Environmental Engineering Reference
In-Depth Information
CO is equivalent in terms of greenhouse gas perturbations to the emission of about
5 Mt CH
4
(IPCC
2001
). The abundance of CO in the Northern Hemisphere is
about twice that in the Southern Hemisphere and has increased in the second half
of the twentieth century along with industrialisation and population growth (IPCC
2001
). The reactive nitrogen species (NO and NO
2
) and the volatile organic com-
pounds, because of their impact over the oxidising capacity of the troposphere,
may act as indirect greenhouse gases both through their influence on ozone and by
impacting the lifetimes of CH
4
and other greenhouse gases via HO
•
scavenging,
although this latter effect is compensated for to a variable extent by the HO
•
gen-
eration upon O
3
photolysis (IPCC
2001
).
The contributions of different anthropogenic greenhouse gases to the 2004
total emissions in terms of CO
2
equivalents have been 56.6 % from fossil fuel
use, 17.3 % from deforestation and decay of biomass, 2.8 % from other sources,
14.3 % from CH
4
, 7.9 % from N
2
O, and 1.1 % from fluorine gases (IPCC
2007a
).
The contributions of the different activity sectors to the total emissions of anthro-
pogenic greenhouse gases in 2004, in terms of CO
2
equivalents are 25.9 % for
energy supply, 19.4 % for industry, 17.4 % for forestry, 13.5 % for agriculture,
13.1 % for transport, 7.9 % for residential and commercial building purposes,
and finally 2.8 % for waste and wastewater treatment (IPCC
2007a
). In addi-
tion, recent studies shows that CO
2
can be significantly released to the atmos-
phere from other sources such as the photoinduced and microbial degradation of
DOM and POM (e.g. algae or phytoplankton) in natural waters (Bozec et al.
2005
,
2006
; Schiettecatte et al.
2006
,
2007
; Borges et al.
2008
; Omar et al.
2010
; Kelley
1970
; Kempe and Pegler
1991
; Hoppema
1990
,
1991
; Borges and Frankignoulle
1999
,
2002a
,
b
). Also the photoinduced and microbial degradation of OM in ter-
restrial plant masses can release CO
2
to the atmosphere (Rutledge et al.
2010
;
Johannessen et al.
2007
).
Among the atmospheric absorbers of long-wave radiation, H
2
O vapor,
clouds, CO
2
, CH
4
and O
3
dominate while the aerosols and other species make
small contributions to the overall effect (Schmidt et al.
2010
). It has been
shown that the contributions of atmospheric greenhouse gases (GHGs) to global
warming are significantly variable depending on the occurrence of the atmos-
pheric constituents and on the long-wave and short-wave fluxes under clear,
cloudy or all-sky conditions (Kiehl and Trenberth
1997
; IPCC
2007a
; Schmidt
et al.
2010
).
The contributions of atmospheric GHGs to global warming are 39-70 % for
H
2
O vapor, 15-36 % for clouds, 14-31 % for CO
2
, 8-18 % for O
3
, and 6-9 %
for other constituents including CH
4
and N
2
O (Kiehl and Trenberth
1997
; Schmidt
et al.
2010
; Harrison et al.
1990
; IPCC
1990
; Clough and Iacono
1995
). In addi-
tion, the atmospheric short-wave (UV-Vis) absorbers are mostly H
2
O vapor
(38-43 W m
−
2
), O
3
(14-15 W m
−
2
), and O
2
(2 W m
−
2
) under both clear and
cloudy conditions. In contrast, CO
2
(1 W m
−
2
) only gives a small contribution
under clear-sky conditions (Kiehl and Trenberth
1997
). It has also been shown
that the all-sky contribution of water vapor and clouds together is approximately
72-80 % after removing all the other absorbers (Schmidt et al.
2010
).
