By constantly sniffing and diluting a smell over a three to five hour period, the team are able to evaluate the odour strength by the number of times the smell has to be diluted with fresh air before it all but disappears.
The work is at the heart of a new approach to dealing with the increasing awareness and growing intolerance of unpleasant smells produced by industry, farming, water treatment and sewage works and others. As farms and industry become increasingly enveloped by housing and with rising environmental expectations, complaints about smells have gone up significantly. Incomers moving into rural areas have been among the most vociferous complainants, unhappy at the robust agricultural odours they encounter.
Unpleasant smells, even when they are not toxic, can affect health in a number of ways, through a reduced sense of well-being, an increase in health-related complaints, and psychological problems. An added problem looming for industrialists and farmers is that new European odour standards are being finalised and are expected to be published soon, to put further pressure on odour polluters to reduce emissions.
While Britain has been in the forefront of odour research, it lags behind others, notably Holland, in odour control. In Holland various government- backed surveys estimate that 21 per cent of the population are annoyed by offensive odours. The aim is that by the year 2000, that level of annoyance should have been cut to 12 per cent at an estimated cost of around pounds 300m.
The problem with policing unpleasant smells is that it has always been a difficult area to monitor and control. Noise, vehicle emissions, water contamination and levels of toxic pollution are all easily measured and are technically simple to monitor. But smells are much more of a subjective area and until relatively recently there has been no obvious or easily determined unit of measurement.
Now the European Odour Unit has arrived and within the next few months the Working Group 2 (Odours) of the Comite European de Normalisation, the European standards body, is expected to pronounce on its future use and applications. The working party says that a single Euro Odour Unit is defined as the pollutant per cubic metre whose smell can just be detected. The concentration of odours will be measured by finding the amount of dilution required to bring a smell down to the threshold levels of that single odour unit. The higher the number of dilutions required, therefore, the greater the smell.
The main tools used by researchers for measuring odour are the human nose and a device known as the olfactometer. In the odour testing process the smell in gas form is collected in a special bag coated with teflon, a material which absorbs very little and adds nothing to the odour captured. The odour, and a quantity of pure air that has been passed through carbon filters to remove any smells, are put separately into the olfactometer which is equipped with two smelling ports. During a smell session Julia Pallowin and her fellow operatives at the Institute of Grassland and Environmental Research in Devon test each of the ports in turn.
"One contains the odour and the other pure air. Over time the odour is gradually diluted with air in steps of binary increments up to 64,000 until the people on the panel can just about detect it," said Dr Philip Hobbs, senior research scientist at the IGER centre. He points out that odours are very complex. "Although we sense them as a single smell, a lot of ingredients go into creating the overall effect. In pig slurry for instance, we have identified 15 major components, including sulphide and methane."
He says that demand for smell assessment is booming. "We have a commercial arrangement with a firm of environmental consultants and the number of odours we are being asked to assess is increasing all the time. People are becoming more aware of smells." Dr Hobbs, who has developed a synthetic pig slurry odour as part of the research, adds that the work on odours aids industry and farmers to combat them. "Smells in slurry for instance are largely caused by too much crude protein in the diet of pigs that cannot be digested. By reducing the amount of protein or changing the diet, the smell is reduced," he says.
IGER is working on measurement with Project Research Environmental Consultants, an offshoot of Project Research Amsterdam which developed the first generation of olfactometers and which has been in the vanguard of research in Europe. "A European standard is being drafted and we expect it to become mandatory in the EU very soon," says Ton van Harreveld, director of PREC. "People now have very clear ideas about the living environment they want - clean water, no noise, clean air and no offensive odours.
"Odour problems are likely to get worse because industry and public utilities are being increasingly enveloped by new housing, because there is increased demands for a clean environment, and because community legal action in environmental cases is becoming more established.
"Our experience as a British odour consultancy is that large companies are increasingly aiming to document their efforts to reduce their impact on the surrounding community. They recognise that minimising the odour annoyance is one of the building blocks for continued operation within the community where they are located, and thus to their commercial durability."
A spokesman for the CEN working party said that member states would first be circulated with the proposals. "The aim of the standard is to provide the method for measurement that can provide a common basis for evaluation of odour emissions in the member states of the EU. The ultimate goal is to reduce odours nuisance," he said.
Some environmentalists believe it is inevitable that there will be enforceable standards on odours, just as there are with other pollutants. But there may well be problems here. The CEN working party itself points out that perceptions of smells vary not only between individuals, but within an individual over time as his or her tastes change. And there are other, geographical and biological, problems too. Animals bred in warmer parts of the EU, like, for example, Spain, emit more methane and hence produce a greater-smelling slurry, making the likelihood of a universal standard for odours even more difficult. !Reuse content