Nigel Chaffey
In Chaos Theory, the butterfly effect refers to the notion that a small change at one place can result in much larger differences to a later state. The example used to illustrate this – and which gives the phenomenon its rather poetic name – is that of a hurricane’s development being contingent upon the flapping of a butterfly’s wings some time before. Well, possibly a more obvious ‘butterfly effect’ has been recorded by NASA (the USA’s National Aeronautics and Space Administration) with its Aura satellite. One of its images (pictured here) – of NO2 levels in central Africa in July 2011 – shows a red butterfly-like pattern that represents the highest levels of NO2 over the southern Democratic Republic of the Congo. The NO2 results from agricultural fires in which croplands are burnt to clear fields post-harvest, and to encourage new growth in pastures for grazing animals.
Unfortunately, NO2 is a major air pollutant that generates low-level ozone in the presence of sunlight, which in turn contributes to smog and poor air quality. And being gaseous the effects are felt not just in the vicinity of the fires, but democratically shared further afield; the smog affects plants and animals, contributing to respiratory problems in humans. In addition to NO2, the satellite-mounted ozone monitoring instrument (OMI) gives daily global coverage of key air quality components such as SO2 and aerosol characteristics, and provides mapping of pollution products from an urban to super-regional scale. Although recording these potentially damaging pollution events doesn’t necessarily stop them being produced it is an important step in understanding their source and prevalence.
Alun Salt
