Voices of Science

By 1972 Sweden presented its case to the UN conference on environment on the question of acid rain damage to trees and fisheries. At that time the OECD set up a programme called EMEP, it was a programme for monitoring and evaluation of long range transmission of air pollutants in Europe. That reported in 1977. In the meantime there was, shall I simply call it, a non-scientific reaction to power station emissions and acid rain. I mean there were cries for, the tall stacks were delivering acid rain to Sweden and Norway, and acid rain was causing the disintegration of cathedral stonework and so on. There was quite a movement there that wasn’t really terribly well founded. There wasn't agreement among all of the scientists concerned about some of the things that were being said. I suspect that Norway sort of considered this as a sort of national insult that our power stations should be spewing acid rain onto their territory. But because at Leatherhead we already had the mathematicians working, and they'd been working for years, on modelling the dispersion of plumes from power stations. And we had a wind tunnel there for modelling this as well, so the mathematical models were verifiable. And it was very clear, you could predict with great accuracy what was happening to the sulphur dioxide in the plume for example. You knew that the mixing layer, the lower level of the atmosphere, isn't just static or moving uniformly, it's turbulent and it mixes things up. The EMEP programme had produced models of the long range transport of air pollutants, and Leatherhead developed our own model of that. And our chemists started to work on the chemistry of this, because what we emit isn't sulphuric acid, its sulphur dioxide and that has to be oxidised into sulphuric acid and that needs an oxidant. I also had contact with the Met Office, Sir John Mason was the director general then, and were able to collaborate with them. They had an aircraft a Hercules equipped for measurements of all the physical things, cloud density and so on, and we were able to fit chemical equipment in their Hercules and we also put some in a Jetstream, and did a lot of work tracking these plumes and seeing what was happening. And it became clear that the oxidation was quite slow, you could actually fly across a plume in a Hercules and you could measure everything including the sulphur dioxide content and the acidity of the water droplets and so on and the oxidation was extremely slow. Out at 650 kilometres from the Eggborough plume, only a tiny percentage of the sulphur dioxide had been oxidised into acid, so there were already questions in our mind as to how could so much wet acid be formed if it hadn’t oxidised that fast? We weren't spewing out acid rain that fell soon on Norway and Sweden, that very likely it was going long distances before it was. It was only a little bit. But more to the point was that the hysteria on acid rain turned out to be, or the Norwegian assumption that because the wind was blowing from the South West and the rain was acid that it was coming from us, the measurements showed that the acidity of rain arriving in Eskdalemuir, for example, in Scotland, from the South West was only a shade less acid than the stuff arriving in Southern Norway, and the EMEP modelling showed that because the air, air patterns and wind patterns you know, are large and sometimes circular and they certainly don't all go in straight lines, that the origin of the sulphur being deposited anywhere in Europe wasn't where the wind had last come from but some kind of accumulation from where it had been in the last God knows how long. And they actually did an analysis, they had a computer model, the EMEP model, which they improved, they came up with figures that the UK contribution, because there were plenty of other countries like Poland, Russia and so on, Germany, to deposition in Norway was not very different from Norway's own deposition because after all Norway was burning fuels with sulphur in. So it was clear to us that the popular impression about acid rain was just not, not adequate.