The LI-7200 is a compact, enclosed CO2/H2O analyser that combines the benefits of open and closed path gas analysers. It is an integrated system designed to provide measurements in harsh weather conditions and environments, with impressively low power consumption.
LI-7200 Key Features
- Based on the proven LI-7500
- High speed in-cell temperature and pressure measurements
- Low power requirements: 12W nominal, <30W nominal with the 7200-101 Flow Module
- High precision: 0.16 ppm CO2; 0.0067 ppt H2O typical RMS noise in ambient conditions @ 20 Hz
- Continuous measurements through rain, snow, and fog
- Analyser mounts atop flux towers for minimal tubing attenuation of CO2 and H2O
- 90-95% temperature attenuation
The LI-7200 includes the LI-7550 Analyser Interface Unit - a weatherproof enclosure that houses the Digital Signal Processing (DSP) electronics. 4 analog input channels and on-board USB data storage allow the LI-7500A to log complete eddy covariance data sets (CO2, H2O, U, V, W, and Ts, and other variables). Ethernet and Serial data are output at selectable speeds of up to 20 Hz, and linearised user-configurable Digital-to-Analog Converters (DACs) output analog signals at up to 20 Hz bandwidth.
The LI-7200 CO2/H2O Analyser is a high-performance non-dispersive infrared gas analyser designed for demanding applications, such as eddy covariance measurements. It maximises the strengths of traditional open-path and closed-path instruments.
Unlike closed-path instruments, the LI-7200 mounts on a flux tower or measurement platform right next to other measurement devices. It uses a short intake tube and an energy efficient flow module (optional) to draw sample air through the optical path. The tube can be as short as few centimetres or as long as many metres, but the optimal length is 0.5 metres to 1 metre. The 1 metre intake tube provided with the instrument minimises attenuation of CO2/H2O, while attenuating temperature by 90-95%. The remaining fluctuations are measured in the cell with two fast temperature sensors and a fast pressure sensor. This virtually eliminates the complications that result from long tubing runs.
Benefits of Closed Path
- Minimal data loss due to precipitation and icing
- No surface heating issues - fast cell temperature measurementes
- Possibility of automated calibrations on tower
- Minimal-to-negligible WPLH correction
- Possible to heat the system to prevent ice build up in extremely cold environments
Benefits of Open Path
- Good frequency response for both CO2 and H2O measurements
- Small and easily corrected flux attenuation in short intake tube
- Tool-free optical cell cleaning
- Low power requirements
- System simplicity, small size, light weight, and weatherproof design
The LI-7200 enables the collection of integrated data sets during long-term eddy covariance deployments. CO2/H2O density, sonic anemometer, and auxiliary data can be logged together to an onboard USB data storage device or output to an external storage device.
7200-101 Flow Module
The 7200-101 Flow Module (optional) is an energy efficient, durable blower unit designed to provide a precisely controlled airflow rate through the LI-7200 optical path. With an internal precision mass flow sensor and intelligent feedback controls, the flow module actively regulates flow to ensure a stable, carefully monitored airflow rate.
The 7200-101 Flow Module outputs mass flow rate, volume flow rate, and pressure drops with the data record, and it provides diagnostic data to indicate when filters need to be cleaned or replaced.
The scientific methods for characterising greenhouse gas flux are well developed theoretically and have been refined through years of research. Eddy covariance is one of the most widely used and theoretically defensible techniques for measuring sensible heat, latent heat, and trace gas exchange between ecosystems and the atmosphere.
In its simplest form, flux refers to the amount of something that moves through a defined area in a defined time. For example, the flux of CO2 is the sum of all CO2 exchanges over a specified time period, over a specified area. In order to characterise this accurately, the instrumentation involved must be able to resolve the concentration of CO2 and vertical air movements at the finest spatial and temporal scale that contributes to the flux.
The LI-7200 is optimised for the eddy covariance technique. With the eddy covariance method, the flux, Fc of gas C (eg, CO2) is given by where c' is the density fluctuations of the gas (mmol/m³), and w' is the vertical wind velocity fluctuations (m/s). The LI-7200 has the high speed and precision required for this method. The flux of CO2 and H2O is obtained from the vertical wind speed (measured with a sonic anemometer) and the concentration of the gas (measured with the LI-7200).
