Acid gases and volatile organic compounds (VOCs)

Chart 1: Sulphur dioxide (SO2)

When sulphur dioxide (SO2) and nitrogen oxides (NOx) gases react in the atmosphere with water, oxygen, and other chemicals, they form various acidic compounds that can then fall back to the ground as acid rain that can impact on soil, vegetation and animals.

Our SO2 emissions fell to 175 thousand tonnes in 2008. We have reduced our total SO2 emissions from our operations by nearly 40% since 1999. Our SO2 emissions were approximately 17% lower than in 2007.

Chart 2: Nitrogen oxides (NOx)

When sulphur dioxide (SO2) and nitrogen oxides (NOx) gases react in the atmosphere with water, oxygen, and other chemicals, they form various acidic compounds that can then fall back to the ground as acid rain that can impact on soil, vegetation and animals.

NOx can not only make rain more acidic. High concentrations of NOx and VOCs in the atmosphere can also react with the sun’s rays to form ozone smog, which can be dangerous to our health. Ozone is a reactive gas that, in high concentrations, can cause respiratory problems.

Our NOx emissions were 150 thousand tonnes in 2008, up from 145 thousand tonnes in 2007. However, we have reduced our NOx emissions by more than 20% since 1999, even though we are now using much more energy to refine cleaner lower sulphur fuels.

Chart 3: Volatile organic compounds (VOCs)

Volatile organic compounds (VOCs) are released when fuel is not completely burnt, when hydrocarbon vapours are released during ship transport, when vapours are vented at storage units or when they escape from joints in valves and pipelines.

VOC emissions from our operations have dropped almost 70% since 1999, to 135 tonnes in 2008, mainly because we stopped venting associated gas (which contain a lot of VOCs) at oil production sites. Our VOC emissions were approximately 22% lower than in 2007.