LAQN Pollution Episodes

Pollution Notification released on 05/03/2018

Moderate and high particle pollution was measured throughout London and the south on Friday and Saturday, and also across large parts of the UK and western Europe including Germany, Belgium and the Netherlands. Within the UK the particle pollution covered all of England except those areas north of a line between Merseyside and Yorkshire and west of Bristol. Some particle pollution was also seen in the south east of Wales.

For the majority of the cold weather period last week winds originated over the south Baltic and northern Germany and particle pollution remained low. A change in wind direction to include a track from east Europe caused increase sulphate particles from Thursday 1st March, indicative of particles from coal burning areas. Air tracks from then onwards included greater time over north western Europe and the UK and particle pollution increased showing contributions from traffic, gas combustion and wood burning. Saturday brought an unexpected recirculation of air that had been over us on Friday.

Wood burning particles slowly increased from Thursday through to Sunday morning. The greatest concentrations from fresh local wood burning were seen on Saturday and Sunday evenings, unusually wood burning was seen throughout the daytime and may be indicative of people remaining at home due to travel disruption and heating their homes all day.

There is evidence that the particle pollution included not just fresh wood smoke but also wood smoke particles that had chemically reacted in the atmosphere to form organo-nitrate particles. The weekend also included nitrate particles more typical of normal spring time episodes produced from chemical reactions between traffic exhausts, natural gas burning, and farming.

This was not predicted by any of the forecasting services operating within the UK. This may be due to the usual emissions patterns with day-long home heating and wood burning, which would not be captured in emissions inventories along with the formation of secondary particles from wood burning which is a topic of current research.

A fresh westerly air flow caused a very sudden clearance of the particle pollution overnight into Sunday but there was still some local wood burning pollution in London on Sunday evening.