̽��ֱ�� of Cambridge - Neil Harris

High ozone levels in tropical Pacific caused by fires burning in Africa and Asia

sc604 — Wed, 13 Jan 2016 10:00:31 +0000

While efforts to limit emissions of greenhouse gases, including ozone, tend to focus on industrial activities and the burning of fossil fuels, a new study suggests that future regulations may need to address the burning of forests and vegetation. ̽��ֱ��study, published in the journal Nature Communications, indicates that ‘biomass burning’ may play a larger role in climate change than previously realised.

Based on observations from two aircraft missions, satellite data and a variety of models, an international research team showed that fires burning in tropical Africa and Southeast Asia caused pockets of high ozone and low water in the lower atmosphere above Guam – a remote island in the Pacific Ocean 1,700 miles east of Taiwan.

“We were very surprised to find high concentrations of ozone and chemicals that we know are only emitted by fires in the air around Guam,” said the study’s lead author Daniel Anderson, a graduate student at the ̽��ֱ�� of Maryland. “We didn’t make specific flights to target high-ozone areas – they were so omnipresent that no matter where we flew, we found them.”

For the study, two research planes on complementary missions flew over Guam measuring the levels of dozens of chemicals in the atmosphere in January and February 2014. One aircraft flew up to 24,000 feet above the ocean surface during the UK Natural Environment Research Council’s Coordinated Airborne Studies in the Tropics (CAST) mission. ̽��ֱ��other flew up to 48,000 feet above the ocean surface during the CONvective Transport of Active Species in the Tropics (CONTRAST) mission.

“International collaboration is essential for studying global environmental issues these days,” said CAST Principal Investigator Neil Harris, of Cambridge’s Department of Chemistry. “This US/UK-led campaign over the western Pacific was the first of its kind in this region and collected a unique data set. ̽��ֱ��measurements are now starting to produce insight into how the composition of the remote tropical atmosphere is affected by human activities occurring nearly halfway around the world.”

Researchers examined 17 CAST and 11 CONTRAST flights and compiled over 3,000 samples from high-ozone, low-water air parcels for the study. In the samples, the team detected high concentrations of chemicals associated with biomass burning—hydrogen cyanide, acetonitrile, benzene and ethyne.

“Hydrogen cyanide and acetonitrile were the smoking guns because they are emitted almost exclusively by biomass burning. High levels of the other chemicals simply added further weight to the findings,” said study co-author Julie Nicely, a graduate student from the ̽��ֱ�� of Maryland.

Next, the researchers traced the polluted air parcels backward 10 days, using the National Oceanic and Atmospheric Administration (NOAA) Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and precipitation data, to determine where they came from. Overlaying fire data from NASA’s moderate resolution imaging spectroradiometer (MODIS) on board the Terra satellite, the researchers connected nearly all of the high-ozone, low-water structures to tropical regions with active biomass burning in tropical Africa and Southeast Asia.

“ ̽��ֱ��investigation utilised a variety of models, including the NCAR CAM-Chem model to forecast and later analyse chemical and dynamical conditions near Guam, as well as satellite data from numerous instruments that augmented the interpretation of the aircraft observations,” said study co-author Douglas Kinnison, a project scientist at the ̽��ֱ�� Corporation for Atmospheric Research.

In the paper, the researchers also offer a new explanation for the dry nature of the polluted air parcels.

“Our results challenge the explanation atmospheric scientists commonly offer for pockets of high ozone and low water: that these zones result from the air having descended from the stratosphere where air is colder and dryer than elsewhere,” said ̽��ֱ�� of Maryland Professor Ross Salawitch, the study’s senior author and principal investigator of CONTRAST.

“We know that the polluted air did not mix with air in the stratosphere to dry out because we found combined elevated levels of carbon monoxide, nitric oxide and ozone in our air samples, but air in the higher stratosphere does not contain much naturally occurring carbon monoxide,” said Anderson.

̽��ֱ��researchers found that the polluted air that reached Guam never entered the stratosphere and instead simply dried out during its descent within the lower atmosphere. While textbooks show air moving upward in the tropics, according to Salawitch, this represents the net motion of air. Because this upward motion happens mostly within small storm systems, it must be balanced by air slowly descending, such as with these polluted parcels released from fires.

Based on the results of this study, global climate models may need to be reassessed to include and correctly represent the impacts of biomass burning, deforestation and reforestation, according to Salawitch. Also, future studies such as NASA’s upcoming Atmospheric Tomography Mission will add to the data collected by CAST and CONTRAST to help obtain a clearer picture of our changing environment.

In addition to those mentioned above, the study’s authors included UMD Department of Atmospheric and Oceanic Science Professor Russell Dickerson and Assistant Research Professor Timothy Canty; CAST co-principal investigator James Lee of the ̽��ֱ�� of York; CONTRAST co-principal investigator Elliott Atlas of the ̽��ֱ�� of Miami; and additional researchers from NASA; NOAA; the ̽��ֱ�� of California, Irvine; the California Institute of Technology; the ̽��ֱ�� of Manchester; the Institute of Physical Chemistry Rocasolano; and the National Research Council in Argentina.

