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25 Years of Atmospheric Measurements

During May 1988 I began measuring solar UV-B using a homemade instrument that detected a sharp decline in UV-B during September 1988 when smoke from the massive Yellowstone fires drifted over Texas. By the end of 1989 I had completed work on a 4-channel sun photometer that used light-emitting diodes as spectrally selective photodiodes. I was also working on TOPS (Total Ozone Portable Spectrometer), a 2-channel UV instrument to measure the ozone layer.

On February 4, 1990, I began making daily measurements at solar noon of the ozone layer. I also continued using the LED sun photometer to measure haze (aerosol optical depth or AOD) and total column water vapor. The latter two parameters were measured with LEDs that detected at 830 nm and 940 nm. AOD was measured at 830 nm and water vapor by the ratio of the two LED signals.

The 25 years of data acquired thus far are shown in the time series plots below. The ozone plot shows the annual variation and a sharp decline in total ozone during the mid-1990s, a phenomenon also measured by the TOMS instrument aboard NASA’s Nimbus-7 satellite. The volcanic eruption of Mt. Pinatubo on June 15, 1992, played a role in the decline. Solar UV-B increased appreciably before the ozone layer began recovering. The ozone is now very close to what  it was prior to 1991. The AOD chart shows the annual variation. Sharp upward spikes are from major aerosol events, including Saharan dust from Africa, smoke from Mexico and sulfate pollution from power plants in the Tennessee and Ohio Valleys. The water vapor data show a sharp increase in 1997-98 associated with a major El Nino. Of interest is that no increase was associated with the El Nino of 2015-16. The NWS forecasts of a cold, damp winter for Texas were also unfilled.

The ozone measurements were made with a succession of 3 instruments and the AOD and water vapor measurements with the original LED sun photometer. Relevant publications are given at my main web site.


The 1954-56 drought in Texas is nicely recorded in these rings from a century old baldcypress (Taxodium distichum) that once grew along the Guadalupe River.

About Forrest M. Mims III

I have worked as a freelance writer and photographer since 1970. I also design, build and use a variety of atmospheric monitoring instruments and have consulted or performed field work for NOAA, NASA (GSFC and LaRC), National Geographic Society, EPA, USDA (through Colorado State University), GLOBE, TERC and the Concord Consortium.

My main website is Some of the science I do is at the main site and also at

My Radio Shack books are available from Master Publishing at and The Amazon site also includes some of my non-Radio Shack books.

“Hawaii’s Mauna Loa Observatory: Fifty Years of Monitoring the Atmosphere” (University of Hawaii Press, 1912) is available from Amazon and

The photo above shows the rings of a century old baldcypress (Taxodium distichum) that stood on the bank of the Guadalupe River in Central Texas until downed by a major flood in 2002. The rings clearly show the impact of the drought of 1954-56.