5.3 SO₂ Emission Estimates

Since 1970 there has been a substantial overall reduction of around 68% in SO₂ emissions (Figure 5.6). The emission profile exhibits a steady decline between 1970 and 1996 with the exception of small peaks in 1973 and 1979 corresponding to the harsh winters in those years and a short period at the end of the 1980s when the profile was relatively flat.

Figure 5.6 Emissions profile for SO₂

Table 5.3 shows emissions broken down by fuel categories. The two main contributors are solid fuel and petroleum products. Emissions from solid fuel use have declined by 63% over the period and those from petroleum by 78%. The most important factors in the fall in emissions from petroleum use are the decline in fuel oil use and the reduction in the sulphur content of gas oil and DERV. The reduction in the sulphur content of gas oil is particularly significant in sectors such as domestic heating, commercial heating and off-road sources where gas oil is used extensively. Although the sulphur content of DERV has reduced its consumption has increased so that overall there has been little change since 1970.

Table 5.3 UK Emissions of Sulphur Dioxide by UNECE¹ Source Category and Fuel (kt)

	1970	1975	1980	1985	1990	1993	1994	1995	1996	1996%
By UNECE Category
Comb. in Energy Prod & Transf.
Public Power	2913	2941	3007	2627	2723	2089	1764	1589	1318	65%
Petroleum Refining Plants	213	218	237	96	108	155	138	124	122	6%
Other Comb. & Trans.	306	120	73	55	44	13	11	10	9	0%
Comb. in Comm/Inst/Resid/Agri
Domestic	522	301	226	202	108	112	91	65	69	3%
Other	320	214	218	133	90	95	81	61	59	3%
Combustion in Industry	1815	1285	903	416	442	476	392	304	260	13%
Production Processes	117	118	117	122	118	108	109	95	99	5%
Extr./Distrib. of Fossil Fuels	5	5	5	9	16	5	6	6	7	0%
Solvent Use	0	0	0	0	0	0	0	0	0	0%
Road Transport	44	48	42	44	63	59	63	51	37	2%
Other Transp & Mach.
Off-Road	33	32	18	9	7	7	6	5	5	0%
Shipping	35	28	25	26	27	30	29	29	30	1%
Other	24	23	18	15	13	12	12	11	11	1%
Waste Treatment & Disp.	4	4	5	5	5	4	4	2	1	0%
Agricult/Forest/Land Use Change	0	0	0	0	0	0	0	0	0	0%
Nature	0	0	0	0	0	0	0	0	0	0%
By Fuel
Solid	3701	2806	3164	2648	2791	2182	1849	1643	1372	68%
Petroleum	2371	2288	1535	908	769	844	720	588	530	26%
Gas	202	164	101	91	85	36	30	22	24	1%
Non-fuel	76	79	94	112	119	105	107	99	102	5%
Total	6350	5337	4894	3759	3764	3166	2705	2351	2028	100%

1 UK emissions reported in IPCC format (Salway, 1998) differ slightly due to the different source categories used.
2 Railways, civil aircraft, shipping, naval vessels and military aircraft.

The geographical distribution of SO₂ emissions is shown in Figure 5.7. A large fraction (~ 81%) of the SO₂ emissions are concentrated into relatively few 1km grid squares containing the major point sources such as refineries and power stations and large industrial plant. The resulting map highlights the main conurbations and some major roads. The map also shows the effect of the current data set used to distribute emissions from small industrial combustion which estimates high coal consumption in Stoke-on-Trent, parts of Manchester, Middlesborough and Wrexham. High emissions in Plymouth and Newport result from a combination of shipping and industry. London and Birmingham, which have smoke control regulations, show relatively low SO₂ emission levels.

Figure 5.7 Mapped SO₂ emissions

The largest contribution to SO₂ emissions is from power stations which accounts for 65% of the total in 1996. Since 1970 there has been a gradual decline in power station emissions of around 55%. This reflects the changes in fuel mix and the types of power plant which have taken place during the period. Up to 1990 the reduction was due to a gradual increase in the use of nuclear plant and improvements in efficiency (See Section 2.2.2). Since 1990, this decline has accelerated because of the increase in the proportion of electricity generated in nuclear plant and the use of Combined Cycle Gas Turbine (CCGT) stations and other gas fired plant. CCGTs are more efficient than conventional coal and oil stations and have negligible SO₂ emissions. It is expected that these reductions will continue in the near future as more CCGT stations are built. Most recently the flue gas desulphurisation plants, constructed at Drax and Ratcliffe power stations have had a significant effect. It is estimated that around 0.39 Mt of SO₂ were removed in 1996 compared with a total emission from coal fired power stations of 1.153 Mt.

5.3.2 Industry

Emissions of SO₂ from industry result from the combustion of coal and oil, some refinery processes and the production of sulphuric acid. Between 1970 and 1996 industrial emissions from combustion sources have fallen by 86% though most of the fall took place between 1970-1985 reflecting the decline in the energy intensive iron and steel industry and other heavy industries. There has been also been a decline in the use of coal and oil in favour of natural gas.

5.3.3 Transport

Transport emissions account for just 2% of the total SO₂ emissions. Between 1970 and the early 1990s, road transport emissions grew with the increase in road vehicles, however more recently emissions have declined with the reduction in the sulphur content of DERV. Similarly the reduction in sulphur content of gas oil is reflected in the emissions from off-road vehicles.

5.3.4 Other

Emissions from the remaining categories are low compared with those discussed above. Emissions from domestic use and other commercial/institutional have declined substantially during the period 1970-1996, reflecting the major changes in fuel mix from oil and coal to gas. The only category that shows any marked increase during the period is extraction and distribution which includes leakage from the gas transmission system and emissions from flaring, natural gas use, venting and well testing from the offshore oil and gas industry. The decrease in emissions from waste reflects the closure of a number of old incinerators due to the introduction of new emission standards.