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EGU 2014: Measuring aerosol climate impacts from Space

In order to understand past climate change and to better project future changes, we need to understand how humans disturbed the radiative balance of our planet. Aerosols are one component of this disruption. The final report from the Intergovernmental Panel on Climate Change (IPCC) physical science basis concluded that aerosols dominate the uncertainty in the total anthropogenic radiative forcing.

Radiative forcing refers to the change in the energy balance of the climate system; carbon dioxide traps energy within our atmosphere, which leads to a warming effect. Aerosols on the other hand stop sunlight from reaching the surface of the Earth, which leads to less energy being retained by the atmosphere and leads to cooling.

I summarised what the IPCC report said about aerosols here, with some further analysis here.

There were several talks at the EGU on Friday that looked to better constrain the important climate relevant properties of aerosol particles in the atmosphere by observing them from space.

Layer cake

Ralph Kahn from NASA’s Goddard Space Center presented measurements of aerosol properties from the Multi-angle Imaging SpectroRadiometer (MISR) instrument, which flies on the TERRA satellite. His abstract is available here.

The MISR instrument views the Earth from nine different angles as it orbits, which allows it to identify 3-D properties of aerosol particles in the atmosphere. One such example that was presented was from Iceland’s Eyjafjallajökull volcano, which famously closed large swathes of European airspace (disrupting EGU 2010 in the process). Such an eruption is an ideal natural laboratory for assessing aerosol properties from satellites with several of the talks during the day making use of it.

The image below shows how MISR was able to measure the height of the plume of ash thrown into the atmosphere by the eruption. The colouring on the left of the image shows the height of the plume; notice how the plume starts out higher (from 4-6km) and then sinks lower (below 3km).

Blah.

Satellite image of the plume of volcanic ash from the Eyjafjallajökull eruption from 7 May 2010. The image on the left is the natural colour image, while the version on the left has the plume height measured by MISR overlaid. Source: NASA/GSFC/LaRC/JPL MISR Team, retrieved from here.

In terms of volcanic ash, such information is useful for aircraft safety. From a climate perspective, the height of aerosol layers in the atmosphere can strongly influence the strength of the radiative forcing and the vertical distribution of aerosol is something that is represented poorly in climate models.

Cloudy with a chance of aerosols

Jens Redemann from the Bay Area Environmental Research Institute and the NASA AMES research center in the USA presented work that took advantage of a collection of satellites that fly in formation high above the Earth. His abstract is available here.

The satellites are known as the ‘A-Train’ and by combining the data from multiple instruments operating in quick succession, he was able to extract more detailed and valuable information than could be achieved with any one single instrument. Their calculations for clear-sky conditions agreed well with model-based results used in the 2007 IPCC report, with more work planned to compare with more recent model estimates.

However, there were more significant differences when looking at so called all-sky conditions i.e. when clouds are added to the mix. Several of the other talks in the session considered methods to improve retrievals of aerosol properties in the vicinity of clouds, with some encouraging results. The famous image of the Earth taken from Apollo 17 is known as the ‘Blue Marble’ but as an atmospheric scientist, I’m often more struck by how white the globe is when observing it from space. This is an important consideration for assessing the role of aerosols when it comes to climate change.

Anthropogenic, vegetable or mineral

Both Kahn and Redemann presented work aimed at categorising aerosol particles into different types e.g. urban pollution, biomass burning smoke, desert dust. Different types of pollution tend to have differing properties, so distinguishing between them can improve estimates of aerosol climate effects.

Another important distinction is separation into natural and human-caused components, so that the anthropogenic influence can be characterised. This is complicated though by human sourced pollution interacting with natural emissions; such aerosol particles are dazed and confused about their origins.

Such information would be particularly valuable as there is a large degree of diversity in climate model estimates of the various aerosol types, even though their estimate of the overall aerosol burden in the atmosphere is quite similar. Such discrepancies are troubling for future projections of climate change as they will introduce significant errors.

I love it when a plan comes together

Ralph Kahn ended his talk with a call for renewed focus to combine satellite and measurements made more directly (known as in-situ) in order to determine aerosol radiative effects independently of climate models. 

Bringing all of this information together is a big opportunity to better constrain the aerosol radiative forcing, which will greatly improve our ability to project future climate changes at both the global and regional scale.