This research was supported by the Natural Environment Research Council, National Science Foundation, NASA, and National Oceanic and Atmospheric Administration.

Reference:
Daniel C. Anderson et al. ‘A pervasive role for biomass burning in tropical high ozone/low water structures’ Nature Communications (2016). DOI: 10.1038/ncomms10267.

Inset image: Air Tracking. Credit: Daniel Anderson

Adapted from a ̽��ֱ�� of Maryland press release.

Study indicates ‘biomass burning’ may play a larger role in climate change than previously realised.

̽��ֱ��measurements are now starting to produce insight into how the composition of the remote tropical atmosphere is affected by human activities occurring nearly halfway around the world.

Neil Harris

Loretta Kuo/Shawn Honomichl

CONTRAST and CAST Mission Planes

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Pollution on the move – human activity in East Asia negatively affects air quality in remote tropical forests

sc604 — Tue, 31 Mar 2015 12:00:01 +0000

Researchers from the UK and Malaysia have detected a human fingerprint deep in the Borneo rainforest in Southeast Asia. Cold winds blowing from the north carry industrial pollutants from East Asia to the equator, with implications for air quality in the region. Once there, the pollutants can travel higher into the atmosphere and impact the ozone layer. ̽��ֱ��research is published today (31 March) in the open access journal Atmospheric Chemistry and Physics.

Rainforests are often associated with pure, unpolluted air, but in Borneo air quality is very much dependent on which way the wind blows. “On several occasions during northern hemisphere winter, pockets of cold air can move quickly southwards across Asia towards southern China and onward into the South China Sea,” said lead author Matthew Ashfold, who conducted the research while at the ̽��ֱ��’s Department of Chemistry, and who is now based at the ̽��ֱ�� of Nottingham Malaysia Campus.

In a new study, the researchers show that these ‘cold surges’ can very quickly transport polluted air from countries such as China to remote parts of equatorial Southeast Asia. ̽��ֱ��pollution travels about 1000 km per day, crossing the South China Sea in just a couple of days.

̽��ֱ��researchers were initially looking for chemical compounds of natural origin: they wanted to test whether the oceans around Borneo were a source of bromine and chlorine, compounds which can affect stratospheric ozone levels. They designed their experiments to measure these gases, but also detected another gas called perchloroethene, or perc, in the air samples they collected from two locations in the Borneo rainforest. Perc is a common ‘marker’ for pollution because it does not have natural sources.

In order to find out where the man-made gas came from, and where it might go, the researchers used a UK Met Office computer model of atmospheric transport to look back in time and determine where the collected air samples had travelled from. ̽��ֱ��experiments suggest the high levels of perc in the air samples were influenced by East Asian pollution.

Perc is produced in a number of industrial and commercial processes, such as dry cleaning and metal degreasing, and exposure to large amounts (above about 100 parts per million) can affect human health. While global emissions of perc have declined in the past 20 years or so, it is not clear whether this has been the case in East Asia, where air pollution has increased over the same period.

̽��ֱ��levels of perc measured in Borneo are low, at a few parts per trillion. But since the gas does not occur naturally, even small concentrations are a sign that other more common pollutants, such as carbon monoxide and ozone, could be present. Ozone, for example, can damage forests in high concentrations, as it reduces plant growth.

̽��ֱ��team’s measurements showed the amounts of perc varied strongly over the course of about a week, and models they analysed indicated this variation to be related to similar changes in carbon monoxide and ozone. During the one cold surge event the team studied in detail, levels of these pollutants over Borneo appeared to be double typical levels.

But diminished air quality in the remote rainforest is not the only way East Asia pollution affects the tropics. “ ̽��ֱ��atmosphere over Southeast Asia and the Western Pacific is home to unusually strong and deep thunderstorms during the northern hemisphere winter. Because of this, the region is an important source of air for the stratosphere,” said Ashfold.

In their study the researchers show that, once in the deep tropics, the polluted air is lifted towards the upper atmosphere. This can introduce a range of industrial chemicals with atmospheric lifetimes of just a few months to the stratosphere, which could have a potentially negative impact on the ozone layer.

“This work shows how quickly increasing pollution in southeast Asia can reach the Borneo rainforest, and even the upper atmosphere,” said Dr Neil Harris of the ̽��ֱ��’s Department of Chemistry, one of the paper’s co-authors. “It means that short-lived compounds, including some ozone-depleting substances, can reach the ozone layer within a couple of weeks. This effect could become more important if emissions of these pollutants continue to increase. At a simple level, it still amazes me how connected our atmosphere is.”

New analysis shows that pollution from human activity in East Asia is having a negative effect on air quality in tropical rainforests thousands of kilometres away, and could harm the ozone layer if levels continue to increase.

This work shows how quickly increasing pollution in southeast Asia can reach the Borneo rainforest, and even the upper atmosphere

Neil Harris

Ch'ien C. Lee

Borneo rainforest

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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