However, the good news is that it is easy to reduce your nitrogen output. With that in mind, James Galloway from the University of Virginia, US, and colleagues have created N-PRINT – a model to calculate your nitrogen footprint, and help you find ways of reducing it.

So what is up with nitrogen? Strictly speaking the problem isn't nitrogen gas, which makes up three-quarters of the air that we breathe, but reactive forms of nitrogen, such as the nitric oxide spewing out of car exhausts. Once nitrogen emerges in its reactive form it creates choking smog, produces acid rain, enlarges the stratospheric ozone hole, feeds toxic algal blooms and contributes to global warming. "I call this the nitrogen cascade," explains Galloway "and it means we can't just work on one issue, such as smog, in isolation."

Go back to 1860 and reactive nitrogen was not a problem – humanity produced just 15 metric tonnes of the stuff. Fast-forward to 1995 and reactive nitrogen production had escalated to 156 tonnes, rising to a whopping 185 tonnes by 2005. The major sources turn out to be fossil-fuel burning and food production, associated mainly with crop fertilizers.

Our love affair with reactive nitrogen began in the early 20th century, when German scientists Fritz Haber and Carl Bosch developed a way of fixing atmospheric nitrogen to make ammonia – the essential ingredient for fertilizer. Just a sprinkle of Haber and Bosch's magic dust turned fallow land into productive fields: hungry mouths were fed and the world's population boomed, tripling in just 100 years.

The problem is that fertilizer easily leaks out of the system. Only around one-fifth of the nitrogen that is applied to crops ends up in the plants we consume; the remainder leaches out into groundwater and bubbles into the atmosphere. For animal production the figures are even worse, with just 10% or so of the fertilizer that is applied to the animal fodder crop ending up in the animal on the dinner table.

But it needn't be this way. Galloway and his colleagues have shown that there are simple ways of preventing so much nitrogen leaving the system. Taking care with the type, timing and amount of fertilizer applied to crops can significantly reduce nitrogen loss. "We need to encourage farmers to carry out these best-management practices and ensure that they are protected from loss of yield with some form of insurance," Galloway told environmentalresearchweb. Meanwhile, giving animals appropriate feeds according to their species and age can ensure that their nitrogen uptake is maximized.

When it comes to fossil-fuel burning the technology already exists to mop up excess nitrogen at power stations and from car exhausts. Indeed, many developed countries already have regulations in place to ensure that nitrogen is captured. "Now we need to pass this technology on to the developing world," says Galloway.

Perhaps more difficult is preventing nitrogen leakage from manure and sewage. "It is possible to process sewage to create drinking water and fertilizer, but it is expensive," explains Galloway. Manure can be treated in a similar way, but unlike sewage there is as yet a lack of infrastructure to collect and process farmyard manure.

If all these interventions were applied globally, Galloway and his colleagues have calculated that over 25% of the nitrogen loss could be prevented. "For regions that have severe nitrogen-related issues this would be of great benefit," says Galloway.

The team hopes that by using N-PRINT individuals will be able to learn more about nitrogen and understand how their own use of food and energy resources contributes to nitrogen loss. Currently N-PRINT has been developed for people in the US and the Netherlands, and calculators will soon be available for inhabitants of Germany and the UK.

The researchers also hope to produce N-PRINT calculators for regions of India, China and Tanzania. Galloway hopes to present early versions of some of these models at the Fifth International Nitrogen Conference to be held in New Delhi in December.

Of course, it's not just individuals who need to change their behaviour: food producers must make changes too. With this in mind Galloway and his colleagues are working on N-PRODUCER – a model that will help with the production of more nitrogen-friendly food. Meanwhile the N-POLICY model will help policy makers to work out where best to focus their attention to clean up nitrogen leakage in their region.

Scientists have recognized the problem of nitrogen loss since the 1970s but as yet there is little public awareness of the issue. Galloway and his colleagues are on a mission to make sure that we all know about nitrogen. N-PRINT will be coming to a computer near you soon.