What are the effects of sulphur oxides on human health and ecosystems?
95% of the SOx emitted from the combustion of fossil fuel is sulphur dioxide. SO2 is
a toxic gas, which is directly harmful to human health. It is heavier
than air and has a suffocating odour at an atmospheric concentration of
around 500 parts per billion (ppb), at which level it can be fatal. At
lower levels, chest pains, breathing problems, eye irritation and a
lowered resistance to heart and lung diseases can be experienced. At 20
ppb or lower there should be no ill effects to a healthy person. The
normal atmospheric background concentration of SO2 is generally less than 10 ppb. [3]
A
secondary effect is the formation of sulphates (and nitrates), in the
form of aerosols or very fine airborne particles, which can comprise a
significant proportion of the particulate matter and have been linked to
increased asthma attacks, heart and lung disease and respiratory
problems in susceptible population groups. [3]
A
third effect can occur further away from the emission source where the
sulphur oxides will have converted to acids by aqueous phase reactions
in the atmosphere. These acidic aerosols are eventually precipitated
as acid rain, snow, sleet or fog but only when they encounter the right
meteorological conditions. In the absence of man made pollution rain
water would be slightly acidic, around pH 5, due to the presence of
carbonic acid from the interaction of water vapour and naturally
occurring levels of CO2. Acid rain on the other hand has been measured with pH levels below 3 corresponding to vinegar. [3]
