Project

Monitoring carbon dioxide levels in caves of the Ardèche & Cèze interfluvium

Goal: This long term study aims to find an explanation for the increase of underground carbon dioxide concentrations, and hopes to contribute to the science of making speleological research safer.
Alternative funding is being sought to carry out this research on associative level. Technical knowledge and scientific expertise of a partnership between speleologists and researchers will permit to develop a network of affordable monitoring instruments within specified conditions.

Methods: Geology, Climate Dynamics, Geological Mapping

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Project log

Erik Van den Broeck
added an update
The CO2-Vking project http://co2.vking.earth which is part of a scientific project carried out by the http://nature-temoin.fr Nature-Témoin association.
We have designed and built several fixed monitoring stations for underground climatology (CO2, O2, radioactivity, temperature, pressure, humidity,...) which are actually functioning in French caves in the departments of Gard and the Ardèche, as the Grotte de la Bartade (Saint-Remèze http://www.labartade.fr), l'Aven-Grotte de la Forestière (Labastide/Orgnac http://www.avengrottelaforestiere.com), and, most recently, in the l’Aven d’Orgnac Grand Site de France (https://www.orgnac.com).
We have also developed two portable instruments:
The Duo-Vking, a dual-gaz 5% or 20% CO2 + 21.5% O2 + temperature/humidity/pressure measuring instrument with Oled display and basic data-logging functions, in a 3D printed ABS housing with fluorecent bio-degradable filter cap;
The newest version of the CO2-Vking, which is measuring only + temperature/humidity/pressure with Oled display. Its thick 4mm ABS housing is especially adapted to use in speleological caves.
 
Super !
bravo
 
Erik Van den Broeck
added an update
This week, our association board has approved a logging multi-sensor device for release as 'Duo-vKing' for air quality monitoring use in confined spaces, after a phase of extensive prototype testing and software updates.
This new generation of CO2-measurement is temperature, pressure and humidity compensated thanks to a factory calibrated 0-5% or 0-20% goldplated tuned NDIR CO2-sensor with PTFE filter membrane, which is a long-life, maintenance-free, fast, ultra-low energy and low budget sensor.
The 4.26 µm tuned narrow-bandgap wavelength absorption avoids spectral influence by other gases as water vapour, methane, NO2, N2O, CO and NO. The measurement is particularly independent from any relative humidity for operation between 0 and 50°C. Furtheron, the LED and photodiode tuned to a relatively narrow bandwidth allow use without filtering, further reducing cost and simplifying design.
Narrowband photonics technology operating at mid-infrared and tuned wavelengths for specific gas detection, are permitting to control optical confinement and are offering advantages in lifetime and stability, compared to traditional LED/photodiode structures. This is permitting an accuracy of 50 ppm +/-3%, with a non-linearity of less than 1% full scale.
The sensor manufacturer claims a calibration free minimum 15 years lifespan, as long as no physical sensor deformation takes place, and only needs periodical zero point calibration like ABC (automatic baseline calibration) in outside fresh air.
O2-measurement is temperature, pressure and humidity compensated thanks to a factory calibrated 0-25% fluorescence-based optical UV-technology sensor with PTFE membrane, which is a long-life, maintenance-free, fast, ultra-low energy and low budget sensor at 1/15th of the price of standard UV-sensors for similar speed and accuracy.
The sensor manufacturer claims a long and calibration free lifespan between 0 and 100 % R.H., as long as no physical sensor deformation or extreme temperature swings take place.
Bosch high definition BME sensors are measuring temperature, barometric pressure, relative humidity with derived optional specific humidity, saturated water vapour pressure indication @ positive and negative temperatures, dew point according Magnus Sonntag 90 formula. Dew Point deviation typ. -0.05°C@ RH >> 30% & 0 °C < Tamb < 25 °C compared to Hardy's 1998 formula.
Other interesting hardware details:
Ultra low power 32-bits Atmel ARM Cortex microcontroller @48MHz switching off display and sensors supply during logger sleep time.
Data logging fuction with temperature compensated crystal controlled real time calendar clock.
Bright 1.3" monochrome OLED display.
Slide switch for battery cutoff during shipping and air expedition transport.
Triple membrane switch keypad for operation.
3D printed protective case adapted for use in rough conditions.
Fluorescent glow-in-darkness interchangeable and bio-degradable slide-on protective sensor-caps with washable and replaceable dust filter.
Supplied protective rubber-caps for µSD and µUSB ports with µUSB charging data cable.
LiPo battery voltage test on startup, wakeup and reset. If battery capacity is insufficient, the device can be powered or charged from a solar power bank through USB.
Automatic hotswap 3.7/4.2 V LiPo BMS battery management system. Automatic switchover to USB power when it's available.
 
