PM2.5 levels  in Eastbourne have spiked twice today to over 50µg/m³ at just after 0700 BST and 1900 BST. PM10 levels followed a similar pattern passing 70µg/m³ this morning and 60µg/m³ this evening.

SDS011 PM2.5 data for Sovereign Harbour Eastbourne, UK on 23 October 2019 (times are GMT)
PM2.5 Data for 23 October 2019 (times are GMT)

Wind speeds were very low overnight and into early morning on Wednesday before rising swiftly from the south around 1000 BST. A MetClim forecast issued on 21 October (i.e. 48 hours earlier) for PM10 levels indicates that the pollution came from continental Europe as a body of air has moved up from the Mediterranean across Italy, Switzerland, Germany, Belgium, and France before crossing the Channel to reach us in two bands. The MetClim forecast's timings for what actually happened on 23 October seem  fairly accurate, to within an hour or so.

24hr average figures at 2300 BST are 28µg/m³ for PM2.5 which is in the Low DAQI range (Index 3), and 34µg/m³ for PM10 which is also Low (Index 3). At the time of writing particulate matter levels are increasing again, meaning that the 24hr average figures will go up too (current levels are PM2.5 at 45.5µg/m³, PM10 at 54.6µg/m³).

I came across the WHO guidelines on particulate matter values again this week and was surprised to be reminded that for PM2.5 they have a 10µg/m³ annual mean value, and a 25µg/m³ 24hr mean value. For PM10 guideline levels are 20µg/m³ annual mean, and 50µg/m³ 24hr mean. This is a double surprise: first that these values are so small, and second that they can be breached while still being in the DAQI "Low" range! That's what happened today – PM2.5 24hr average figure at 28µg/m³ is in breach of WHO Air Quality Guideline values, while still only being with the Defra's DAQI Low range. This sentence on the same page was sobering,

ʻSmall particulate pollution have health impacts even at very low concentrations – indeed no threshold has been identified below which no damage to health is observed.ʼ (WHO - Air Pollution)