DOAS as an Analytical Tool for Effective Air Pollution Management

Air pollution measurements are aimed at improving our understanding of the chemical properties of the atmosphere, addressing mainly three issues with very different space and time scales: • Measurement of critical or peak values of air pollutant in densely urbanized/industrialized sites. • Long term observation and trend analysis on air quality. • Evaluation of photochemical pollution (smog) episodes on a time scale of a few days. For each of these issues, the DOAS (Differential Optical Absorption Spectroscopy) technique has developed into one of the practical high performance techniques. Based on the UV-visible molecular absorption of atmospheric gases, DOAS is a spectroscopic technique well suited for a simultaneous detection of many atmospheric trace gases including the criteria compounds, NO2, SO2, and O3. Furthermore the DOAS technique is based on the optical absorption of gases over long path lengths ranging from some hundreds of meters up to several kilometers long. Thus the DOAS values, in the case of non-folded optical paths, give in general pollutant concentrations averaged over relatively large distances, thus avoiding large local perturbations that can be observed in point measurements. In the case of photo-smog events, the DOAS system provides an ideal database for comparison with results obtained from a mesoscale eulerian air quality model as the spatial resolution is comparable between model and measurement, and the time resolution of the measurement is short enough for useful comparison. Such models are at this point scientifically the most relevant tools to predict the impact of different air pollution abatement strategies on air pollution events. This paper summarizes the significance of the DOAS technique in air pollution management. ∗ Currently at Atmospheric Sciences Division, Chemistry and Dynamics Branch NASA Langley Research Center Mail Stop 401A, Hampton, VA 23681-0001, USA [email protected]; +1 (757) 864-7790 Fax