Details of Hoddesdon Plume Plotter

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

The plume plotter models both the proposed ERF [1] and ATT [2].

Stacks and buildings

The image below (left) shows the layout of all stacks and buildings modelled. North is at the top. Numbers show the heights of buildings and stacks, in metres. Higher buildings are a lighter shade of pink. The 30m building in the west is the Rye House power station. Buildings in the north comprise the ERF while those in the southeast comprise the ATT.

The image below (right) shows the ERF only, at a larger scale.

    

Stack measurements

The ERF has two identical stacks which are modelled separately because of the large distance between them. The details of the first stack (from [1]) are:

The location of the second ERF stack is 6.2m east and 5.8m north of the first stack.

The ATT has two identical stacks which are modelled as a single stack by doubling the area and the emission rate. The details of the merged ATT stack (from [2]) are:

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

Emissions

The ERF has two identical stacks which are modelled separately because of the large distance between them. The emission rates of pollutants per stack are as given in [1], except the emission rates of dioxins and furans and PCBs, which seem to have been miscalculated in [1] as 1.75 ng/s and 87.6 μg/s, respectively. The emission rates (per stack) that we use are listed below:

PollutantEmission rate
per second
Oxides of nitrogen6.531 g
Particulates327 mg
Sulphur dioxide1.633 g
VOCs327 mg
Carbon monoxide1.633 g
Hydrogen chloride327 mg
Hydrogen flouride32.7 mg
Ammonia327 mg
Cadmium and thallium1.633 mg
Mercury1.633 mg
Other metals16.33 mg
Dioxins and furans3.27 ng
PAHs32.7 μg
PCBs163.3 μg

The emission rate of the merged ATT stack is (2.13 x 2 =) 4.26 g/s for oxides of nitrogen [2]. We assume that all other pollutants are emitted in the same ratios as in the above table: the values above are all multiplied by 4.26/6.531.

Background levels

The background levels of pollutants are taken from [1]. These are:

PollutantBackground
concentration per m3
Oxides of nitrogen23.5 μg
Particulates25 μg
Sulphur dioxide4.6 μg
VOCs500 ng
Carbon monoxide33.2 μg
Hydrogen chloride700 ng
Hydrogen flouride3 ng
Ammonia1.66 μg
Cadmium and thallium200 pg
Mercury4.4 pg
Other metals39.88 ng
Dioxins and furans26 fg
PAHs6 ng
PCBs10 pg

The background level shown above for oxides of nitrogen (NOx) is actually the nitrogen dioxide (NO2) background level. This is because background levels of NOx are not measured in most locations.

Weather data

Wind speed, wind direction, temperature, pressure, and solar radiation are the latest values reported by one of two weather stations. If a value is not available from the primary weather station it is obtained from the secondary weather station. (Some weather stations do not measure solar radiation at all.) The primary weather station is ISTANSTE11 and the secondary weather station is IHARLOW8.

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

Validation

Using the details above and the 2015 weather data from Stansted airport, Plume Plotter generated this plot (below left) of the mean concentration of nitrogen dioxide for 2015. (This is calculated as 70% of the concentration of oxides of nitrogen.) The second plot (below right) shows the same thing but for the proposed ERF only. This should be compared with Figure A-3 of [1]. Clearly these two plots are very similar, suggesting the correctness of both.

    

References

1. Rye House Energy Recovery Facility, Hoddesdon, Hertfordshire: Environmental Statement Volume 2 - Appendix 7.1 - Air Quality Dispersion Modelling Assessment. AECOM. November 2016.

2. Hoddesdon Sustainable Energy Facility, Hoddesdon, Hertfordshire: Environmental Statement Chapter 7 - Air Quality. RPS. 2010.