A Brief Overview of the UV DOAS Technique

 Sulfur dioxide (so2) enters the atmosphere through the combustion of fossil fuel, oxidation of organic materials in soil, volcanic eruptions and biomass burning. Coal burning accounts for approximately 50% of the annual so2 global emissions with oil burning accounting for a further 25% to 30%. Sulfur dioxide is measured in a number of applications and industries must comply with legal regulations to control environmental pollution. A perfect so2 analyzer is the uv doas system that provides more accurate data than conventional gas monitoring systems. The uv doas monitoring equipment can easily detect sulfur dioxide among all the other gases present in an area as well as provide periodic updates on the changes in concentration.

UV DOAS as an effective tool for the management of air pollution

The uv doas system has developed into one of the more practical and high performance techniques for the evaluation of pollutants in the atmosphere.  The uv doas is the spectroscopic technique well suited for simultaneous detection of many atmospheric trace gases which includes no2, so2 and o3. The degradation of air quality in the environment is cause for concern particularly in urban and industrial areas. Air pollution has reached levels that are considered hazardous to human health and the environment. Once emitted into the air, the pollutants are transported by wind, turbulence and diffusion which later on undergo chemical reaction. One of the solutions to monitor air quality is early detection of the trace gases through uv doas techniques.

Understanding the DOAS technique

A typical DOAS system consists of

  • Light emitter that collimates the light from a suitable light source
  • Telescope that collects the attenuated light beam
  • Spectrograph
  • Single channel scanner or multi-light detection system
  • Computer for hardware control, data acquisition and processing

DOAS systems can overcome some of the disadvantages of conventional gas monitors on several aspects.

  • Simultaneous analysis – three of the criteria air pollutants – o3, so2 and no2 – can be monitored using a single uv doas apparatus. A number of other important trace species can also be monitored and measured like benzene, toluene, ethyl benzene and xylenes.
  • Integrated path measurements – the DOAS measurements provide a more representative concentration of pollutants in a single area than single point measurements which can be easily biased by local distortions.
  • Non-contact measurement – unlike point monitors and sampling systems, uv doas can perform without any sample air manipulations; hence it can be considered as a non-invasive technique. This will provide the assurance regarding the absence of wall loses through absorption or chemical reaction which makes uv doas suited for measurements of highly reactive species.
  • Low maintenance and operational costs – the DOAS system does not require routine gas calibration once it is furnished with an appropriate reference spectrum. Maintenance downtime is quite minimal which minimizes the total operating costs.
  • Fenceline and flux measurement – the DOAS technique is particularly suited for fenceline monitoring and measurement. By combining the DOAS system with anemometric measurements, rough estimations of pollutant fluxes and budgets can be achieved.  

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