Page 36 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

1.3 Effects of Air Pollution and GHGs 9

average total ozone over the northern hemisphere’s mid-latitudes since 1979. As the
ozone layer thins, more UVB radiation reaches the surface of the Earth, resulting in
global warming and climate change. Ozone depletion is also expected to lead to
increased skin cancer rates and suppression of the immune system. It also impacts
the ecosystem by slowing down the growth of certain food plants.
Scientists had linked several substances associated with human activities to
ozone depletion, including the use of chlorofluorocarbons (CFCs), halons, carbon
tetrachloride, and methyl chloroform. These chemicals are emitted from such
industrial processes as commercial air conditioners, refrigerators, and insulating
foam.
Climate change due to GHG emissions has become a prominent issue on the
global stage. Although there is a disagreement of the causes, it is doubtless that the
global climate is changing. The global temperature has a very close correlation with
the atmospheric CO 2 concentration. Over the past century, the atmospheric CO 2
concentration increased from *280 to 370 ppmv, with a rapid increase in last few
decades. The global temperature has risen by 0.5 °C during this time period [11].
This change rate is unmatched in the past 1,000 years, and 11 of the 12 years from
1995 to 2006 were the warmest years in the instrumental record of global tem-
perature since 1850. The temperature increase is widespread over the globe and is
greater in cold and remote areas. Climate change is believed to be caused by human
activity, primarily the burning of fossil fuels, resulting in a buildup of GHGs [13].

1.4 Roots of Air Pollution and GHGs

Air emissions originate from both natural and anthropogenic sources. Nature has
been producing many materials that are now being considered as air emissions. For
example, carbon monoxide (CO), sulfur dioxide (SO 2 ), and ash particles are
abundant in volcanic emissions. Methane is naturally produced by the digestion of
food by animals and the degradation of biomass. Radon gas from radioactive decay
within the Earth’s crust, and wildfires generate smoke and CO. However, these
sources are not the major concern to society.

1.4.1 Anthropogenic Air Emissions

Anthropogenic sources are related to the production and combustion of different
fuels. Human activities are responsible for the increases in ground-level O 3 and
GHGs in recent years. About 95 % of NO x (nitric oxides) from human activity come
from the burning of fossil fuels in power plants, engines, homes, and industries.