National Atmospheric Emissions Inventory

5.4 Hydrogen Chloride Emission Estimates

Table 5.5 and Figure 5.8 summarise the UK emissions of hydrogen chloride. Emissions have fallen by 60% since 1970. The main source of these emissions is coal combustion so the fall is a result of the decline in coal use and also the installation of flue gas desulphurisation at Drax and Ratcliffe since 1993. The other significant source of hydrogen chloride is waste incineration. Here the commissioning of new incinerators and the closure or upgrading of old plant has resulted in a significant fall in emissions in 1996.

Table 5.4 Emissions of Hydrogen Chloride:

  1970 1975 1980 1985 1990 1993 1994 1995 1996
By UNECE Category
Comb. in Energy Prod. & Transf.
    Public Power 235.84 227.86 273.49 225.81 252.08 188.90 157.51 131.52 94.76
    Public Power (waste) 0.00 0.00 0.00 0.00 1.82 2.88 4.74 3.12 3.27
    Petroleum Refining Plants 0.04 0.03 0.04 0.02 0.02 0.02 0.03 0.02 0.02
    Other Comb. & Trans. 4.54 2.82 1.56 0.78 0.27 0.11 0.05 0.02 0.02
Comb. in Comm., Inst., Resid. & Agri
    Residential Plant 47.34 27.27 21.02 20.29 9.96 10.90 9.17 6.32 6.36
    Comm., Public & Agri. Comb 9.85 4.64 4.27 4.03 2.86 1.95 1.71 1.24 1.36
Combustion in Industry
Iron & Steel Combustion 2.00 0.75 0.44 0.17 0.15 0.12 0.12 0.25 0.38
Other Comb. in Industry 37.25 14.93 11.98 11.84 12.11 13.27 11.37 9.82 7.42
Glass Production 0.16 0.17 0.18 0.16 0.19 0.17 0.18 0.17 0.17
Processes in Industry 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09
Road Transport 0.35 0.41 0.42 0.37 0.12 0.09 0.07 0.06 0.05
Other Mobile Sources & Machinery 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00
Waste Incineration 10.57 10.58 10.58 10.58 8.77 7.71 5.85 5.76 3.24
Total 348.04 289.56 324.08 274.16 288.44 226.22 190.88 158.40 117.14

Figure 5.8 Hydrogen chloride emissions 1970 to 1996

5.5 Non-methane Volatile organic Compounds

Interest in NMVOC emissions has grown as their role in the photochemical production of ozone has been appreciated. The diversity of processes which emit NMVOCs is huge, covering not only many branches of industry, but also transport, agriculture and domestic sources.

The NMVOC inventory is summarised in Table 5.5. Unlike SO2 and NOx , only about 33% of the UK estimate of NMVOC emissions come from combustion sources of which the majority arise from the transport sector. Other major sources of NMVOC emissions are the use of solvents and production processes. The NMVOC emission profile, Figure 5.9, shows a small overall increase in emissions between 1970 and 1989 with minor peaks in 1973 and 1979, followed by a steady reduction in emissions during the 1990s. The latter reflects the increasingly stringent emission limits.

Table 5.5 UK Emissions of NMVOCs by UNECE1 Source Category and Fuel (kt)


