Abstract
Abstract. We investigate the potential of polarization lidar to provide vertical profiles of aerosol parameters from which cloud condensation nucleus (CCN) and ice nucleating particle (INP) number concentrations can be estimated. We show that height profiles of particle number concentrations n50, dry considering dry aerosol particles with radius > 50 nm (reservoir of CCN in the case of marine and continental non-desert aerosols), n100, dry (particles with dry radius > 100 nm, reservoir of desert dust CCN), and of n250, dry (particles with dry radius > 250 nm, reservoir of favorable INP), as well as profiles of the particle surface area concentration sdry (used in INP parameterizations) can be retrieved from lidar-derived aerosol extinction coefficients σ with relative uncertainties of a factor of 1.5–2 in the case of n50, dry and n100, dry and of about 25–50 % in the case of n250, dry and sdry. Of key importance is the potential of polarization lidar to distinguish and separate the optical properties of desert aerosols from non-desert aerosol such as continental and marine particles. We investigate the relationship between σ, measured at ambient atmospheric conditions, and n50, dry for marine and continental aerosols, n100, dry for desert dust particles, and n250, dry and sdry for three aerosol types (desert, non-desert continental, marine) and for the main lidar wavelengths of 355, 532, and 1064 nm. Our study is based on multiyear Aerosol Robotic Network (AERONET) photometer observations of aerosol optical thickness and column-integrated particle size distribution at Leipzig, Germany, and Limassol, Cyprus, which cover all realistic aerosol mixtures. We further include AERONET data from field campaigns in Morocco, Cabo Verde, and Barbados, which provide pure dust and pure marine aerosol scenarios. By means of a simple CCN parameterization (with n50, dry or n100, dry as input) and available INP parameterization schemes (with n250, dry and sdry as input) we finally compute profiles of the CCN-relevant particle number concentration nCCN and the INP number concentration nINP. We apply the method to a lidar observation of a heavy dust outbreak crossing Cyprus and a case dominated by continental aerosol pollution.
Highlights
Field studies of aerosol–cloud-dynamics interaction are presently in the focus of atmospheric research
Aerosol particles can serve as cloud condensation nuclei (CCN) in liquid droplet nucleation processes and/or as ice-nucleating particles (INP) in ice nucleation processes, which include the conversion of liquid droplets into ice crystals
Based on an in-depth correlation study applied to long-term and field campaign Aerosol Robotic Network (AERONET) observations, it has been demonstrated that a solid path exists from the particle extinction coefficients, as measurable with lidar, to the basic aerosol parameters from which the nCCN and nINP profiles can be estimated
Summary
Field studies of aerosol–cloud-dynamics interaction are presently in the focus of atmospheric research. 2. Section 3 presents our methodology to obtain profiles of n50,dry, n100,dry, n250,dry, sdry, nCCN, and nINP from lidar profiles of ambient particle extinction coefficients σ for the three basic aerosol types (desert, marine, continental). The conversion of measured optical properties into particle number and surface area concentrations requires good knowledge of the correlation between optical and microphysical particle properties This knowledge is gained from the mentioned long-term AERONET measurements and the specific dust field campaigns.
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