2 New Bandings for Air Pollution

AEAT-3844

Before 18 November 1997 the DETR classified air quality using the four banding levels for O₃, NO₂ and SO₂ shown in Table 2.1.
Table 2.1: United Kingdom Department of the Environment, Transport and the Regions Air Quality Guidelines (ppb, hourly average) (until 18 November 1997)

	very good	good	poor	very poor
O3	< 50	50 - 89	90 - 179	³ 180
NO2	< 50	50 - 99	100 - 299	³ 300
SO2	< 60	60 - 124	125 - 399	³ 400

Since 19 November 1997 a new banding scheme has been in use. This scheme includes bandings for PM₁₀ and CO as well as the three pollutants previously forecast and these pollutants are now forecast every day (Committee on the Medical Effects of Air Pollutants, 1997). The new banding levels which the DETR now uses to classify air pollution for O₃, NO₂, SO₂, CO and fine particles are shown in Table 2.2. We have assessed the forecasting success rate for the "Information" threshold between moderate and high.

Table 2.2: United Kingdom Department of the Environment, Transport and the Regions Air Quality Guidelines (ppb, hourly average) (since 19 November 1997)

	Standard Information Alert
	LOW	MODERATE	HIGH	VERY HIGH
Sulphur Dioxide (ppb, 15 minute mean)	less than 100	100 - 199	200 - 399	400 or more
Ozone (ppb)	less than 50 (8 hour running mean)	50 - 90 (hourly mean)	90 - 179 (hourly mean)	180 or more (hourly mean)
Carbon Monoxide (ppb, 8 hour running mean)	less than 10	10 - 14	15 - 19	20 or more
Nitrogen Dioxide (ppb, hourly mean)	less than 150	150 - 299	300 - 399	400 or more
Fine Particles (mg/m3, 24 hour running mean)	less than 50	50 -74	75 - 99	100 or more

In the last forecasting report (Stedman et al, 1997) the likely number of exceedances for 1995 and 1996 under the new banding scheme was discussed. The findings were that there would be a similar number of ozone episodes as under the old scheme, fewer SO₂ episodes and virtually no NO₂ episodes. During 1996 and 1995 there were very few days with HIGH or even MODERATE levels of CO, under the new scheme, but there were a large number of days with HIGH levels of PM₁₀. Table 2.3 lists the number of days with measured HIGH or VERY HIGH pollution levels for each pollutant for 1997 for the country as a whole, if the new bandings had been used throughout the year. A comparison with the number of POOR and VERY POOR days defined by the old bandings confirms earlier conclusions, and since there are such a large number of episode days for PM₁₀ it is important to have good forecasting techniques.

Table 2.3: Total number of episode days in 1997 classified by new and old bandings

	1997 Network Data
	HIGH	VERY HIGH	POOR	VERY POOR
Ozone	8	0	8	0
Nitrogen Dioxide	0	0	72	0
Sulphur Dioxide	17	1	30	1
Carbon Monoxide	0	0	-	-
Particles	49	14	-	-
Total	74	15	110	1

INDEX

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