Application of Raman Lidar Advancements in Meteorology and Air Quality Monitoring

摘要

Raman lidar techniques provide vertical profiles of the key parameters needed for better understanding of meteorological and air pollution processes. The time sequence of atmospheric profiles is most valuable for understanding meteorological processes and describing the evolution of episodes and exposure associated with air pollution. The vibrational and rotational Raman lidar signals provide simultaneous profiles of ozone and airborne particulate matter, as well as several meteorological properties. The first operational prototype Raman lidar, Lidar Atmospheric Profile Sensor (LAPS), makes use of 2nd and 4th harmonic generated beams of a Nd:YAG laser to provide both daytime and nighttime measurements. The Raman scatter signals from vibrational states of water vapor and nitrogen provide robust profiles of the specific humidity in the lower atmosphere. The temperature profiles are measured using the ratio of rotational Raman signals at 530 and 528 nm from the 532 nm beam of the NdrYAG laser. Optical extinction profiles can be determined from the measured gradients in each of several molecular species profiles by comparing with the molecular scale height. Wavelengths at 284 nm, 530 nm and 607 nm have been used routinely to determine profiles of optical extinction. The ozone profiles in the lower troposphere are measured using a DIAL analysis of the ratio of the vibrational Raman signals for nitrogen (284 nm) and oxygen (278 nm), which are on the steep side of the Hartley band of ozone. Examples from several measurement campaigns are used to demonstrate the utility of Raman lidar for describing the evolution of air pollution events. The examples presented have been selected to show the new level of understanding of air pollution events and meteorological processes that is gained from applications of lidar techniques.