Some thoughts on the Sahara dust, aka "smog", aka "pollution"

From today's BBC website - the so-called "smog".

Once again, the UK media is fouling up spectacularly, through conflating numerous factors that need to be separated.

Yes, there is Sahara dust settling on our cars after rain. The phenomenon has been known at least since the reports of Darwin, sailing across the Atlantic.  And yes, airborne dust may irritate the airways or lungs of susceptible people, those with pre-existing conditions especially, but keeping children at home instead of school is a massive over-reaction. Who created an instant scare and why?

If it is Saharan dust alone, then all I can say is "get real". I was in the savannah north of Ghana in the late 60s when visibility was down to a mile or less, thanks to the Harmattan (fine dust blown in from the Sahara).

Ghana during the Harmattan season  (Akosombo dam).

But I never coughed, and don't recall others doing so. The main concern was cracked skin on lips, due to the dry air.

So are there other nasty ingredients in the mix, responsible for the "smog" description?  Is it photochemical smog? Maybe, that's easy enough to check, since the chief particulate there is  likely to be miniature suspended crystals of ammonium nitrate or sulphate. Have we been given data for grown ups? Nope. We're talking about the UK media here with its exceptional inertia and resistance to getting on to experts in universities, the learned societies and elsewhere who know about such things.

Maybe it's plain old diesel engine pollution, giving rise to excessive levels of nitrogen oxides or small carbon particulates (PM10s). Any hard evidence for that? Nope. We're talking about the UK media here. Don't bother asking for hard evidence.

More later, once we have some data, some numbers that might justify the current headlines that would have us believe that the air we breathe is essentially no different from that of Beijing's.

See this blogger's previous posting on Saharan dust, photographed while on holiday in Pisa, with some speculation re a possible role in spreading foot-and-mouth disease. (OK, a bit of a long shot).


Update:  Telegraph:  Saharan dust and pollution. We need a sense of proportion says Boris Johnson.

And here's a link to a video clip on the BBC's site, an interview with a senior ' air quality analyst" talking about "pollution" without specifying its nature, except to say it's "sometimes" washed out of air by rain, but not always, because, wait for it, "it's a bit complicated". 

http://www.bbc.co.uk/news/uk-26864896

To think that I and most of my fellow countrymen and women pay a hefty annual licence fee for that condescension, that banality!

What was interesting was to hear that London is now at the top of our local 10 point scale for "pollution" (whatever that means). But don't run away with the idea that we now match Beijing, where the top of its scale is described  as "100 times higher".  The issue-obscuring, dare one say media smog  gets  progressively worse, progressively dumbed-down,  year on year.

Update: Friday 4th April

Today I'll be attempting to dissociate the various conrtibutions  to what our media are presently describing as a 'killer smog'. A few more perceptive outlets are referring to a "cocktail" though for many "dog's dinner: might be a more appropriate description.

We'll start by conidering the origin of the term smog as a mixture of smoke and fog, and why it came to such prominence in connection with the London 'peasoupers' in the 1950s, which this blogger recalls vividly (one could stretch one's arm in front of one and be unable to see one's finger - but were still expected to find one;s way to infant and junior school). We'll look at the meaning of smoke, in a scientific context, as an aerosol of suspended solid particles in air or gas generally, and ask if it was really "smoke" that was killing thousands of people when raw coal provided the chief ,means of heating homes, until the Clean Air Acts arrived, requiring first smokeless fuel, and then gradually encouraging cleaner alternatives to solid fuel, notably gas and electricity.

We'll then look at 'photochemical smog' associated with vehicle pollution, and of great concern in US cities especially in the 60s and 70s, and consider the nature of vehicle exhaust emissions, before and after the introduction of now obligatory catalytic converters, and the crucial role that sunlight plays (thus the 'photo' of 'photochemical'). We'll find ourselves discussing ozone (that's ground-level ozone, one of the nastiest and most insidious of the air pollutants), and how it comes to accompany photochemical smogs,  but also ask what the solid components are of a photochemical smog (since ozone, nitrogen oxides, sulphur oxides, unburnt hydrocarbons etc are gases and/or vapours, not solids).

Finally, we'll briefly consider the difference (if any) between a smoke and a dust-laden atmosphere.

The Great Smog of 1952

Here's a link to essential background reading (and very readable too):component of the smog that brought visibility down to feet and sometines inches.



http://martinfrost.ws/htmlfiles/great_smog.html

I shan't try  to summarise it here. Suffice it to say that what descended and got trapped over London would have been  "smog" literally, i.e. a combination of fog (minute swirling airborne droplets of condensed water vapour) and solid particles, The latter, the suspended solid "smoke" component was derived from the burning of soft coal prior to replacement with smokeless solid fuel (coke, anthracite etc) . (Light porous coke is coal that has had volatiles driven off first, so that it produces fewer gases and vapours,  little if any flame, and much less sending aloft of solid carbon and ash particles). That's the visual aspect. But it's unlikely that smog as described here was the real killer. The latter was almost certainly due to the "passengers" in that smog, notably oxides of sulphur (SO2, SO3, i.e. sulphur dioxide and trioxide) and especially droplets of sulphuric acid, H2SO4, which form when oxides of sulphut react chemically with moist air.

So while the killer smogs of the coal-burning era are of limited relevance in modern UK, Europe and the US (though still a major contibutor in China) they provide a pointer as to the multifactorial nature of man-made air pollution. There is visual pollution one can see - suspended solids especially. But there are the less visible or indeed invisible components that one cannot - noxious gases and liquid acids derived therefrom.

Is the present smog over the UK a killer,or potential killer? Are the mortuaries filling up with old people especially who have wheezed and coughed to a premature grave, as was the case in 1952, when there was suddenly a shortage of coffins, and when florists shelves were cleared of flowers?

