The recent warm weather has led to a number of SO2 events affecting London, Kent and further north into Hertfordshire and Bedfordshire. In response to interest from network members, we have prepared a brief note covering the differences between these episodes and their likely sources.
Several events have been detected causing brief periods of elevated SO2 over most of London with one episode reaching across north London and into Bedfordshire and further events affecting Sevenoaks.
It must be emphasised that the SO2 concentration peaks measured during these events have been modest, not more than 60% of the AQS 15 minute objective concentration. However the concentration of 60 ppb, measured at Sevenoaks on 1st July, some 43 km from the source raises the possibility of a breach of the AQS Objective concentration closer to the source.
During the 2006 heat wave a combination of power demand in London and maintenance at several north England power stations lead to Littlebrook being used. The consequential earnings for owners RWE was subsequently reported in the Financial Times newspaper. During July 2006 a pattern of SO2 plume grounding was seen in London including a breach of the AQS objective concentration in west London around Teddington and Richmond.
At the time of writing (2nd July 12:45) a further SO2 plume was crossing London east to west, with over 60 ppb being measured in Bexley and Lewisham and a risk of moderate sulphur dioxide as the plume progresses. This is the second plume of the day to ground in east London and travel west wards. At the time of writing SO2 from the early morning grounding was centred over inner south London around Lewisham, Lambeth and Crystal Palace.
A link to the briefing note can be found below. A update to this will be issued if required. Further O3 episode analysis will be posted on the LondonAir website in due course.
Picture thanks to D Bullock.

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Item date 02/07/2009