Pollution, Mountains and Rainfall

Pollution seems to be affecting rainfall in mountainous areas, there have been many reports of this over the last few years but now there is some hard evidence for this effect.

Daniel Roesnfeld of the Hebrew University in Jerusalem has been studying rainfall, and the amount of pollution on Mt Hua, a sacred mountain in China, over the last few decades. He has compared this rainfall with an area of plains a few km away. As the pollution has increased the amount of rain the mountain gets compared to the plain has decreased.

Rain is produced on mountains (orthographic rainfall) is produced when humid air is blown into the mountain, so it has to rise, this causes it to cool, and the moisture condenses onto bits of dust etc into small drops, then these collide and grow to the point they fall out of the cloud as rain.

If the air is clean, not very many drops form to start with, so they grow quite large and it doesn't take them long to grow big enough to fall as rain, however if the air is polluted, there is much more dust, so far more drops form to start with, so they are much smaller and it takes them many more collisions and much longer to grow large enough to fall as rain, by which point the air is often down the other side of the mountain.

This could be a big issue for many polluted areas that are dependent on mountain rains for their water.

4th Mar 2007

Putting the brakes on car accidents

Canadian researchers have come up with a way to make the roads safer, with a revolution in brake-light design. University of Toronto researchers Zhonghai Li and Paul Milgram realised that although brake lights signal when a car in front may be
slowing down, they give no indication of how hard the brakes have been applied. To get around this problem they came up with triangular brake lights that grow larger and also move outwards the harder the brakes are applied. They start off as a triangular cluster of three lights on each side close to the middle of the car. With more urgent use of the brakes the lights enlarge and move outwards. When they tested the system on 40 drivers using a simulator the biggest gains were during poor driving conditions.

The team hope that their new invention, which they aim to build using low-power LEDs, will make a significant dent in the numbers of rear-end collisions, which make up about 30% of road crashes in countries like the US, UK and Australia.

11th Mar 2007

Making light of asteroid spin

Scientists in Helsinki have spotted an asteroid behaving badly, and it's all down to light. Mikko Kaasalainen, from the University of Helsinki in Finland, has been watching an asteroid called Apollo, which is about 1 mile across and spinning. But careful measurements have revealed that the asteroid is very slowly altering its rotational period, by about one 4000th of a second every year. It's the result of a phenomenon called the YORP effect, short for Yarkovsky-O'Keefe-Radzievskii-Paddack effect. This occurs when light hits a surface and gives it a push. But because the asteroid is an irregular shape some parts of it receive a bigger push when sunlight hits it than other parts. The result is that the object's rotational period begins to change. So could this push an asteroid into the path of the Earth, provoking a collision? "Theoretically yes," says Kaasalainen, "but the reverse is also true and scientists have suggested making part of the surface of an Earth-bound asteroid more reflective to take advantage of this effect and avoid a collision". The observations are published in this week's Nature.

11th Mar 2007

Finding the killer asteroid

NASA have just published a report on how the should look for asteroids that may be on killer orbits and collide with the Earth, like in the Hollywood blockbuster Deep Impact.

Space is unfortunately a big place and asteroids are pretty tiny by comparison, being only metres or kilometres across. This makes them very hard to spot. Despite this NASA estimates that there are around 20,000 asteroids bigger than 140 metres across that would wipe out a whole city if they hit the Earth, and we don’t know where most of them are. Such an asteroid would leave a crater around 3 miles in diameter and destroy everything for miles around. We believe that a much smaller object, about 10 metres across, hit Siberia in the early 1900s and laid waste to 2,000 square km. We estimate that an object on this scale hits the Earth roughly once every 250 years. There may even be some huge asteroids bigger than 10 km on collision course with Earth. These are much rarer, hitting about ever 25 million years, but one of these would cause Tsunamis, climate change, earthquakes and volcanic eruptions, devastating whole continents.

