Winter smog ("London smog")
consists mainly of dust, sulphur dioxide, sulphuric acid, and water droplets (smoke + fog = smog).
Main source of the pollutants is the combustion of coal and oil in power stations, in industrial processes, and in domestic stoves. Special weather conditions must also prevail (calm, cold air topped by warmer one) .
People mainly suffer from respiratory and circulation problems.
Smog episodes last for days, until the weather changes.
In December 1952, in London smog killed some 4,000 people.
Summer smog ("Los Angeles smog")
consists mainly of irritants such as aldehydes, ozone, and peroxyacyl nitrates ("PAN"). These are formed by photochemical processes from nitrogen oxides and hydrocarbons. Hence, the weather must be "fine" to produce summer smog.
Chiefly, the precursor substances of summer smog are emitted from cars and lorries; another important source of hydrocarbons (and of non-methane volatile organic compounds, NMVOC, in general) is the use of solvents in trade and industry.
Summer smog irritates the mucuos membranes and the respiratory tract.
Pollutant concentrations vary strongly with the time of the day; irritants are most abundant in the early afternoon.
Chemical pathways in Summer Smog
Photosmog ("Los Angeles-Smog")
· intensity of light
peroxyacetyl nitrate (a PAN)
M: any molecule, takes over energy
EC-limits for atmospherical ozone (directive 92/72/EEC)
to protect human health:
("should not be exceeded for a prolonged time")
to protect plants:
("vegetation may be impaired")
to inform people:
("limited and short-term health effects")
to alarm people:
("danger to health imminent")
(will stop traffic tomorrow)
German exposure limit for the workplace (withdrawn): 200 µg/m³
Emissions of man-made NMVOCs
in EC-Europe in 1985 were estimated to amount to some 10,000,000 t / y.
Of these, about 53 % were attributed to transport and about 34 % to the use of organic solvents (approx. 3,400,000 t / y).
Major solvent consumers were
painting and coating 47.2 % surface cleaning 13.2 % private use 11.4 % printing 5.5 % glues and adhesives 4.8 % dry cleaning 2.3 %
Thus, in 1985 about 190,000 tones of solvents were emitted by the printing industry.
Reduction of solvent emissions
is a major aim of EC environmental policy.
It was agreed that between 1990 and 1999 a reduction of solvent emissions of 30 % should be achieved.
Hence, the commission devised several drafts for a directive to reduce emissions, which included
- the obligation to reduce solvent emissions as far as technically and economically feasible;
- general emission limits for certain dangerous solvents;
- detailed regulations for the most prominent solvent-consuming trades, including the graphic arts industry;
- the obligation to set up solvent management plans;
- schedules for existing enterprises to comply with the directive.
Requirements were reduced from draft to draft; it is not so certain that the directive will ever come into force.