GeoLog

aerosols

Imaggeo on Mondays: Airplane views of the Alps

Imaggeo on Mondays: Airplane views of the Alps

The forward scattering of sunlight, which is caused by a large number of aerosol particles (moist haze) in Alpine valleys, gives the mountain massifs a rather plastic appearance.

The hazy area in the foreground lies above the Koenigsee lake; behind it the Watzmann, Hochkalter, Loferer Steinberge and Wilder Kaiser massifs loom up behind one other to the right of the centre line. Behind them is the wide Inn valley, which extends right across the picture. In the far distance in the middle of the picture, the Wetterstein massif projects upwards with the Zugspitze mountain as its highest peak.

The left side shows Steinernes Meer, Leoganger Steinberge and a sequence of at least 10 mountain chains that extend as far as Kellerjoch, which is in front of the whitish area of haze above Innsbruck. The noon sounding from Munich showed that relative humidity exceeded 75% up to 1,400 m above sea level, with distinctly lower values above (less than 20 %).

The view is from an aircraft window approximately 10 km to the east of the Salzach valley.

Description by Hans Volkert, as published previously on imaggeo.egu.eu

GeoTalk: How are clouds born?

GeoTalk: How are clouds born?

Geotalk is a regular feature highlighting early career researchers and their work. In this interview we speak to Federico Bianchi, a researcher based at University of Helsinki, working on understanding how clouds are born. Federico’s quest to find out has taken him from laboratory experiments at CERN, through to the high peaks of the Alps and to the clean air of the Himalayan mountains. His innovative experimental approach and impressive publication record, only three years out of his PhD, have been recognised with one of four Arne Richter Awards for Outstanding Early Career Scientists in 2017.

First, could you introduce yourself and tell us a little more about your career path so far?

I am an enthusiastic atmospheric chemist  with a passion for the mountains. My father introduced me to chemistry and my mother comes from the Alps. This mix is probably the reason why I ended up doing research at high altitude.

I studied chemistry at the University of Milan where I got my degree in 2009.  During my bachelor and master thesis I investigated atmospheric issues affecting the polluted Po’ Valley in Northern Italy and since then I have always  worked as an atmospheric chemist.

I did my PhD at the Paul Scherrer Institute in Switzerland where I mainly worked at the CLOUD experiment at CERN. After that, I used the acquired knowledge to study the same phenomena, first, at almost 4000 m in the heart of the Alps and later at the Everest Base Camp.

I did one year postdoc at the ETH in Zurich and now I have my own Fellowship paid by the Swiss National Science Foundation to conduct research at high altitude with the support of the University of Helsinki.

We are all intimately familiar with clouds. They come in all shapes and sizes and are bringers of shade, precipitation, and sometimes even extreme weather. But most of us are unlikely to have given much thought to how clouds are born. So, how does it actually happen?

We all know that the air is full of water vapor, however, this doesn’t mean that we have clouds all the time.

When air rises in the atmosphere it cools down and after reaching a certain humidity it will start to condense and form a cloud droplet. In order to form such a droplet the water vapor needs to condense on a cloud seed that is commonly known as a cloud condensation nuclei. Pure water droplets would require conditions that are not present in our atmosphere. Therefore, it is a good assumption to say that each cloud droplet contains a little seed.

At the upcoming General Assembly you’ll be giving a presentation highlighting your work on understanding how clouds form in the free troposphere. What is the free troposphere and how is your research different from other studies which also aim to understand how clouds form?

The troposphere, the lower part of the atmosphere, is subdivided in two different regions. The first is in contact with the Earth’s surface and is most affected by human activity. This one is called the planetary boundary layer, while the upper part is the so called free troposphere.

From several studies we know that a big fraction of the cloud seeds formed in the free troposphere are produced by a gas-to-particles conversion (homogeneous nucleation), where different molecules of unknown substances get together to form tiny particles. When the conditions are favourable they can grow into bigger sizes and potentially become cloud condensation nuclei.

In our research, we are the first ones to take state of the art instrumentation, that previously, had only been used in laboratory experiments or within the planetary boundary layer, to remote sites at high altitude.

Federico has taken state of the art instrumentation, that previously, had only been used in laboratory experiments or within the planetary boundary layer, to remote sites at high altitude. Credit: Federico Bianchi

At the General Assembly you plan on talking about how some of the processes you’ve identified in your research are potentially very interesting in order to understand the aerosol conditions in the pre-industrial era (a time period for when information is very scarce). Could you tell us a little more about that?