The solution is to put a telescope in space to look specifically for them. But where? It seems that the best place is near Venus. This is because sometimes asteroids come from the direction of the sun, which makes them hard to spot, like a fighter pilot attacking from the sun. Because Venus is closer to the Sun than Earth we can spot any asteroids coming from that direction. Unfortunately this mission would cost about 700 million pounds (1 billion dollars) and NASA don’t have the budget to do it. Until they do we’ll just have to keep our fingers crossed that the next killer asteroid hasn’t already got us in its sights.

11th Mar 2007

Science Update - Polio and Viruses

Chelsea - Since 1955 America has spent 35 billion dollars on Polio vaccination, that might seem like a lot but that spending has generated a net saving of over 180 billion dollars, that's according to a new analysis by scientists at the Harvard School of Public Health. Lead author Kimberly Thompson says they modelled how the disease would have spread without vaccinations and then estimated how much it would have cost to treat it.

Kimberly - People often don't realise that its hard to get credit for things that don't happen. This is a real challenge because with respect to public health because if people don't see the benefits of intervention but they look at the cost, then they might misperceive in fact how very valuable public health interventions are.

Chelsea - She says that's an important lesson not only for efforts to eradicate Polio in developing countries, but also for healthcare systems in developed countries where emergency treatment often trumps preventative care.

Bob - A new kind of drug may fight viruses and other causes of disease by silencing their genes. The key ingredient is small interfering RNA, a molecule that can block specific genes from making proteins. Julie Leberman from Harvard Medical School says such drugs would have broad potential.

Julie - Since the machinery for RNA interference exists in all cells, this natural pathway can be used to silence any gene that might be involved in disease.

Bob - In animal studies, Leberman's team found a way to get interfering RNA into infected cells without affecting healthy cells. Now she and her colleagues are working RNA therapies for a respiratory virus, pandemic 'flu and even high cholesterol.

Chelsea - Thanks Bob, next time we'll look at how global warming could break up some happy symbiotic relationships. Back to you Naked Scientists...

March 2007

Silicone in Petrol

Chris - Earlier this week there were a whole number of retailers who admitted that stocks of their petrol had been contaminated with something that had caused hundreds of cars to grind to a halt, but what was that substance and how did it get into the petrol in the first place? To tell us what he's flushed out in the fuel line about this story, Richard Van Noorden is here from Cambridge-based Chemistry World. Richard what have you found out about this story?

Richard - Well Chris, the culprit was silicone in the petrol causing the cars to judder to a halt. Slightly confusingly though it probably wasn't the element silicon as the silvery-grey semi-metal that you find in computer chips; that wouldn't have got in to the petrol as its not soluble in petrol. What actually happened, was that people who were testing for silicon found the presence of silicon atoms in the petrol and the way you do that – its a bit like your old school flame test – you heat up the petrol and each atom gives off a characteristic wavelength of light and you get that colour that's characteristic to silicon.

Chris - Because this is the way that people work out what is in the sun, if you look at the sun's spectrum you can work out what elements there must be in the sun and in roughly what quantity, because you get light of a very characteristic wavelength coming off.

Richard - Exactly, so sodium street lamps give off that characteristic orangey sort of colour.

Chris - Why was the silicone in the petrol? Do we know?

Richard - We don't actually know why the silicone contaminated the petrol, it shouldn't be in the petrol. As silicones, which is when the element silicon combines with oxygen to form long SI-O -SI-O silicon-oxygen chains with Carbon and Hydrogen hanging off the end of the silicon, these kind of polymers, called silicones, can be gel-like, rubbery

Chris - Its bath sealant isn't it?

Richard - Yes, used also as breast implants, as lubricants as greases so its very likely that silicone which is soluble in petrol caused cars to judder to a halt, because when the silicones burnt when the petrol was combusted, the hydrocarbon bits (the carbon and hydrogen atoms) were burnt off leaving silicon and oxygen – silica which is of course sand, glass.

Chris - So you made sand in your engine?

Richard - You made sand, its going to come out as a kind of whitish deposit and that will clog up the oxygen sensors in the engine. The oxygen sensors just gave up, they said “look we're controlling the flow of fuel and we're being clogged up so we're going to give up and your car is going to judder to a halt.”