The answer so far seems to be NO. In fact, the London Ambulance service reckoned there were an extra 27 call-outs for the entire city that could be attributed to the "killer" smog.  That is reassuring, while no grounds for complacency. Let's press on all the same with the science, and ask whether the poor visibility and air pollution readings really justify the term "smog" or whether dust-laden wind from the south, with additional vehicle pollutants from the Continent, with or without appreciable photochemical endproducts, are the cause of the hundreds of scare stories in our media.

Here's a link to the latest from the BBC's website. I recommend careful reading.
What seems increasingly clear is that our EU masters are using the visibility of this pollution episiode, due to an entirely natural phenomenon, in ordre to justify ongoing legal action against the UK for excessive levels of nitrogen oxides.

But the main cause of nitrogen oxide pollution is diesel engines , which previously have been promoted for their greater fuel economy on a mile per gallon/kilometre per litre basis.  Catalytic converters are supposed to deal with the greater amounts of nitrogen oxides, formed primarily by reaction between atmospheric nitrogen and oxygen under higher compression/temperature compared with a petrol engine - but which clearly do not. It's hard to escape the thought that the EU are being incredibly opportunist right now, and need to step back and think through the science, pollutant by pollutant, source by source. Our control freak masters in Brussels also need to bear in mind  that air pollution, especially from vehicles and industry, is no respecter of national boundaries.

Photochemical smog

Here's a good link that explains the complexity of photochemical smog. 

Why is it good? First, it focuses attention on end-product ozone, O3. a very nasty airways irritant. Secondly it shows how those nitrogen oxides, undesirable in themselves, operate as recycling catalysts to cause oxygen conversion to ozone. Thirdly it shows the permissive role that is played by petrol fumes released into air when you fill up your car, the socalled VOC component of air pollution (VOC = volatile organic compound) which through complex chemical cycles results in far more end-product ozone than would otherwise be the case.

Update: Friday 10:30  Comment under the Boris Johnson article in the Telegraph:

Latimer Alder • 5 hours ago

I cycled 15 miles on Wednesday, 35 miles yesterday. It was only when a friend berated me for 'not heeding the warnings' that I even knew we supposedly had a 'pollution' problem. Though the air had seemed a little hazy, there were no other noticeable effects
I'm in my late 50s and line in the South-East - supposedly the epicentre of the disaster
But I do recall a similar incident of Saharan dust back in the 60s. The major worry then was not about people's health, but about the need to redo the washing which was hanging on the line.


Update: Middle England: the day started very overcast and gloomy, and my first thought was: Are the Jeremiahs maybe right after all? Is there an exceptional weather event, bringing exceptional air pollution?Well, it's now mid-morning. It's still gloomy but there is no problem as regards visibility. The wooded ridge, about a mile away, that I see from my window is in plain view with no hint of haze in the air. It's simply overcast with grey skies, and children are playing happily outdoors in the nearby school. Next apocalyptic crisis please, dear UK media.

 I shall now take a break, needed to go through 44 pages of  the EU's pdf setting out limits on common air pollutants (oxides of sulphur, nitrogen, fine particulates etc). Not surprisingly, ozone limits are not specified, it being assumed that limits on the primary precursors (nitrogen oxides especially) should prevent excessive O3 production.


Update: 5th April. The story has now died the death, glad to say. Once again, the way this story broke did not reflect terribly well on our print media, especially the tabloid end with its "killer" smog headlines (but what else is new?). I still have to track down (if possible) the actual data that got the Government claiming there was a conjunction of both Sahara dust and top-end levels of normal pollutants (yes, I'm sticking with this topic for a while longer, if only to be better prepared to respond to the next alert tha keeps children off school, probably needlessly). I had a sudden thought last night. That 10 point scale the Govt use is made up of different pollutant concentrations (SO2, NOx, and, wait for it, particulates, especially the smallest particles - PM 2.5 and PM10s): the latter are often, dare I say usually taken to mean fine carbon particles, especially from diesel engines. You don't suppose that Saharan dust particles upped the PM figures, and that the assumption was made that any fine particle, capable in theory of being trapped in the lungs, was as bad as another? Evidence? To return to my earlier point, what is the evidence if any that people who live in the savannah regions bordering the Sahara desert, who have an annual harmattan season with poor visibility, suffer an appreciably higher rate of airway and lung disorders than those who live elsewhere?


Update: Sunday 6th April. Spotted that the Sunday Times had done a front page feature on diesel fumes this morning, and not having an online subscription, went out to buy the dead tree version (first time I've done that in year).
In fact there are three items in today's  paper no less, all focusing on what is seen as the grozing menace of diesel engine pollution, prompted, rightly or wrongly, by the Saharan dust.
As I say,the first is on Page 1 and 2, entitled: "Diesel deadlier than petrol". The second is on Page 11: "Diesel fumes hard children's brains" and then there's the much-respected Camilla Cavendish on Page 23: "With every extra breath, children demand we are weaned off diesel".There are some alarming statistics in those three articles about the growing levels of atmospheric nitrogen dioxide and fine particulates that have been linked  diesel-powered commercial vehicles AND especially to the growing popularity of diesel-engined cars. I'll be back later with some details. Suffice it to say that modern research indicated that those fine particulates are not just a threat to lung function. They transported to all parts of the body - heart and brain included -  and are now implicated in a much wider range of pathology than previously (strokes, heart attacks, age-related memory loss, even autism). Living as I do less than a mile from one of England's major motorways, and (subjectively) aware that I cough a lot more than I did before moving here, I shall be keeping a closer watch on air pollution issues from now on, reporting anything that appears noteworthy, or areas of possible miunderstanding in the media.Update: 1st May 2014: articles in Daily Mail: "The Deadly Diesel Deception"