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]:

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


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:

PollutantEmission rate
per second
Oxides of nitrogen329.6 mg
Particulates16.48 mg
TOC16.48 mg
Hydrogen chloride16.48 mg
Hydrogen flouride1.648 mg
Sulphur dioxide82.4 mg
Carbon monoxide82.4 mg
Cadmium and thallium82.4 μg
Mercury82.4 μg
Other metals824 μg
Dioxins and furans164.8 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:

concentration per m3
Oxides of nitrogen16.57 μg
Particulates13.59 μg
TOC198 ng
Hydrogen chloride1.84 μg
Hydrogen flourideN/A
Sulphur dioxide3.98 μg
Carbon monoxide103 μg
Cadmium and thallium1.617 ng
Mercury5.273 ng
Other metals85.86 ng
Dioxins and furans48.7 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.


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