EGU 2014 Day 1: A day in the life of an aerosol particle

My first day at EGU 2014 in Vienna was principally spent listening to various speakers describe the life and death of tiny particles in the atmosphere, known as aerosols. These aerosol particles come from a variety of sources – one of the major sources is through burning of fossil fuels, which produces a cocktail of pollutants that form these particles. They can also arise from natural sources, such as bursting bubbles on the ocean surface, strong odours from trees and high winds whipping up sandstorms in the desert.

Pinning these sources down is tough but we also have to understand how they evolve in the atmosphere from their birth, their growth during their adolescent years and ultimately their adult years, where they can influence our climate and health. At some point, they are removed from the atmosphere where they become an ex-aerosol. Understanding these different changes is necessary if we are going to be able to understand their impact both in the past, present and future.

Baby steps

One of the major routes for an aerosol to be born is via ‘nucleation’ where the particles form tiny clusters, which are around 100,000 times smaller than the width of a human hair. These clusters form due to the combination of different gas phase molecules, which given the right cocktail and conditions, can condense to form these initial tiny particles. I’ve previously written about these early steps here.

There was work presented here at the EGU by Jasmin Tröstl from the Paul Scherrer Institute in Switzerland showing that chemical species known as oxidised organics take part in this initial process. The abstract for the work is available here.

For a long time, sulphuric acid was thought to be the vital ingredient for this nucleation process but recent work at a laboratory at CERN (known as the cleanest box in the world) has illustrated the importance of several other species. You can read more about two studies in Nature that were published in the past few years on these here and here. Oxidised organic species are abundant in the atmosphere, so it isn’t a huge surprise that they are important but it has only been through the development of the new laboratory at CERN and sophisticated new instrumentation that the importance of this key ingredient has been demonstrated.

The difficult years

The same study also illustrated that these oxidised organic species were vital for the growth of these nucleated particles. This is the key stage for such particles as they essentially either grow or suffer an early death. When they start out, they are too small to become cloud particles, which is their main route to impacting our climate. So without growing they will never know the wet embrace of a cloud droplet.

Not only did the oxidised organics strongly increase the growth of these particles but their addition was enough to reconcile the laboratory measurements with observations of the real world. This is an enlightening step as it has previously proven difficult to mix up the right cocktail to represent what really goes on in the atmosphere, which suggests a deficit in our knowledge of this important process.

All grown up

Once they reach adulthood, these particles become important from a human health and climate perspective. They can build-up in the atmosphere over a matter of hours or days and influence our lives.

Rongrong Shen from Karlsruhe Institute of Technology, Germany, presented measurements of spring time pollution in Beijing during 2012, focusing on the chemical makeup of the pollution. Her abstract is available here. Beijing is well known as a hotspot for pollution, with over 20 million people living in the city and over 5 million vehicles on the road frequently creating a heavy chemical soup. The average concentration for PM2.5 (aerosol particles with a diameter less than 2.5µm) was 89µg/m3, which is far in excess of what is considered healthy. Even the ‘clear’ days in terms of visibility saw average concentrations of around 45µg/m. The World Health Organisation guidelines recommend the daily average values should remain below 25µg/m3, while annual values should be 10µg/m3 or lower.

Haze over Beijing and surrounding region from 22 March 2007. Image credit: NASA Earth Observatory

Haze over Beijing and surrounding region from 22 March 2007. Image credit: NASA Earth Observatory

More severe pollution episodes were typically driven by species such as sulphate and nitrate, which are known as ‘secondary’ species. This means that they start out as a gas and then condense onto pre-existing aerosol, such as nucleated particles or direct emissions from car exhausts and other forms of combustion. The results also indicated that such episodes were not solely driven by emissions within the city; the wider region played a role, including industrial sources and other Chinese cities. This is a common feature of pollution episodes in Western Europe also, which I wrote about recently here and here.

This is an ex-aerosol

Urs Baltensperger from the Paul Scherrer Institute, Switzerland gave the Vilhelm Bjerknes Medal Lecture and included a discussion of the fate of aerosols in the atmosphere. His abstract is available here. Aerosols are typically removed from the atmosphere via crashing into something, such as the ground, or by forming cloud droplets. These cloud droplets either evaporate, leaving an aerosol particle behind or they can grow to form rain, which removes the aerosol from the atmosphere. The rainfall can also washout other aerosols by catching them on the way down.

He referred to several previous studies, including measurements very early in the aerosol life cycle in an urban environment (Paris) and more mature aerosol at a high altitude site in the Swiss Alps at the Jungfraujoch.

The urban study illustrated that aerosol particles are quite diverse in this environment, which affects how readily they would form cloud droplets. Black carbon is known to be a poor candidate for making a cloud droplet, which the study showed. However, the results also illustrated that adding some other chemical components to the mix can vastly increase the likelihood of the particle joining the cloud droplet gang. This is important as the removal of black carbon from the atmosphere is poorly understood and can have significant implications when trying to predict its climate impact.

At the high altitude site at ‘the top of Europe’, the aerosol properties are more uniform. This makes it somewhat easier to predict how many particles will form a cloud droplet. This is an important result for models of aerosol impacts, as such a situation is more reflective of the scales that atmospheric models work in, particularly for climate change studies. This result is not true everywhere though, so as aerosol scientists we need to work towards understanding the differences across the globe, so that we can understand the ultimate fate of aerosol particles.

JFJ_Small

Image of the Swiss Alps during a research flight on the FAAM BAe-146 research aircraft. Photo credit: Will Morgan

That concludes this diary in the life of an aerosol particle; they have a hard and complex life, which often lasts just a few days or maybe weeks.

I’ll be back with more later this week.

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Edit 03/05/14: Urs Baltensperger was originally spelt incorrectly.

Conference top tips for EGU 2014

Vienna hosts the 2014 European Geosciences Union this week so I thought I would post my own top tips for getting the most of conferences. These are very much my own opinions on this; feel free to disagree and/or add to them in the comments or on Twitter!

1. Don’t go to too many talks

The number of talks at a conference varies somewhat but using EGU as an example, you would be looking at attending 24 talks per day plus poster sessions. On top of this, there are often lunch time and evening forums and workshops etc. If you try to take all of that in, you will very likely fail! Once you reach talk number 20 of the day, you’ll be thinking “this means nothing to me” and you will not be gaining anything from being at the conference.

Instead, I find it much more worthwhile to limit the number of talks I attend and get out of the presentation rooms. What you do in that time is up to you of course but you’ve probably got some terribly important emails in that one hour period where you didn’t check them, so you could respond to those. Alternatively, you could browse around the conference venue (the posters are often up early), grab a coffee or perhaps even speak to people…

2. Chat to people

Probably one of the most fun and valuable elements of attending a conference is talking to people. This can include friends, colleagues and compatriots from other institutions. Such conversations don’t have to end with an outline for a grant proposal or manuscript…it is acceptable to simply chat about life, the universe and everything. Talking to other scientists is often an enlightening experience and you’ll likely meet people in the future at other conferences or during fieldwork etc. This can be very beneficial and also, fun.

3. Check out what is happening in terms of social media

Many of the larger conferences now include a healthy amount of engagement online. Personally I’ve found that following conferences like the EGU and AGU on Twitter very helpful, as you hear about other work being presented, hear about upcoming sessions of interest and discuss the implications of the science. Also, it extends the reach of the conference outside of those attending, which I’ve appreciated myself in the past when I haven’t been at a conference/meeting in person. It is also a good way of meeting people…the introductory line of “I follow you on Twitter” is becoming more and more common!

The EGU have their own Twitter account (@EuroGeosciences), which is a good place to start and you can also check out the official hashtag #EGU2014.

4. Keep a note pad handy

Over the course of the week, you’ll take in a lot of information which will spark ideas in your head about your own work. I often find that this is a very creative time as I think of ideas to apply and test on my own analysis, so jotting these down before they disappear in a haze of coffee/beer is a good idea. Also, be sure to check back through your notes after the conference so that you remember your potential eureka moment!

5. Spread your wings

It is tempting to just stick to sessions that are very close to your research area but one of the benefits of attending conferences (especially large ones like the EGU) is that there are lots of sessions that are aligned to your research but don’t necessarily directly relate to it. This is a good opportunity to broaden your horizons and see what else is going on in the world of science. Obviously this doesn’t extend to people who crush rocks for a living – they should be left to their own devices.

The Riesenrad

The Riesenrad. Stop by for Orson Welles style reflections on human existence or just take in the view. Photo credit: Will Morgan

6. Specifically for EGU: refer to the Ultravox classic, Vienna, as frequently as possible.

I’ll be writing about the conference throughout the week, so please check back here. Have a good week!