As leaders in gas analysis and detection of volatile organic compounds, ION Science are at the forefront of the latest news and developments. Terminology in the field is often changing or alters between countries and legislative bodies. No definition is more important to the industry than that of the VOC.
Typically, we understand the term VOC to mean volatile organic compound. This refers to any organic compound that can be found as a gas in the atmosphere. However, not all VOCs are harmful or dangerous. Some can be in certain concentrations or environments, but regardless of the risk, monitoring them is essential to manage exposure. Particularly for the industries that ION Science supports, having essential gas detection and analysis capabilities is critical, therefore having universally understood terminology is essential.
VOC is a term that can be applied to any volatile organic compound, generally it is more commonly used for health and safety and indoor air quality. Although, the general term used for outdoor air quality is non methane volatile organic compound, or NMVOC.
The reason for specifying whether the VOC is methane or non-methane has become more important in recent years, as the rules around how certain VOCs and other gases are monitored has shifted.
Definition of an NMVOC
The technical definition of an NMVOC, as given in the official guidelines from the European Monitoring and Evaluation Programme (EMEP) is as follows:
“NMVOCs comprise all organic compounds except methane which at 293.15 K show a vapour pressure of at least 0.01 kPa (i.e. 10 Pa) or which show a comparable volatility under the given application conditions”
The Air Quality Expert Group (AQEG) define NMVOCs as:
“…a broad class of organic chemicals that are, in a small number of cases, directly harmful to health, but that more generally act as precursors to the formation of ozone and particulate matter (PM).”
The volatility of a compound is generally higher the lower its boiling point temperature, the volatility of organic compounds is therefore sometimes defined and classified by boiling points. Importantly this definition can differ by geography, for example, the European Union uses the boiling point, rather than its volatility in its definition.
Why is methane excluded?
Methane is a common emission resulting from many activities, such as road transport, manufacturing, and agriculture. However, methane is excluded from VOC monitoring in many cases, as it is relatively non-toxic and poses little harm to human health (although it does pose notable environmental concerns). By excluding methane from VOC analysis and detection by isolating non-methane volatile organic compounds, it is easier to understand the impact of NMVOCs on human health.
Methane is also typically present in high concentrations in atmospheric conditions. Although, PID instrumentation doesn’t detect methane, and environmental concentrations of methane don’t adversely affect PID readings. Methane concentrations are at 2ppm, whereas NMVOCs are much lower than this. Therefore, if the instrumentation detected Methane, it would mask the other elements. This is one of the reasons why PIDs are effective at measuring/detecting outdoor VOCs. When you are aiming to detect potentially trace amounts (parts per million or billion) of highly potent VOCs, being able to have analysis and detection that is not impacted by more common compounds is vital for accuracy and appropriate levels of safety and protection.
ION Science develop, manufacture, and supply gas detection instruments that can detect a range of VOCs and NMVOCs, depending on the requirements of the customer. To keep staff and the public safe in all environments, ION Science gas detection offers unrivalled capabilities and unbeatable accuracy. Discover more about the portable, personal, and fixed instruments today, or explore the range of industry leading PID sensors.
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