Greenhouse Gas Sensors Facilitate Global Climate Studies

Regardless of what skeptics may say the scientific community accepts as fact that our climate is changing. To measure and quantify this change will require precise monitoring of the underlying indicators and vital signs, providing us with accurate data from which to predict what’s to come.

This article looks at sensor technologies that can and will be used to measure and report on the subtle (and not so subtle) climate changes taking place. This includes systems to measure real-time conditions as well as those designed to track the slow-moving metrics that foreshadow long-term trends. All technologies, parts, and development systems referenced here can be found on the DigiKey website.

CO₂ analysis

The correlation between heat-trapping CO₂ levels in the atmosphere and average global temperature has been well documented. Ice core samples going back 800,000 years have allowed researchers to measure the relative amounts of CO₂ dissolved in the ice when it froze to indicate the how much of the gas was in the atmosphere at the time. Scientists point out that, like the rings of a tree, the thickness of the layered ice and relative amount of CO₂ measured can be used to determine average temperature (there is, however, a time lag between changes in CO₂ levels and changes in temperature).

While historic geological data (Figure 1) shows anomalous periods with relatively high levels of CO₂ while temperatures were statistically lower than expected, it is known that orbital patterns, sunspot cycles, relative glacier surface areas, volcanic activities, and other negative feedback factors have influenced this data.¹

Figure 1: Historic geological data shows semi-cyclical changes in CO₂ levels, but at present we are detecting higher-than-ever levels in the atmosphere.

Looking at CO₂ levels from 1950 to the present it is clear that CO₂ levels are significantly higher than ever before and it is strongly suspected that we are living in the grace period of the lag time before global temperatures begin to soar.

Sensor solutions

This means that sensors for measuring CO₂ levels in real time are critical in ascertaining the present levels and predicting the forthcoming impact of this greenhouse gas on temperature. While measurements can be taken from orbital satellites using spectral and RF technologies, ground and atmospheric sensors at specific locations are very useful to help accumulate a database that can be studied. This is especially true in large cities where smog also affects health on a daily basis.

Among CO₂ sensors well suited for these tasks is the Grove 101020067 from Seeed Technologies. It is a high-sensitivity, high-resolution (1 ppm resolution at 0-2000 ppm range) device that uses non-dispersive IR technology to measure airborne levels of carbon dioxide through varying humidity levels (from 0% to 90% relative humidity). Integrated temperature sensors allow the Grove sensor to compensate for temperature variations, and the simple UART output is easy to interface to virtually any microcontroller-based system.

Other competitive solutions are also worth considering for this application, such as the Amphenol T6713  gas sensor that also provides a 0-2000 ppm range and uses an I²C serial interface instead of a UART (Figure 2). A corresponding T6713-EVAL kit from Amphenol is also ready to ship for quick and low-risk testing of this technology. 

Figure 2: This compact, surface-mountable CO₂ sensor has +/- 2% accuracy over a –10° to +60°C temperature range, making it an ideal low-weight, small-sized solution for measuring atmospheric CO₂ levels.

Methane: A bigger culprit

Methane is the second most prevalent gas that contributes to global warming. In our lifetime, around 60% of the methane released into the atmosphere will come from human activities such as leakage from fossil fuel-based facilities, agriculture, waste management, etc. (Figure 3).

Figure 3: Methane is emitted by various sources, and while carbon dioxide accounts for 82% of all human-contributed greenhouse gases, the 9% methane contribution is described by scientists as 100 times worse from a global-warming perspective.

While lower in overall percentage, methane traps over 100 times more heat in the atmosphere than CO₂ over a 5-year period and over a 20-year period it can trap 72 times more heat. The good news is that the methane has a shorter half-life than carbon dioxide (7 years for methane, 19 to 49 years for CO₂ with a reasonable average being 31 years with some estimates as high as 90 years).²

While some older studies tend to conclude that man-made methane levels have been declining overall, recent examinations have revealed that excessive leakage from the controversial fracking technique (hydraulic fracturing, or “fracking” is the process of drilling and injecting fluid into the ground at a high pressure in order to fracture shale rocks and release natural gas) may be releasing considerably more methane — as natural gas is mostly methane — into the atmosphere.

What is more, observations are showing vast amounts of methane release is occurring in oceans around the world.³

This means that if we are to stand a fighting chance, monitoring and controlling methane is a necessary part of our strategy to combat global climate change. Like CO₂ monitoring, terrestrial as well as space-based sensor technologies will be needed to find and eliminate as many sources of methane release as possible.

The good news here is that established sensor-based technologies as well as new MEMs sensor technologies are yielding usable solutions to allow vast deployment of sensor arrays to accurately gather the necessary data.

Readily available heater-based sensors like the Parallax 605-00008 provide resistance variations based on gas concentrations using tin-dioxide layers in aluminum-trioxide tubes (Figure 4). Temperature and humidity must be monitored and applied as part of the sense algorithm to more accurately discern gas levels and make this type of sensor work effectively, but once designed, this solution provides fast-response times, high sensitivity, and uses a relatively simple interface circuit.

Figure 4: Volatile gas detection is critical in determining the overall magnitude and duration of greenhouse gases like methane. Sensors such as this Parallax 605-00008 can be biased to detect various volatile gas types.

While suitable for many terrestrial-based designs where size and power may not be constraints, the 160 mA drive current needed for the heater may be detrimental to balloon-based and environmentally-isolated designs that may need some form of energy harvesting to allow long-term monitoring. On the plus side, this sensor can also be biased to monitor LPG, butane, propane, alcohol, and hydrogen sulfate.

Another volatile gas sensor that may provide a good solution comes from ams and is based on newer MEMs technology. The IAQ-CORE C is a smaller, lower-power, and surface-mountable volatile gas sensor that is primarily aimed at indoor air quality measurements, but may be adaptable for airborne measurement systems as well (Figure 5). The sensor can monitor CO₂ as well as volatile gas concentrations using MEMS metal-oxide sensor technology.

Figure 5: Modern MEMs-based volatile gas sensors require less power and are small enough and low-power enough to use in remote locations as part of a vast network of sensors.

The sensor itself is protected by a plastic cap and a filter membrane. The sensor module can be soldered directly to a host circuit board with selective or reflow soldering via the edge connectors. It is protected by a membrane (which should not be removed). This sensor system uses I²C as a serial communications mechanism, allowing engineers to specify virtually any low-cost microcontroller to directly interface to it. In continuous mode it dissipates 67 milliwatts but can operate in a pulsed mode using a much lower 9 milliwatts of power.

In summary

We are all in this together, and bickering over the source, cause, and effect of Greenhouse Gases on global climate is pointless without relevant data. What everyone should be able to agree on is the need to monitor all sources of these gases, including natural sources. As we have shown in this article, the necessary sensor solutions are available to engineers engaged in developing designs aimed at measuring both real-time conditions as well as the slow moving metrics that determine long-term trends.

For more information about the parts discussed in this article, use the links provided to access product pages on the DigiKey website.

References

1. Global CO₂ Emissions
2. The lifetime of excess atmospheric carbon dioxide
3. Scientists discover vast methane plumes escaping from Arctic seafloor