Atmospheric
Optics
The UK/Ireland Ozone Hole
~ The episode of rare polar stratospheric clouds (PSCs) over Ireland and UK started on 31st January and has so far lasted three days. The picture above was taken after sunset on 2nd February and shows extensive Type I (acid droplet) and some Type II (nacreous ice) stratospheric cloud. More pictures are below – earlier images here 1,2,3.
French Alps
Dawn on Feb 1st.
Far south for PSCs but the stratospheric temperature there was low enough for them to form.
Sightings in The Netherlands afternoon and evening of 2nd February.
At left the scene suggests predominantly Type I (acid) PSCs as in the topmost image.
Daytime.
Another daytime sighting at Deventer in The Netherlands.
PSCs come in several types. Only Type II (nacreous) are the bright and strongly iridescent ones. Nacreous clouds are tiny ice crystals and are fairly benign. Type I PSCs are another matter! They are very small droplets of nitric and sulphur acids. Strange as it seems, these clouds are completely natural. But they act on chemicals that we emit into the air.
The acid droplets destroy the stratospheric ozone layer that protects us from harmful solar ultra-violet rays. They catalyse unreactive forms of man-made chlorine into active free radicals (for example ClO, chlorine monoxide). The radicals destroy many ozone molecules in a series of chain reactions. Type I clouds also remove gaseous nitric acid from the stratosphere which would otherwise combine with ClO to form less reactive forms of chlorine.
The Type I clouds have produced an ozone hole over UK/Ireland
Ozone concentrations at noon on February 1, '16
Blue is lowest. There is a hole over Ireland/UK
From NASA Arctic Ozone Watch, GSFC