Aerosols are defined as solid or liquid particles suspended in a gas. They are very important because they can have an influence on the Earth’s climate, mainly by interacting with the solar radiation and cooling temperatures.

The human influence on the global warming estimated by the Intergovernmental Panel for Climate Change (known as the IPCC) is calculated based on a difference between the pre-industrial era climate indicators and the present day conditions. While we are starting to understand the aerosols present currently, in the atmosphere, we still know very little about the conditions before the industrial revolution.

For many years it has been thought that the atmosphere is able to produce new particles/aerosol only if sulphur dioxide (SO2) is present. This molecule is a vapor mainly emitted by combustion processes; which, prior to the industrial revolution was only present in the atmosphere at low concentrations.

For the first time, results from our CLOUD experiments, published last year,  proved that organic vapours emitted by trees, such as alpha-pinene, can also nucleate and form new particles, without the presence of SO2. In a parallel study, we also observed that pure organic nucleation can take place in the free troposphere.

We therefore have evidence that the presence of sulphur dioxide isn’t necessary to make such a mechanism possible. Finally, with all this new information, we are able to say that indeed, in the pre-industrial era the atmosphere was able to produce new particles (clouds seeds) by oxidation of vapors emitted by the vegetation.

Often, field work can be a very rewarding part of the research process, but traditional research papers have little room for relaying those experiences. What were the highlights of your time in the Himalayas and how does the experience compare to your time spent carrying out laboratory experiments?

Doing experiments in the heart of the Himalayas is rewarding. But life at such altitude is tough. Breathing, walking and thinking is made difficult by the lack of oxygen at high altitudes.

I have always been a scientists who enjoys spending time in the laboratory. For this reason I very much liked  the time I spent in CERN, although, sometimes it was quite stressful. Being part of such a large international collaboration and being able to actively do science was a major achievement for me. However, when I realized I could also do what I love in the mountains, I just couldn’t  stop myself from giving it a go.

The first experiment in the Alps was the appetizer for the amazing Himalayan experience. During this trip, we first travelled to Kathmandu, in Nepal. Then, we flew to Luckla (hailed as one of the scariest airport in the world) and we started our hiking experience, walking from Luckla (2800 m) up to the Everest Base Camp (5300 m). We reached the measurement site after a 6 days hike through Tibetan bridges, beautiful sherpa villages, freezing nights and sweaty days. For the whole time we were surrounded by the most beautiful mountains I have ever seen. The cultural element was even more interesting. Meeting new people from a totally different culture was the cherry on the cake.

However I have to admit that it was not always as easy as it sounds now. Life at such altitude is tough. It is difficult to breath, difficult to walk and to install the heavy instrumentation. In addition to that, the temperature in your room during nights goes well below zero degrees. The low oxygen doesn’t really help your thinking, especially we you need to troubleshoot your instrumentation. It happens often that after such journey, the instruments are not functioning properly.

I can say that, as a mountain and science lover, this was just amazing. Going on a field campaign is definitely the  best part of this beautiful job.

To finish the interview I wanted to talk about your career. Your undergraduate degree was in chemistry. Many early career scientists are faced with the option (or need) to change discipline at sometime throughout their studies or early stages of their career. How did you find the transition and what advice would you have for other considering the same?

As I said before, I studied chemistry and by the end of my degree my favourite subject moved to atmospheric chemistry. The atmosphere is a very complex system and in order to study it, we need a multidisciplinary approach. This forced me to learn several other aspects that I had never been in touch with before. Nowadays, I still define myself as a chemist, although my knowledge base is very varied.

I believe that for a young scientist it is very important to understand which are his or her strengths and being able to take advantage of them. For example, in my case, I have used my knowledge in chemistry and mass spectrometry to try to understand the complex atmospheric system.

Geotalk is a regular feature highlighting early career researchers and their work.

Imaggeo on Mondays: A single beam in the dancing night lights

Laser and auroras. (Credit: Matias Takala distributed via imaggeo.egu.eu)

Laser and auroras. (Credit: Matias Takala distributed via imaggeo.egu.eu)

Research takes Earth scientists to the four corners of globe. So, if you happen to have a keen interest in photography and find yourself doing research at high latitudes, chances are you’ll get lucky and photograph the dancing night lights: aurora (or northern lights), arguably one of the planet’s most breath taking natural phenomenon. That is exactly the position Matias Takala, a researcher at the Finnish Meteorological Institute (FMI), was in when he was able to take this incredible photograph of the swirling aurora and a single beam of green penetrating the Finnish night sky.

The green beam is emitted by Lidar (the Mobile Aerosol Raman Lidar, MARL, to be more precise). This lidar system is designed to measure tropospheric and stratospheric aerosol profiles (backscatter, size distribution, mass), tropospheric water vapour and clouds, with the ability to distinguish between particulates such as dust, ash, and smoke from biomass burning. The system is based at the Arctic Research Centre (ARC) at Sodankylä. Because environmental change is most pronounced in the Polar Regions, the location is ideal to study the effects of a warming climate as a result of environmental changes brought about by the activities of humans.

The high latitude position of the research station means it is also ideally located to contribute to the continuous monitoring of ionospheric activity. Think of the ionosphere as a ring, 85 km to 600 km above the Earth’s surface, of electrons, electrically charged atoms and molecules that surround the Planet. It is here that aurora are generated as incoming charged particles from solar wind collide with the electrons and atoms of gas in the ionosphere. A network of FMI auroral cameras and magnetometers continually survey the sky to provide space weather services, including alerts for when the best auroral displays are likely.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Geosciences Column: Is it possible to quantify the effect of natural emissions on climate?

Geosciences Column: Is it possible to quantify the effect of natural emissions on climate?

The air we breathe is full of tiny particles that can have a big impact on our climate. Industrial activities have greatly increased the number of these particles, cooling the climate and potentially offsetting some of the warming due to greenhouse gases. In this post Kirsty Pringle introduces new research that suggests that it might not be possible to quantify the effect of industrial emissions on climate unless we constrain estimates of the natural emissions (Carslaw et al 2013). Kirsty is a member of Ken Carslaw’s research group at the University Of Leeds (UK) which performed the research.

Deserts, oceans, fire and even pine forests emit tiny particles called aerosol into the atmosphere. Human (anthropogenic) activities also play a role; burning fuel, e.g. in cars or power-plants, emits particles and aerosol concentrations have increased substantially since the start of the industrial revolution. One effect of these particles is to change the properties of clouds, causing them to become brighter, producing a net cooling that can offset some of the warming due to greenhouse gases. Treating this effect in climate models is challenging and it remains one of the most poorly quantified areas of climate science.

Schematic of the first aerosol indirect forcing: Human (anthropogenic) emissions add aerosol particles to the atmosphere, these particles can act as condensation sites, which aids cloud droplet formation.  Anthropogenic emissions result in clouds with more, smaller, cloud droplets.  These clouds are brighter and reflect more solar radiation, resulting in a net cooling. The first aerosol indirect forcing (AIE) is the change in the reflected solar radiation between the present day and the pre-industrial scenarios due to this effect. (Credit: Kirsty Pringle)

Schematic of the first aerosol indirect forcing: Human (anthropogenic) emissions add aerosol particles to the atmosphere, these particles can act as condensation sites, which aids cloud droplet formation. Anthropogenic emissions result in clouds with more, smaller, cloud droplets. These clouds are brighter and reflect more solar radiation, resulting in a net cooling. The first aerosol indirect forcing (AIE) is the change in the reflected solar radiation between the present day and the pre-industrial scenarios due to this effect. Click image for a larger version. (Credit: Kirsty Pringle)

This cloud brightening effect is called the first aerosol indirect effect (AIE). It is thought to produce a global average cooling that is sufficient to offset between 25 to 90% of the warming due to long lived greenhouse gases (IPCC). The AIE is challenging to treat in climate models as atmospheric aerosol has a range of sources, the magnitudes of which are quite uncertain. They also undergo a series of processing steps in the atmosphere, which can change their properties; affecting both their lifetime and their ability to interact with clouds. These processing steps are difficult to represent in climate models and this complexity contributes to the large range of estimates.

As the aerosol indirect effect (AIE) is potentially large, but very uncertain, it is important to try to understand where this uncertainty arises. This has been a focus of Ken Carslaw’s research group for the past four years where a new collaboration between aerosol scientists and a statistician has resulted in some very long meetings, a new approach to uncertainty analysis, and the first study that has identified and quantified the factors that contribute to uncertainty in model estimates of the AIE.

I should clarify that Carslaw just considered parametric uncertainty, this is the uncertainty associated with inputs to the model, e.g. the magnitude of the emissions or uncertain values used within parameterisations. There are other types of model uncertainty, e.g. structural uncertainty, that were not considered in this study. Parametric uncertainty is, however, intrinsic to all climate models, so it is an important starting point.

