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You can estimate the altitude of stratospheric ozone’s peak with a sky-pointed twilight photometer: a 620 nm LED detects changing twilight light, a high-gain circuit amplifies its signal, and a data logger records it for later analysis. The result is an experimental peak-height estimate—not a direct air sample, a complete ozone profile, or a measurement of total ozone.
What does “height of the ozone layer” mean?
The ozone layer is a region of the stratosphere where ozone is concentrated, not a solid sheet at one fixed altitude. NASA describes it as extending roughly 11–50 km (7–31 miles), while ozone’s vertical distribution varies with location and conditions. Stratospheric ozone helps protect life from ultraviolet radiation; ozone near the ground is a pollutant. See NASA Science’s ozone overview.
This project targets the altitude of the ozone concentration peak. The Make: article frames a peak around 25 km for the central United States, reports a 20–30 km range at the author’s Texas latitude, and notes thinning around 40 km. These are regional descriptions, not universal boundaries for the ozone layer. The estimate does not tell you how much ozone is in the entire atmospheric column.
How does a twilight photometer estimate the ozone peak?
The method infers altitude from changes in twilight light rather than measuring ozone in a sample of air. Before sunrise or after sunset, the instrument points straight up and tracks the changing illumination associated with the altitude of Earth’s shadow. A red LED rated at 620 nm acts as the light sensor. A very high-gain amplifier boosts its small signal, and a data logger records the output for analysis in spreadsheet software.
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- Collect the signal: Set the instrument up for an hour or more before sunrise or after sunset, pointing it vertically.
- Record the changing twilight: The LED’s response is amplified and stored by the logger.
- Analyze the trace: Interpret the recorded signal to estimate the ozone peak altitude.
For setup, the Make: article recommends choosing a site away from artificial lights, leveling the instrument, and preferring clear skies. It says thin clouds may still allow data collection, but clouds and aerosols can affect the trace.
What parts and tools does the build need?
The Make: project is a specialized electronics build, not just an LED connected to a meter. Its component list includes:
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- Printed circuit board and ADA4530 surface-mount electrometer amplifier
- 20 pF feedback capacitor, 0.01 μF capacitor, and optional 100 nF capacitor
- 620 nm red LED and a 5 GΩ or 10 GΩ feedback resistor
- 4-pin connector, 9 V battery and connector, switch, enclosure, bubble level, and wire
- Onset UX120 16-bit data logger with voltage sensor cable
The more elaborate optical arrangement uses Thorlabs lens tubes and a 150 mm lens; the article also describes a lower-cost option using a credit-card-sized Fresnel lens. Tools listed include a soldering iron, solder, desoldering wick, step drill, gloves, isopropyl alcohol, tweezers, pliers, and an illuminated magnifier. Check exact package and electrical specifications before substituting parts.
Make: estimated the project cost at $80–$350 in its July 28, 2026 article. This is the article’s estimate, not a current independently verified shopping total; component availability and prices can change.
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What do the measurements show, and what can interfere?
Make: reports Forrest M. Mims III’s observations, not a universal performance guarantee for all builds. While preparing the article, he reported a mean peak altitude of 25.13 km across 11 twilight ozone measurements. For one comparison on July 20, 2016, the photometer indicated a 25.3 km peak at Mauna Loa, while a balloon ozonometer launched from Hilo indicated 25.9 km—a reported difference of 0.6 km, or about 2.5%.
The author says aerosol interference makes the instrument more useful for estimating peak height than for reconstructing a complete vertical ozone profile; aerosol-driven fluctuations can affect traces. The reported results should therefore be read as the author’s experimental observations, not evidence that every amateur instrument will achieve the same agreement.
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How does the DIY method compare with established ozone measurements?
Different instruments answer different questions. The twilight photometer estimates a peak altitude from optical changes; established systems can sample ozone locally or measure it remotely across broad areas. The United Nations Environment Programme Ozone Secretariat describes both local and remote approaches in its 20 Questions and Answers.
| Method | What it measures | How it observes ozone | Coverage or constraint |
|---|---|---|---|
| DIY twilight photometer | Experimental estimate of peak altitude | Infers the peak from twilight optical signals; does not sample air | Requires careful setup and interpretation; aerosols can interfere, and it does not yield a complete profile |
| Balloon ozonesonde | Local ozone measurements at successive altitudes | Measures ozone as the balloon ascends | UNEP says ozonesondes can reach approximately 32–35 km |
| Satellite and other remote optical instruments | Total ozone or altitude distribution, depending on instrument | Use optical absorption methods to infer ozone remotely | Satellites measure ozone across much of the globe; other instruments provide vertical-distribution information |
A Dobson Unit (DU) is not a unit for peak altitude. It expresses the total ozone column above a location. NASA Ozone Watch says, “The Dobson Unit is the most common unit for measuring ozone concentration.” The page, last updated September 23, 2024, gives about 300 DU as an average total column and explains that this would form a compressed ozone layer about 3 mm thick. That compressed equivalent is not the ozone layer’s in-atmosphere thickness or peak height. See NASA Ozone Watch’s Dobson Unit explanation.
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