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. The use of automated lidar ceilometer (ALC) systems for theaerosol vertically resolved characterization has increased in recentyears thanks to their low construction and operation costs and theircapability of providing continuous unattended measurements. At the same timethere is a need to convert the ALC signals into usable geophysicalquantities. In fact, the quantitative assessment of the aerosol propertiesfrom ALC measurements and the relevant assimilation in meteorologicalforecast models is amongst the main objectives of the EU COST Action TOPROF(“Towards operational ground-based profiling with ALCs, Doppler lidars andmicrowave radiometers for improving weather forecasts”). Concurrently, the E-PROFILE program of the EuropeanMeteorological Services Network (EUMETNET) focuses on the harmonization ofALC measurements and data provision across Europe. Within these frameworks,we implemented a model-assisted methodology to retrieve key aerosolproperties (extinction coefficient, surface area, and volume) from elasticlidar and/or ALC measurements. The method is based on results from a largeset of aerosol scattering simulations (Mie theory) performed at UV, visible,and near-IR wavelengths using a Monte Carlo approach to select the inputaerosol microphysical properties. An average “continental aerosol type”(i.e., clean to moderately polluted continental aerosol conditions) isaddressed in this study. Based on the simulation results, we derive meanfunctional relationships linking the aerosol backscatter coefficients to theabovementioned variables. Applied in the data inversion of single-wavelengthlidars and/or ALCs, these relationships allow quantitative determination ofthe vertically resolved aerosol backscatter, extinction, volume, and surfacearea and, in turn, of the extinction-to-backscatter ratios (i.e., thelidar ratios, LRs) and extinction-to-volume conversion factor( cv) at 355, 532, and 1064 nm. These variables provide valuableinformation for visibility, radiative transfer, and air quality applications.This study also includes (1) validation of the model simulations with realmeasurements and (2) test applications of the proposed model-based ALCinversion methodology. In particular, our model simulations were compared tobackscatter and extinction coefficients independently retrieved by Ramanlidar systems operating at different continental sites within the EuropeanAerosol Research Lidar Network (EARLINET). This comparison shows goodmodel–measurement agreement, with LR discrepancies below 20 %. Themodel-assisted quantitative retrieval of both aerosol extinction and volumewas then tested using raw data from three different ALCs systems(CHM 15k Nimbus), operating within the Italian Automated LIdar-CEilometernetwork (ALICEnet). For this purpose, a 1-year record of the ALC-derivedaerosol optical thickness (AOT) at each site was compared to direct AOTmeasurements performed by colocated sun–sky photometers. This comparisonshows an overall AOT agreement within 30 % at all sites. At one site, themodel-assisted ALC estimation of the aerosol volume and mass (i.e., PM10 ) in the lowermost levels was compared to values measured atthe surface level by colocated in situ instrumentation. Within thisexercise, the ALC-derived daily-mean mass concentration was found toreproduce the corresponding (EU regulated) PM10 values measured bythe local air quality agency well in terms of both temporal variability andabsolute values. Although limited in space and time, the good performances ofthe proposed approach suggest it could possiblyrepresent a valid option to extend the capabilities of ALCs to providequantitative information for operational air quality and meteorologicalmonitoring.

atmospheric measurement techniques

A multiwavelength numerical model in support of quantitative retrievals of aerosol properties from automated lidar ceilometers and test applications for AOT and PM&amp;lt;sub&amp;gt;10&amp;lt;/sub&amp;gt; estimation