Details of Portskewett Plume Plotter

This page should be read in conjunction with How Plume Plotter Works. It provides more details specific to the Portskewett version of Plume Plotter.

Stacks and buildings

Building measurements are taken from [1]. This image shows the layout of the stack and buildings modelled. North is at the top; colours and numbers indicate the heights of the buildings and the stack:

Stack measurements

All of these are taken from [1]:

Stack location: 51.587826,-2.7325497. Second stack is 2m east.
Stack height: 15.5 m (each stack).
Stack diameter: 0.5 m (each stack).
Stack gas exit velocity: 11.74 m/s. Second stack is 7.75 m/s.
Stack gas temperature: 109 °C. Second stack is 85 °C.

The following values are used for albedo, Bowen ratio, and roughness length. Roughness length is as specified in [1]:

Albedo: 0.2.
Bowen ratio: 1.
Roughness length: 0.5.

Emissions

There are two sources of emissions, each from a separate stack. The first stack emits 1.6478 Nm³/s while the second stack (2m to the east) emits 1.1253 Nm³/s.

The concentrations of pollutants in the emissions are given in [1]. These are mostly the IED emissions limits but sometimes reduced concentrations are used, especially for the first source. To simplify things, we have assumed IED limits for all pollutants for both emission sources. Because the two sources have different temperatures and velocities, we have modelled them separately, rather than combining them into a single source.

Emission rates for the first source are listed here:

Pollutant	Emission rate per second
Oxides of nitrogen	329.6 mg
Particulates	16.48 mg
TOC	16.48 mg
Hydrogen chloride	16.48 mg
Hydrogen flouride	1.648 mg
Sulphur dioxide	82.4 mg
Carbon monoxide	82.4 mg
Cadmium and thallium	82.4 μg
Mercury	82.4 μg
Other metals	824 μg
Dioxins and furans	164.8 pg

The second source has the same emission rates multiplied by 0.6829 (= 1.1253/1.6478).

Background levels

The background levels of pollutants are taken from [1]. That document provides several different background values and fails to provide a summary, so we have chosen one value for each pollutant. These are:

Pollutant	Background concentration per m³
Oxides of nitrogen	16.57 μg
Particulates	13.59 μg
TOC	198 ng
Hydrogen chloride	1.84 μg
Hydrogen flouride	N/A
Sulphur dioxide	3.98 μg
Carbon monoxide	103 μg
Cadmium and thallium	1.617 ng
Mercury	5.273 ng
Other metals	85.86 ng
Dioxins and furans	48.7 fg

Weather data

Weather data is taken from METAR reports from a local airport: Bristol.

Upper air data is the latest reported by the Camborne upper air station.

References

1. Unit 4, Severn Bridge Industrial Estate, Caldicot NP26 5PW: Air Quality Assessment (3rd Issue). WYG. February 2018."