Forecast published on Fri, 19 Jul 2019 06:00:00 +0100.
Values are for predicted maximum pollution levels, ranging from 1 (lowest pollution, best air quality) to 10 (highest pollution, worst air quality).
Colour key: Lowest pollution
There are no Defra monitoring locations in Hertfordshire
Data supplied by the Met Office via Defra. © 2019 Crown copyright Defra via uk-air.defra.gov.uk, licenced under the Open Government Licence (OGL).