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About Air Pollution
The gas sulphur dioxide (SO2) is commonly emitted from industrial ...

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Pollution Map & Complaints
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Frequently Asked Questions
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Support & Frequently Asked Questions

Technical Terms

What is ppb?
What is SO2?

Complaints Procedure

To be updated...

Dispersion Modelling

Atmospheric dispersion modelling is the mathematical simulation of how air pollutants disperse in the ambient atmosphere. It is performed with computer programs that solve the mathematical equations and algorithms which simulate the pollutant dispersion. The dispersion models are used to estimate or to predict the downwind concentration of air pollutants or toxins emitted from sources such as industrial plants, vehicular traffic or accidental chemical releases.

Such models are important to governmental agencies tasked with protecting and managing the ambient air quality. The models are typically employed to determine whether existing or proposed new industrial facilities are or will be in compliance with the national ambient air quality standards. The models also serve to assist in the design of effective control strategies to reduce emissions of harmful air pollutants.

Air dispersion models are also used by public safety responders and emergency management personnel for emergency planning of accidental chemical releases. Models are used to determine the consequences of accidental releases of hazardous or toxic materials, Accidental releases may result fires, spills or explosions that involve hazardous materials, such as chemicals or radionuclides. The results of dispersion modelling, using worst case accidental release source terms and meteorological conditions, can provide an estimate of location impacted areas, ambient concentrations, and be used to determine protective actions appropriate in the event a release occurs. Appropriate protective actions may include evacuation or shelter-in-place for persons in the downwind direction.

The dispersion models vary depending on the mathematics used to develop the model, but all require the input of data that may include:

- Meteorological conditions such as wind speed and direction, the amount of atmospheric turbulence (as characterized by what is called the "stability class"), the ambient air temperature, the height to the bottom of any inversion aloft that may be present, cloud cover and solar radiation.

- Source term (the concentration or quantity of toxins in emission or accidental release source terms) and temperature of the material.

- Emissions or release parameters such as source location and height, type of source (i.e., fire, pool or vent stack) and exit velocity, exit temperature and mass flow rate or release rate.

- Terrain elevations at the source location and at the receptor location(s), such as nearby homes, schools, businesses and hospitals.

- The location, height and width of any obstructions (such as buildings or other structures) in the path of the emitted gaseous plume, surface roughness or the use of a more generic parameter "rural" or "city" terrain.

RBCAA Website – Ambient Air Quality Standards

Air quality limits and thresholds are fundamental to effective air quality management, providing the link between the potential source of atmospheric emissions and the user of that air at the downwind receptor site. Ambient air quality limits indicate generally safe exposure levels for the majority of the population, including the very young and the elderly, throughout an individual’s lifetime.

South African ambient air quality standards for SO2
South African ambient air quality standards for SO2 are listed below.

South African ambient air quality standards for SO2

Organisation

Variable

10-min average

Hourly average

Daily average

Monthly average

Annual average

NEMAQA [a]

SO2

500 µg/m³ [c]

350 µg/m³ [d]

125 µg/m³ [e]

-

50 µg/m³ [f]

191 ppb [c]

134 ppb [d]

48 ppb [e]

-

19 ppb [f]

Notes:

[a] SA Government Gazette 32816 (published 24th December 2009) in terms of the National Environmental Management: Air Quality Act 39 of 2004

[c] Not to be exceeded more than 526 times in one year.

[d] Not to be exceeded more than 88 times in one year.

[e] Not to be exceeded more than 4 times in one year.

[f] Not to be exceeded.


South African ambient air quality standards for TRS

Total reduced sulphur compounds, often associated with rotten egg or cooked cabbage odour, refer to a gaseous mixture of compounds consisting mainly of hydrogen sulphide (H2S), methyl mercaptan (CH3S‑H), dimethyl sulphide (CH3‑S‑CH3) and dimethyl disulphide (CH3‑S‑S‑CH3). While there are other ambient TRS compounds, these four are the most common, abundant and the ones generally referred to in discussions about TRS. Once released into the atmosphere, oxidation products of TRS compounds, such as sulphuric acid, contribute to the acidity of the environment. The most commonly reported health concerns related to TRS substances are nausea and headaches, although each component has its own characteristics and effects. There are no South African guidelines or standards for TRS; however the odour threshold for H2S is 4.5 ppb.


South African ambient air quality standards for PM-10 particulates
Among the most common categorizations imposed on particulates are those with respect to size, referred to as fractions. As particles are often non-spherical (for example, asbestos fibres), there are many definitions of particle size. The most widely used definition is the aerodynamic diameter. A particle with an aerodynamic diameter of 10 micrometers moves in a gas like a sphere of unit density (1 gram per cubic centimetre) with a diameter of 10 micrometers. PM diameters range from less than 10 nanometers to more than 10 micrometers. These dimensions represent the continuum from a few molecules up to the size where particles can no longer be carried by a gas. The notation PM-10 is used to describe particles of 10 micrometers or less and PM2.5 represents particles less than 2.5 micrometers in aerodynamic diameter.

Particulate size classifications

Fraction

Size range

PM-10 (thoracic fraction)

<=10 μm

PM-2.5 (respirable fraction)

<=2.5 μm

PM-1

<=1 μm

Ultrafine (UFP or UP)

<=0.1 μm

PM-10 to PM-2.5 (coarse fraction)

2.5 μm – 10 μm

 

South African ambient air quality standards for PM-10 particulates

Organisation

Variable

10-min average

Hourly average

Daily average

Monthly average

Annual average

NEMAQA [a]

PM-10

-

-

120 µg/m³ [e]

-

50 µg/m³ [f]

Future
NEMAQA[b]

PM-10

-

-

75 µg/m³ [e]

-

40 µg/m³ [f]

Notes:

[a] SA Government Gazette 32816 (24th December 2009) in terms of the National Environmental Management: Air Quality Act 39 of 2004, effective from 2010

[b] Effective from 2015

[e] Not to be exceeded more than 4 times in one year.

[f] Not to be exceeded.

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For more information, contact :

The Richards Bay Clean Air Association:

Public Officer - Mrs Sandy Camminga
Tel: + 27 35 786 0076
Mobile: + 27 83 515 2384
Fax: + 27 35 907 5340
Email: info@rbcaa.co.za

RBCAA
PO Box 10299
Meerensee
3901