COST-EFFICIENT TECHNIQUES FOR URBAN AND BACKGROUND MEASUREMENTS OF SO2 AND NO2

Urban and background concentrations of SO2 and NO2 have been measured in Sweden for the last 30 yr. During this time the measuring technique s have continuously been improved. Today very cost-efficient, sensitiv e and accurate techniques are used to measure concentrations on a mont hly and on a daily basis. Background as well as urban concentrations a re measured on a monthly basis using diffusive samplers. Diffusive (pa ssive) samplers have also been used extensively in workplace environme nts. When exposing diffusive samplers to outdoor air it is important t hat the wind does not affect the sampling rate by creating turbulent d iffusion inside the sampler, and thereby increasing the sampling rate in an unpredictable way. This wind effect was first solved for a long tube sampler, aimed only for urban measurements. Later, a shorter and wider sampler was developed with a measuring range for monthly samplin g of about 0.1-200 mu g m(-3) for SO2 and 0.1-400 mu g m(-3) for NO2 i .e. sensitive enough for background measurements but still satisfactor y in town centres. The samplers can be stored at room temperature prio r to as well as after sampling. 24 h average concentrations can be det ermined using an automatic sampler (active sampling). Comparison betwe en diffusive and active techniques have been made under realistic cond itions (routine monitoring) in both background and urban air. The two techniques agree within ca. +/- 15% which today is reasonable for rout ine monitoring. (C) 1998 Elsevier Science Ltd. All rights reserved.