temperatures resulting in increased
coal burning. In addition to the colder temperatures are stable atmospheric boundary layers,
which suppress the dispersion of pollution. Further exasperating the situation are very stable
surface-mixing layers 100–200 m deep, which
trap the pollution and confine the pollution to a
thick layer close to the ground.
+0.38 [+0.06 to +0.70]
Mainland Europe
1950
−1.0
1.0
2.0
0.0
T diff 1961–1990 (°C)
1960
1970
1980
1990
2000
−0.07 [−0.29 to +0.15]
+0.19 [+0.09 to +0.29] °C dec
−1
Aerosol in Global Atmosphere, Fig. 19 Temperature
rise over mainland Europe since 1950. Annual temperature
differences for the period 1950–2005 with respect to the
1961–1990 climatological mean for mainland Europe
(45_–55_N; 5_–15_E). Linear regression lines and decadal
trends with 95% confidence interval show the temperature
decline from 1950 to 1980 (green), and the temperature rise
to be twice as large for the period 1981–2005 (blue) than
for the whole period 1950–2005 (red). (Copyright American Geophysical Union 2009. Reprinted from [96])
270
Aerosol in Global Atmosphere