Multiwavelength differential absorption lidar to improve measurement accuracy: test with ammonia over a traffic area

The development and improvement of techniques to monitor off-normal concentrations of chemicals in the atmosphere are crucial to guarantee human and environmental health, safety, and security. An interesting technique for use in research activities is the differential absorption lidar (DIAL); an improvement of the lidar technique able to provide information about the concentration of chemicals in the atmosphere. This work is focused on the use of DIAL, using a multiwavelength approach to increase the accuracy of gas concentration measurements in the atmosphere. The authors perform the uncertainty propagation analysis of this method, and highlight the advantages and the limits of this technique. Then, they applied this multiwavelength technique to preliminary DIAL measurements of ammonia in the atmosphere using three couples of laser wavelengths. The measurements are performed over a traffic area and are compared with water vapour measurements. A strong correlation between ammonia and water has been found a symptom that both chemicals belong to the exhaust gases of vehicles.