For those with a keen eye, you may have spotted a red balloon soaring high above the EGU Centre this week. The little white box attached underneath is the Light Optical Aerosol Counter (LOAC), a device that has been measuring the aerosols it the air around the conference.

LOAC hangs from the red balloon outside the EGU. Picture Courtesy: Eric Hamonou.

Aerosols are air borne particles that can be liquid or solid, natural or manmade. Salt, fog, sand, plaster and carbon are common aerosols found in the air.

Studies have shown particles less than 2.5 micrometres (mm) and 10 mm can be detrimental to human health as they are small enough to get into your lungs and enter your cells. An average human hair for example is about 200 mm. Regulations set thresholds for the amount of a particular particle size that should be in the air we breathe.

LOAC is an optical instrument that sends a beam of light through particles and the way the light scatters determines the size and shape. From this, the scientists can work out if the aerosol is carbon, mineral or liquid.

EGU GeoLog reporters managed to catch up with Jean-Baptiste Renard to explain his experiment this week…

So what did you find in the air around the EGU?

Indoor air pollution was worse than outside. On Wednesday as it was too windy outside to fly; we flew the balloon in the exhibition hall. Particle levels sized10 mm (the dangerous kind) were at least five times more inside, almost reaching the threshold of alert levels.

Results from the indoor flight – minerals are reaching threshold levels. Graphs: Jean-Baptiste Renard.

These particles come from our clothes, in our hair, the dirt we scuff on the floor, is all lifted back up into the air. We are full of dust!

Outside, the concentration changed a lot during the day. In the morning there was a lot of carbon measured, possibly from the traffic that you would expect in a big city or the direction of the wind.

Measurements in the afternoon showed more mineral particles. This may be because of all of the building work going on in the towers on the right of the conference centre entrance. Every time someone uses a saw or hammer, tiny particles are produced and we can measure them in the air.

In the morning there is more carbon, and in the afternoon more minerals. Graphs: Jean-Baptiste Renard.

But won’t they measure the same – on the ground or in the sky?

No – the ground level concentration of aerosols can be completely different to 100 meters in the air. The higher you are, the greater more mixture of aerosols you find because up there, the particles that have been transported from elsewhere. At ground level, it is much more localised and the aerosols present are specific to what is close by.

Is that what’s so great about LOAC, you can put it on a balloon?

The key to LOAC is that it is airborne. As it is so small and lightweight, it can be attached to any kind of balloon. Before, the instruments had to be attached to planes or much larger balloons. Now, we can accurately trace if particles are locally produced or if the conditions in a small area, say on a specific street, are reaching an unhealthy threshold.

Being able to measure particles less than 1 mm is also totally new. We can distinguish between aerosols too. Before LOAC, instruments had to be set to detect a certain particle in the air, say salt. You would need to calibrate to look for salt. If there were no particles in the air, there would be no results, but now we can use one piece of equipment for multiple measurements, we can always collect data!

 by Becky Summers, City University, London

video by Sue Voice, University of Otago

New results presented this week at the EGU General Assembly have scientists adjusting the assumptions that have longed acted as bookends on the way we understand the evolution of planetary atmospheres. On one side, researchers have identified a previously unrecognised greenhouse effect that could have warmed the early Earth. On the other, the Curiosity rover has uncovered evidence that Mars has lost up to 95% of its original atmosphere, resolving a lost-standing discrepancy between previous estimates and confirming that conditions in the past could have been much more hospitable to life than they are today. Together, these new insights show how humble gases like hydrogen, nitrogen and argon hold the key to some of the great mysteries of the universe.

Source: Wikimedia Commons.

The early Earth continues to fascinate our imaginations, evoking images of seething volcanoes and fiery meteorites raining down on barren landscapes. It also continues to confound efforts by scientists to understand a seemingly straightforward question: how come the entire planet was not swaddled in ice? In 1972, the famous cosmologist, Carl Sagan and his colleague, George Mullen, posed what came to be known as the Faint Young Sun Paradox: if our sun is like other stars, it should have been about 30% weaker 4 billion years ago than it is today. Such a dimming of our solar furnace should have plunged our planet into global glaciation. But among the few pieces of geologic evidence to survive from the early Earth are unequivocal signs of liquid water. How can this be?

Researchers have proposed numerous mechanisms to warm the Earth, including insulating it with high levels of greenhouse gases or reducing the amount of solar radiation reflected back to space by small, young continents. Both hypotheses have merit, but they have also been plagued by complications. New work by Robin Wordsworth and Raymond Pierrehumbert at the University of Chicago presented at EGU on Tuesday raises yet another possibility: the very different composition of the early atmosphere may have allowed inert gases like H₂ and N₂ to act like powerful greenhouse gases.

The modern atmosphere lacks hydrogen because these light molecules easily defy Earth’s gravitational pull and escape into space. However, this loss takes time, and Wordsworth believes that the atmosphere could have been rich in hydrogen 3.8 billion years ago, the era of the Faint Young Sun. At this time, the atmosphere also contained two to three times more nitrogen than today — an inference deduced by the abundance of nitrogen now stored in the Earth’s mantle that does not appear to have originated there. Full of H₂ and N₂, the atmosphere could have experienced some unexpected phenomena.

The atmosphere allows most incoming solar radiation to reach the surface, but traps outgoing radiation in the bands of shaded grey. Most of the long wave radiation that cools the Earth escapes through the “water vapor window” centered around 10 um. Source: Wikimedia Commons.

H₂ and N₂ do not absorb radiation on their own, but at high concentrations they can act like greenhouse gases when they interact. “There are two basic processes,” explains Wordsworth, “first, H­-N₂ dimers can have additional vibrational and rotational modes, and allow for absorption in new regions of the spectrum. You can also have intense collisions between molecules that can allow previously forbidden transitions to occur.” The end result is that H₂-N₂ interactions can allow absorption at frequencies inside the so-called water vapor window, a region of the spectrum where outgoing radiation can escape to space and cool the Earth without being trapped by water vapor, the most abundant greenhouse gas of all. For this reason, says Wordsworth, “a little bit of absorption can have a big effect.”

In the conditions likely to have prevailed on the early Earth, their new study suggests the H₂-N₂ effect could account for 10-15°C of warming. And while this is not enough to explain the Faint Young Sun Paradox by itself, it can help if several mechanisms are allowed to work in tandem. As is often the case in nature, there may be no single “smoking gun”. In fact, Wordsworth thinks it may be time to shift how we think about the Faint Young Sun Paradox altogether. “The Faint Young Sun problem is important as a motivation for studying the early Earth”, he says, “but there is also the broader, more long-term aim of just understanding what the climate was like”.

The habitable zone is defined as the range of distances from a host star that planets could be warm enough to host life. Source: Wikimedia Commons.

With this expansive mindset, Wordsworth has also started extending the H₂-N₂ mechanism beyond our own planet to understand what conditions might be like on exoplanets and whether or not they could host life. “The habitable zone is defined as a runaway water vapor greenhouse on the inner edge and the maximum possible greenhouse you can have from CO₂ alone on the outer edge,” says Wordsworth of the traditional conception of planets where life might thrive. In light of this new greenhouse effect, the definition of the outer edge has grown blurry; planets that once seemed frigid could now be balmy. Now, he says, “You can have a greenhouse that is very efficient at warming very far away from the host star”.

But you don’t have to look all the way to exoplanets to find a place where the H₂-N₂ effect might have significant implications; Mars presents a great opportunity closer to home. While Wordsworth was unable to comment on the details of this situation, he confirmed that such a mechanism could indeed be important. “Thinking of additional greenhouse effects that we’ve ignored is very important for early Mars because the Faint Young Sun problem is much harder to explain there. There’s a lot of thinking going on at the moment about how we can get to situations where we increase surface temperatures so you get transient periods of liquid water or episodic melting.”

Surish Atreya of the University of Michigan, on the other hand, was eager to share new results about the modern Martian atmosphere at an EGU press conference showcasing updates from the Curiosity rover on Monday. Curiosity carries a suite of instruments onboard collectively known as SAM, for Sample Analysis at Mars. One of these instruments is a mass spectrometer that recently measured the ratio of heavy and light isotopes of argon in the Martian atmosphere (isotopes are molecules which differ in the numbers of neutrons and their atomic weight). Their new results, which achieve unprecedented precision for an argon measurement on Mars, help clear up a long-standing question: how much of its atmosphere has Mars lost over time?

New results from the Curiosity rover show argon ratios that indicate that Mars has lost most of its original atmosphere. Source: NASA/JPL-Caltech

“Argon isotopes are the clearest indication of atmospheric loss”, explained Dr. Atreya. This is because Argon does not participate in any reactions – it is an inert noble gas – so any deviation from the expected ratio must be due to preferentially losing the light isotope to space. Previous measurements from the early Viking rover and from Martian meteorites gave conflicting results, suggesting Mars could have lost all or none of its atmosphere. The new results from SAM show that Mars has probably lost 85-95% of its original atmosphere, a conclusion supported by similarly disproportionate abundances of the heavy isotopes of carbon and oxygen. While these results are not proof of life on Mars, they at least suggest that conditions could have been much friendlier early in the planet’s history when its atmosphere was thicker.

Together, these studies show how simple gases like hydrogen and nitrogen may have shaped the evolution of our planet, and how argon may contain the secrets of another. They reveal how much a planet can change over its history, and how we might need to rethink the way we understand planets far from home. All in all, it seems as though the universe has been, and might be, growing more hospitable by the day.

By Julia Rosen, Freelance science writer and PhD student in Earth, Ocean, and Atmospheric Sciences at Oregon State University

I’ve been ruminating over the idea for this post for some time now; since last October in fact, when the EGU Twitter Journal Club discussed a paper about tagging (You can find the Storify for the discussion here). Not tagging as in the playground favourite, but the idea of keeping track of certain molecules in your chemical transport model, so you can follow them as they move through the atmosphere and undergo chemical transformations.

I’ve decided to offer my opinion on tagging, which I’ve come to through after much deliberation; reading, listening and discussing the topic with colleagues. I thought this might be of general interest, as the concept of tagging frequently sparks debates (in my experience) and seems to arouse stronger and more varied views than I would usually expect from a modelling technique. So with this post, I want to answer the question “what is tagging and what is it used for?” and at least attempt to answer “why does it generate such mixed feelings?”.

I think that the answer to the second may lie in the answer to the first, so let’s start with that. One way of describing tagging is as an accounting method. Doesn’t sound very geophysical? Well, we’re talking the model world here, and we can keep track of – or account for – every little thing we do in our model world. To try and understand the composition of the Earth’s atmosphere, people have constructed computer models to describe both the physical and chemical processes in the atmosphere. I’m particularly interested in trace gases like ozone, which is found in parts-per-billion quantities in the troposphere (roughly the lowest 10-15 km of the atmosphere). Tropospheric ozone is a popular species to study, as it is a greenhouse gas, it’s bad for human and plant health, and it’s one of the key oxidants in the atmosphere.

The Troposphere, the lowest and most dense part of the atmosphere (source: Wikimedia Commons, photo by Nick Juhasz).

Another interesting thing about ozone is that it’s not emitted directly. Many other pollutants and greenhouse gases, like methane or nitrogen oxides, are emitted by both natural and anthropogenic sources, but ozone is formed through photochemical reactions, which occur in the presence of both sunlight and nitrogen dioxide. So, to study the ozone in the atmosphere using a model, it needs to include emissions of relevant gases, motions in the atmosphere that move these gases around, chemical reactions that transform one gas into another, as well as other processes like deposition of certain gases to surfaces or removal in rain.

With all this going on, it can be hard to disentangle one process from another, particularly since all the different processes are interlinked. This is where tagging can come in handy as an accounting tool. Say we are interested in how much ozone is added to the atmosphere as a result of activity in a particular city – let’s call it Mega-City One. How could you find this out? Well, one quite common way is to run the model as normal, and then to repeat the simulation but with Mega-City One removed. So you take out any emissions coming from Mega-City One and see what difference it makes. This tells you what would happen if you simply removed that city.

