Fifty Years of Balloon-Borne Ozone Research

In 1967, scientists launched a weather balloon from Marshall Mesa, in Colorado. The balloon carried a new instrument that could measure ozone levels from the ground to the edge of outer space — and radio the data back to a ground receiver. The instrument was an early version of today’s ozonesonde. This modest research project was undertaken out of curiosity to learn about the distribution of ozone– a trace gas that blocks the sun’s harmful ultraviolet rays in the stratosphere and protects us.

The project was started by the federal Environmental Science Services Agency (ESSA) which later became the National Oceanic and Atmospheric Administration (NOAA). The balloon-borne ozonesonde helped NOAA develop knowledge and expertise that enabled them to learn that ozone was depleting and the ozone layer above Antarctica had been particularly impacted by pollution. In May 1985, scientists with the British Antarctic Survey announced that they had discovered a huge hole in the ozone layer over Antarctica. The largest ozone hole area recorded to date was on September 9, 2000, at 11.5 million square miles (29.9 million square kilometers).

The Antarctica ozone hole was 9.3 million square miles (24.1 million square kilometers), in September 2013 and 2014. Photo credit: NOAA

Scientist Sam Oltmans’ first assignment was ozone research, when he started with ESSA in Boulder in 1969.

“At the time, we had very limited measurements of ozone in the atmosphere,” said Oltmans, a retired NOAA Global Monitoring Division scientist who continues to work with the agency. “We were just trying to get a basic understanding of what stratospheric ozone was like.  No one had the foggiest idea about stratospheric ozone depletion.”

Clues to the cause of the Antarctic ozone hole

When the discovery of the Antarctic ozone hole galvanized the international scientific community in the 1980s, ozonesonde measurements taken by NOAA in Boulder and at the South Pole were essential for scientists to make sense of observations from satellites, which could gather ozone readings from across large areas.

The first instrument to measure ozone – the Dobson spectrophotometer – was a ground-based device that measures the total amount of ozone in a column of the atmosphere above it, but not how it is distributed.  Like the Dobson spectrophotometer, early satellites could not resolve the distribution of ozone in the atmosphere. But the ozonesonde does.

An ozonesonde takes continuous readings from the ground to as high as the balloon can float before it pops – at about 130,000 feet altitude – producing a high-resolution, vertical record of ozone readings. This level of detail – and NOAA’s lengthy South Pole ozone data record – was critical for identifying the lower stratosphere as the region where chlorine atoms from chlorofluorocarbons, cold temperatures around the poles, and sunlight combined to destroy the ozone layer.

“Without balloon measurements, diagnosing the cause of the Antarctic ozone hole would have been extremely difficult, if not impossible,” said Chemical Sciences Division Director David Fahey, who co-chairs the scientific assessment panel for the Montreal Protocol on Substances that Deplete the Ozone Layer.

Today, scientists still use ozonesondes to validate and correct satellite data.

Ozonesondes are also widely used to study ground-level ozone pollution, which forms when sunlight bakes emissions from industrial and transportation sources.

NOAA’s ozonesonde now the world’s workhorse

CIRES scientist Patrick Cullis releases an ozone research balloon on the 50th anniversary of ozone research at Marshall Mesa south of Boulder. Credit: Theo Stein/NOAA

NOAA’s Walter Komhyr, who built the first prototypes used in the initial research project, later patented a design that pumps air into a small sensor that measures ozone levels via an electrochemical reaction. Over time, the ECC ozonesonde became the standard instrument for investigating the protective stratospheric ozone layer as well as for measuring harmful ozone pollution close to the ground. Three different companies have been licensed to manufacture the ozonesonde. Close to 100,000 have been made so far.

The knowledge gained from the government’s early ozone studies and the lengthy data set that it produced is a good example of why fundamental scientific research is so important,” said  James Butler, director of NOAA’s Global Monitoring Division.

“High-quality, scientifically driven, long-term records from measurement systems like these allow us to identify and understand changes in the Earth system,” Butler said. “This is true whether you’re talking about ozone depletion, pollutant transport, or climate change.”

Adapted in part by Sitara Maruf
Source: NOAA

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