Development of an automated sampling and measurement equipment to determine the greenhouse gas methane on the waterair surface of urban canals

Methane (CH4) emission from the aquatic environment is considered as one of the sources of greenhouse gas contributes significantly important to the global warming. For measuring continuously the methane emission from the water-atmospheric interface an automatic sampling and measurement system using floating chamber integrated methane sensor (Automated Floating Chamber integrated Methane Sensor - AFCMS) has been fabricated including the control and PIC datalogger boards with a lower cost than a commercial product. The floating chamber integrated a methane sensor (Panterra, Neodym Technologies, Canada) which works well not only on the quiet water surface but even on the oscillated one. The sensor (coded 1501-1) has a low LOD = 0.45 ppm and a good linearity (R2 = 0.9947) of methane concentration ranging from 2 to 30 ppm. AFCMS system shows a good performance of the equipment deployment for sampling and measuring the methane emissed from the urban canals.

Technical note: A simple and cost-efficient automated floating chamber for continuous measurements of carbon dioxide gas flux on lakes

Freshwaters emit significant amounts of CO2 on a global scale. However, emissions remain poorly constrained from the diverse range of aquatic systems. The drivers and regulators of CO2 gas flux from standing waters require further investigation to improve knowledge on both global-scale estimates and system-scale carbon balances. Often, lake–atmosphere gas fluxes are estimated from empirical models of gas transfer velocity and air–water concentration gradient. Direct quantification of the gas flux circumvents the uncertainty associated with the use of empirical models from contrasting systems. Existing methods to measure CO2 gas flux are often expensive (e.g. eddy covariance) or require a high workload in order to overcome the limitations of single point measurements using floating chambers. We added a small air pump, a timer and an exterior tube to ventilate the floating chamber headspace and passively regulate excess air pressure. By automating evacuation of the chamber headspace, continuous measurements of lake CO2 gas flux can be obtained with minimal effort. We present the chamber modifications and an example of operation from a small forest lake. The modified floating chamber performed well in the field and enabled continuous measurements of CO2 gas flux with 40 min intervals. Combining the direct measurements of gas flux with measurements of air and waterside CO2 partial pressure also enabled calculation of gas exchange velocity. Building and using the floating chamber is straightforward. However, because an air pump is used to restart measurements by thinning the chamber headspace with atmospheric air, the duration of the air pump pause–pulse cycle is critical and should be adjusted depending on system characteristics. This may result in shorter deployment duration, but this restriction can be circumvented by providing a stronger power source. The simple design makes modifications of the chamber dimensions and technical additions for particular applications and systems easy. This should make this approach to measuring gas flux flexible and appropriate in a wide range of different systems.

A simple and cost-efficient automated floating chamber for continuous measurements of carbon dioxide gas flux on lakes

Freshwaters emit significant amounts of CO2 on a global scale. Yet, emissions remain poorly constrained from the diverse range of aquatic systems. The drivers and regulators of CO2 gas flux from standing waters require further investigation to improve knowledge on both global scale estimates and system scale carbon balances. Often lake-atmosphere gas fluxes are estimated from empirical models of gas transfer velocity and air-water concentration gradient. Direct quantification of the gas flux circumvents the uncertainty associated with the use of empirical models from contrasting systems. Existing methods to measure CO2 gas flux are often expensive (e.g. eddy-covariance) or require a high workload in order to overcome the limitations of single point-measurements using floating chambers. We added a small air pump, timer and an exterior tube to ventilate the floating chamber headspace and passively regulate excess air pressure. By automating evacuation of the chamber headspace, continuous measurements of lake CO2 gas flux can be obtained with minimal effort. We present the chamber modifications and an example of operation from a small forest lake. The modified floating chamber performed well in the field and enabled continuous measurements of CO2 gas flux with 40-minute intervals. Combining the direct measurements of gas flux with measurements of air and waterside CO2 partial pressure also enabled calculation of gas exchange velocity. Application of the described floating chamber is straightforward and modifications are both simple and cost-efficient to perform. Changing the chamber dimensions to particular applications and systems makes this approach to measure gas flux flexible and appropriate in a range of different systems.

Sniffle: a step forward to measure in situ CO2 fluxes with the floating chamber technique

Understanding how the ocean absorbs anthropogenic CO2 is critical for predicting climate change. We designed Sniffle, a new autonomous drifting buoy with a floating chamber, to measure gas transfer velocities and air–sea CO2 fluxes with high spatiotemporal resolution. Currently, insufficient in situ data exist to verify gas transfer parameterizations at low wind speeds (<4 m s–1), which leads to underestimation of gas transfer velocities and, therefore, of air–sea CO2 fluxes. The Sniffle is equipped with a sensor to consecutively measure aqueous and atmospheric pCO2 and to monitor increases or decreases of CO2 inside the chamber. During autonomous operation, a complete cycle lasts 40 minutes, with a new cycle initiated after flushing the chamber. The Sniffle can be deployed for up to 15 hours at wind speeds up to 10 m s–1. Floating chambers often overestimate fluxes because they create additional turbulence at the water surface. We correct fluxes by measuring turbulence with two acoustic Doppler velocimeters, one positioned directly under the floating chamber and the other positioned sideways, to compare artificial disturbance caused by the chamber and natural turbulence. The first results of deployment in the North Sea during the summer of 2016 demonstrate that the new drifting buoy is a useful tool that can improve our understanding of gas transfer velocity with in situ measurements. At low and moderate wind speeds and different conditions, the results obtained indicate that the observed tidal basin was acting as a source of atmospheric CO2. Wind speed and turbulence alone could not fully explain the variance in gas transfer velocity. We suggest that other factors like surfactants, rain or tidal current will have an impact on gas transfer parameterizations.

Surveying emissions of greenhouse gas CO2 in the canals of Ho Chi Minh city by floating chamber method

Carbon dioxide (CO2) is one of the most important greenhouse gases and atmospheric CO2 concentrations have been recorded increasing. Floating chamber associated with Non-Dispersive Infrared (NDIR) technique as Licor-820 has been used for measuring the CO2 flux F(CO2) (mmol m-2 h-1) that emitted from the water surface on the various canals of Ho Chi Minh City. The highest values at 3 sites: CH – Kenh Đoi, DBP – Kenh Nhieu Loc – Thi Nghe and CD – Rach Cau Son ranged from 35 to 186 mmol m-2 h-1 while much higher at OB site – Rach Ong Lon from 120–474 mmol m-2h-1. Climate characteristics also greatly affect the CO2 emissions in natural waterways with low F(CO2) values in dry season – the highest value fluctuated between 35 and 181 mmol m-2 h-1 while in the rainy season the highest F(CO2) value was 446 mmol m-2 h-1 for OB site and ranged from 65 to 186 mmol m-2 h-1 for 3 other sites CH , DBP and CD. Pollution of waterways also affected on the CO2 emissions.