Standardisation of methods for long-term monitoring

A monitoring programme should be designed for duration. This means that met hods should not only be appropriate with respect to detection limits and ac curacy, but they should also be as simple as possible and they should be do cumented in such a way that measurements will be comparable over many decad es. In this connection, it is particularly important to understand that res ults are dependent on methods, instruments and procedures. Within the Europ ean monitoring network (EMEP) there are several different sampling procedur es for the main air components, SO2, NO2, SO42-, NO3- + HNO3, and co-locate d experiments have therefore been initiated to quantify the difference betw een the measurements. Reference methods and reference instruments correspon ding to the recommendation in the EMEP Manual have been run together with t he usual measurements at EMEP sites in several countries. The results are g enerally satisfactory, especially in the case where identical methods are u sed. However, there are also some unacceptable differences, e.g. when compa ring NO2 and SO2 monitors with the reference methods. The monitors do have a main advantage of providing easily accessible data with short time resolu tion; nevertheless, the accuracy at low concentrations is usually poor. The traditional reference methods need development and simplification in the d irection of the more appealing automatic instruments.