Methane has a direct influence on climate change as well as an indirect effect on human health, plant yield, and productivity due to its role as an important precursor to ground-level ozone formation. Therefore, CH4 monitoring is an efficient way to detect the buildup of CH4 levels and take necessary actions. This article covers information on methane gas, its sources in the ambient air, permissible levels, health and environmental impact, possible corrective measures, the need for methane monitors as well as different methods of CH4 monitoring.
What is CH4?
Methane (CH4) is a colourless, odourless, tasteless, non-toxic gas with the chemical composition of one carbon and four hydrogen atoms. It is a major component of natural gas. CH4 is highly flammable at very high concentrations of about 50,000 ppm. Methane acts as an asphyxiant at extremely high concentrations.
Methane is the second most important greenhouse gas. It is 28 times ( for 100 years timeframe) more potent than carbon dioxide at trapping the sun’s heat into the atmosphere. However, it has an atmospheric lifetime of around 12 years, much shorter than carbon dioxide.
CH4 in Atmosphere
Methane is the most abundant hydrocarbon in the atmosphere. It is produced as a result of the decomposition of organic matter in absence of oxygen by microorganisms (called methanogens). However, It is naturally present under the ground or underwater (seabed).
Methane is a short-lived climate pollutant. It readily gets converted to carbon dioxide (another greenhouse gas, although less potent) releasing other harmful air pollutants such as volatile organic compounds (VOCs) and ozone.
According to the World Meteorological Organization Global Atmosphere Watch Programme, methane’s current average global background level is 1824 ppb. Moreover, natural resources emit 40% of methane and human activities including intensive livestock farming cause emission of the other 60%.
- Extraction of fossil fuels such as coal, oil, and specifically, natural gas
- Biomass burning
- Agricultural activities, specifically livestock farming
- Landfill sites
- Manure or Sewage treatment plants
- Power generation, specifically coal-fired power plants
Permissible exposure limits for CH4
NIOSH (National Institute for Occupational Safety and Health) has recommended a maximum safe concentration i.e. Threshold limit value (TLV) of 1000 ppm (0.1%) for an 8-hr period. However, there are no permissible exposure limits subscribed by OSHA (Occupational Safety and Health Administration) for methane. It is potentially explosive at 5% to 15% levels i.e. 50,000 – 150,000 ppm concentration. For instance, it is an asphyxiant at extremely high concentrations of 500,000 ppm.
Health & Environmental Impact of CH4
Methane is not toxic in nature and does not harm at low levels. However, it displaces oxygen causing asphyxiation at high concentrations. A human requires about 18% of the oxygen to breathe, hence at high methane levels in confined spaces becomes extremely dangerous.
Subsequently, high-level exposure to CH4 may cause suffocation, loss of consciousness, headache and dizziness, nausea and vomiting, slurred speech, mood changes, vision problems, memory loss, etc. In severe cases, it may also cause rapid breathing, loss of coordination, and numbness. In short, long-term exposure can lead to coma and death.
Firstly, methane is a highly potent greenhouse gas, second to carbon dioxide making it highly efficient in trapping heat. As a result, it is a major contributor to global warming.
CH4 is a major precursor of another greenhouse gas, carbon dioxide. While converting to CO2 in the atmosphere, methane reacts to form volatile organic compounds and leads to the formation of ground-level ozone when mixed with NOx.
Possible corrective measures
The primary action is CH4 monitoring i.e. to measure how much CH4 concentrations you are exposed to. In addition to this following corrective measures can be taken:
- Avoid going to or staying in enclosed the source of CH4.
- On detection of high levels of CH4, immediately vacate the area and provide proper ventilation to remove the gas.
- Avoid open disposal of animal waste
- Also, promote the use of methane gas in applications such as cooking
Measurement methods of CH4 monitoring
Different working principles for methane monitoring in the ambient environment are flame ionization detection (FID), semiconductor, electrochemistry, and nondispersive infrared absorption (NDIR)
Flame ionization detection (FID)
CH4 monitors based on the principle of FID use a hydrogen flame to ionize the methane in the air. The ionized methane gas produces an electric current proportional to the concentration of methane in the sample air which is detected by the detector.
When a metal oxide semiconductor-based methane monitor is exposed to air samples, the CH4 molecules react on the metal oxide surface of the sensor and dissociate into charged ions which alter the resistance of the film. This interaction is measured as a signal and is converted to the gas concentration.
CH4 monitors working on the electrochemical principle are operated based on the diffusion of methane gas into the sensor, resulting in the production of electrical signals proportional to the CH4 concentration.
Nondispersive infrared absorption (NDIR)
Methane absorbs infrared radiation at a particular frequency. When the gas sample is exposed to infrared radiation, the CH4 molecules present in the gas sample absorb the infrared radiation. This is measured by the detector in a non-dispersive photometer.
Among all the above principles of CH4 monitoring, methane monitors based on the principle of NDIR are typically found to be preferred for ambient air monitoring as they yield more accurate CH4 concentrations.
Oizom’s working principle for CH4 monitoring
Oizom’s ODOSENSE is the real-time odour emission tracking solution. It continuously detects, measures, and monitors the odourful gaseous contaminants including hydrogen sulfide, ammonia, sulfur dioxide, methyl mercaptan, TVOC, formaldehyde, methane, and weather parameters like temperature, humidity, wind speed, and wind direction. The sensor that measures CH4 works on the principle of nondispersive infrared absorption (NDIR). Odosense is a proactive approach to measure real-time odour emissions. This makes it an ideal choice for landfill sites, wastewater treatment facilities, fertilizers, paper-pulp industries, and soil-treatment sites, etc.
Reasons why CH4 monitoring is important
- CH4 is a colorless, odorless, tasteless, non-toxic gas. Its natural production takes place during the anaerobic decomposition of organic compounds. It tends to rise and accumulate near the higher, stagnant parts of enclosed spaces.
- CH4 is the second most important greenhouse gas with 28 times higher global warming potential than carbon dioxide. Its presence in the atmosphere increases the abundance of other greenhouse gases such as CO2, O3, water vapor, etc.
- CH4 is an asphyxiant at higher concentrations leading to various issues such as suffocation, loss of consciousness, nausea, rapid breathing, numbness, etc., and may lead to coma and death.
- CH4 monitoring is an efficient way to detect the buildup of CH4 levels and take necessary actions.
- Real-time monitoring of CH4 levels helps determine their source and formulate an action plan to control CH4 emissions.