However, you may not want to know about this unrealistic “annihilation” situation, as a city won’t simply disappear overnight. You may be more interested in your normal run (which you think best represents the real world) and what is contributing to the ozone in that run. The non-linearly minded amongst you will see the subtle difference between the two questions. If we were talking about an inert tracer, there would be no difference, as what was emitted by Mega-City One would just stay in the atmosphere unchanged, and would be directly attributable to Mega-City One. The difference with ozone is that it’s not emitted, and the chemistry that creates and destroys it can and does behave nonlinearly.

So to answer the attribution question (in my model simulation, how much ozone is a result of Mega-City One emissions?), tagging is one method that is used. The idea is that you ‘tag’ tracers that you are interested in, and follow them through the model. So you can ‘tag’ all the emissions from Mega-City One, and when one of the nitrogen dioxide molecules from this city undergoes photolysis to make an oxygen atom, which then reacts with molecular oxygen (O₂) to form ozone (O₃), you know that this ozone molecule can be attributed to Mega-City One. This is done by solving a set of equations for the tags alongside the usual chemistry scheme. This does not disturb the normal running of the model, and you will find that the total amount of ozone attributed to Mega-City One will be different from calculating the difference in ozone between your normal and your annihilation runs.

Why would you want to do either of these things anyway? Well, you might want to know what effect different cities or other sources are actually having, or would have on the atmosphere if they were built. So you’d use the annihilation method. Or, you might want to know what the biggest culprit was for particularly bad air quality in a particular place. So you’d use tagging to find out if it was Mega-City One or Mega-City Two, or if it was the road transport or the power stations that was the biggest source.

I hope I’ve achieved my first aim of answering my first question, about what tagging is and what it’s used for. The second question is not quite so straightforward, but I’ll give my thoughts on the matter: I think the key to why – to put in bluntly – some people aren’t so keen on tagging, and some people aren’t so keen on the annihilation method, stems from different notions of what tagging is really being used for. Ultimately, I think this boils down to finding ways of communicating complex ideas and their applications, without being misconstrued. Existing pre-conceptions probably also play a part, as these will (rightly or wrongly) fill the gaps when someone else’s explanation is incomplete.

Successful communication of complex ideas isn’t easy! It takes time and effort, but it really pays off in the end. Just think, how often have you heard (or taken part in) a heated discussion in which you find everyone was actually in agreement all along, they just didn’t know it yet?

By Michelle Cain, post-doc at the University of Cambridge & NERC policy placement fellow at Defra

Reference:

Grewe, V, Dahlmann, K, Matthes, S and Steinbrecht, W. (2012) Attributing ozone to NO_x emissions: Implications for climate mitigation measures. Atmospheric Environment. Vol. 59, pp 102-107.

In this week’s Imaggeo on Mondays, brought to you by the photographer herself, Jacqueline Isabella Gisen (Delft University of Technology, The Netherlands) tells us about light refraction and reflection in a beautiful Autumnal landscape.

“Light reflection” by Jacqueline Isabella Gisen, distributed by EGU under a Creative Commons licence

This shot was taken spontaneously on my way to Clingendael Park in The Hague, Netherlands, for an Autumn’s photography activity on 4 October 2011. It was misty and sunny that morning, after a week of rain, and the weather was cold.

The phenomenon in the photo occurs only under certain conditions with the existence of saturated air moisture (mist) and sunlight. When fully saturated air cannot further hold the evaporation of water, water particles are suspended in the air. Then, when the sunlight penetrates through the gaps between the leaves, it is refracted and reflected by these suspended particles, which makes the beams of light visible.

In this photo you can also see the beams of sunlight that were reflected upward again due to the reflective property of the water in the lake, completing this astonishing reflection and refraction scene. As the surroundings were shaded by the trees, the background was dark, allowing even the weak reflected rays to contrast brightly and stand out in the photo.

When the density of the particles in the water is further increased, the visibility of the light is reduced, because the water particles will reflect and scatter more light photons. This reduction of visibility can cause disturbance in transportation systems, such as in the takeoff and landing of airplanes.

