Air quality in Europe has declined in recent years, according to a report from the European Topic Centre on Air and Climate Change (ETC/ACC), which also cautions that the short time period involved makes it difficult to draw reliable conclusions. March 2008

Crop residue burning results in the emission of many a toxic pollutants. These emissions can travel long distances affecting thereby the entire region. Due to these emissions the air quality of the region worsens, which results in nose and throat itching and burning, and irritation of the airway tract.

To alleviate traffic congestion in Central London, the Mayor introduced the Congestion Charging Scheme (CCS) in February 2003.

Rates of atmospheric deposition of biologically active nitrogen (N)are two to seven times the pre-industrial rates in many developed nations because of combustion of fossil fuels and agricultural fertilization. They are expected to increase similarly over the next 50 years in industrializing nations of Asia and South America. Although the environmental impacts of high rates of nitrogen addition have been well studied, this is not so for the lower, chronic rates that characterize much of the globe. Here we present

Perhaps genetic engineering could help to increase the efficiency with which crops absorb nitrate from soil (5 January, p 28). However, the claim by Arcadia Biosciences that this will substantially cut agricultural emissions of the greenhouse gas nitrous oxide appears Utopian rather than Arcadian. (Letters)

Farming contributes more to global warming than all the world's cars, trains, ships and planes put together. And the single biggest problem with farming is not carbon but nitrogen. From the maize fields of Kansas to the emerald rice paddies of China, today's bountiful harvests depend on generous applications of nitrogen fertiliser. Although only a tiny proportion escapes into the atmosphere as nitrous oxide, it is an extremely potent greenhouse gas. It's a vexing problem, but Eric Rey believes he has some of the answers, in the form of crops genetically modified to require less fertiliser.