Vertical profiling of geometrical, optical and microphysical particle properties over Nothern India using a multi-wavelength lidar system

A one-year-long campaign of Raman lidar measurements has been performed in Gual Pahari (30 km from Delhi), India in the frame of EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions) project. The measurements were performed from March 2008 to March 2009 with a multi-wavelength Raman lidar of the type PollyXT. The lidar measurements were carried out continuously and during one year we have selected 183 days with almost 2500 hours of measurement time in total. The range-corrected backscatter signal at 1064nm is used to determine the geometrical boundaries of aerosol layers for each of the one-hour period averaged data. Then we identify the main source of the identified atmospheric layers using backward trajectory analyses with HYSPLIT. Back-trajectory analysis has revealed the advection of different types of aerosols. The seasonal cycle of geometrical, optical and microphysical properties over Northern India was observed. The profiles of the backscatter coefficients show a clear seasonal variation. The summer had the largest mean backscatter coefficient, averaged between 1 and 3 km height, while the winter had the lowest backscatter values. The seasonal profiles of backscatter coefficients had distinctly different shapes. In summer, the values of these coefficients had the steepest decrease from 1 to 3 km. The autumn, and especially the winter, had a relatively shallow aerosol layer near the ground. The value of the backscatter coefficient was highest near the ground and then it decreased moderately with increasing altitude. The main seasonal variation of extinction coefficients followed in a similar fashion. The seasonal averages of the lidar ratios at 355 nm varied from 45 sr in the spring to 77 sr in the autumn, and the corresponding variability at 532 nm was from 36 to 60 sr. The lidar ratios at 532 nm were below 40 sr in the spring and winter, indicating the presence of a cleaner air mass with relatively more aged aerosols than during the other seasons. In the winter though, the aerosol layer was thin and strong near ground, as seen in the extinction profiles. During the summer and autumn, the average lidar ratios were larger than 50 sr, suggesting the presence/dominance of absorbing aerosols from biomass burning. A data set consisting of backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm measured with a multi-wavelength aerosol lidar allow us to retrieve microphysical properties by optical data inversion. The results indicate larger aerosols during spring and more absorbing aerosols during winter. Additionally, microphysical properties were calculated for the well-defined aerosol layers for each of the aerosol types. The inversion was only possible in the height ranges where the intensive optical properties were calculated. The potential correlation between different microphysical properties for each of the aerosol types was also investigated.