Zhanqing Li, Min Lv, Jun Chen, Zhien Wang, Richard Ferrare, Dong Liu
The vertical distribution of aerosols and their capability of serving as cloud condensation nuclei (CCN) are important for improving our understanding of aerosol indirect effects. Although ground-based and airborne CCN measurements have been made, they are generally scarce, especially and even much fewer at cloud base where it is needed most. We have developed an algorithm for profiling CCN number concentrations using backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm from multi-wavelength lidar systems. The algorithm considers three distinct types of aerosols (urban industrial, biomass burning, and dust) with bimodal size distributions. The algorithm uses look-up tables, which were developed based on the ranges of aerosol size distributions obtained from the Aerosol Robotic Network, to efficiently find optimal solutions. CCN number concentrations at five supersaturations (0.07–0.80%) are determined from the retrieved particle size distributions, based on the assumption that the various constituents are internally mixed. Retrieval simulations were performed with different combinations of systematic and random errors in lidar-derived extinction and backscatter coefficients. The potential of this algorithm to retrieve CCN concentrations is further evaluated through comparisons with surface-based CCN measurements with near surface lidar retrievals. Systematic errors range from -20% to 20% and random errors are up to 15%. As CCN is closely linked with the hygroscopic growth of aerosol particles. Attempts are also made to derive the growth function with relative humidity from Raman lidar. The function is found to have a strong dependence on aerosol chemical composition which is investigated using data from an aerosol chemical speciation monitor (ACSM), and a hygroscopic tandem differential mobility analyzer (H-TDMA) deployed during a field experiment in China. Two distinct cases were chosen with marked differences in their hygroscopic growth that was that was fitted by the Kasten model. The differences were attributed to different amounts of chemical species.
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