ABSTRACT
Air pollution concentrations vary greatly from place to place at any one time, and with time of day and from year to year at any one place. This chapter discusses the measurement networks in the UK and elsewhere that have given us our current understanding of the occurrence of air pollutants, and presents some results that demonstrate key aspects of the conclusions so far. It also looks in some detail at the factors that determine both the short-and long-term airborne concentrations and the rates of dry and wet deposition of gaseous pollutants. The chapter relates much of the discussion of gases to sulphur and nitrogen oxides and to ozone, since they have been the subjects of the longest-established and most systematic measurement programmes. It also highlights the difference between regional-scale measurements of concentrations and deposition across the country at large, and local-scale measurements that are more appropriate to urban areas.
