A Scanning Multi-Axis Differential Optical Absorption Spectroscopy System for Measurement of Tropospheric NO₂ in Beijing

A scanning multi-axis differential optical absorption spectroscopy (DOAS) system is developed for monitoring tropospheric NO₂ abundance. Measurements at different viewing angles near the horizon can be performed sequentially with one telescope collecting scattered sunlight reflected by a moving mirror. Tropospheric NO₂ diurnal variations can be derived from slant column densities (SCDs) of different elevation angles. The result from a field campaign in Beijing in summer of 2005 reveals potential possibility for the monitoring of tropospheric NO₂ by multi-axis DOAS technique.