Advantages of the LI-7200 for Eddy Covariance Measurements
- Based on the proven LI-7500 Open Path CO2/H2O Analyser. Provides continuous measurements through rain, fog, and snow
- The LI-7200 integrates and stores data from any fast sonic anemometer (ATI, CSI, Gill, Kaijo, Metek, RM Young)
- Includes the LI-7550 Analyser Interface Unit for datalogging
- The 7200-101 Flow Module provides an efficient, integrated air-flow solution for the enclosed analyser
The LI-7200 can deliver high precision measurements where other instruments cannot. The design of the LI-7200 allows it to operate equally well in nearly any environment - from extremely cold to extremely hot, and from extremely humid to extremely dry. It delivers exceptional performance for both bench-top and field applications.
The LI-7200 corrects for small fluctuations in temperature and pressure in situations where these rapid fluctuations are significant (ie, airborne measurements or measurements made in urban or mountainous areas). In addition, the high speed in-cell temperature measurements ensure that it delivers accurate measurements in cold and rainy environments, including Polar Regions.
With the increased concern of global greenhouse gas emissions, scientists are researching ways to limit the amount of CO2 entering the atmosphere in an effort to mitigate the atmospheric CO2 concentration increase. Currently there is a global push to limit CO2 emissions through Carbon Capture and Storage (CCS) technologies. These large projects require strategic planning and public acceptance for them to be successful.
One of the biggest concerns with CCS is whether or not the CO2 remains within the geologic formation into which it was injected. The post-injection migration of CO2 in time scales of years, decades, and even centuries is not well understood. Despite the fact that CO2 is injected thousands of feet below the surface, the risks and potential for failure are very real. A well organised surface monitoring campaign should include a pre-injection background study to better understand the natural variation in soil CO2 flux over the surface of the injection area. By establishing baseline CO2 fluxes, the researcher can say with confidence that routine post-injection monitoring is effective and can provide quantitative data to prove a leak has not taken place. An active surface monitoring campaign can also be used to ease public perception of any potential leak concerns. Even though the risk of a leak in most cases is very low, using surface monitoring techniques is a valid way to convince the public that the CO2 has not escaped to the surface.
Surface Monitoring Instrumentation for Geologic Sequestration
LI-COR Biosciences has specialised in ambient CO2 monitoring for over 25 years. Our open and closed path CO2 analysers are used worldwide in many different applications. In terms of CCS technology, LI-COR offers a modular LI-8100 Automated Soil CO2 Flux System that can be used to monitor surface leaks and natural background fluxes in multiple locations. The LI-8100 uses a chamber accumulation technique to determine the diffusion rate of CO2 out of the soil. LI-COR also offers the LI-7500A Open Path CO2 /H2O Analyser that is commonly used in Eddy Covariance measurements to determine the vertical CO2 flux over a relatively large area. The Eddy Covariance method is an effective way to monitor large areas where CO2 may escape from the subsurface.
The LI-8100 System is already being used in a number of CCS projects all over the world. One example is in the Southeast Regional Carbon Sequestration (SECARB) Partnership's Central Appalachian Coal Seam Project. The Virginia Center for Coal and Energy Research (VCCER) at Virginia Tech is using the LI-8100 to acquire baseline data prior to an injection at a coalbed methane (CBM) well. Their field validation objectives are to assess and verify the sequestration capacity and performance of mature CBM reservoirs in the Central Appalachian Basin through injection-falloff and production testing, as well as the implementation of monitoring programs. These tests will demonstrate the potential geologic sequestration into Appalachian coals as a safe and permanent method to mitigate greenhouse gas emissions. Monitoring will be divided into pre-injection, injection and post-injection phases. The pre-injection monitoring phase started in the Spring of 2008 by obtaining a soil CO2 flux baseline.
Surface Monitoring for Geologic Carbon Sequestration: Monitoring Methods, Instrumentation, and Case Studies
Guide to the Eddy Covariance Method
The following guide on the eddy covariance method is presented as a service to the scientific community. The content was developed as an introduction for researchers who wish to know more about eddy covariance and how to properly make these measurements. It emphasises the general principles, requirements, applications, and processing steps of the eddy covariance method – from deploying the equipment through processing the data. Additional information is provided on frequently overlooked details and basic concepts of eddy covariance measurements. This guide draws together information from numerous academic sources to provide an easy to understand, objective overview of eddy covariance measurements.
