WP2 Changes in atmospheric composition (CTM simulations)
 

Task 2.1 Emission perturbations (for CTM simulations)
 

Objectives

The main objective of Task 2.1 is to define a set of emission perturbations to be used in the chemistry transport models.
 

Methodology and scientific achievements related to Task including contribution from partners

Base case

The base case simulation for both models (OSLO CTM2 and LMDZ-INCA, see description below) is defined based on the IPCC (2001) OXCOMP intercomparison exercise. The protocol for model simulation is provided in Annex 2.1. Only a brief overview is provided here.
 

Perturbation scenarios

An initial set of 6 emission scenarios has been prepared for the METRIC chemical model simulations. The simulation will be conducted for 2 years and the second year will be used for intercomparison and as input for GCM perturbation studies. In order to test the sensitivity to emission pulse location, 2 regions have been retained with approximately the same area.

Region 1: Mid-latitude location corresponding to Western Europe and defined with the boundaries [40N-60N], [10W-20E].
Region 2: Tropical region corresponding to South-East Asia and defined with the boundaries [10N-30N], [100E-120E].

The 6 initial scenarios are:
1. CO Fossil fuel surface emissions increased by 40 Tg over Region 1 on an annual basis. The emissions are uniformly increased within the region in order to provide a total 40 Tg.
2. CO Fossil fuel surface emissions increased by 40 Tg over Region 2 on an annual basis.
3. NOx Fossil fuel surface emissions increased by 1 TgN over Region 1 on an annual basis.
4. NOx Fossil fuel surface emissions increased by 1 TgN over Region 2 on an annual basis.
5. NOx Aircraft Emissions increased over Region 1 on an annual basis.
6. NOx Aircraft Emissions increased over Region 2 on an annual basis.
 

Socio-economic relevance and policy implication

No direct socio-economic or policy implications are related to this work package.
 

Discussion and conclusion

An initial set of 6 scenarios has been defined in order to simulate the response of the chemistry (tropospheric ozone and OH burden) to emission perturbations of CO and NOx and to investigate the sensitivity to perturbations applied at mid-latitudes and in the tropics. These scenarios have been provided to the CTM simulation WP (Task 2.2). At this stage, due to a delay in the definition of 2000 aircraft emissions only perturbations 1 to 4 have been simulated with the CTMs.
 

Plan and objectives for next period

The aircraft emissions for 2000 conditions and the modified emissions (scenarios 5 and 6) will be prepared and provided to the CTMs. A second set of perturbations will also be defined depending on the outcome of the CTM result analysis. This new set of simulations will mainly aim at refining the analysis and understanding additional features and model discrepancies.
 
 
 
 

Task 2.2 CTM runs
 

Objectives

The objectives of Task 2.2 are

Table 2.1:
Globally and annually averaged ozone and OH changes as calculated by the 2 models LMDz-INCA (first row each) and OSLO CTM2 (second row each)
 
Base Case Scenario 1
CO, region 1
Scenario 2
CO, region2
Scenario 3
NOx, region1
Scenario 4
NOx, region 2
Methane Lifetime (years) 11.534 0.072 0.069 -0.014 -0.054
  8.532 0.032 0.031 -0.031 -0.097
OH density (10^5 molec./cm³) 7.624 -0.053 -0.058 0.010 0.043
  10.306 -0.039 -0.047 0.033 0.110
O3 burden (Tg) 388.399 0.796 0.885 0.179 1.232
  316.995 0.394 0.547 0.884 2.842
Normalised O3 change (x100)   1.991 2.213 17.896 123.157
    0.985 1.368 22.100 71.050
Normalised OH change (x100)   -0.123 -0.146 0.981 4.333
    -0.098 -0.118 0.825 2.750

 
 

Methodology and scientific achievements related to Task including contribution from partners

The 2 CTMs used in this task are LMDz-INCA for CNRS and Oslo CTM2 for CICERO. A description of the models is provided in Annex 2.2. Table 2.1 provides a summary of the various perturbations and gives the globally and annually averaged ozone and OH change for the 2 models and for scenarios 1-4. The results for LMDz-INCA are given in blue (first line) and for Oslo CTM2 in green (second line). Please note that the simulations 3 and 4 for Oslo (shaded area) have been performed for different conditions (4 TgN perturbation instead of 1 TgN) in order to provide some insight into the non-linear behaviour of the system. Even if the model results differ in terms of magnitude of the response, several basic features emerge from the results.
 

