Measuring CO₂
Carbon emissions versus carbon concentrations
Carbon dioxide (CO2) is measured all around the world for climate change research. When we measure CO2 we are measuring the concentrations, not the emissions. Carbon emissions and carbon concentration are both about quantifying carbon but they mean different things. Carbon emissions is the amount of carbon (usually as CO2) that is being released into the air. This happens when we burn things like coal, oil and gas or through activities like cutting down trees. The concentration is the amount of CO2 in proportion to the total volume of the air.
Measuring CO2
CO2 concentration is measured in the parts per million (ppm). If the concentration is 415 ppm, this means that, for every million molecules of air, 415 of them are CO2 (415/1,000,000). Because of the changing atmospheric mixing, figuring out emissions from measurements of CO2 concentration can be complicated. For example, emissions in the morning are into a smaller volume of air than emissions in the afternoon when the atmospheric boundary layer is lower in the sky and the concentration of CO2 measured will be larger.
In Auckland, scientists from GNS Science and NIWA are measuring CO2 concentrations around the city as part of the CarbonWatchNZ and CarbonWatch-Urban projects.
How do you measure CO2?
Scientists use several methods and tools to help determine the concentration of different gases. Here are some ways scientists can measure atmospheric concentration of CO2:
Remote sensing – for example, the use of drones or satellites to measure gases from the sky.
Gas collection flasks – samples of the air are collected in flasks for analysis. (This is one of a number of methods used at the NIWA Baring Head facility in New Zealand. You can see the flasks in the video Journey of the greenhouse gas data.)
Gas analysers – these measure gases directly using light such as infrared sensors and spectroscopy techniques.
Each method has its own advantages and is chosen based on where it’s being measured and how accurate the results need to be.
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