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

vicinity of the plant. Terrain has not been included in the model as there are
no significant elevations in close proximity to the site.
Surrounding Land Use
The pre-analysis of the meteorological and terrain data has reflected the land
use in the vicinity of the Project which is characterised primarily by a mixture
of generally degraded forest, secondary vegetation and agricultural land.
Percentage Oxidation of Nitric Oxide to Nitrogen Dioxide
During the combustion process, two nitrogen based pollutants are generated,
namely NO 2 and nitric oxide (NO) and together these comprise emissions of
oxides of nitrogen. NO 2 is the pollutant of interest from a health perspective
as this is considered the more toxic of the two, with NO being largely inert.
The emissions from the combined stack will comprise, initially, primarily NO,
but through various chemical reactions that will take place in the atmosphere,
the NO will be converted to NO 2. A worst case assumption would be that all
the NO is converted to NO 2 by the time the emissions reach ground level and
therefore human receptors. However, in reality this does not occur and only a
proportion of the NO emitted will be converted to NO 2. This is due to the
chemical reactions taking time to occur and also 'mopping up' other
atmospheric chemicals such as ozone, a process which will limit the reaction
rate and therefore limit the generation of NO 2. The conversion of NO to NO 2
is in part a function of the amount of ozone in the ambient air, and the travel
time of the plume in the atmosphere (allowing more ozone be to entrained
into the plume, and thus more conversion). It is expected that, in the area
most impacted by the plume from the power plant, ozone concentrations will
be low due to the absence of significant ozone precursor emissions upwind of
the plant. Furthermore, this most impacted area is within 1 km of the
proposed power plant stack, and at an average wind speed of 4 m/s ie plume
travel time of about 250 seconds, there is very little time for ozone to be
entrained. Therefore there is only minimal NO to NO 2 conversion likely to
occur.
A number of international agencies have developed guidelines for including
in assessments the conversion of NO to NO 2. A summary of the main
guidelines and ratios are set out below in Table 7.6 and indicate that a wide
range of ratios to convert NO to NO 2 are recommended by a variety of
country agencies.
Table 7.6
Recommended NO to NO 2 conversion ratio
Country Averaging period Recommended NO to NO 2
conversion ratio
United States
24 hour 75%
Annual 75%
Germany
24 hour
Annual
60%
60%
AZURA EDO IPP
7-16
DRAFT EIA REPORT