Not Just a Lot of Hot Air; Air Pollution: Trace Gases Have Changed, but the Basic Composition of Air Remains Stable

Article excerpt

Byline: CHARLES LEGGE

QUESTION Has the make-up of air, nitrogen 78.08 per cent, oxygen 20.95per cent, argon 0.93 per cent and carbon dioxide 0.03 per cent, altered withglobal warming, pollution and deforestation?

FOR the past 200 to 250 million years, the Earths atmosphere is thought to havebeen a relatively stable oxygen-nitrogen system, maintained by biologicalproductivity and geological forces seem-ingly working hand-in-hand to maintainsteady levels of gases.

In recent history, that composition seems barely changed but the levels of manytrace gases and aerosol particles have been changing, largely as a result ofhuman activities. Although totalling less than 0.1 per cent of the mass of theatmosphere, these constituents determine much of its chemical and physicalstate.

Best documented of these is CO2. Researchers have shown through analysis ofcarbon dioxide in the ancient Antarctic ice that at no point in the past650,000 years did levels approach todays carbon dioxide concentrations ofaround 380 parts per million (ppm).

TheIntergovernmentalPanelonClimate Change (IPCC) projects that atmospheric carbon dioxide levels couldreach 450-550 ppm by 2050.

Theheatingeffectofextracarbondioxide, methane, nitrous oxide and many other minor gases can be calculatedwith confidence based on the absorption properties that have been measuredcarefully in the laboratory.

Currently, the total heating produced by the increases of all long-livedgreenhouse gases since pre-industrial times is equal to about 1 per cent of allsolar radiation absorbed at the surface.The effect would be somewhat similar if the sun had started to shine 1 per centmore brightly during the 20th century. This could potentially gather Airpollution: Trace gases have changed, but the basic composition of air remainsstable pace over the next few decades with well documented consequences.

Other trace compoundssuch as the chlorofluorocarbons, their replacements, and sulphur hexafluoridearesynthetic,recently appearing in the atmosphere for the first time. Trace gasconcentrations are low (parts per million or much less),and as such they have not been a direct threat

to human health.

But many trace gases have important chemical and physical characteristics, evenat these low concentrations. They intercept electro-magnetic radiation from theSun and from the Earth and have large effects on climate.

They can react with other components of the atmosphere, in some cases veryeffectively, such as the role of chlorine atoms in stratospheric ozonedestruction.

QUESTION Are steak tartare,tartar sauceand dental tartar related?

THEoriginofsteaktartar,a combinationofrawmeat(beefor horse) with raw egg, capers, pickles andotherseasonings,isderived fromoneofthegreatoldfood myths. Legend has it that the Mongolian and Turkic tribes known as Tartarswouldplacesteaksunder theirsaddlestocushionand soothe their mounts during days of riding.Whentheyretrievedthe meat,itwould be so tenderised from the saddles friction that they could eat it raw.

Steak tartare is thought to have beenknown in Europe since the 14th century.

TheoriginofthewordTartar, referring to the people themselves, is uncertain but is believed to bederived from a tribe that inhabited thenorth-easternGobidesert called the Ta-ta or Da-da. These were driven south in the ninth centuryby the Chinese before founding the Mongol Empire under Genghis Khan.

The Tatars were fierce warriors and its commonly held that the r was addedduring the Mongolian invasionsto link the tribe with Tartarus, the classical notion of The

Underworld or Hell.

Tartar sauce is mayonnaise flavoured with chopped capers, dill picklesandolives,nowusually servedwithdeep-friedfish. …