The first step was to choose which parameters to focus on. The team did this by talking with other scientists to identify which input parameters everyone felt were most uncertain; together they estimated the maximum, minimum and median value for each parameter. They identified 28 uncertain parameters in total; these can be grouped into three categories:

  • Natural emissions (e.g. volcanic emissions, marine sea spray emissions), 6 parameters.
  • Anthropogenic (human-caused) emissions (e.g. fossil fuels emissions, biofuel emissions), 8 parameters.
  • Process parameters used within the aerosol microphysics (e.g. the rate of aerosol aging, or the wet deposition parameter), 14 parameters.

The contribution of each parameter to the uncertainty in the AIE calculation can be found using a statistical technique called Monte Carlo analysis, but to perform Monte Carlo sampling on 28 uncertain parameters one would need to run tens of hundreds of model simulations, which isn’t possible with a complex model. To avoid this, Carslaw ran a few hundred simulations and used a statistical emulator to carry out the Monte Carlo sampling much faster. The emulator is a statistical package that “learns” from the output of the computer model, it can be used to interpolate from the hundreds of runs performed to the thousands of runs needed for the statistical analysis.

Schematic showing the methodology used by Carslaw to perform a sensitivity analysis on the first aerosol indirect effect (AIE). (Figure courtesy of Lindsay Lee).

Schematic showing the methodology used by Carslaw to perform a sensitivity analysis on the first aerosol indirect effect (AIE). (Figure courtesy of Lindsay Lee).

Carslaw found that by varying the values of the uncertain parameters, the model produced a range of estimates of the strength of the AIE forcing that was similar to, but slightly smaller than, the range of values estimated by the multi-model estimate from the IPCC. Surprisingly 45% of the uncertainty was found to be due to uncertainty in natural emissions, 34% was due to uncertainty in anthropogenic emissions and the rest due to uncertainty in process parameters.

Caption: Magnitude and sources of uncertainty in the model estimate of the first aerosol indirect forcing. (Credit: Carslaw et al, 2013)

Caption: Magnitude and sources of uncertainty in the model estimate of the first aerosol indirect forcing. (Credit: Carslaw et al, 2013)

Although the forcing is caused by anthropogenic emissions, the amount of natural emissions has a large effect on how sensitive the climate is to these anthropogenic emissions: the natural emissions don’t produce the forcing but they contribute a lot to the uncertainty in the forcing.

This effect arises because the relationship between aerosol emissions and cloud brightness is not linear; instead it is curved with higher sensitivity of cloud brightness to emissions when emissions are low (as they were in the pre-industrial atmosphere). This means that in the clean pre-industrial atmosphere a change in the amount of natural aerosol emissions has a large effect on the cloud brightness: when natural emissions are small, the initial cloud brightness (albedo) is low and any anthropogenic emissions have a big impact on cloud brightness, so the calculated forcing is larger.

Schematic explaining why the calculation of the first aerosol indirect forcing is sensitive to the magnitude of the natural aerosol emissions.  (Credit: Kirsty Pringle).

Schematic explaining why the calculation of the first aerosol indirect forcing is sensitive to the magnitude of the natural aerosol emissions. (Credit: Kirsty Pringle).

This sensitivity to the natural aerosol emissions is important as it is very difficult to constrain estimates of natural aerosol emissions as measurements taken in today’s atmosphere are almost always affected by anthropogenic emissions. This means that some of the uncertainty in the estimates of the first aerosol indirect effect may be irreducible, but it will still need to be considered in future estimates of warming due to greenhouse gases.

By Kirsty Pringle, Research Fellow, School of Earth and Environment, University of Leeds

 References

Carslaw, K.S., et al.: Large contribution of natural aerosolos to uncertainty in indirect forcing, Nature, 503, 67-71, 2013

Lee, L. A., et al.: The magnitude and causes of uncertainty in global model simulations of cloud condensation nuclei, Atmos. Chem. Phys., 13, 8879-8914, 2013

Lee, L. A., et al.: Emulation of a complex global aerosol model to quantify sensitivity to uncertain parameters, Atmos. Chem. Phys., 11, 12253-12273, 2011

 

GeoLog regularly brings readers information about recent research in the geosciences as well as updates on the EGU’s activities. Part of what makes GeoLog a great read is the variety that guest posts add to our regular features, and we welcome contributions from scientists, students and professionals in the Earth, planetary and space sciences. If you want to report on a recent Earth science event, conferences or fieldwork, comment on the latest geoscientific developments or highlight recently published findings in peer-reviewed journals, like Kirsty has done here, then we welcome your contribution. If you’ve got a great idea, why not submit a post?