Page 29 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

2 1 Air Emissions

Table 1.1 Pure dry air at sea
Gas Symbol Percent by volume (%)
level
Nitrogen N 2 78.084
Oxygen O 2 20.9476
Argon Ar 0.934
Carbon dioxide CO 2 0.0314
Neon Ne 0.001818
Methane CH 4 0.0002
Helium He 0.000524
Krypton Kr 0.000114
Hydrogen H 2 0.00005
Xenon Xe 0.0000087

In another example, if there is over 78 % of nitrogen in the air, it is not
considered as an air pollutant, because it does not impose any noticeable negative
effect on human beings or the environment. On the other hand, although CO 2 has
been a component of clean dry air (Table 1.1) before human history, it was not
labeled as an GHG emission until recently, when scientists observed a strong
correlation between the increased level of atmospheric CO 2 and global warming (or
climate change), which could eventually eliminate the existence of human beings
on this planet.

1.2.1 Air Pollution

Air emissions have natural or anthropogenic origins; however, this book focuses
primarily on the latter, which include industrial activities and the burning of fossil
fuels. These constituents of pollution have the potential to affect the majority of
people in a region.
Air pollutants comprise primary and secondary air pollutants. Primary air pol-
lutants are emitted directly from sources. They include, but are not limited to,
particulate matter (PM), sulfur dioxide (SO 2 ), nitric oxides (NO x ), hydrocarbon
(HC), volatile organic compounds (VOCs), carbon monoxide (CO), and ammonia
(NH 3 ). Secondary air pollutants are produced by the chemical reactions of two or
more primary pollutants or by reactions with normal atmospheric constituents.
Examples of secondary air pollutants are ground level ozone, formaldehyde, smog,
and acid mist.
Particulate matter is a mixture of solid particles and liquid droplets suspended in
the air. In this book, particulate matter is interchangeable with aerosol, which is a
suspension of solid or liquid particles in a gas. It is a two-phase system consisting of