6.3.4. Nitrogen Oxides and Volatile Organic Compounds
184.108.40.206. Nitrogen Oxides Emissions
The 1990 NOx emissions in the six SRES models range between 26.5 and 34.2 MtN,
but not all the models provide a comprehensive description of NOx missions.
Some models do not estimate NOx emissions at all (MARIA, MiniCAM), whereas others
only include energy-related sources (MESSAGE) and have adopted other sources
of emissions from corresponding scenarios derived from other models (i.e. MESSAGE
uses corresponding AIM scenarios). Standardized (see Box
5-1 on Standardization) 1990 NOx emissions in the SRES scenarios, measured
as nitrogen, amount to 31 MtN (Figure 5-9 in Chapter
As mentioned in Chapter 4, the volume of fossil fuels
used for various energy purposes varies widely in the SRES scenario families.
In addition, the level and timing of emission controls, inspired by local air
quality concerns, is assumed to differ. As a result the spread of NOx emissions
is largest within the A1 scenario family (28-151 MtN by 2100), almost as large
as the range across all 40 SRES scenarios (see Table
6-2b). Only in the highest emission scenarios (the fossil fuel intensive
A1C and A1G scenario groups within the A1 scenario family and the high population,
coal intensive A2 scenario family) do emissions rise continuously throughout
the 21 st century. In the A1 ("balanced") scenario group and in the B2 scenario
family, NOx emission levels rise less. NOx emissions tend to increase up to
2050 and stabilize thereafter, the result of a gradual substitution of fossil
fuels by alternatives as well as of the increasing diffusion of NOx control
technologies. Low emission futures are described by various B1 family scenarios,
as well as in the A1T scenario group that describe futures in which NOx emissions
are controlled because of either local air quality concerns or rapid technological
change away from conventional fossil technologies. Overall, the SRES scenarios
describe a similar upper range of NOx emissions as the previous IS92 scenarios
(151 MtN versus 134 MtN, respectively, by 2100), but extend the IS92 uncertainty
range toward lower emission levels (16 versus 54 MtN by 2100 in the SRES and
IS92 scenarios, respectively).
220.127.116.11. Volatile Organic Compounds, Excluding Methane
Non-methane volatile organic compounds (NMVOCs) arise from fossil fuel combustion
(as with NOx , wide ranges of emission factors are typical for internal combustion
engines), and also from industrial processes, fuel storage (fugitive emissions),
use of solvents (e.g., in paint and cleaners), and a variety of other activities.
As chemical reactivities of the various substances grouped under the NMVOCs
category are very different, so are their roles in ozone formation and the (potential)
health hazards associated with them. In this report, NMVOCs are discussed as
one group. In 1990, the estimated emissions range was between 83 and 178 Mt
NMVOC, which after standardization (see Box 5-1)
translates into 140 Mt NMVOC. As for NOx emissions, not all models include this
emissions category or all of its sources; the most detailed treatment of NMVOC
emissions is given in the ASF model.
A relatively robust trend across all 40 scenarios (see Figure
5-10 in Chapter 5) is a gradual increase in NMVOC emissions up to about
2050, with a range of between 190 and 260 Mt. Beyond 2050, uncertainties increase
with respect to both emission levels and trends. By 2100, the range is between
58 and 552 Mt, which extends the IS92 scenario range of 136 to 403 Mt by 2100
toward both higher and lower emissions (see Table 6-2b).
As for NOx emissions, the upper bounds of NMVOC emissions are formed by fossil
fuel intensive scenario groups within the A1 scenario family (A1C, A1G, combined
into one fossil intensive scenario group A1FI in the Summary for Policymakers,
see also footnote
2), and the lower bounds by the scenarios within the B1 scenario family.
Characteristic ranges are between 60 and 90 Mt NMVOC by 2100 in the low emissions
cluster and between 370 and 550 Mt NMVOC in the high emissions cluster. All
other scenario families and individual scenarios fall between these two emissions
clusters; the B2 marker scenario (B2-MESSAGE) closely tracks the median of global
NMVOC emissions from all the SRES scenarios (see Figure
5-10 in Chapter 5).
18.104.22.168. Carbon Monoxide
CO emissions in 1990 are estimated to range between 752 and 984 Mt CO (880
Mt CO after standardization) across the models used to derive the SRES scenarios.
The same caveats as for NOx and NMVOC emissions also apply to CO emissions -
the number of models that represent all the emission source categories is limited
and modeling and data uncertainties, such as emission factors, are considerable.
As a result, CO emission estimates across scenarios are highly model specific
and future emission levels overlap considerably between the four SRES scenario
families (see Table 6-2b). By 2100, emissions range
between 363 and 3766 Mt CO, a considerably larger uncertainty range, particularly
toward higher emissions, than in IS92, for which the 2100 emission range was
between 450 and 929 Mt CO (see Table 6-2b).
As for the NOx and NMVOC emissions discussed above, the highest CO emission
levels are associated with the high-growth fossil fuel intensive scenarios (A1C
and A1G scenario groups, combined into one fossil intensive scenario group A1FI
in the Summary for Policymakers; see also footnote
2) within the A1 scenario family, and the lowest emission levels are generally
associated with the B1 and B2 scenario families. However, inter-model variability
is considerable, which indicates that uncertainties are equally large with respect
to scenario driving forces (such as energy demand and supply growth) and other
factors that influence CO emissions (such as local air quality concerns or technological