Erik Van den Broeck
added an update
Actually, we are developing smaller data loggers containing components consuming less energy. Changing microcontroller type was a necessary choice, and by using tuned narrow-midband infrared carbon dioxide and ultraviolet oxygen detection cells, power consumption was further reduced. The new prototypes are similar to our new underground fluorescent dye-loggers based on flash memory, who are sleeping 99.9% of the time, consuming almost no energy. The first long-duration tests will happen this automn.
 
Erik Van den Broeck
added an update
Project goal
This long term study aims to find an explanation for the increase of underground carbon dioxide concentrations, and hopes to contribute to the science of making speleological research safer.
Alternative funding is being sought to carry out this research on associative level. Technical knowledge and scientific expertise of a partnership between speleologists and researchers will permit to develop a network of affordable monitoring instruments within specified conditions.
Background and motivation
Linked to global warming and human activity, levels of carbon dioxide in the atmosphere are increasing. As a matter of fact, CO2-levels in underground cavities are also increasing. Several years without frost have seen carbon dioxide accumulating underground, instead of being evacuated during winter, which has inevitably lead to very high concentrations of CO2 in caves.
Out of several thousands of known caves and karstic phenomena in the Ardèche and the Gard departments of Southern-France, we are planning to monitor CO2-levels in various types of caves, in order to understand the mechanism of actual carbon-dioxide accumulations, its effects on our environment, and the influence of global warming.
However, due to the specific environment of caves, the complexity of cave instrumentation equipment, this project cannot be carried out by traditional scientific channels, who are dependent on a tremendous payload of budgets and bureaucracy resulting in high operational cost and low sampling frequencies.
Instead, a unique partnership with a group of speleologists who are coordinating the project on associative level, permits the achievement of multiple goals. Our technical and scientific knowledge and expertise will be used to build a network of affordable air-quality monitoring devices within specified conditions. Speleologists will execute the follow-up of the instruments after installation, and will collect the data which can't be acquired by traditional wired or wireless communication techniques. This project aims to contribute to a scientific knowledge of which depend health and safety conditions of speleologists, scientists, and also a public of tourist cave visitors.
Since several years, we have been regularly following-up the climatological and meteorological conditions in a number of caves in the area. Actually, we are permanently monitoring carbon dioxide levels and related parameters in some representative cave systems.
 
Erik Van den Broeck
added a project goal
During recent decades, carbon dioxide levels in caves in the South of France have been seriously increasing. More specifically, in caves around the interfluvium of the Ardèche and Cèze rivers, CO2 concentrations are sometimes reaching levels at which underground exploration becomes impossible.
Since several years, we have been regularly following-up the climatological and meteorological conditions in a number of caves in the area. Actually, we are permanently monitoring carbon dioxide levels and related parameters in some representative cave systems. This long term study aims to find an explanation for this increase, and to make speleological research safer.
Due to the complexity of cave instrumentation and the high operational cost, such a study could not be carried out by traditional scientific channels. Instead, alternative funding is being sought to carry out this research on associative level. Technical knowledge and scientific expertise of our speleologists and researchers will permit to develop a network of monitoring instruments within a specified budget.