5.5 Impact Assessment (Phase 3)
87
equivalents. Examples of the calculated 100-year GWP for various substances
include CH 4 (28 kg CO 2 -eq./kg), N 2 O (265 kg CO 2 -eq./kg), and CCl 2 F 2 (10,200 kg
CO 2 -eq./kg) (Myhre et al., 2013):
CF GWP,j =
T
0 e j × c j (t) dt
T
0 e CO 2 × c CO 2 (t) dt
(5.7)
• CF GWP,j : global warming potential as the characterization factor of climate
change for substance j [kg CO 2 -eq./kg j ]
• e j : radiative efficiency change due to a unit increase in atmospheric concentration
of substance j [W m −2 kg −1 ]
• c j (t): time-dependent concentration of substance j after an instantaneous release
[kg/m 3 ]
• T : time frame considered (often set as 100 years)
5.5.3.3 Photochemical Ozone Creation
Another midpoint impact category is the potential of an emitted substance to create
ozone in the troposphere. Ozone is created from nitrogen oxides (NO x ), which
are emitted from vehicles and other sources of combustion, and volatile organic
compounds (VOCs), which are emitted from incomplete combustion, industrial
processes, and vegetation. In the presence of sunlight, these chemicals can react
with one another and produce ground-level ozone, i.e., in the troposphere, which can
be damaging to human and environmental health. The amount of ozone generated
depends on the concentration of NO x and VOCs in the atmosphere, as well as on
the meteorological conditions.
The characterization factor for photochemical ozone creation is based on the
reference substance ethylene (C 2 H 4 ). Figure 5.15 illustrates the generation of
ozone (O 3 ) through reaction of VOCs (depicted as RCH 3 in the figure), NO x ,
and hydroxyl radicals (·OH). The primary source of tropospheric hydroxyl radicals
in the environment is a pair of reactions starting with the photodissociation of
ozone by solar UV radiation. Equation 5.8 defines the characterization factor for
the photochemical ozone creation potential (POCP) using ethylene as the reference
substance:
CF POCP,j =
δ[O 3 ] j
δ[O 3 ] Ethylene
(5.8)
• CF POCP,j : characterization factor representing tropospheric photochemical ozone
creation potential (POCP) of substance j [kg C 2 H 4 -eq./kg j ]
• δ[O 3 ] j : tropospheric ozone concentration change per kg of substance j emitted
into the atmosphere (integrated over a time period of 0 to 5 d)
Within the ReCiPe method, POCP characterization factors that were developed
under European conditions with a 5-day trajectory model for various products
87
equivalents. Examples of the calculated 100-year GWP for various substances
include CH 4 (28 kg CO 2 -eq./kg), N 2 O (265 kg CO 2 -eq./kg), and CCl 2 F 2 (10,200 kg
CO 2 -eq./kg) (Myhre et al., 2013):
CF GWP,j =
T
0 e j × c j (t) dt
T
0 e CO 2 × c CO 2 (t) dt
(5.7)
• CF GWP,j : global warming potential as the characterization factor of climate
change for substance j [kg CO 2 -eq./kg j ]
• e j : radiative efficiency change due to a unit increase in atmospheric concentration
of substance j [W m −2 kg −1 ]
• c j (t): time-dependent concentration of substance j after an instantaneous release
[kg/m 3 ]
• T : time frame considered (often set as 100 years)
5.5.3.3 Photochemical Ozone Creation
Another midpoint impact category is the potential of an emitted substance to create
ozone in the troposphere. Ozone is created from nitrogen oxides (NO x ), which
are emitted from vehicles and other sources of combustion, and volatile organic
compounds (VOCs), which are emitted from incomplete combustion, industrial
processes, and vegetation. In the presence of sunlight, these chemicals can react
with one another and produce ground-level ozone, i.e., in the troposphere, which can
be damaging to human and environmental health. The amount of ozone generated
depends on the concentration of NO x and VOCs in the atmosphere, as well as on
the meteorological conditions.
The characterization factor for photochemical ozone creation is based on the
reference substance ethylene (C 2 H 4 ). Figure 5.15 illustrates the generation of
ozone (O 3 ) through reaction of VOCs (depicted as RCH 3 in the figure), NO x ,
and hydroxyl radicals (·OH). The primary source of tropospheric hydroxyl radicals
in the environment is a pair of reactions starting with the photodissociation of
ozone by solar UV radiation. Equation 5.8 defines the characterization factor for
the photochemical ozone creation potential (POCP) using ethylene as the reference
substance:
CF POCP,j =
δ[O 3 ] j
δ[O 3 ] Ethylene
(5.8)
• CF POCP,j : characterization factor representing tropospheric photochemical ozone
creation potential (POCP) of substance j [kg C 2 H 4 -eq./kg j ]
• δ[O 3 ] j : tropospheric ozone concentration change per kg of substance j emitted
into the atmosphere (integrated over a time period of 0 to 5 d)
Within the ReCiPe method, POCP characterization factors that were developed
under European conditions with a 5-day trajectory model for various products