By Jacqueline Isabella Gisen

Imaggeo is the online open access geosciences image repository of the European Geosciences Union. Every geoscientist who is an amateur photographer (but also other people) can submit their images to this repository. Being open access, it can be used by scientists for their presentations or publications as well as by the press. If you submit your images to imaggeo, you retain full rights of use, since they are licenced and distributed by EGU under a Creative Commons licence.

In this week’s Imaggeo on Mondays, brought to you by the photographer himself, Lukas Hörtnagl (University of Innsbruck, Austria) tells us about the ‘blue haze’ or ‘tule fog’ of California’s Sequoia National Park.

“Blue haze” by Lukas Hörtnagl, distributed by EGU under a Creative Commons licence

I was visiting the United States to attend the Fall Meeting of the American Geophysical Union in December 2011 and decided to stay four more weeks to visit some of the National Parks in California, Arizona and Nevada. Soon, it was obvious that each park seemed eager to look its best on camera. California’s Sequoia National Park was no exception.

This photo was taken in January 2012 while driving down the Generals Highway — a road that crosses the National Park and is named after two of its most famous trees, the General Sherman and General Grant sequoias — looking west/south-west at the western borders of the park. Further in the background is the Great Central Valley in California.

The thick ground fog visible in the photo is called ‘tule fog’ and typically forms during the winter months when longer nights result in an extended period of ground cooling. The combination of relatively high humidity (e.g. after rain events) and the loss of heat by radiation can lead to the formation of this fog, which can last for days. While the fog layer is cold, the air directly above is typically warm and — as you can see in the picture — clear. However, the visibility down in the valley was much better than it seemed from above.

By Lukas Hörtnagl, Biomet Innsbruck

Imaggeo is the online open access geosciences image repository of the European Geosciences Union. Every geoscientist who is an amateur photographer (but also other people) can submit their images to this repository. Being open access, it can be used by scientists for their presentations or publications as well as by the press. If you submit your images to imaggeo, you retain full rights of use, since they are licenced and distributed by EGU under a Creative Commons licence.

The EGU’s Twitter Journal Club had its fourth virtual meeting yesterday, this time focusing on a paper from the journal Atmospheric Environment. The work examines methods of assessing contributions of individual emissions to ozone and hence to climate change. Read a full transcript of the discussion on our Storify page!

Emissions of nitrogen oxides (NOx) lead to formation of ozone, which is an important greenhouse gas. (Photo: Edvard Glücksman)

It’s time for the fourth edition of the EGU’s Twitter Journal Club, our interactive online discussion about a timely scientific article. If you have not yet taken part in one of these discussions, read more about it in our introductory post and make sure to participate when we meet online next week! 

This time, we will be discussing a recent Open Access article from the journal Atmospheric Environment, covering the various approaches used to calculate contributions of individual nitrogen oxide emissions to creating ozone – and hence towards climate change.

The discussion will take place on Twitter next Thursday 25 October at 14:00 CEST, and you can take part by following the EGU’s Twitter account (@EuroGeosciences) and using the hashtag #egutjc4 on your tweets. Please email the EGU’s Science Communications Fellow Edvard Glücksman if you have any further questions.

Happy reading!

Nitrogen oxide emissions from burning fossil fuels are important contributors to the formation of ozone, and hence to climate change. (Source: Wikimedia)

