The project in several steps used dispersion modeling for the environmental impact assessment
of a capacity expansion of 144 MW of the current 305 MW Delimara Thermal Power Station on Malta. The
resulting changes in ambient level of air pollution, increase over the baseline,
and compliance with the air quality standards defined by the Air Quality Framework Directive
(2008/50/EC), and (2004/107/EC) were evaluated.
The AirWare model system is used.
The substances to simulate include NO2, PM10 and PM2.5, metals (cadmium, aresenic, nickel)
and Benzo-a-Pyrene (BaP). The relevant (EU) substance specific standards
are used, see: Table of Air Quality Target and Limit values.
The simulation uses a range of air quality models with nested grid, starting from a European scale
and EMEP emisison data to account for long-range transport.
The simulation runs are based on three to five year periods of
meteorological data to analyse interannual variability due to
specific meteorological situations. For the years, 2008, 2009, 2010 and 2010, 2011
detailed meteorological fields (interpolated down to 1 km hourly values) are used.
They are generated with MM5, a 3D non-hydrostatic
prognostic model system based on NCEP/NOAA re-analysis data.
The basic assessment approach is straight forward:
- Baseline runs for the historical period of available data
including specific sampling periods and programs; they are used for model calibration
where necessary and model validation; this includes measured emission from
the Delimara plant with an hourly resolution and the matching hourly air quality data.
The scenarios use dynamic regional background (simulated from the European EMEP level down to local).
- Scenarios analysis for the extension (additional emission corresponding
to the 144 MW additional generating capacity, different fuel qualities (conversion to natural gas),
plant configurations (OCGT, CCGT, different stack parameters)
runs of several models with predicted emissions (in part extrapolated from
the sampling and monitoring program, in particular for traffic generated emissions)
with up to three years (five in a second batch) of historical monitoring and emission data.
- The annual scenarios were run with re-analysis meteorology for up to 5 years, to also include
the effects of inter-annual variability in the meteorological drivers for the assessment.
Primary assessment model is the USEPA regulatory (Gaussian) guideline model AERMOD
(current release: 15181) run with AERMAP terrain data and AERMET meteorology input
files generated (mcip) from MM5 re-analysis, hourly runs over a year at a time.
Episodes that indicate potential violations of standard, or the episode with the predicted maxima of
concentration are then re-run with different models such as CAMx (with the TPS represented as PIG),
short-term AERMOD (output of individual hourly concentration matrices),
AERMOD/OLM (for direct calculation of NO2 estimates), TRAFFIC (for line sources including a mixing zone),
and PUFF to realistically represent low wind
(or no wind) situations the basic Gaussian AERMOD model can not represent.
The scenarios covered both ambient concentrations (with and without background) at a large number of
sensitive receptor locatiopn around the plant, but also the incremental contribution of plant
emissions in the area od ground-level maxima, expressed as a precentage of the applicable
air quality standards (2008/50/EC).
Comparison of baseline and future expansion scenarios, analysis of compliance.
In addition to the direct comparison (same meteorology) of baseline and extension scenario,
this includes the comparison against the applicable EU air quality standards
for the entire model domain, the speciffied 6 km radius around the power plant,
and the impacts at a set of specific (sensitive) receptor points. These cover both open-air ambient concentrations,
as well as resulting indoor air quality.