Chris - So presumably only some cars which would have had high-tech oxygen sensors like this would have been affected?

Richard - Yeah, it looks like older cars actually carried on ok, despite the fact they had an engine full of sand.

Chris - Are there any fuels in which you would normally place silicones?

Richard - Yeah, you would put silicones in diesel where they're anti-foaming agents so they stop the diesel literally foaming up as you're pouring it in. You should never have it in petrol.

Chris - So why don't they form sand in a diesel engine then?

Richard - Diesel is not combusted by sparks, in the same way as petrol is, in diesel you use pressure it also ignites whereas in petrol you're using a spark to burn off the carbon and hydrogen.

Chris - But that shouldn't make a difference to whether there's a heat there that can burn silicone and react with oxygen surely?

Richard - I'm not exactly sure of the answer to that question Chris, but I know there isn't that problem on diesel.

Chris - Maybe its just because diesel engines are so robust that they'll burn anything, what do you think Dave?

Dave - I guess if a diesel engine doesn't have an oxygen sensor its just like an old-fashioned petrol engine so it would just keep on going, there's nothing to gum up.

Chris - Sure, we've now got to the bottom of it – we think its silicone, it got into the petrol it shouldn't have done. Is there any way that we can prevent this happening again?

Richard - One of the problems with finding out that it was silicone was that the standard test for petrol doesn't include a test for silicone because it shouldn't be in there. They test for all the additives in petrol – lead, copper and so on. So harvest energy who are one of the suppliers to the supermarkets like Tesco, that the faulty petrol came from; they say that they are going to now include a standard test for silicone in the petrol whenever they check it. So there's obviously a quality-control, 'how should we check our petrol' issue there.

Chris - Has it ever happened before Richard?

Richard - As far as we know, not in the UK but intriguingly according to the American oil company Chevron's website used toluene which is a solvent, from a manufacturing process containing soluble silicon, has apparently found its way into gasoline as the Americans call petrol and again fouled up oxygen sensors. Now that's on our website and when I checked this with a specialist from the American petroleum institute he couldn't remember details of that so I'm just throwing this out, nonetheless I have had people say this to me; that it has happened in America and somehow re-cycled toluene with silicon in caused the problems and got in to the petrol. Now of course I don't know if that's happened here and no doubt in the next few weeks we'll find out exactly what has happened.

Chris - Thank you Richard, from Chemistry World of the Royal Society of Chemistry, you can see the article Richard has written about this on their website: www.chemistryworld.org

March 2007

Seeing the invisible

Carbon Dioxide is an invisible gas that amongst other things we breath out. In this experiment you can see it.

What you need

What to Do

In a reasonably still room:

Put 2-3 teaspoons of bicarbonate of soda into the glass

Add vinegar, until the glass has been filled with foam

Wait for the foam to die down

Turn on the torch

Carefully put the glass beween it and a white wall - or if it is a sunny day in front of a sunlit white wall will work too as long as you are inside.

Imagine the glass is full of a fluid and pour that fluid out.

Look at the wall as you are doing this.

What may Happen

You should see very faint shimmery patterns pouring out of the glass, even though you can't see anything there.

What is going on?

There is a gas called carbon-dioxide locked up in the bicarbonate of soda. When you add the vinegar you will release forming lots of bubbles and foam. When the foam dies away this gas sits in the cup because it is heavier than air.

This also means that when you pour the carbon-dioxide out of the glass it will fall down in a stream.

Light travels slightly slower in carbon-dioxide than it does in normal air which means that the light gets bent if it hits the carbon-dioxide at an angle (see the Pyrex in Oil experiment)

This means that in some places light from a few areas of the stream is bent together, focussing it and making parts of the paper brighter. There will also be shadows where the light would have gone if it hadn't been bent somewhere else.

If you put a glass up to the light you will see a similar effect. These patterns are in the general shape of the carbon-dioxide allowing you to see the otherwise invisible gas.

Written by Dave Ansell