D E S C R I P T I O N O F W O R K - MEGAPOLI - Dmi

MEGAPOLI 212520
parameterisation for future model development); the UCAM model, with its high resolution capabilities for a global
model, will be particularly useful in providing this information. The sensitivity runs in both T5.4.1 and T5.4.2 will
make use of the two special emissions sensitivity datasets – emissions removal and redistribution – developed in WP1,
Task 7.
Task 5.4.1: Regional scale impacts (lead: FMI). The improved regional CTMs, and selected global models, will be used
to quantify the contribution of the megacity emissions (NOx, ozone, and ultrafine, fine, and coarse PM) in the
surrounding regions of selected megacities. Full-chemistry model computations will be performed in the regions
surrounding Paris for a period of at least a year that contains the campaigns. Longer-term simulations with simplified
chemistry will be conducted for a longer, climatologically representative period. We will also conduct source
apportionment studies using selected models (e.g., PMCAMx), and use reactive tracers (e.g., CHIMERE).
Task 5.4.2: Global impacts (lead: MPIC). Similarly, the global CTMs and CCMs with full chemistry will be used to
assess the impacts of present-day megacity emissions on regional and global ozone and aerosol chemistry, including
deposition fluxes. This will be done for the full set of megacities collectively (level 3 in the pyramid), as well as for
selected megacities or clusters of megacities individually. The redistribution sensitivity runs will provide directly
relevant information to policy makers, and will feed information into WP8 for assessment of mitigation possibilities.
The model output from this task will provide input for WP6.
Task 5.4.3: Megacity pollutant dispersion characteristics (lead: NILU). Calculations will be performed with the global
models to simulate the dispersion of representative artificial tracers released from selected megacities to study their
transport characteristics, including their inter-annual variability, and to discriminate between pollutant build-up in the
surface layer surrounding the cities, long-range export to neighbouring regions, and export to the upper troposphere.
The characteristic time scales will be determined, over which megacity plumes disperse into the hemispheric
background. The results of the regional and global simulations will be inter-compared over common computational
domains. This is useful for the QA/QC of the modelling. These results can also be used for designing similar numerical
experiments within the TF-HTAP (Task Force on Hemispheric Transport of Air Pollutants, http://www.htap.org/).
Task 5.5: The influence of non-urban pollution sources in megacities, and intercontinental transport (lead: DMI, NILU)
Task 5.5.1: The influence of regional-scale pollution on megacities, and inverse modelling of the emissions of
megacities (lead: DMI). In specific episodic conditions, the regional scale emissions (e.g., wild land fires, wood
burning for heating, sea spray, wind-blown dust and various biogenic emissions) can have a substantial, or even a
dominating impact on air quality in megacities. We will analyze their influence on the concentrations in selected
megacities. Inverse model computations will be performed in order to quantify better the contributions of urban
emissions on a regional scale. The inverse computational techniques take advantage of data assimilation methods, such
as 4D-VAR.
T.5.5.2: Intercontinental transport of plumes from megacities or agglomerations of megacities (lead: NILU). Megacity
plumes can have a significant impact on atmospheric composition even after transport across intercontinental distances.
However, this impact is difficult to detect in observational data. Transport of pollution from North American
megacities, in particular the Boston/New York/Washington (Bosnywash) megalopolis, has probably the strongest
impact on Europe of all intercontinental upwind regions. This will be evaluated using existing measurement data from
European background stations (e.g., EMEP) and previous airborne campaigns. The data will be screened for
observations of aged pollution plumes, which will be combined with the FLEXPART simulations to identify periods
influenced by transport from the Bosnywash region. This task will address objectives 5.3 and 5.4.
Task 5.6: Megacity impacts in the future (lead: MetO)
Changes in emissions as well as in climate will affect the impacts of megacities on regional and global atmospheric
composition. These changes will be examined by the global models in this task. The model simulations in Tasks 5.4.1
and 5.4.2 will be used as baseline scenarios. Similar sensitivity runs will then be performed for the future. In one set of
runs, only the emissions (of all types) will be modified to future scenarios (most likely using the IIASA 2030 scenarios
which were employed in the IPCC atmospheric chemistry model intercomparison), and the emissions from megacities
will be removed or redistributed as done in 5.4.2, where the scenarios will be developed in collaboration with WP 8. In
the second set of runs, in addition to the changed emissions, the driving meteorology will also be modified to represent
future climates; the meteorological fields will be obtained through WP6, from the same models as used in this WP. The
analysis will be done in coordination with WP7. By comparing the three types of runs we can determine individually
the role that changes in emissions and changes in climate play in determining how megacities affect atmospheric
composition.
Deliverables
D5.1 Characterization of megacity impact on regional and global scales using satellite data (month 18)
D5.2 Provision of global and regional concentrations fields from initial baseline runs (month 18)
D5.3 Evaluation and improvement of regional model simulations of megacity plumes (month 24)
D5.4 Prediction of megacity impact on regional and global atmospheric composition (month 30)
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