̽��ֱ�� of Cambridge - Centre for Atmospheric Science

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

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New research highlights the key role of ozone in climate change

sc604 — Mon, 01 Dec 2014 15:02:33 +0000

Many of the complex computer models which are used to predict climate change could be missing an important ozone ‘feedback’ factor in their calculations of future global warming, according to new research led by the ̽��ֱ�� of Cambridge and published today (1 December) in the journal Nature Climate Change.

Computer models play a crucial role in informing climate policy. They are used to assess the effect that carbon emissions have had on the Earth’s climate to date, and to predict possible pathways for the future of our climate.

Increasing computing power combined with increasing scientific knowledge has led to major advances in our understanding of the climate system during the past decades. However, the Earth’s inherent complexity, and the still limited computational power available, means that not every variable can be included in current models. Consequently, scientists have to make informed choices in order to build models which are fit for purpose.

“These models are the only tools we have in terms of predicting the future impacts of climate change, so it’s crucial that they are as accurate and as thorough as we can make them,” said the paper’s lead author Peer Nowack, a PhD student in the Centre for Atmospheric Science, part of Cambridge’s Department of Chemistry.

̽��ֱ��new research has highlighted a key role that ozone, a major component of the stratosphere, plays in how climate change occurs, and the possible implications for predictions of global warming. Changes in ozone are often either not included, or are included a very simplified manner, in current climate models. This is due to the complexity and the sheer computational power it takes to calculate these changes, an important deficiency in some studies.

In addition to its role in protecting the Earth from the Sun’s harmful ultraviolet rays, ozone is also a greenhouse gas. ̽��ֱ��ozone layer is part of a vast chemical network, and changes in environmental conditions, such as changes in temperature or the atmospheric circulation, result in changes in ozone abundance. This process is known as an atmospheric chemical feedback.

Using a comprehensive atmosphere-ocean chemistry-climate model, the Cambridge team, working with researchers from the ̽��ֱ�� of East Anglia, the National Centre for Atmospheric Science, the Met Office and the ̽��ֱ�� of Reading, compared ozone at pre-industrial levels with how it evolves in response to a quadrupling of CO2 in the atmosphere, which is a standard climate change experiment.

What they discovered is a reduction in global surface warming of approximately 20% – equating to 1° Celsius – when compared with most models after 75 years. This difference is due to ozone changes in the lower stratosphere in the tropics, which are mainly caused by changes in the atmospheric circulation under climate change.

“This research has shown that ozone feedback can play a major role in global warming and that it should be included consistently in climate models,” said Nowack. “These models are incredibly complex, just as the Earth is, and there are an almost infinite number of different processes which we could include. Many different processes have to be simplified in order to make them run effectively within the model, but what this research shows is that ozone feedback plays a major role in climate change, and therefore should be included in models in order to make them as accurate as we can make them. However, this particular feedback is especially complex since it depends on many other climate processes that models still simulate differently. Therefore, the best option to represent this feedback consistently might be to calculate ozone changes in every model, in spite of the high computational costs of such a procedure.”

“ ̽��ֱ��results reported here do not imply that climate change ceases to be an issue: rather that the sorts of impacts predicted by recent UN IPCC reports for later this century may be delayed - and even then by only by a few years,” said Dr Manoj Joshi of the ̽��ֱ�� of East Anglia, one of the paper's co-authors.

“Climate change research is all about having the best data possible,” said Nowack. “Every climate model currently in use shows that warming is occurring and will continue to occur, but the difference is in how and when they predict warming will happen. Having the best models possible will help make the best climate policy.”

̽��ֱ��models which are used to predict how climate change will occur could be much improved by including the key role of ozone, which is often overlooked in current models.

These models are the only tools we have in terms of predicting the future impacts of climate change

Peer Nowack

Wisconsin Department of Natural Resources via flickr

Milkweed with Ozone Damage

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Unclouding uncertainty in climate modelling

bjb42 — Fri, 01 May 2009 00:00:00 +0000

Our climate is the net result of many complex processes that transfer and redistribute the Sun’s energy through the Earth’s atmosphere, oceans, land and ecosystems. Because these processes are basically nonlinear, their interaction unavoidably leads to chaotic variability of climate and weather on various time scales, and we rely on climate models to achieve some sense of the dynamics of weather and to predict future climate. Currently, one of the greatest sources of uncertainty in climate modelling is posed by clouds, which are not resolved individually but instead are averaged. Professor Hans-F. Graf’s group, based in the Department of Geography and part of the Centre for Atmospheric Science (see panel), is developing a new technique for global and regional climate modelling that moves beyond treating clouds as ‘one-size-fits-all’.

Cloudy issues

Climate models consist of a set of coupled differential equations based on first principles of physics that are solved numerically by dividing the planet into a three-dimensional grid. Available computer power dictates that each grid is typically 100–300 km in size. Unfortunately, any processes that are smaller cannot be explicitly resolved and have to be ‘parameterised’ as an average. Among these are clouds: the standard approach has been to create an average cloud that has to mimic all the effects of the cloud spectrum of different-sized convective clouds. Of course, in nature, the cloud spectrum is highly variable depending on the actual weather situation and location, and clouds can range from a few hundred metres to a few kilometres in scale.

