It's been calm since Christmas Day, and PM levels have been steadily climbing towards unhealthy levels. Certainly the PM2.5 values anyway. PM10 has also been rising but not to the same degree.

The weekly graphs tell the story most clearly. There was a higher peak in PM10 levels on six days ago on Friday, but that was likely due to rain and wind. PM2.5 levels rose a bit then, but not at the same rate. Yesterday and today it is the other way round.

Is this another case of calm winds allowing a build up of exhaust fumes in the Eastbourne area which is not cleared by the usual sea breeze? Yesterday's average wind speed was 1 mph (gusting 8 mph), and today's is the same (gusting 7 mph). Nighttime minimum was 8.1°C yesterday and 3.1°C today, ie. getting colder leading to more fuel burned for heating.

PM2.5 levels hit 42ug/m³ (AQI 117 "Unhealthy for sensitive groups") shortly after 0600hrs (GMT) this morning, PM10 reached 46ug/m³ at the same time.
PM2.5 levels week ending 2018-12-27 PM10 levels week ending 2018-12-27