LAQN Pollution Episodes

Pollution Notification released on 04/04/2014

Monday started with many people waking to find their cars covered in Saharan dust which attracted considerable press coverage.
While this was forecast to continue throughout the week, and further deposits were seen, the extent to which this contributed to the air pollution at ground level is the subject of ongoing research.
The particles that have a health impact (PM10 & PM2.5) are much smaller than the visible Saharan dust deposits.

The light southerly winds that arrived in the UK between Monday and Thursday had travelled over France at low altitude for around three days, accumulating urban and industrial pollution.
Once they arrived over the UK, our own local emissions added to the pollution mix.

Throughout the episode exhaust emissions, both continental and local, were identified as a major component of the pollution

Monday 31st and Tuesday 1st April London saw widespread ‘moderate’ particulate, both PM10 & PM2.5. The air arriving on these days would have been carrying weekend emissions from France.

On Wednesday 2nd, the weekday emissions from France started to arrive and combined with our own emissions. PM2.5 showed a steady rise throughout Wednesday and into the early hours of Thursday. PM10 however showed a marked increase during the Wednesday morning rush hour; indicating the mixed nature of the pollution sources during this episode.

Widespread ‘High’ PM10 & PM2.5 was recorded throughout London on both Wednesday 2nd and Thursday 3rd. Outside London, widespread ‘moderate’ levels of pollution occurred across the south-east and a single site beside the A1 in Bedfordshire reached ‘High’.

Overnight on Thursday a change to winds from the Atlantic started to bring a clearance although, with winds still light, this was initially slow.

Although this episode attracted significant press and public interest, pollution levels were actually higher during the previous episode of mid-March (12th – 14th) when levels reached ‘Very High’.