Attributing ozone to NOx emissions: Implications for climate mitigation measures

Atmospheric Environment 59 (2012) 102-107

Abstract. Emissions of nitrogen oxides (NOx) lead to formation of ozone, which is an important greenhouse gas. Despite its relevance, little emphasis was previously given on verifying approaches to calculate contributions of individual emissions to ozone and hence to climate change. Basically two methods (perturbation method and tagging method) were used in the past. We demonstrate that both methods are valid and have their area of application, but only tagging calculates contributions of emissions to concentrations, whereas the perturbation method identifies changes in the ozone concentrations due to emission changes. Our results show that the contribution of road traffic emissions to climate change is underestimated by a factor of 5 in the perturbation method. This is caused by non-linear compensating effects from other emission sectors, which are concealed in the perturbation method but disclosed with tagging. Consequently, the effectiveness of mitigation measures for individual sectors (i.e. concentrating on road traffic induced ozone) is only correctly expressed by the tagging method. The perturbation method provides accurately the total impact (i.e. total ozone) of a mitigation measure. However, current approaches, which evaluate the effectiveness of a mitigation measure based on the perturbation approach, do not reflect changes in the chemical state of the atmosphere (i.e. ozone production rates). These largely affect the effectiveness of subsequent measures and hence make the evaluation of the effectiveness of two measures dependent on their chronology of application. We show that also in this regard, the tagging method is better suited to evaluate the effectiveness of a mitigation measure than the perturbation method.

Questions to think about:

1. How would you summarise this article in a tweet?

2. What are the broader implications of this study?

3. Which approach seems to be the most effective in calculating contributions of individual emissions to ozone?

4. What would be an interesting follow-up study to this work?

“Cumulonimbus-lenticularis” by Pablo Saavedra Garfias, distributed by the European Geosciences Union under a Creative Commons license.

Lenticular clouds, also known as ‘flying saucer clouds’ or ‘cloudships’, have captured the imagination of humans since Biblical times. Normally aligned at right-angles to the direction of the wind, lenticular clouds are stationary, lens-shaped formations that form at high altitudes. Pilots of powered planes tend to avoid flying near lenticular clouds because of turbulence. Glider pilots, on the other hand, actively seek them out because they tend to form at the top of a rising air mass, large vertical air movements that provide the lift necessary for gliding. ‘Wave lift’, as it is known in the gliding community, is often smooth and strong, and has powered gliders to record breaking distances (over 3,000 km) and altitudes (14,938 m).

Cumulonimbus clouds are tall and extremely dense, and are often responsible for thunderstorms and other inclement weather. They extend high into the sky, their peak easily reaching 12,000 m in altitude and consisting mostly of ice droplets because of the freezing temperatures. Lower levels of cumulonimbus clouds are made of water droplets.

Pablo Saavedra Garfias, a physicist at the University of Bonn, stumbled across this beautiful scene in 2012 during a NASA GPM field experiment at the Brazilian Space Agency’s Alcântara launch center. He describes the double cloud formation overhead in the context of his study, “The picture is a synthesis of a thunderstorm under formation over the ocean, far away from the experimental site. The nimbus cloud grew to an altitude of around 8 km. The lenticularis cloud is usually caused by a moist stream of air flowing over a high mountain peak, but in this case was formed over a cumulonimbus cloud as a proxy of a high mountain. The scene is therefore unusual because it features a combination of both nimbus and lenticularis clouds, the former causing the latter. This type of scenario is more frequent in the tropics, where high moisture levels feed into the convective air motion in order to form huge cloud systems. The resulting precipitation was the main scientific subject during this field campaign. The better understanding of this kind of system will help us better understand precipitating clouds from satellite observations.”

Garfias was quick to capture the fleeting scene, “The phenomenon lasted only a few minutes, not enough to allow me to find an optimal position to capture the picture. After some minutes the lenticularis vanished and only the cumulunimbus stayed for a while, but no precipitation was initiated. I used a Canon PowerShot SX1 IS (1/250 second exposure time, aperture F4.5, focal length 23.8 mm).”

Imaggeo is the online open access geosciences image repository of the European Geosciences Union. Every geoscientist who is an amateur photographer (but also other people) can submit their images to this repository. Being open access, it can be used by scientists for their presentations or publications as well as by the press. If you submit your images to imaggeo, you retain full rights of use, since they are licenced and distributed by EGU under a Creative Commons licence.

This week’s guest post introduces a book recently published by Cambridge University Press.

Written by William I. Newman, a Professor at the University of California, Los Angeles, Continuum Mechanics in the Earth Sciences provides an introduction to continuum mechanics and essential mathematical and physical approaches in the Earth sciences. It also contains problem sets and worked examples, altogether providing a valuable first step towards understanding continuum mechanics, related tensor notation, and mathematical-background concepts. Clearly structured and merging basic with advanced topics, this textbook will capture the attention of both expert researchers and beginners in the area.

