Forecast Methodology

How are the forecasts produced?

The air quality forecasts are provided by the Met Office on a daily basis, 365 days a year, for locations across Sussex. These forecasts are checked, and whenever there is a predicted exceedance of the “moderate” air quality banding, alerts are triggered and sent out to recipients.

The Met Office weather forecast and climate prediction model uses UK and European maps of annual average pollutant emissions to simulate the release of chemical species into the atmosphere. These are then allowed to chemically react according to prescribed reaction rates, which depend on factors including the concentration of the species, the temperature and the amount of sunlight. Species are then transported and dispersed within the model according to the winds, and the concentrations are re-evaluated. Using the concentrations calculated in this way throughout the forecast period, the Daily Air Quality Index is calculated as an average over prescribed time periods. We have found that our Air pollution forecasts can be improved by using recent observations of air quality from across the UK, together with our forecast model, to give an adjusted forecast. We, therefore, use observations from the Automatic Urban and Rural Network (AURN) as part of our forecast system. (Source: https://www.metoffice.gov.uk/weather/guides/air-quality-forecast).

Band	Index	Ozone	Nitrogen Dioxide	Sulphur Dioxide	PM2.5 Particles	PM10 Particles
		Running 8 hourly mean	Hourly mean	15 minute mean	24 hour mean	24 hour mean
		µg m-3	µg m-3	µg m-3	µg m-3	µg m-3
Low
	1	0-33	0-67	0-88	0-11	0-16
	2	34-66	68-134	89-177	12-23	17-33
	3	67-100	135-200	178-266	24-35	34-50
Moderate
	4	101-120	201-267	267-354	36-41	51-58
	5	121-140	268-334	355-443	42-47	59-66
	6	141-160	335-400	444-532	48-53	67-75
High
	7	161-187	401-467	533-710	54-58	76-83
	8	188-213	468-534	711-887	59-64	84-91
	9	214-240	535-600	888-1064	65-70	92-100
Very High
	10	241 or more	601 or more	1065 or more	71 or more	101 or more