Seaweed Seeds Clouds

Chris Smith - So we have heard about the developments in monitoring pollution in enclosed urban environments but other systems also contribute to the quality of air across the country and Dr. Stephen Ashworth is in the University of East Anglia in Norfolk where he studies the gases that come from marine systems to find out how they contribute to the chemistry in the air around us and that means on the scope of the whole planet.

Stephen, hello, welcome to the Naked Scientists.

Stephen Ashworth - Hello.

Chris Smith - So what are the big questions you are trying to answer?

Stephen Ashworth - Well, this work came out of a campaign that goes ahead of Mayshead. We heard in a piece just a moment ago about the natural background levels and one thing that's very important for us atmospheric scientists to know is what those natural background levels are. Now one place this is done is at Mayshead in island and the idea behind that is the prevailing wind is from the Atlantic so there's very little pollution. So on days when it's blowing from the west we can get a very good idea of what natural background levels of various components of the atmosphere are.

But one thing that came out of one of these campaigns was that there were very high levels of particles detected, these aerosols that we have been talking about and having detected these particles the question was what goes to make them up, and it turns out that these particles have a lot of iodine in them and the iodine was traced to the seaweed on the foreshore at Mayshead.

Now the question is then is this a local phenomenon or does it affect the whole globe?

Chris Smith - So what you are saying is that the iodine which is coming presumably from the sea, could be getting into the atmosphere in clouds and therefore triggering things like cloud formation and therefore influencing rainfall?

Stephen Ashworth - Exactly, certainly the seaweeds give off a lot of iodine in compounds and that iodine then gets processed by the atmosphere and turns up in these aerosol particles and they are just the sort of surfaces you were talking about right at the beginning that would enable water to condense and form clouds.

Chris Smith - How does the iodine get out of the seaweed and into the atmosphere?

Stephen Ashworth - Well, it seems that this is mechanism against stress. If the seaweed feels stressed it releases these compounds and one of the things that stresses seaweed is the tide going out so they tend to get dry and release compounds containing iodine.

Chris Smith - So that would then be blown up on the pervading wind into the atmosphere where it would then have downstream, excuse the water pun, effects on the weather.

Stephen Ashworth - Yes, exactly. The sun shines on these compounds, the light, it's the interaction with the light of the sun that causes the iodine to be broken off these compounds. It then turns out and reacts with ozone in the atmosphere to produce iodine oxides and there what go on to make up these, the particles.

Chris Smith - So how are you trying to understand more about this iodine and to understand more about the chemistry as to how it gets into the atmosphere and how much width there is?

Stephen Ashworth - Well the idea here is that we can measure in the atmosphere what's there. We want to answer the question how was it produced and what's it going on to make at a later date with interaction with other chemicals in the air, with sunlight and whatever. So we need to take things back to the laboratory and make these compounds under as controlled conditions as possible and analyse how fast they react, what they react with and what they turn into once they have reacted.

Chris Smith - And how are you doing that?

Stephen Ashworth - Well we can mimic this process by producing ozone in the sample cell and feeding in some iodine containing compounds. We can also mimic sunlight in the laboratory fairly well and we find that we make lots of particles. Another experiment that we have done is to actually try and break down the production of the particles into a series of steps and so that we build up the iodine oxides one step at a time.

We find to do this, these compounds don't absorb very much light. This is how we measure how much we have got and how fast it is reacting. We use a laser to see how much light is absorbed.

Chris Smith - All right, so you know the different chemicals absorb laser light at different wavelength so if you shine a laser beam of the right wavelength through it, the amount of laser light that get soaked up must be proportional to how much of the chemical is there.

Stephen Ashworth - That's exactly right but because we need a lot of chemical in this case to actually see the change in the laser light and we have to do a little trick by trapping the laser light between two mirrors and that makes it bounce up and down through our sample lots of times, and if we are lucky with the right combination of circumstances we can get effective lengths. So it makes it look as though the sample maybe 10 kms long.

Chris Smith - Has anyone actually done this in terms of really shining a laser beam through 10 kms of atmosphere rather than bouncing it on a light path, 10 kms long between two mirrors like this?

Stephen Ashworth - There are experiments which do that, you can shine a laser beam 90 kms up into the atmosphere and get a signal back in an experiment called LIDAR but it's a slightly different principle that's involved there.

Chris Smith - But do the results agree? So you think you've got a good model with your mirror bouncing system to accurately predict this important aspect of atmospheric chemistry?

Stephen Ashworth - Okay, I misled you a bit there, the LIDAR results aren't actually used on the iodine chemistry but we believe through modeling - again we have heard earlier in the program about the various modeling that can be done - by modeling the systems using the results from the kinetics that we measure and how fast these reactions go and what's produced, we can be confident that we have a fairly good understanding of this system.

Chris Smith - Genius, thank you very much Stephen.

Stephen Ashworth - My pleasure.

克里斯·史密斯——斯蒂芬·阿什沃思博士是谁from UEA, University of East Anglia working on ways to detect the chemicals that are important to climate and the earth's atmosphere.