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AGU13

AGU 2013 roundup

Now that the 2013 AGU Fall Meeting has ended, I thought I would roundup what I’ve been involved with over the week for both this blog and the Barometer Podcast, which I was recording each day with Sam Illingworth. Links to each piece are available below. Many thanks to all who have read and shared these over the past week.

Recording the podcast at conferences is becoming a trend as we’ve covered AGU now in 2012 and 2013 plus the EGU in 2013. Recording these is a lot of fun and particular thanks should go to Dave ToppingBethan Davies and Mark Brandon for giving up their time to chat to us this week. Lastly, many thanks to Sam for his infectious enthusiasm and for being the only person I’ve ever met with a louder laugh than me.

The conference itself was excellent throughout, even if the amount of science on offer was overwhelming at times. The sessions on science communication I attended were also fantastic, thought-provoking and often inspiring. I’m planning to write a separate post on this aspect over the coming days.

So long San Francisco! Image: Will Morgan

So long AGU 2013 and thanks for all the science! Image: Will Morgan

Blog posts

Podcasts

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AGU 2013 Days 4 & 5: measurements & models

My fourth and fifth days at the AGU Fall Meeting involved dashing between multiple sessions to take in a number of talks on (surprise, surprise) aerosols! The main strand running through them from my point of view was how there are major efforts to construct large datasets of aerosol properties that can be used to test our understanding via numerical models.

Aerosols are complex and tend to stick around in the atmosphere for hours-to-weeks, rather than years-to-centuries. This means that they are spatially very diverse and also vary with time e.g. with the passage of seasons. This presents a challenge for our understanding but by constructing large datasets, it can also be used to constrain our numerical models.

For example, by looking at years of winter data for European pollution we might find that our models represent this quite well but it might be that there are significant errors when we look at the summer. This information is useful and might point us towards places to study further and improve our understanding. Just looking at a global annual average, this information is lost.

Image of the global aerosol distribution produced by NASA. The image was produced using high-resolution modelling by William Putman from NASA/Goddard. The colours show the swirls of aerosol particles formed from the numerous sources across the globe. The colours show aerosol particles as dust (gold/brown), sea-spray (blue), biomass burning/wildfires (green) and industrial/urban (white).

Image of the global aerosol distribution produced by NASA. The image was produced using high-resolution modelling by William Putman from NASA/Goddard. The colours show the swirls of aerosol particles formed from the numerous sources across the globe. The colours show aerosol particles as dust (gold/brown), sea-spray (blue), biomass burning/wildfires (green) and industrial/urban (white).

There were several talks detailing efforts to build satellite data sets of aerosol properties over long periods and use these to assess numerical models. Phillip Stier from the University of Oxford sounded a cautionary note by illustrating how different satellites can sometimes deliver different results for certain properties. He showed three different satellite images of cloud effective radius, which is a property of clouds that is important for how they interact with sunlight, and they were all very different. One of them agreed with his model but which set of measurements do you believe? He ended with a call to expand initiatives that seek to collate data from surface and aircraft measurements to test satellite measurements and models.

Dan Murphy from the National Oceanic & Atmospheric Administration paper presented some work on trends in aerosol over the past decade. He showed that while at a global level, the amount of aerosol in the atmosphere hasn’t really changed, it has changed significantly at the regional level. Aerosol concentrations have decreased in the USA and Western Europe, while they have increased in East Asia and in the Middle East. Aerosol has moved around a lot but there has not been a discernible change in their radiative effect at the global level. However, he said we couldn’t rule out that aerosols haven’t caused other adjustments such as circulation changes and clouds. You can access his Nature Geoscience paper on his work here. His work is consistent with several other papers that have shown negligible trends in global aerosol after the past decade.

These were highly interesting talks and should serve us well as we attempt to improve our understanding of aerosols, although there is much work still to do. No doubt we can anticipate much more work on this in the future – one of the talks did proclaim that:

Aerosol reanalysis is trendy.

No doubt we’ll be seeing the influence of this in the fashion houses of London, Paris and New York soon.

AGU 2013 Day 3: secondary organic aerosol – animal or vegetable?

My third day at the AGU 2013 Fall Meeting involved lots of talks on one of the trickiest parts of aerosol science – secondary organic aerosol (SOA). We’ve known for several years now that SOA is ubiquitous across the globe and it is often the most dominant aerosol chemical species in many environments and this is particularly true in the industrialised regions of the Northern Hemisphere. The trouble, we’re not sure where it comes from and how it forms…

SOA represents the carbon-containing fraction of atmospheric aerosol that forms as a consequence of chemical processes in the atmosphere. Instead of being directly emitted in particle form e.g. from a car exhaust, they form from gases known as volatile organic compounds (VOCs) which can be emitted by both ourselves via burning fossil fuels or from natural sources such as trees. This latter glass of “biogenic” compounds is what gives pine trees and others their distinctive smell.