Introduction to the Eddy Covariance Method
Although CO2/H2O analysis tends to focus on atmospheric CO2 and global climate change, there are many other applications that require CO2 and water vapor measurements. These include research, industrial, and management applications such as volcano monitoring, plant productivity research, greenhouse monitoring, in-door air quality monitoring, industrial process control, and others.
Common research fields that use CO2/H2O analysis are:
- Atmospheric monitoring
- Eddy covariance flux measurements
- pCO2/DIC measurements
- Photosynthesis measurements
- Soil CO2/H2O exchange
Common management and industrial processes that use CO2/H2O analysis:
- Industrial process control
- In-door air quality management
- Food quality control
- Fruit and vegetable storage
- Greenhouse control systems
- CO2 Sequestration and storage
- Semiconductor industry
As the lists above indicate, CO2/H2O analysis is used in a large variety of applications. No single analyser fits the diverse needs of this variety of applications.LI-7200 Enclosed CO2/H2O Gas Analyser: Combining the Best of Open and Closed Path Analysers - High Speed, High Precision, Low Power Consumption
CO2/H2O Gas Analysers, for Eddy Covariance Systems
When considering an analyser for your application, some things to consider include power requirements, response time, accuracy requirements, precision, and whether open or closed path is needed. In addition, some applications require the use of automated communications protocols and on-board data storage capacity. By addressing the needs of your application, you can choose the analyser that is best suited for your application. Contact us to learn more about how our CO2/H2O analysers can be used in your application.
pCO2/Dissolved Inorganic Carbonates Measurements
While it is possible to build your own pCO2 or Dissolved Inorganic Carbonates (DIC) system, it is not a trivial undertaking. Building a pCO2 system requires many sophisticated components, precise construction, access to expertise on a variety of topics, and knowledge of the materials that will be required. Research quality pCO2 systems are often designed following years of research and development. Whether to purchase or build depends on whether you have access to the expertise needed to build your own system or whether commercial systems meet your specific needs.
Scientists have studied the exchange of carbon dioxide between natural ecosystems and the atmosphere in remote rural areas around the globe for many years. Now, with the concern over increasing greenhouse gas emissions and industrial pollutants, many studies have been launched to understand the details surrounding urban carbon fluxes. By comparing the carbon dioxide and water vapor budgets of agricultural or natural ecosystems against those of urban areas, we can gain better insight into turbulent fluxes of heat, H2O, and CO2 in urban areas. This, in turn, will provide insight into the fate of urban air pollutants such as particulate matter, nitrogen oxides, and volatile organic compounds.
Pollution-related health problems for people that live in urban and high traffic areas are well documented, but information regarding the sources, sinks, and chemistry of air pollutants is less well defined. The Eddy Covariance technique has not been used much in this area historically, in part because of the complexity of system designs, implementation, and data processing. With this technology now available, urban CO2 and H2O fluxes, as well as fluxes of common urban air pollutants can be properly characterised. This data can be used to support current and future environmental policies.
The Eddy Covariance method, which is the most direct and defensible way to measure such fluxes, has been used for many years in the micrometeorology community. Modern instruments and powerful computational software are expanding the use of Eddy Covariance to a broad range of scientists including biologists, ecologists, and others who are interested in understanding urban flux.
Researchers around the world use LI-COR instruments for carbon cycle-related studies. The LI-7500A Open Path CO2/H2O Analyser is commonly used in Eddy Covariance measurements to determine the vertical carbon dioxide and water vapor fluxes over relatively large areas. LI-7000 CO2/H2O Analyser is also an excellent option for monitoring CO2 fluxes, especially in areas with high precipitation.
An important component in the overall carbon balance of urban areas is the impact that green spaces have on absorbing carbon through photosynthesis. Green roofs are an emerging trend among efforts to increase the beneficial impacts of live plants in urban areas. Green roofs have a positive impact on urban microclimates, but much like overall urban carbon fluxes, scientists have yet to characterise the impact of green roofs. The LI-8100 can be used to help quantify the effects of green roofs and other green spaces by measuring carbon exchange at the soil surface.
Although urban fluxes have been largely ignored until recently, the significant role that they have in the global carbon cycle cannot be ignored. As urban areas continue to expand around the globe, the importance of monitoring urban fluxes will expand as well.