Environmental Engineering Reference
In-Depth Information
Other Emissions from Energy Conversion Processes Leading to Air Pollution
The
chemical conversion of fuels to generate (mechanical) power and heat, generally
involving a combustion step, also results in emissions other than CO
2
. For example,
acid rain precursor emissions
, such as NO
x
(NO and NO
2
) and SO
x
(SO
2
and SO
3
),
are of concern. These gaseous compounds lead to the formation of nitric acid and sul-
furic acid in aqueous droplets in the atmosphere. These acids can precipitate both wet
(e.g., via droplets) or dry (adhered to solids that deposit on Earth), causing water and
soil acidification. In particular, forests and lakes are impacted by this effect. Also,
infrastructural works, such as buildings, are prone to decay due to chemical attack
by acid rain on metals (corrosion), paints, and stone materials. Though recognized
already in the nineteenth century, further research followed upon increased awareness
and action was initiated in the 1970s (see, e.g., Likens and Bormann, 1974). Substan-
tial abatement efforts and stringent policies to reduce NO
x
and SO
x
emissions have
already been carried out worldwide since the 1970s; this resulted in reduced emissions
in large parts of the world (Wright and Schindler, 1995). Still, there is concern for
acidic environmental pollution in emerging economy areas such as China and India,
where fossil fuel burning and motorized traffic have shown remarkable growths
(Larssen et al., 2006). Emission abatement of acid rain precursor gases is dealt with
in Chapter 9.
Another type of emission that is to be seriously considered, from both human,
animal, and plant health and climate change perspectives, is
PM
(particulate matter).
PM is released into the air in energy conversion processes that comprise combustion,
in particular of solid and liquid fuels but also of gaseous fuels under nonoptimized
combustion conditions. Especially, the respirable and very fine particles dispersed
in the air, also termed aerosols, are of concern. Nature also generates them via natural
processes such as fires, dust bowls, and storms (e.g., winds over salty seas) as well as
volcanic activity. Aerosols have several effects with regard to atmospheric radiation
(tinyurl.com/48sqk6o). Two effects are briefly described here. The so-called direct
effect of PM comprises the effective scattering of radiation, causing negative radiative
forcing (e.g., by fine salt aerosols), and the absorption of light, contributing to global
warming (carbon black and sooty material). The
of PM relates to
cloud formation. Clouds consist of droplets that form with initiation (partly) based
on preexisting aerosols, so-called cloud condensation nuclei. When these particles
increase in number concentration, increased scattering of radiation in the shortwave
domain of frequency occurs. This effect is also attributed as cloud albedo effect.
Another effect of increased number concentration of aerosols and thus droplets in
clouds is the suppression of precipitation formation and augmentation of the lifetime
of clouds. This is also referred to as the Albrecht effect.
Apart from these environmental effects, PM also has a direct negative impact on
human health: particulates can lead to respiratory diseases, including lung cancer, and
cardiovascular problems.
Several countries and regions in the world have set restrictions on PM emissions.
These restrictions distinguish between PM10 and PM2.5, being PM with sizes up to
10 and 2.5
“
indirect effect
”
m, respectively. Chapter 9 deals with technologies for the reduction of
PM in the energy conversion industry where combustion plays a key role.
μ
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