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Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →A DIY twilight photometer can estimate the altitude of the ozone layer’s peak by recording changes in twilight light—not by sampling ozone directly. The project uses a red LED as a light sensor, a very high-gain amplifier and a data logger; its result is an experimental peak-height estimate, not a complete ozone profile or a total-column reading in Dobson Units.
What does “height of the ozone layer” mean?
The ozone layer is a region of the stratosphere where ozone is relatively concentrated, not a solid shell with a sharply defined top and bottom. NASA describes it as extending roughly 11–50 km (7–31 miles) above Earth, while the amount of ozone varies with altitude and location. Stratospheric ozone helps shield life from ultraviolet radiation; ozone near the ground is a pollutant. NASA Science explains the ozone layer and its role.
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A “peak height” is the altitude where ozone concentration reaches a maximum in a vertical distribution. It is not the same as the full vertical extent of the ozone layer or the total amount of ozone above a location. For context, NASA Ozone Watch says the average total ozone column is about 300 Dobson Units (DU). Compressed to standard temperature and pressure, that column would form a layer about 3 mm thick. NASA calls the Dobson Unit “the most common unit for measuring ozone concentration.” DU describes total column ozone, not the altitude of its peak. NASA Ozone Watch defines the Dobson Unit.
How does a twilight photometer estimate the ozone peak?
In the project by Forrest M. Mims III, published by Make: on July 28, 2026, the instrument points straight upward before sunrise or after sunset for an hour or longer. A 620 nm red LED is used as a light sensor. Its weak signal passes through a very high-gain amplifier, and a data logger records the output for later analysis in spreadsheet software. The changing twilight illumination reflects the movement of Earth’s shadow through the atmosphere; interpreting the trace can provide an estimate of the ozone peak’s altitude. The Make: project article describes the circuit and observing method.
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This is an indirect optical measurement: the instrument does not collect an air sample or detect ozone molecules one by one. The result depends on interpreting a twilight signal, so the author presents the method as useful for estimating peak height rather than reconstructing the complete vertical ozone profile.
What parts and tools does the build need?
The Make: bill of materials combines a sensitive analog circuit, optics, power and a logger. Its listed components include:
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- A printed circuit board and ADA4530 surface-mount electrometer amplifier.
- A 20 pF feedback capacitor, a 0.01 μF capacitor and an optional 100 nF capacitor.
- A 620 nm red LED and a 5 GΩ or 10 GΩ feedback resistor.
- A 4-pin connector, 9 V battery and connector, switch, enclosure, wire and bubble level.
- An Onset UX120 16-bit data logger with voltage sensor cable.
- For the higher-end optical arrangement, Thorlabs lens tubes and a 150 mm lens; the article also describes a lower-cost, credit-card-sized Fresnel lens option.
Assembly calls for a soldering iron and solder, desoldering wick, step drill, gloves, isopropyl alcohol, tweezers, pliers and an illuminated magnifier. The author estimates the project at $80–$350 in the 2026 article; this is an article estimate, not a current independently verified shopping total. Check component packages and electrical specifications before choosing substitutes, particularly for the high-value resistor and amplifier.
How should you collect a twilight trace?
- Choose a dark, open observing site. Set up away from artificial lights so they are less likely to contaminate the sky signal.
- Level and aim the instrument. Use the bubble level and point the optical assembly straight up.
- Observe near twilight. Record continuously for an hour or more before sunrise or after sunset, as described in the Make: project.
- Prefer clear conditions. Mims says thin clouds may still permit data collection, but clouds and aerosols can affect the trace.
- Review the logger data afterward. Use spreadsheet software to examine the changing signal and estimate the altitude associated with the ozone peak.
What do the reported measurements show?
The Make: article frames a peak near 25 km for the central United States and notes a 20–30 km range at the author’s Texas latitude. These are regional observations and context, not fixed boundaries or a universal peak altitude.
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Mims reports a mean peak of 25.13 km across 11 twilight ozone measurements made while preparing the article. He also reports one comparison at Mauna Loa on July 20, 2016: the photometer’s estimated peak was 25.3 km, while a balloon ozonometer launched from Hilo gave 25.9 km. The 0.6 km difference—about 2.5% of the balloon value—applies to that reported comparison only. These are the author’s observations as reported in Make:, not a general validation guarantee for every amateur build.
The article describes ozone thinning around 40 km in its regional framing. That observation should not be read as the top of the ozone layer; NASA’s broader description extends through roughly 50 km, and the vertical distribution varies.
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What can interfere with the estimate?
Mims identifies aerosols as a source of interference and notes that aerosol-driven fluctuations affect traces. Clouds and artificial light are also practical observing concerns. A trace may therefore be noisy or difficult to interpret even when the electronics are assembled correctly. The author’s reported results do not establish how accurately every build will perform under different skies, locations or assembly conditions.
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How does this DIY method differ from established ozone measurements?
Different instruments answer different questions. The UN Environment Programme’s Ozone Secretariat describes both local and remote approaches to ozone monitoring. Its ozone measurement overview outlines local and remote techniques.
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| Method | What it measures | How it observes ozone | Coverage or constraint |
|---|---|---|---|
| DIY twilight photometer | Experimental estimate of peak altitude | Infers a peak from changing twilight optical signals; does not directly sample air | Ground-based observation; sensitive to aerosols and observing conditions |
| Balloon ozonesonde | Ozone at successive altitudes along the balloon’s ascent | Samples local atmospheric air while rising | UNEP says ozonesondes can reach approximately 32–35 km; a launch samples a limited location and time |
| Satellite optical instruments | Total ozone or ozone distributions, depending on the instrument and technique | Uses optical absorption methods to observe ozone remotely | Can measure ozone across much of the globe; remote coverage differs from a local balloon profile |
The twilight project is valuable as an accessible atmospheric observation experiment, but it is not a replacement for routine monitoring. Ozonesondes provide local vertical sampling, while satellites and other remote instruments contribute broad-area or vertical-distribution measurements. A total-column DU value answers yet another question: how much ozone lies in the column above a location, not where its peak sits. UNEP’s overview discusses balloon and satellite measurement approaches; NASA Ozone Watch explains total-column Dobson Units.
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