Hardback; ISBN: 9780521562898; Publication date: March 2012; 194 pages; Price: £40 (~€50)

The text is divided into nine main chapters, with the first three covering geometrical definitions of the material body and the response of materials under different forces. These definitions start with a review of essential mathematics for continuum problems, with the purpose of their geometrical descriptions in addition to covering rotation, transformation, and kinematics. The text continues, mainly in Chapter 2, by covering the most important physical quantities in continuum mechanics, like temperature, force, and stress.

The fourth chapter is devoted to fundamental laws and equations. This part of the text starts by introducing new terminology and is followed by the derivation of conservation laws. The following subsections cover some well-known constitutive equations, describing the internal mechanical, thermal, and other properties, of the constitutive quantities of the continuum materials. These parts are followed by thermodynamic considerations, which play a key role in the geosciences, particularly in the context of flows in Earth materials where the temperature can undergo dramatic change.

Chapter 5 is dedicated to linear elastic solids. It defines a body of material as elastic if at each body point the strain is a one-to-one function of stress at that point regardless of its history of loading. This chapter continues with discussions on statics and dynamical equations of isotropic bodies, homogeneous deformation equations, and the role of temperature on body deformation. It ends with a quick review on microscopic structure of crystals and their behaviour.

The next two chapters, on classical fluids and geophysical fluid dynamics, discuss the motion of fluids and their behaviour under stationary and dynamic inertial environments. Examples include the interior of Earth as well as the motion of the oceans and atmospheres.

The book ends with two chapters covering computations in continuum mechanics and nonlinearity in the Earth. The first one deals with partial differential equations used in numerical methods with the purpose of solving complicated real-word problems of continuum bodies rather than using simplified and linearized solutions.

Finally, the last chapter starts with some comments on the role of nonlinearity and its manifestation in the Earth sciences and continues by reviewing both friction, as the oldest mechanical aspect, and fracture, as one of the most challenging aspects of continuum mechanics. The last subsections cover percolation models, used to demonstrate self-organization under specific conditions, as well as fractals, used for the generation of noticeably realistic details of the objects.

Although on the whole an informative volume, this book unfortunately does not provide sufficient rigorous examples to work with, as is common in other continuum mechanics books. In addition, more examples about applications of continuum mechanics into real life Earth science problems could have made the book a little more interesting for student readers even in other fields within engineering.

By Arash Maghsoudloo, Research Assistant at Middle East Technical University

Geotalk, featuring short interviews with geoscientists about their research, continues this month with a Q&A with Dr Pedro Jiménez Guerrero (University of Murcia) focusing on air pollution and climate change. If you’d like to suggest a scientist for an interview, please contact Bárbara Ferreira.

Pedro Jiménez Guerrero at the time he received the Outstanding Young Researcher Award of the Spanish Royal Academy of Engineering. (Credit: Ana I. Domenech)

First, could you introduce yourself and let us know a bit about your research topic(s)? 

I was born in Murcia, Spain in 1978. I got my Ph.D. in Environmental Engineering at the Technical University of Catalonia in 2005 (Doctoral Prize to the Best Thesis in Environmental Science and Sustainability), being a visiting researcher at the University of California UCI (USA) and the Max Planck Institute for Chemistry (Germany). After that, I was a post-doc at the Goddard Institute for Space Studies, NASA (USA), the Earth Sciences Department of the Barcelona Supercomputing Center (Spain) and the University of California UCLA (USA). Two years ago, I took a position at the University of Murcia as a researcher and senior lecturer. Recently I received the Outstanding Young Researcher Award of the Spanish Royal Academy of Engineering.

My main research topics cover the analysis of the magnitude and extension of the potential impacts of climate change at a regional scale and their impacts on future air pollution. Some pollutants, such as ozone and aerosols, are recognized as important climate agents affecting the radiative forcing, but are also the most important contributors to poor urban and regional air quality over Europe. Therefore, my research focuses on the effects of climate change on air quality (and vice-versa) analyzed under the wider framework of chemistry-climate interactions. Just by modeling systems that comprehensively simulate the climate system (with special emphasis on the interactions atmosphere-ocean-chemistry), it becomes possible to explore changes in future climate caused by the increase of the emissions of anthropogenic greenhouse gases and the concentration of atmospheric pollutants.

