Azura-Edo Independent Power Plant Environmental Impact ... - IFC

7.3 AIR QUALITY
The assessment has been undertaken using computer-based dispersion
modelling and this section sets out the approach and methodology for the
assessment, as well as the model inputs, assumptions and limitations.
7.3.1 Methodology and Assumptions for Dispersion Modelling
The dispersion modelling for the Project considered the following:
• Emissions of dust arising during construction activities; and
• Emissions arising from the combustion process during operation of the
facility.
The study area is primarily defined as an area within 2 km of the proposed
development location. This study area is defined as such, as the maximum
ground level concentration will be within this zone based on the local terrain
and exhaust height. As the air quality standards are applicable anywhere offsite,
this is considered appropriate for the purposes of this assessment.
Road traffic emissions have been excluded from consideration in the
dispersion model. The UK Highways Agency Design Manual for Roads and
Bridges (DMRB) suggests that impacts on air quality are unlikely where a
scheme generates less than 200 additional HGVs per day, or less than 1000
vehicles per day. In this case it is predicted that during operations there will
be little over ten percent of this number. In addition, there are considered to
be insignificant impacts associated with odour, as there are no significant
emission sources on site during the project lifecycle.
Assessment of Stack Emissions
The power plant will be operated on Natural Gas and as a result, the
pollutants of concern will be:
• Oxides of nitrogen (expressed as both NO x and NO 2); and
• CO.
The emission values used in the dispersion model were provided by Azura
Power. The model used in the assessment is the USEPA AERMOD dispersion
model, one of a number of ‘new generation’ models, characterised by two
main features:
• The description of the boundary layer in terms of two parameters: the
boundary layer depth and the Monin-Obhukov length, and;
• Dispersion under convective meteorological conditions uses a skewed
Gaussian concentrations distribution.
AZURA EDO IPP
7-12
DRAFT EIA REPORT