LAQN Pollution Episodes

Pollution Notification released on 27/01/2017

‘Very high’ pollution episode Summary for 20th - 26th January, issued 27th January 2017 from King’s College London


Recent cold, calm and settled weather conditions resulting from a high pressure system have contributed to a widespread particulate pollution episode with levels reaching ‘very high’. In addition, analysis has shown that a large contribution to this episode has been from wood burning as can be seen from the large PM2.5 levels measured on Sunday 22nd.
This has been the most significant London PM2.5 episode, in terms of number of locations measuring ‘very high’, since the Daily Air Quality Index was put in place in 2012.
On Friday 20th, ten monitoring sites across London reached ‘moderate’ PM2.5, along with locations in Sussex and Bedfordshire. ‘Moderate’ PM10 was recorded at seven roadside locations in London, and also in Windsor and Maidenhead, Bexhill in Sussex, and Eastleigh in Hampshire.
By Saturday 21st, despite the lower weekend traffic, thirteen roadside sites reached ‘moderate’ PM10 including Bexhill in Sussex, and Windsor and Maidenhead. Two busy roadside sites in London reached ‘high’ and ‘very high’. Two sites in London reached ‘moderate’ for PM2.5 as well as Sussex sites in Eastbourne and Horsham.
On Sunday22nd, an import of pollution from the continent during the afternoon was followed in the evening by cold foggy conditions with almost no dispersion. The rapid rise in pollution at this time was caused by a combination of traffic pollution and also air pollution from wood burning. This was the largest contribution from wood burning measured during the winter so far and wood burning from Sunday night was still present in London’s air throughout Monday.
The PM2.5 peak on Sunday evening was the highest recorded, as an average across London, since April 2011 (measured as an hourly average). Right across the south east and London, ‘high’ or ‘very high’ PM2.5 particulates was measured. On this evening, PM10 reached ‘very high’ at three sites in London and ‘high’ at twenty three sites in London, Reigate, and Windsor and Maidenhead.
On Monday 23rd, the ‘very high’ threshold was exceeded again at an even greater number of sites as weekday emissions added to the already elevated pollution levels. Continuing very light winds causing poor pollution dispersion resulted in ‘very high’ particulate pollution at over twenty sites in both roadside and background locations across the Greater London area. This is the largest number of sites measuring ‘very high’ pollution concentrations since the Daily Air Quality Index was introduced in January 2012. All other sites in the London Air Quality Network measured ‘moderate’ or ‘high’ PM10 and PM2.5.
The Mayor of London issued a ‘very high’ pollution alert on Monday to warn Londoners, advising them to take precautions to protect themselves against the very poor air quality.
On Tuesday 24th there was a general decrease in pollution levels across the Greater London area and the south east. No sites exceeded the ‘very high’ threshold. However, eight sites, including roadside and background sites, exceeded the ’high’ threshold for particulates. ‘Moderate’ particulate was widespread, measured at forty two sites in London, one site in Hampshire and three sites in Essex. A combination of higher ambient temperatures and a gentle westerly breeze for a few hours in the afternoon helped disperse some of the locally emitted pollution which had accumulated over the past week in calm conditions. Continued on page 2


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