Morning fog in the Great Smoky Mountains. Image from EGU Imaggeo image repository and is provided by Oliver Pratt.

Morning fog in the Great Smoky Mountains. See also the haze in the background in the top left. Image from EGU Imaggeo image repository and is provided by Oliver Prat.

An area where there are large emissions of these biogenic compounds is the South-East of the USA and they are responsible for the ‘smokiness’ of the Great Smoky Mountains, which are pictured above. The SE USA is also interesting as parts of it have not warmed like other parts of the USA due to global warming – in fact, some areas have actually shown a cooling trend. One theory is that aerosols formed from the biogenic compounds are involved.

Many of the talks on SOA this week have been based on measurements from an array of projects that took place in the SE USA in 2013. Some of the main themes/conclusions include:

  1. SOA from biogenic emissions of a VOC called isoprene are an important component. Isoprene is the most abundant biogenic VOC worldwide (aside from methane), so it potentially represents a large source of SOA.
  2. Several of the measurements showed a strong link between isoprene SOA and sulphate aerosol, which is typically from human sources such as power plants. This is consistent with the work of Jason Surratt’s group and others.  This is particularly important as it demonstrates how emissions from human activities can interact with biogenic emissions to form pollution, which was postulated to be important by Allen Goldstein in 2009. Yet another example of our impact on the atmosphere.
  3. Condensed water is a significant part of aerosols in the SE USA, which is important for the impact of aerosol on climate. However, the evidence for it being a major driver of SOA formation, as suggested by Annmarie Carlton was limited. Further studies are required klaxon!
  4. ISOPOOH is an important oxidation product of isoprene that forms when Tigger and Winnie have an argument and potentially leads to SOA formation.

New toys

Overall, the talks on SOA from these measurement studies were a fantastic demonstration of many of the new techniques to characterise SOA. These new techniques will certainly improve our understanding of SOA formation, particularly in areas where large volumes of our own emissions interact with the biogenic emissions.

AGU 2013 day 2: aerosol emissions, climate & the IPCC

My second day at the AGU 2013 Fall Meeting revolved around more short-lived climate forcers, which I wrote about yesterday and also a broader session on the results from the recent IPCC Working Group 1 report. The latter was an opportunity for the community to quiz some of the lead authors of the report on a variety of issues including observations of the climate system, aerosol and clouds (yippee!), carbon cycle feedbacks, sea level rise and future changes.

Oliver Boucher gave a very nice overview of the aerosol and clouds chapter that he was a coordinating lead author for. I suspect it was a condensed version of the presentation he gave at the “Next steps in climate science“ meeting at the Royal Society, which I summarised here previously.

Desert fires feeding a convective cloud system over Mono Lake, California. Image from EGU Imaggeo image repository and is provided by Gabriele Stiller.

Smoke aerosol feeding a convective cloud system over Mono Lake, California. Image from EGU Imaggeo image repository and is provided by Gabriele Stiller.

One of the key messages for me was his conclusion that there has been substantial improvements in our understanding of aerosol and cloud processes since the previous IPCC report in 2007 but that this ‘knowledge’ hasn’t quite made its way into current global climate models. As someone who works on understanding aerosol processes from observations of the ambient atmosphere, this is something I very much agree with!  The implication here is that aerosol uncertainty will reduce in the future as this knowledge is translated to future climate models. We can but hope.

Some of the other key points from his talk included:

  1. Confidence in satellite based global average aerosol optical depth trends is low.
  2. Black carbon dominates uncertainty in aerosol radiative forcing.
  3. Many gaps in understanding including absorption by black carbon, trends and circulation changes due to aerosol forcing.
  4. Low level clouds are the “joker in the pack” of cloud feedbacks as they are the least understood area for clouds.

Still plenty of work to do!

Emission reductions

The short-lived climate forcers session in the afternoon included a very nice study of how emission regulations in California have affected air pollutant emissions, including black carbon. Tom Kirchstetter presented measurements of trucks using the Oakland port just across the bay from the AGU venue in San Francisco. The neat thing about the study was that this was done over several years both before the regulations were in place and afterwards. The regulations required diesel particle filters to be installed in new trucks, while old trucks had to be retro-fitted with them.

These new regulations have seen an 80% decrease in black carbon emissions over 4 years. The reduction is about 5-times faster than ‘natural’ fleet turnover, which occurs more gradually as new vehicles with improved engines replace older models. The new rules apply to 10,000-20,000 vehicles and will likely significantly improve air quality in the area. Further regulation will soon come into force for 1 million buses and trucks, which could have profound impacts on black carbon emissions in California.

This will likely be an interesting area to keep an eye on in terms of the wider potential impacts on air quality and climate.