Dianne Bryant of Dunedin asks :-

Do large public firework displays do any damage to the atmosphere or the ozone layer?

Anthony Lealand, of Firework Professionals Ltd (www.firework.co.nz) who manufacture pyrotechnics and produce large public displays, special effects for theatre, films and indoor pyrotechnics throughout New Zealand and South Pacific, responded.

Our largest star shell (400mm) bursts at an altitude of 700 metres and the burst radius may extend the highest particle to 1000 metres, which is very low compared to volcanos and aeroplanes. Large public firework shows involve many types of fireworks but when averaged are equivalent to using about 2000 100 mm star shells. Each of these has a propellent charge of 50 grammes of black powder and a similar amount for the explosive charge. This gives a total of 200 kg of black powder per event which is 20 per cent carbon. This releases 73.4 kg of carbon dioxide into the atmosphere.

Other oxidisers and fuels are used producing the colours and finally solid by-products which is seen as smoke - for example, MgO and Al2O3 (white), BaO (green), SrO (red), and CuO (greens and blues). The main gas produced is carbon dioxide, followed by approximately half the weight of sulphur dioxide.

By comparison a typical jet aircraft (777) flies at 10 km altitude burning 6000 kg of jet fuel per hour which when burnt produces 18,500 kg of carbon dioxide. Concorde burnt even more fuel, 22,500 kg hour.

If the 50,000 people going to the firework show travel by cars, each holding four people, and travelled an average of 20 kilometres there and back, we would have 12,500 cars, travelling a total of 250,000 kilometres. A reasonably modern European subcompact car will emit approximately 140 grams of carbon dioxide per km. Therefore 50,000 people attending the show produce 35,000 kg of carbon dioxide.

The firework display is thus a very minor part of this total, less than 0.3 per cent.