Optical measurement of atmospheric carbon dioxide

Team members

Ta Na

Cao Yuan

Gao Yihan

Qi Kaiyi

Chen Yiming

Idea

Climate change has already become one of the most important challenges humanity faces. Carbon dioxide, the major greenhouse gas, is 'heating up' the Earth's atmosphere as they have an absorption peak in infrared wavelengths.

This project aims to build a portable and accurate carbon dioxide concentration measurement device.

Possible measurement mechanisms

1. Spectroscopy. Carbon dioxide has absorption peaks at 15, 4.3, 2.7 and 2 μm. With a laser/source of such wavelength and the correct filter, we could judge the concentration by absorption levels. See viasala for inspiration of a potential real-time reference design.
2. Interferometry. Carbon dioxide has a slightly different refraction index for all wavelengths. By observing the change in interference patterns, we can tell if there is a change in carbon dioxide concentration due to a change in effective path length.

In the end we chose single-wavelength spectroscopy, i.e. absorbance measurement to measure the CO₂ content.

Experiment process

Components

• Light source:
  • A thermal/blackbody radiation/light source that can emit EM radiation at 4 micrometers. Done with a 12W halogen lamp, mounted on an IKEA SVALLET lamp stand.

• Sensor:
  • Thermopile detectors: G-TPCO-035 / TS418-1N426: Thermopile detector with a built-in optical bandpass filter for light around 4μm wavelength for CO₂ absorption
  • multimeter

• Gas chamber:
  • airtight acrylic box surrounding all optical components (chosen)
  • metal (stainless steel) extrusion with hollow structures sealed with transparent SiO2 cover glass (chosen)
  • gas chamber with specific materials (Si/SiO2) transparent to 4 micrometer wavelength

• Power supply and micellaneous electronics
  • banana wires

• CO₂ source
  • bottled CO₂
  • dry ice

• to look up
  • extinction coefficient of CO₂

Measurements

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