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January 1999

Windmill Software
Data Acquisition Intelligence
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Issue 6: Emission Monitoring and Windmill Survey


Windmill News | Data Acquisition Survey | Emission Monitoring | Glossary P-R


Regulatory bodies around the world are compelling establishments to reduce air pollutants. Windmill's new software, Test-Seq for Incinerators, records emissions and checks whether they are within the prescribed limits. It monitors, for example, concentrations of carbon monoxide, nitrogen dioxide and particulates, adjusted for the percentage of oxygen present. It also calculates daily averages, maxima and minima and so on. With additional software, alarms can be triggered if emissions exceed their thresholds and the information displayed on the World Wide Web. For more information contact Windmill Software Ltd.

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Emission Monitoring: Why, What and How?

Why Monitor?

Organisations such as the European Union (EU), the US Environmental Protection Agency (US EPA) and the World Health Organization (WHO) issue air quality standards which are becoming more and more stringent. The EU's Integrated Pollution Prevention and Control directive (IPPC) for example, requires many more installations to monitor and control their emissions than currently do so, and member countries must implement it by November 1999. Other countries have their own regulations and guidelines to protect people's health.

What Substances Need to be Monitored?

Commonly monitored substances include Oxides of Nitrogen (NOx), Carbon Monoxide (CO), Sulphur Dioxide (SO2) and Particulates.

Nitrogen Oxides
NOx, comprising nitrogen oxide and nitrogen dioxide, are produced from high temperature combustion in air. Nitrogen dioxide (NO2) is also formed by oxidation of NO in the atmosphere. NO2 dissolves in water droplets creating nitric acid in the air and contributing to acid rain. Nitrogen oxides act as precursors for the formation of ground-level ozone which can constitute a health hazard.

Carbon Monoxide
Colourless, odourless, poisonous gas produced by the incomplete combustion of carbon compounds.

Sulphur Dioxide
Formed by the oxidation of sulphur impurities in fuels during combustion. In the atmosphere is usually oxidised to form sulphur trioxide, a secondary pollutant. Sulphur trioxide is very soluble in water, forming sulphuric acid and contributing to acid rain.

Airborne particulate matter is a mixture of organic and inorganic substances. Physical attributes that may be recorded include mass concentration measured in micrograms per cubic meter (mg/m3).

Methods of Monitoring: a Simple Example System

A computerised incinerator monitoring system might continually measure temperature, oxygen, carbon monoxide, nitrogen dioxide and particulates. Other substances, such as dioxins, may need to be batch monitored - once a year say. The equipment needed for continuous emission monitoring would include:

  • K-type thermocouples to measure temperature.
  • A gas analyser to measure gas concentrations.
  • A particulate analyser to measure particulate concentration. This would probably be an optical analyser (how dense is the smoke?) or maybe a counter.
  • A computer with a data acquisition interface - perhaps in the form of a card which plugs into an expansion slot of a PC, and provides analogue and digital inputs and outputs. (See our on-line catalogue for an example of such a multi-function card.)
  • Data logging and calculating software.

To comply with regulations, the system has to correct gas and particulate measurements to a percentage of oxygen - 11% for example. Otherwise the concentration measurements would be meaningless: the emissions could be diluted with any amount of fresh air. This is one of the jobs the software undertakes.

Most gas analysers will correct readings back to standard temperature and pressure (STP). Particulates may have to be corrected back to STP in software. (European STP is 273 K and 1 bar.)

In many countries, regulations insist that companies submit reports to the pollution inspectorate. These contain, for example, averages over different periods and number of times limits were exceeded. Again, the calculations and report generation are jobs for the software.

The above account only scratches the surface of the topic of emission monitoring, for more details contact Windmill Software or visit the resources below.

By Jill Studholme

Internet Resources on Emission Monitoring

Books on Emission Monitoring

  • Industrial Air Pollution Monitoring, by A.G. Clarke, 320 pages, 1997, Kluwer Academic Publishers.
    Developed from a short course taught at Leeds University, this book covers methods of monitoring emissions of air pollutants from stationary sources.
    More details at or


(For letters A-O please see our web site Glossary.)

Personal computer. Generally applied to computers conforming to the IBM designed architecture.
Personal computer memory card international association.
Peer-to-Peer Communication
A communication between networked devices in which any device can initiate data transfer.
Proportional gain, integral action time and derivative action time. PID software, for example, compares an analogue input value with a set point and if there's a discrepancy outputs an appropriate analogue or digital control value, according the PID calculations.
Piping and instrumentation diagram.
Programmable Logic Controller.
The external connector on a device.
Positive Temperature Coefficient
An increase in resistance due to an increase in temperature.
A set of rules used in data communications.
A temporary change in voltage of any length
Quality assurance.
Electromechanical device that opens or closes contacts when a current is passed through a coil.
Reed Relay
Consists of two thin magnetic strips (reeds). When a coil close to the reeds is energised, they are magnetised and drawn together making a connection between leads attached to the reeds.
Resistance Temperature Device (RTD)
Resistance temperature devices (or detectors) rely on the principle that the resistance of a metal increases with temperature. When made of platinum, they may be known as platinum resistance thermometers (PRTs).
A measure of the smallest change that can be detected.
The ability of an instrument to give the same reading under repeated identical conditions.
Root mean square. The square root of the sum of the squares of a set of quantities divided by the total number of quantities. Used when monitoring ac (alternating current) signals. Many power supplies, for example, issue an ac signal. This needs to be converted to a dc (direct current) signal for the PC interface. The solution is a signal conditioning input that produces a dc signal proportional to the rms of the amplitude of the input signal. The rms operation means the reading will always be positive.
An EIA (Electronic Industries Association) standard that defines a protocol for serial data communications. An RS232 link will run at up 38400 baud (bits per second) over short distances, and at lower speeds as the distance increases. You can plug the RS232 lead directly into the computer's serial (COM) port.
Another EIA protocol for serial communications. Allows several devices to be connected to a single cable, distributed over a wide area.

Do you have a comment or suggestion for this newsletter? Why not email the editor - Jill - at [email protected]

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