Figure 2.1: Change in total ozone (DU) calculated for scenario 1 (CO perturbation applied over Europe) as simulated by LMDz-INCA.

In particular, both models show that NOx much more efficiently catalyses the ozone production than CO as can be noticed from the much higher normalised ozone response (global change in ozone relative to the perturbation in precursors for scenario 3 and 4. An important feature is the dramatically higher efficiency in producing ozone in the case of a perturbation in the tropics. This finding is associated with a more efficient chemistry in the tropics and different mixing regimes between the 2 regions. Due to a shorter lifetime, the NOx distribution is more affected by dynamics than in the case of CO. The annual and geographical distribution of the perturbation is similar in both models. In the case of perturbation at mid-latitudes of the northern hemisphere a strong seasonal cycle is calculated peaking in summer when photochemistry is more intense (Figure 1). In contrast (not shown), the seasonal cycle is weaker if the perturbation is located in the tropics.

Results in Figure 2.1 are given for LMDz-INCA. The results by OSLO CTM2 show a very similar pattern for both the seasonal and geographical distribution. Again, the magnitude of the perturbation is different in the two models. In the case of LMDz-INCA, the ozone change reaches 0.5 DU in NH summer over Europe, while the respective signal in the case of Oslo CTM2 is only 0.25 (see also Table 2.1). This discrepancy is currently being investigated and has been tentatively attributed to differences in the simulated background NOx conditions.

An important difference between the two types of perturbations (Europe versus South East Asia) is the difference in dynamic regimes. In the tropics, rapid upward transport prevails and the precursors are vigorously redistributed in the vertical. Figure 2.2 illustrates this feature and shows the change in ozone (ppbv) calculated for scenario 4 (change in NOx in SE Asia). In this case, the ozone perturbation peaks clearly in the upper troposphere during July and reaches about 1 ppbv. Since the radiative forcing of ozone is the most sensitive to perturbations occurring in this region, we anticipate a higher radiative forcing when the change in emissions is applied in the tropics.
 
 

Figure 2.2: Change in ozone (ppbv) calculated for scenario 4 (NOx perturbation in SE Asia) and for January, April, July, and October conditions as simlualted by LMDz-INCA.


 

Socio-economic relevance and policy implication

No direct socio-economic or policy implications are related to this work package.
 

Discussion and conclusion

The simulations show that ozone is most sensitive to perturbations in NOx applied in the tropics. Even if the two model results differ in terms of the magnitude of the ozone change, the seasonal and geographical distributions are quite similar. A strong seasonal cycle is predicted for a mid-latitude perturbation peaking in summer. In the tropics, a maximum ozone perturbation is calculated in the upper troposphere where the impact on the radiative forcing is the largest.
 

Plan and objectives for next period

Over the next period, the analysis of the CTM results for simulations 1 to 4 will be continued and differences between the models explored. Scenarios 5 and 6 will be performed and results analysed. Additional simulations will be performed as specified by Task 2.1.
 
 
 
 

Task 2.3 Calculation of RF
 

Objectives

The objectives of this task are

Methodology and scientific achievements related to Task including contribution from partners

Due to a delay in the CTM simulations (Task 2.2) this task has not started yet.
 

Socio-economic relevance and policy implication

n.a.
 

Discussion and conclusion

n.a.
 

Plan and objectives for next period

This task will start with a delay of 4 month. Apart from this no changes to the plan are necessary.