The issue has been controversial for many years, with some studies suggesting the self-cleaning power of the atmosphere is fragile and sensitive to environmental changes, while others suggest greater stability. And what researchers are finding is that the atmosphere’s self-cleaning capacity is rather stable.
Aidan Colton at NOAA\'s Mauna Loa Observatory (MLO) demonstrates how early flask samples were filled at the site. Air collected year-round at MLO and eight other remote sites
around the world has been analyzed for the industrial solvent methyl chloroform. Variability in the decay of this chemical has helped scientists understand the oxidizing or cleansing power of the global atmosphere and its sensitivity to natural and human-induced perturbations. (Credit: NOAA)
New analysis published online today in the journal Science shows that global levels of the hydroxyl radical, a critical player in atmospheric chemistry, do not vary much from year to year. Levels of hydroxyl, which help clear the atmosphere of many hazardous air pollutants and some important greenhouse gases — but not carbon dioxide — dip and rise by only a few percent every year; not by up to 25 percent, as was once estimated.
“The new hydroxyl measurements give researchers a broad view of the ‘oxidizing’ or self-cleaning capacity of the atmosphere,” said Stephen Montzka, the study’s lead author and a research chemist at the Global Monitoring Division of NOAA’s Boulder, Colo., laboratory.
“Now we know that the atmosphere’s ability to rid itself of many pollutants is generally well buffered or stable,” said Montzka. “This fundamental property of the atmosphere was one we hadn’t been able to confirm before.”
The new finding adds confidence to projections of future air pollutant loads. The hydroxyl radical, comprised of one oxygen atom and one hydrogen atom, is formed and broken down so quickly in the atmosphere that it has been extremely difficult to measure on global scales.
“In the daytime, hydroxyl’s lifetime is about one second and is present at exceedingly low concentrations,” said Montzka. “Once created, it doesn’t take long to find something to react with.”
The radical is central to the chemistry of the atmosphere. It is involved in the formation and breakdown of surface-level ozone, a lung- and crop-damaging pollutant. It also reacts with and destroys the powerful greenhouse gas methane and air pollutants including hydrocarbons, carbon monoxide and sulfur dioxide. However, hydroxyl radicals do not remove carbon dioxide, nitrous oxide or chlorofluorocarbons.
To estimate variability in global hydroxyl levels — and thus the cleansing capacity of the atmosphere — researchers turned to studying longer-lived chemicals that react with hydroxyl.
The industrial chemical methyl chloroform, for example, is destroyed in the atmosphere primarily by hydroxyl radicals. By comparing levels of methyl chloroform emitted into the atmosphere with levels measured in the atmosphere, researchers can estimate the concentration of hydroxyl and how it varies from year to year.
This technique produced estimates of hydroxyl that swung wildly in the 1980s and 1990s. Researchers struggled to understand whether the ups and downs were due to errors in emissions estimates for methyl chloroform, for example, or to real swings in hydroxyl levels. The swings would be of concern: Large fluctuations in hydroxyl radicals would mean the atmosphere’s self-cleaning ability was very sensitive to human-caused or natural changes in the atmosphere.
To complicate matters, when scientists tried to measure the concentration of hydroxyl radical levels compared to other gases, such as methane, they were seeing only small variations from year to year. The same small fluctuation was occurring when scientists ran the standard global chemistry models.
An international agreement helped resolve the issue. In response to the Montreal Protocol – the international agreement to phase out chemicals that are destroying the Earth’s protective stratospheric ozone layer – production of methyl chloroform all but stopped in the mid 1990s. As a result, emissions of this potent ozone-depleting gas dropped precipitously.
Without the confounding effect of any appreciable methyl chloroform emissions, a more precise picture of hydroxyl variability emerged based on the observed decay of remaining methyl chloroform. The scientists studied hydroxyl radicals both by making measurements of methyl chloroform from NOAA’s international cooperative air sampling program and also by modeling results with state-of-the-art models.
The group’s findings improve confidence in projecting the future of Earth’s atmosphere.
“Say we wanted to know how much we’d need to reduce human-derived emissions of methane to cut its climate influence by half,” Montzka said. “That would require an understanding of hydroxyl and its variability. Since the new results suggest that large hydroxyl radical changes are unlikely, such projections become more reliable.”
Co-authors of the new paper, “Small Inter-Annual Variability of Global Atmospheric Hydroxyl,” include Maarten Krol (University of Utrecht and Wageningen University in the Netherlands); Ed Dlugokencky and Bradley Hall (NOAA Earth System Research Laboratory); Patrick Jöckel (Max-Planck-Institute for Chemistry in Mainz, Germany, and the Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany); and Jos Lelieveld (Max-Planck and the Cyprus Institute in Nicosia, Cyprus).
NOAA’s mission is to understand and predict changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and to conserve and manage our coastal and marine resources. Find us online and on Facebook.
Jana Goldman | EurekAlert!
Devils Hole: Ancient Traces of Climate History
24.05.2017 | Universität Innsbruck
Supercomputing helps researchers understand Earth's interior
23.05.2017 | University of Illinois College of Liberal Arts & Sciences
Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.
The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....
An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.
We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.
In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...
24.05.2017 | Event News
23.05.2017 | Event News
22.05.2017 | Event News
24.05.2017 | Physics and Astronomy
24.05.2017 | Physics and Astronomy
24.05.2017 | Event News