  1970 1975 1980 1985 1990 1993 1994 1995 1996 1996%
By UNECE Source
Comb. in Energy Prod & Transf. 7 6 6 7 7 8 9 7 8 0%
Comb. in Comm/Inst/Resid/Agri
   Domestic 228 130 100 91 50 47 37 29 31 1%
   Other 5 3 3 3 2 2 2 2 2 0%
Combustion in Industry 18 12 9 8 9 8 8 8 8 0%
Production Processes 359 355 351 339 348 325 326 311 285 13%
Extr./Distrib. of Fossil Fuels
   Petrol Marketing 82 93 109 116 130 123 118 113 114 5%
   Gas Leakage 2 13 17 19 19 18 18 18 17 1%
   Offshore 4 7 97 164 140 138 166 154 162 8%
Solvent Use 634 634 617 617 680 619 620 616 604 29%
Road Transport
   Combustion - petrol 451 479 542 582 690 599 553 505 453 22%
   Combustion - DERV 104 109 117 116 130 114 109 98 90 4%
   Evaporation 81 92 110 118 141 126 111 98 91 4%
Other Transp & Mach.
   Off-Road 118 114 109 104 99 100 99 96 97 5%
   Other 24 24 24 23 23 23 22 22 22 1%
Waste Treatment & Disp. 18 20 64 48 49 45 52 44 46 2%
Agricult/Forest/Land Use Change 27 27 48 54 35 0 0 0 0 0%
Nature 80 80 80 80 80 80 80 80 80 4%
By Fuel
Solid 242 132 99 89 47 42 32 23 23 1%
Petroleum 703 731 796 828 945 838 786 724 667 32%
Gas 6 9 11 13 13 15 16 15 17 1%
Non-fuel 1292 1325 1497 1559 1627 1480 1497 1438 1404 67%
Total 2243 2197 2403 2489 2632 2375 2331 2200 2111 100%

Figure 5.9 NMVOC Emissions Profile 1970-96

The spatial disaggregation of NMVOC emissions in the UK is shown in Figure 5.10. As a large proportion of solvent use is dependent on population and solvent use is a significant fraction of the UK total emissions, the map is heavily influenced by the population distribution. Unlike the maps presented previously for SO2 and NOx, the VOC map has little major road definition except where the major roads go through rural areas. This reflects the fact that NMVOC emissions are dependent on vehicle speed and are higher on minor and urban major roads than on the high speed motorways and major roads. The maps also indicate the refineries as major point sources.

Figure 5.10 Map of NMVOC Emissions


5.5.1 Solvent use and production processes

Solvent use and production processes are responsible for 29% and 13%, respectively, of the 1996 emission. These estimates are based on a combination of solvent consumption data and industrial production data. Although NMVOC estimates are being continuously improved (Appendix 2), they remain fairly uncertain and little trend is apparent although since 1990 there is a steady reduction reflecting the stricter emission controls.

5.5.2 Transport

Total transport emissions are currently responsible for 36% of NMVOC emissions of which 30% are a result of road transport. The emission rose gradually with increasing car numbers to a peak in 1989. Since then it has declined by 36% owing to the increased use of catalytic converters and fuel switching from petrol to diesel cars; it is currently at approximately the same level as in 1970.

5.5.3 Other Sectors

Offshore oil and gas emissions have increased substantially since 1970 with the growth of the UK's offshore industry and now constitute 8% of the total. The most important sources of NMVOC emissions are tanker loading, venting and fugitives.

Emissions from gas leakage currently comprise around 1% of the total NMVOC emission. This source is declining as a result of the gas main replacement programme underway since 1990. The evaporative losses from distribution and marketing petrol rose between 1970 and the early 1990s reflecting the growth in road transport but more recently have remained relatively constant, probably as a result of recent fuel switching to diesel. They currently account for around 4% of national NMVOC emissions.

The contribution from domestic heating has fallen by a factor of 7 over the period 1970-1996 as the use of coal for domestic heating has declined. It now accounts for just 1% of the UK emission.

NMVOC emissions from waste treatment and disposal contribute 2% to national emissions. New data from the Environment Agency (1997) shows emissions from municipal waste incinerators to be insignificant.

5.5.4 Speciation of NMVOCs

As mentioned previously, the term NMVOC covers a wide range of compounds and although a total NMVOC inventory is sufficient for some purposes, in other cases greater detail is required concerning the nature and concentration of individual compounds. For example, when assessing the photochemical production of ozone, individual species have different ozone forming potentials hence information is required on the concentration of individual species (QUARG, 1993). Table 5.6 shows the 1996 NMVOC emission disaggregated as far as possible by source and species.

Table 5.6 The 50 Most Significant NMVOC Species in Terms of Mass Emission