1 Introduction
The estimation of greenhouse gas fluxes in the natural environment, human facilities and industrial activities is the basis for studying global climate change. Ecologists have done a lot of work in the process of greenhouse gas emissions and driving factors in forests, grasslands, wetlands, farmlands, waters and other natural landscapes; biologists have effectively explored the estimation of greenhouse gases in poultry fattening and breeding sites ; Greenhouse gas emission reduction in industrial production activities has become the focus of people to reduce environmental pollution.
The traditional greenhouse gas estimation mostly adopts on-site sampling and the laboratory adopts gas chromatography analysis method, which is time-consuming, random error is large, and accuracy is low.
2 Design of the observation system
2.1 Purpose
Greenhouse gases refer to the general name of the six gases specified in the Kyoto Agreement, including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (Hydrofluorocarbons (HFCs), perfluorocarbons Perfluorocarbons ( PFCs), Sulfur hexafluoride (SF6). The types of greenhouse gases that actually need to be monitored vary due to different estimates and research purposes. The AZ-M0510 greenhouse gas online observation system has become indispensable for ecological research, environmental restoration, farmland fertilization measures, animal nutrition research due to its real-time, online measurement, automatic recording, simultaneous measurement of 5 gases, and multiple greenhouse gas options. s method.
2.2 Layout of observation points
Open the gas sampling site as far as possible. For single-point measurement, the length of the sampling trachea is preferably within 150 meters. When using a multi-channel sampler, the length of the trachea does not exceed 50 meters.
When the instrument room is located in a small building (height does not exceed 5m), the height of the sampling air inlet from the roof plane should be 1.5m-2m.
When the instrument room is located in a large building (height exceeds 5m), the location of the sampling port should be selected on the windward side or the top of the building, and the height of the sampling air inlet from the roof plane should be appropriately increased.
When there are dense trees around, the height of the sampling air inlet should be more than 1m above the canopy height. At least in the 270 ° sector of the windward surface of the air inlet, the distance between the barrier and the sampling inlet is greater than 10 Times.
The size of the closed box can be customized according to the research needs.
The host of the AZ-M0510 greenhouse gas analyzer should be placed steadily, with a heat dissipation space not less than 0.1m around, and try to avoid other heat, vibration, electromagnetic interference and strong corrosion.
2.3 Sampling frequency
The AZ-M0510 greenhouse gas online observation system uses infrared photoacoustic spectrum measurement technology, and different gases can be measured by selecting different filters.
It takes 13 seconds to measure one gas and water vapor, and it can be completed in 40 seconds if five gases and water vapor are measured at the same time. The system can repeat measurement, up to 40 repeats, if it is 12-point measurement mode, each point can reach 3 repeats.
For single point measurement:
l Ensure that the sampling tube is preheated the day before the measurement
l Remove the sampling tube warm-up time, the equipment needs 30 minutes to warm up
l Discard the first ten concentration measurements
l Maximum pipe length 150m
l
For multiple point measurements:
l Ensure that the sampling tube is preheated the day before the measurement
l In addition to the preheating time of the sampling tube, the equipment needs 4 hours to warm up
l Repeat (three times)
l Discard the primary and secondary concentration measurements
l Maximum pipe length 50m
2.4 Observation content
The measurement gas types include hundreds of gases such as CO2, CH4, N2O, NH3, CO, SO2, H2S, TOC, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride SF6. The detection limit reaches ppb level.
Select up to 5 different filters (plus water vapor filter) at the same time, and measure 5 kinds of gas and water vapor at the same time.
2.5 System composition and technical indicators
The AZ-M0510 greenhouse gas flux online observation system consists of a host of photoacoustic spectrum greenhouse gas analyzer, a sampling tube, a multi-point sampler, and software. After configuration calculation, the measured value can be displayed on the spot in real time.
Technical index:
Host: Infrared photoacoustic spectroscopy technology, response time: one gas: ~ 13s, flushing: 5 gases + water vapor: ~ 27 s; detection limit: ppb level
Multi-point sampler: 12 channels
Closed box: customized size
Sampling tube: 150 meters
System software: The measurement results are displayed directly on the display and updated in real time. Real-time calculation of statistical data such as average value, mean square error, maximum and minimum concentration.
3 data processing
The gas flux in the closed box can be calculated according to the following formula
formula:
0-start time; f-end time; h-sampling measurement at a height h from the gas release surface
C (0), C (t), C (f)-gas concentration at the beginning (0), 0.5f, f
J (0) —— The gas flux at the beginning. According to this method, the gas flux at different times can be calculated.
4 Application case
4.1 Monitoring of contaminated soil to provide basic data for soil remediation.
4.2 The impact of Canadian N fertilizer application on greenhouse gas emission reduction
The project "Effects of Fixed N Fertilizer Application on Greenhouse Gas Emissions Reduction" funded by the Canadian Food and Agriculture Commission was chaired by Dr. R. Gary Kachanoski of the University of Alberta and conducted research on cultivated land in Canada. The project adopts the static box method and the photoacoustic greenhouse gas analyzer of the AZ-M0510 system to measure N2O and CO2 in real time at the sampling points of the static box method, and simultaneously measure the soil temperature and soil water content, and complete the following work:
In different soil types and climatic zones in Canada, quantify the greenhouse gas (N2O, CO2) flux under different fertilization conditions at existing fertilization sites. Combine the soil and crop data of these points into a public database to prepare for modeling. In addition, evaluate the potential impact of different fertilization measures on greenhouse gas emission reduction, and develop and test the random spatial scale theory of greenhouse gas flux in the field.
4.3 Determination of ammonia and greenhouse gases in farmland with pig manure applied: comparison of three methods
The project was chaired by the USDA-ARS Animal Waste Management Institute of the United States Department of Agriculture and compared the ammonia, greenhouse gas, and greenhouse gas emissions at the beginning, 72 hours, and 216 hours of the three fertilization methods (Row injection, Surface Spray injection, and Aerway injection).
The fluxes of ammonia and greenhouse gases (CO2, CH4 and N2O) (calculated by concentration) were measured using a closed box and a host-photoacoustic gas analyzer of the AZ-M0510 system. The closed box is 10cm high and made of aluminum. During each measurement, an anchor with a width of 38cm and a length of 102cm is embedded in the ground 15cm. The height of the exposed surface is 18cm. After the box is covered, the ammonia and greenhouse are measured with the AZ-M0510 host The gas concentration, the host is set to 1s sampling, 2s resides in the measurement chamber, 3s pumping, a measurement cycle (measurement of ammonia, CO2, CH4 and N2O and dew point temperature) time is 70s. There are two fans in the closed box for mixing gas before and during sampling. At the same time, the gas concentration in the air at a distance of 5 cm from the ground is also measured to see the effect of wind dilution and dissipation. In addition, the background gas concentration at the upwind and downwind of the sampling point is also measured. The Fickian diffusion model is used to calculate the gas flux.
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