Essentially, they have disclosed the information which was asked for,i.e. details of exactly which "colourless, odourless, non-toxic" gases, and the quantities which were released into the atmosphere, in the Marylebone / Westminster area of London, to help refine computer models of urban airflows, for chemical and biological warfare or terrorism planning purposes.
As suspected, the gases released are non-toxic, but that does not mean that they are harmless - they are,in fact very potent Greenhouse Gases.
It does seem that they were originally contemplating using Sulphur Hexafluoride, which is the most potent Greenhouse Gas ever tested, which , due to its inertness and stability, is estimated to be equivalent to 23,900 times the equivalent amount of Carbon Dioxide, in terms of its Greenhouse Gas warming effect on the atmosphere, over 100 years.
As it happens, the 3 gases chosen, are the next 3 most potent Greenhouse Gases, equivalent to hundreds of tonnes of Carbon Dioxide, even for the small amount used in the Tracer Gas Trials, which planned to release a few grammes, on about 30 occasions.
This is a Carbon Equivalent which would be similar to a car, circumnavigating the planet several times.
Under the Environmental Information Regulations, the Home Office should have published the Environmental Impact Assessment pro-actively, before the gas emissions began. Why could they not have published these details as part of Home Office Minister Tony McNulty's original Statement ?
For clarity, the corrections in the Home Office email, to the number sequence of our original Questions, have been omitted: