The change in emissions for these pollutants, is summarised in the following plot. The change is given as the difference between the 1990 and 1999 emissions, expressed as a percentage of the 1990 values.

The greenhouse gas SF₆ is the only pollutant showing an increase across this period. SF₆ emissions arise from a relatively small number of sources (magnesium production, high voltage switchgear, electronics and manufacture of trainers)- each of these giving increased emissions since 1990.

However, the primary importance of SF₆ is that it is a greenhouse gas, and the emissions should be placed in context by considering the other pollutants which also contribute to this effect. Comparison of the 1990 and 1999 emissions of all greenhouse gases indicates a 14% decrease in the contribution to global warming. Therefore the impact of the increased SF₆ emissions is more than counteracted by the decreased emissions of other greenhouse gases.

3. CO₂ – Emission estimates for CO₂ (as Carbon) from the UK show an overall decrease from 185 Mt in 1970 to 145 Mt in 1999. The most significant reductions arise from the public power and industrial combustion sectors. 1999 road transport emissions account for 22% of the total emission and indicate a small decrease on the 1998 emission estimates. Since 1990 total emissions have declined by 9.0%.
4. CH₄ - Estimates of methane emissions show a decline from 3.76 Mt in 1970 to 2.63 Mt in 1999. The largest sources are landfills, agriculture, natural gas distribution and coal mining. The reduced emissions are dominated by the decline in the coal mining industry- in addition, increased levels of methane recovery are now present on landfill sites. The uncertainties associated with the emission estimates of methane are high.
5. N₂O - UK emissions of nitrous oxide were 0.138 Mt in 1999. Emissions of nitrous oxide are dominated by agricultural emissions and the production of nylon and nitric acid. Reductions have primarily arisen from the production processes sector.
6. HFC, PFC and SF₆- Estimates of emissions of halocarbons which contribute to climate change are discussed. The 1999 UK emissions were 2.7 kt HFCs, 98 t PFCs and 55 t sulphur hexafluoride.
7. PM – The UK emissions of PM₁₀ declined from 0.52 Mt in 1970 to 0.19 Mt in 1999. This reflects a trend away from coal use particularly by domestic users. However, more recent increases in road transport emissions (particularly from diesel road transport) have off-set a more dramatic decline in PM₁₀ emissions. Coal use and road transport contribute 44% of UK emissions of PM₁₀ in 1999. Other PM size fractions are also included in this report. PM_2.5 emissions have also fallen- the largest source sector being road transport, accounting for 27% of the 1999 total emission.
8. BS - Black smoke emissions in the UK declined from 1.07 Mt in 1970 to 0.27 Mt in 1999. This is largely due to a switch away from coal to solid smokeless fuels and natural gas by domestic users. The reduction in emissions from domestic sources has been partially offset by an increase in emissions from diesel engined vehicles.
9. CO - UK emissions of CO are dominated by those from road transport (69% of UK emissions in 1999). Emissions in 1999 (4.76 Mt) represent a 44% reduction on the 8.53 Mt emission in 1970 and a 33% decrease on the 1990 emission of 7.16 Mt. The change in emissions between 1990 and 1999 is dominated by the reduction in emissions from the road transport sector, caused by the increased use of catalytic converters in cars.
10. Benzene –Fuel combustion in the road transport sector is the most significant source of benzene, accounting for some 67% of the 1999 UK emission. The use of benzene in the chemical industry gives rise to stack and fugitive emissions, which sum to contribute only 6% to the UK total emission.
11. 1,3-Butadiene – Emissions of 1,3-butadiene are dominated by fuel combustion in the road transport sector, which account for some 85% of the 1999 UK emission. There have been significant reductions in the emissions from this sector due to the increase in the number of cars equipped with catalytic convertors.
12. NO_x - UK emissions of NO_x were 2.50 Mt in 1970, and 2.76 Mt in 1990. However, emissions have fallen significantly to 1.61 Mt in 1999, representing a 42% reduction on the 1990 emissions estimate. This is primarily a consequence of: abatement measures in road transport, abatement measures in coal fired power stations and the increased use of other fuels for power generation. Road transport and coal combustion combine to account for 62% of UK emissions in 1999.
13. SO₂ - UK emissions of sulphur dioxide have fallen from 6.52 Mt in 1970 to 1.19 Mt in 1999. This is a result of reduced emissions from the industrial and public power sectors arising from the decreasing use of coal, and increasing use of abatement equipment. However, coal combustion still accounts for 70% of the 1999 UK SO₂ emissions.
14. HCl - UK emissions of hydrogen chloride have fallen from 0.34 Mt in 1970 to 0.10 Mt in 1999 largely as a result of declining coal use.
15. NMVOC - UK emissions of NMVOC are estimated as 2.20 Mt for 1970, 2.66 Mt for 1990 and 1.74 Mt for 1999. Reductions from 1990 to 1999 arise primarily from the road transport and industrial sectors.
16. NH₃ - The total UK emission of ammonia for 1999 is estimated at 0.35 Mt, compared to the 1990 estimate of 0.37 Mt. The agricultural sector dominates the total ammonia emissions. The reductions made in NH₃ emissions from changes in agricultural practises more than offset the increased emission from the road transport sector (caused by increased use of catalytic convertors). The NH₃ emissions inventory has undergone significant improvement since the 1998 inventory.
17. HF – The total HF emissions for 1999 are estimated to be 3.7 kt, compared with the 1990 emissions estimate of 13.6 kt. As with HCl the dominant source is coal combustion for public power. The HF emissions estimates for the UK are presented here for the first time.
18. POPs – The 1999 UK emissions of persistent organic compounds may be summarised as follows: 1414 t PAH (USEPA 16), 346 gTEQ PCDD/F (grammes of "toxic equivalent" of dioxins & furans) and 2.07 t PCB. Emissions from all three of these pollutant groups have greatly decreased. Emissions in 1999 equate to decreases of 77%, 70% and 70% on the 1990 emission, for PAHs, PCDD/Fs and PCBs respectively.
19. Pb - UK Emissions of lead have declined sharply following reductions in the lead content of leaded petrol and the increasing use of unleaded petrol. Emissions in 1999 are estimated to be 0.55 kt compared with 7.36 kt in 1970. Road transport still contributes 59% of UK emissions in 1999. Emissions of other metals are also reported, and show a strongly declining trend.
20. The 1999 emission inventory indicates that many of the total emission estimates for pollutants are dominated by emissions from road transport and the use of coal (see table below).

It is therefore likely that future trends in emissions will be substantially determined by market demand and UK Government/devolved administration policies associated with these areas.