Regarding the relation between climate and air pollution, could you explain in what ways can climate change impact air quality?

Climate change alone may influence future air quality through modifications of gas-phase chemistry, transport, removal, and natural emissions. This influence is particularly important in the context of the intercontinental and transboundary transport and in hemispheric air pollution. Conversely, air pollutants can affect climate in different ways. Apart from typical greenhouse gases (CO2, methane), other chemical tracers, such as ozone, can absorb infrared terrestrial radiation, while aerosols reflect and absorb solar radiation. Both these processes exert a direct radiative forcing on the climate system (the so-called ‘direct effect’), with associated semi-direct effects due to the changes in the atmospheric structure. In addition, we can find an ‘indirect effect’ since aerosols act as cloud condensation nuclei, thereby modifying the microphysical and optical properties of clouds, affecting the climate.

What can be done to improve future air quality in a warming world? Do scientists have a role to play in this process, or does the reduction of air pollution rest only on decision-makers?

Scientists must play a role in the strategies aimed at reducing air pollution. According to recent studies of the European Environmental Agency, air pollution is the environmental factor with the greatest impact on health in Europe and is responsible for the largest burden of environment-related diseases. Recent estimates indicate that 20 million Europeans suffer from respiratory problems every day. So, the challenges posed by anthropogenic climate change and its influence on air quality call for a proper assessment of these impacts. In this sense, scientists must help decision-makers to establish the magnitude and extent of potential impacts of climate change on air quality and to advice major government authorities about the best strategies to abate air pollution and to define the most appropriate mitigation measures with the most current and complete information as possible (based on their knowledge and their research).

In an interview with ABC last year, you mentioned that “climate scientists would be nothing without supercomputers”. Why is that so? How have supercomputers contributed to improve our knowledge of the Earth system?

The dependence of climate scientist on high-performance computing relies on very different factors. There is a need for high resolution, quality and comprehensive climate information over long periods. Modern high-resolution full transient simulations (covering several decades or even centuries), as those proposed in the CORDEX initiative of the World Climate Research Program, demand important computing resources. On the other hand, considerable uncertainty affecting climate simulations still exists. For instance, diverse regional climate models produce different results even when driven by the same boundary conditions provided by a global model. Another source of uncertainty is the definition of emission scenarios, or the inherent internal variability. Moreover, the interactive coupling of complex climate models and full chemistry schemes is computationally demanding. Therefore, ensemble approaches (multi-model or intra-model approaches) demanding huge computational resources are commonly conducted to further improve our understanding of the behavior of climate models and ultimately reduce this uncertainty. Hence, there is a clear need for high-performance computing if we want to improve our knowledge of the Earth system.

Last but not the least, can you tell us a bit about your future research plans?

My research plan in the long term includes the study of the feedbacks between climate change and air pollution in the next decades over Europe, the Western Mediterranean, and the Iberian Peninsula. These possible impacts include potential excesses of critical levels causing changes in the patterns of extreme events, high levels of air pollutants, modifications in the kinetics and atmospheric chemistry, feedbacks (both positive and negative) with the regional climate systems, etc. For that purpose, the methodology I’m working on includes the development of an integrated framework of regional climate models applied with very high resolution, taking into account the interactions between atmospheric, oceanic, and chemistry transport processes.

One of my most pressing current objectives is the quantification of the different sources of uncertainty inherent to air quality modeling from a climatic perspective, including the frequency distribution of extreme events (e.g. exceeding the thresholds for the protection of human health or ecosystems). Also, I plan to study several topics, from the influence of the selection of the physics and chemistry of the models in the forecast of climatic impacts on air quality to the definition of the chemical weather types associated to air pollution. I am currently working on a paper studying the influence of North Atlantic Oscillation (NAO) on the atmospheric dynamics affecting the patterns of air quality over the European continent.