In addition to the London-type smog, there is a
chemically produced smog known as photochemical
smog. Photochemical smog is produced through gas
phase reactions typically involving hydrocarbons,
NO, and ozone and is a frequent phenomenon
encountered in many megacities such as Los
Angeles, Mexico City, Tokyo, Beijing, Johannesburg, and Athens.
The main health impacts of PM relate to respiratory and cardiovascular effects and, additionally, some of the smoke products are considered
carcinogenic, all potentially resulting in premature mortality. The European Union’s Clean Air
for Europe Programme estimated that 348,000
premature deaths occur in Europe due to exposure to PM 2.5 . Figure 20 illustrates the estimated
losses in life expectancy attributable to exposure
to PM 2.5 from anthropogenic emissions in
Europe [97]. The data are calculated for emissions for the year 2000 and for targeted emission
reductions by the year 2020.
While air pollution, particularly aerosol air
pollution, has been steadily reducing in the developed world, it has become an increasing problem
in developing countries, not only on urban megacity scales but also on regional and almost hemispheric scales. Intercontinental and hemispheric
transport of pollution is now regarded as a serious
concern, impacting on local- and regional-scale
air quality.
Future Directions: Interactions Between
Aerosol Air Pollution and Climate
Atmospheric aerosol has played an important role in
partly offsetting global warming due to greenhouse
gases. The IPCC AR4 quantifies the best atmospheric composition component estimates of radiative forcing since 1750–2005 (Fig. 21). From this
assessment, the combined direct and indirect effect
amounts to ~À1.2 W m
À2
, which effectively can be
regarded as a reduction in the positive forcing by
greenhouse gases to an equivalent amount. The
IPCC estimate the net forcing due to anthropogenic
activities as ~+1.5 W m
À2
. This positive forcing has
led to a global temperature increase of the order of
0.8
C. The European Union, leading the way in
climate policy development, have set a long-term
(i.e., by year 2050) target of an upper limit of 2
C to
the increase in global temperature.
Until recent times, climate policy has been handled separately to air pollution problems, where in
the latter case, adverse health effects from PM and
ecosystem damage have been the biggest drivers of
policies to improve air quality. What has become
evident is that the air pollution policies in recent
decades have impacted on global warming in a
manner that has accelerated temperature rise as
dirty air was cleaned up. The current decadal rate
of temperature increase is estimated to be
0.3–0.4
C per decade. As a result, by the year
2030, the predicted temperature increase is
~1.9
C – that is, almost reaching the long-term
target limit. Figure 22 illustrates the problem
[99]. If there were only long-lived greenhouse
gases (LLGHG), the past temperature increase
would have been approximately double the actual
increase since the preindustrial era. Without emission reductions, looking into the future, temperature will increase by about 0.2
C per decade.
However, taking account of the presence of aerosols, the approximate 50% masking of temperature
increase is evident up until the 1990s and then the
current day and near future rapid rise in temperature from aerosol emission controls is evident,
rapidly approaching the increase seen by treating
the system as only containing LLGHG. With both
a reduction on aerosol emissions and LLGHG,
only then can the dual target of clean air and
minimal temperature rise be achieved. Such combined policy development, while in the near term
will accelerate temperature rise, in the long term, a
sustainable temperature rise can be expected.
The development of sophisticated policy development is underpinned by the development of
sophisticated climate and air pollution assessment
Aerosol in Global Atmosphere
271
chemically produced smog known as photochemical
smog. Photochemical smog is produced through gas
phase reactions typically involving hydrocarbons,
NO, and ozone and is a frequent phenomenon
encountered in many megacities such as Los
Angeles, Mexico City, Tokyo, Beijing, Johannesburg, and Athens.
The main health impacts of PM relate to respiratory and cardiovascular effects and, additionally, some of the smoke products are considered
carcinogenic, all potentially resulting in premature mortality. The European Union’s Clean Air
for Europe Programme estimated that 348,000
premature deaths occur in Europe due to exposure to PM 2.5 . Figure 20 illustrates the estimated
losses in life expectancy attributable to exposure
to PM 2.5 from anthropogenic emissions in
Europe [97]. The data are calculated for emissions for the year 2000 and for targeted emission
reductions by the year 2020.
While air pollution, particularly aerosol air
pollution, has been steadily reducing in the developed world, it has become an increasing problem
in developing countries, not only on urban megacity scales but also on regional and almost hemispheric scales. Intercontinental and hemispheric
transport of pollution is now regarded as a serious
concern, impacting on local- and regional-scale
air quality.
Future Directions: Interactions Between
Aerosol Air Pollution and Climate
Atmospheric aerosol has played an important role in
partly offsetting global warming due to greenhouse
gases. The IPCC AR4 quantifies the best atmospheric composition component estimates of radiative forcing since 1750–2005 (Fig. 21). From this
assessment, the combined direct and indirect effect
amounts to ~À1.2 W m
À2
, which effectively can be
regarded as a reduction in the positive forcing by
greenhouse gases to an equivalent amount. The
IPCC estimate the net forcing due to anthropogenic
activities as ~+1.5 W m
À2
. This positive forcing has
led to a global temperature increase of the order of
0.8
C. The European Union, leading the way in
climate policy development, have set a long-term
(i.e., by year 2050) target of an upper limit of 2
C to
the increase in global temperature.
Until recent times, climate policy has been handled separately to air pollution problems, where in
the latter case, adverse health effects from PM and
ecosystem damage have been the biggest drivers of
policies to improve air quality. What has become
evident is that the air pollution policies in recent
decades have impacted on global warming in a
manner that has accelerated temperature rise as
dirty air was cleaned up. The current decadal rate
of temperature increase is estimated to be
0.3–0.4
C per decade. As a result, by the year
2030, the predicted temperature increase is
~1.9
C – that is, almost reaching the long-term
target limit. Figure 22 illustrates the problem
[99]. If there were only long-lived greenhouse
gases (LLGHG), the past temperature increase
would have been approximately double the actual
increase since the preindustrial era. Without emission reductions, looking into the future, temperature will increase by about 0.2
C per decade.
However, taking account of the presence of aerosols, the approximate 50% masking of temperature
increase is evident up until the 1990s and then the
current day and near future rapid rise in temperature from aerosol emission controls is evident,
rapidly approaching the increase seen by treating
the system as only containing LLGHG. With both
a reduction on aerosol emissions and LLGHG,
only then can the dual target of clean air and
minimal temperature rise be achieved. Such combined policy development, while in the near term
will accelerate temperature rise, in the long term, a
sustainable temperature rise can be expected.
The development of sophisticated policy development is underpinned by the development of
sophisticated climate and air pollution assessment
Aerosol in Global Atmosphere
271