Clouds are extremely important for realistic model simulations since they are the ultimate drivers of the global atmospheric circulation. Water vapour carrying latent heat is transported upwards by convection or in large weather systems (fronts), where it cools and eventually forms clouds; precipitation as rain then releases the latent heat. This convection is strongest in the tropics, where the vapour-laden trade winds from both hemispheres converge, forming deep, rain-producing convective clouds. It is here that the atmosphere receives the energy that drives the whole global circulation.

Clouds are also highly relevant to changes in climate that result from human activities. Changes in land use affect reflectivity and evaporation from soil and vegetation, and hence the transfer of energy to the atmosphere; fossil fuel burning and industrial processes increase aerosols that reflect sunlight or absorb solar and terrestrial radiation. Both land use change and aerosols have an effect on cloudiness and precipitation at both the local and the micro scale.

Predator–prey

̽��ֱ��innovative approach adopted by Professor Graf’s group has been to simulate the behaviour and microphysics of convective clouds using a concept more familiar within population dynamics: they treat clouds as individuals that compete for food.

This technique allows the separation of individual clouds from a larger set of clouds that can potentially evolve under a given weather situation (that is, at a specific time and in a specific grid cell of the model). ̽��ֱ��system is based on the solution of a set of Lotka–Volterra-type differential equations, also known as predator–prey equations from their use for describing biological systems: the clouds (the ‘predators’) have a limited ‘food’ supply of convective available potential energy (the ‘prey’, this being the amount of energy available for convection), for which clouds of different characteristics (size, depth) are competing.

By capturing the variations of cloud spectra in a statistical sense, cloud microphysics can be treated explicitly and it is now possible to determine in-cloud vertical velocities, interactions with aerosols, convective transport, rainfall intensity and radiation effects.

Forest fires and volcanic ash

̽��ֱ��team has been focusing on a variety of different types of cloud – most notably the effects of smoke on clouds and precipitation over Amazonia and Indonesia. Initially funded by the European Union, the project is now contributing to the Danum-OP3 consortium that spans eight UK institutions and is funded by the Natural Environment Research Council (NERC) to investigate the effects of the replacement of pristine rain forest by oil palm plantations in northern Borneo. Recently published data show how the smoke from the extreme peat fires that plagued Indonesia and surrounding countries for months during 1997–8 reduced the amounts of rainfall in the area. ̽��ֱ��reduced rainfall, in turn, increased the residence time of the smoke particles in the atmosphere, thus aggravating the situation.

A second focus has been the development and application of the Active Tracer High-resolution Atmospheric Model (ATHAM). ̽��ֱ��development of this high-resolving model started immediately after the eruption of the Mount Pinatubo volcano on the Philippines in the early 1990s, when Professor Graf was at the Max Planck Institute for Meteorology in Hamburg. ̽��ֱ��model simulates convective plumes at resolutions down to a few tens of metres and was initially used to understand the dynamic, microphysical and chemical processes within volcanic eruption plumes. An important question was whether these vigorous convective systems could effectively transport magmatic halogen compounds into the stratosphere, where they could harm the ozone layer. ̽��ֱ��model has also been used successfully to simulate big fire storms induced by wild fires, and the results have proved that pollutants from these fires are introduced into the lower stratosphere.

Further applications of ATHAM are under current investigation by Dr Michael Herzog in Professor Graf’s group, particularly in relation to aviation safety. Fine silicate ash from volcanic eruptions poses a severe risk for aeroplanes. Although ash clouds can be detected by satellite monitoring, they are often obscured by ice particles residing above the ash, and ATHAM can be used to predict whether ice is formed within a volcanic plume. Further plans with ATHAM are ongoing with support from a joint Chinese–German research project that will study the effects on weather and climate in Southeast Asia resulting from the dramatic changes of land use and ecology on the Tibetan plateau during the past 60 years.

For more information, please contact the author Professor Hans-F. Graf (hans.graf@geog.cam.ac.uk) at the Department of Geography.

New understanding of the physics of clouds is helping to model both climate change and the impact of volcanic eruptions and wild fires.

Professor Graf’s group has simulated the behaviour and microphysics of convective clouds using a concept more familiar within population dynamics: they treat clouds as individuals that compete for food.

Flickr - Marsha Jorgensen

Clouds 1 - free to use

Centre for Atmospheric Science

̽��ֱ��Centre for Atmospheric Science is one of the premier groups in the UK for atmospheric studies. It encompasses research in three departments:

Department of Chemistry: Numerical modelling of tropospheric and stratospheric chemistry/climate (Professor John Pyle), instruments and measurements (Professor Rod Jones), measurements of gas kinetics (Dr Tony Cox) and studies of atmospheric aerosols (Dr Markus Kalberer).
Department of Applied Mathematics and Theoretical Physics: Investigation of fundamental aspects of atmospheric dynamics and physical processes (Professors Peter Haynes and Michael McIntyre).
Department of Geography: Research on convection, modelling plumes and stratospheric dynamics (Professor Hans-F. Graf and Dr Michael Herzog).

̽��ֱ��Centre is co-directed by Professor John Pyle and Professor Peter Haynes. For more information, please contact Professor Haynes (P.H.Haynes@damtp.cam.ac.uk) or visit www.atm.ch.cam.ac.uk

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