As it has been established – and continues to be substantiated – that even the most state-of-the-art technology can have shortcomings in monitoring and measuring the presence of ambient gases in harsh environments. Interestingly, African Mining Brief has noticed that, alternatively, some companies are using UV Differential Optical Absorption Spectroscopy (DOAS). How does this technology work?
UV DOAS identifies and measures different gases, based on Beer-Lambert’s absorption law. It states the relationship between the quantity of light absorbed and the number of molecules in the lightpath.
Swedish company, OPSIS AB, a Swedish company, in commentary on the technology, describes how UV DOAS works: “Because every type of molecule, every gas, has its own unique absorption spectrum properties, or “fingerprint”, it is possible to identify and determine the concentrations of several different gases in the light path at the same time.”
Typically, light from a special source – a high-pressure xenon lamp – is beamed over a chosen path, and then advanced computer calculations are used to evaluate and analyse the light losses from molecular absorption along the path. The light from the xenon lamp is very intense, and includes both the visible spectrum and ultraviolet and infrared wavelengths.
Addressing shortcomings of conventional gas monitors
Curiously, after going around finding out where this technology would fit amongst conventional gas monitors that dominate in mining, interesting trends emerge. They are listed below lucidly encapsulated in a review by research firm, Unisearch Associates, which indicates that UV DOAS can address some of the inadequacies of conventional gas monitors.
A single DOAS apparatus has the following capabilities: simultaneous gas monitoring, integrated path, non-contact measurement, low maintenance and operational costs, fence line and flux measurement.
- Simultaneous gas monitoring
A single instrument can monitor and measure three of the most common, yet difficult to monitor, air pollutants – o3, so2 and no2. In addition, it can monitor and measure benzene, toluene, ethyl benzene and xylenes.
- Integrated path
Commonly, single point measurement of pollutants can be easily biased by local area distortions. Handily, through DOAS measurements, one can get a more representative concentration of pollutants.
- Non-contact measurement (non-invasive)
Point monitors and sampling systems need sample air manipulations. On the other hand, as a non-invasive technique, UV DOAS can perform without any sample manipulations. This eliminates wall loses through absorption or chemical reaction, making UV DOAS suited for measurements of highly reactive species.
- Low maintenance and operational costs
Once furnished with an appropriate reference spectrum, the UV DOAS system does not require routine gas calibration. Considerably, this reduces maintenance downtime, minimising the total operating costs.
- Fenceline and flux measurement
The DOAS technique is best suited for fence line monitoring and measurement.
What makes UV DOAS effective?
There should be no doubt why UV DOAS is regarded as one of the more practical and high performance procedures for the evaluation of pollutants in the atmosphere. As a spectroscopic technique, well-suited for simultaneous detection of many atmospheric gases, DOAS is a practical solution for handling the challenge of managing rising air pollution, which has become a hazard to human health and the environment. As a result of movement, the pollutants undergo chemical reaction, which proves difficult to detect. In these conditions, UV DOAS is effective.