This has led to a burgeoning of interest in particulate pollutants, although the base of data has been severely limited. For reasons which were sound at the time, airborne particulate matter in the UK atmosphere has traditionally been measured by the Black Smoke method. This Network, which is still growing, has provided invaluable high quality data upon the concentrations of PM10 particles in our major towns and cities. The data available to the policy makers and research workers from this network, to be made available in due course to the general public, probably equals that of any other country in the world and far exceeds the quality of data available in many other developed countries in terms of the time response and speed of availability to the user. Airborne particles in the UK atmosphere arise from a wide variety of sources.
Traffic also generates particles from the wear of rubber tyres and of the road surface itself.
Both sea spray and de-icing salt lead to the presence of sodium chloride particles in the atmosphere, even at locations remote from the sea. The other main source of particles arises from the emission of sulphur dioxide, mostly from power stations and other industry, and of nitrogen oxides from road traffic, power stations and other combustion sources. These gases are oxidised in the atmosphere to form sulphuric and nitric acids which are neutralised with atmospheric ammonia to form the so-called secondary aerosol of mainly ammonium sulphate and ammonium nitrate. Because of its rather slow formation and long atmospheric lifetime, concentrations of secondary particles are far more uniform across the UK than the primary emissions from road traffic, which are concentrated mainly in urban areas. The European continent contributes significantly to the airborne loading of secondary particles in the UK atmosphere.