Abstract
Abstract. A new methodology based on combining active and passive remote sensing and simultaneous and collocated radiosounding data to study the aerosol hygroscopic growth effects on the particle optical and microphysical properties is presented. The identification of hygroscopic growth situations combines the analysis of multispectral aerosol particle backscatter coefficient and particle linear depolarization ratio with thermodynamic profiling of the atmospheric column. We analyzed the hygroscopic growth effects on aerosol properties, namely the aerosol particle backscatter coefficient and the volume concentration profiles, using data gathered at Granada EARLINET station. Two study cases, corresponding to different aerosol loads and different aerosol types, are used for illustrating the potential of this methodology. Values of the aerosol particle backscatter coefficient enhancement factors range from 2.1 ± 0.8 to 3.9 ± 1.5, in the ranges of relative humidity 60–90 and 40–83%, being similar to those previously reported in the literature. Differences in the enhancement factor are directly linked to the composition of the atmospheric aerosol. The largest value of the aerosol particle backscatter coefficient enhancement factor corresponds to the presence of sulphate and marine particles that are more affected by hygroscopic growth. On the contrary, the lowest value of the enhancement factor corresponds to an aerosol mixture containing sulphates and slight traces of mineral dust. The Hänel parameterization is applied to these case studies, obtaining results within the range of values reported in previous studies, with values of the γ exponent of 0.56 ± 0.01 (for anthropogenic particles slightly influenced by mineral dust) and 1.07 ± 0.01 (for the situation dominated by anthropogenic particles), showing the convenience of this remote sensing approach for the study of hygroscopic effects of the atmospheric aerosol under ambient unperturbed conditions. For the first time, the retrieval of the volume concentration profiles for these cases using the Lidar Radiometer Inversion Code (LIRIC) allows us to analyze the aerosol hygroscopic growth effects on aerosol volume concentration, observing a stronger increase of the fine mode volume concentration with increasing relative humidity.
Highlights
The influence of atmospheric aerosols in the Earth’s climate is still affected by a high uncertainty
To be considered are especially the indirect effects, as the affinity of atmospheric aerosols for water vapor is highly related to their ability to act as cloud condensation nuclei (CCN) (Charlson et al, 1992; Feingold and Morley, 2003; Padró et al, 2010)
Lidar measurements were always running in coincidence with the radiosounding launches. These lidar measurements have been exhaustively analyzed together with the RH profiles provided by the radiosoundings in order to detect cases of aerosol hygroscopic growth
Summary
The influence of atmospheric aerosols in the Earth’s climate is still affected by a high uncertainty. Scientific knowledge on the interaction between atmospheric aerosol and solar radiation is quite low compared to other atmospheric constituents mainly due to atmospheric aerosol high spatiotemporal variability (IPCC, 2013). As it is well known, atmospheric aerosol can affect the Earth’s atmosphere energy budget by means of direct effects (by scattering or absorbing solar radiation) and indirect effects (mainly by changes in cloud properties). Changes in aerosol properties can highly influence the Earth’s climate. To be considered are especially the indirect effects, as the affinity of atmospheric aerosols for water vapor is highly related to their ability to act as cloud condensation nuclei (CCN) (Charlson et al, 1992; Feingold and Morley, 2003; Padró et al, 2010)
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