10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Towards Statistical Analysis of Aerosol Hygroscopic Properties Using Raman Lidar Measurements
FRANCISCO NAVAS-GUZMÁN, Giovanni Martucci, Maxime Hervo, Martine Collaud Coen, Bertrand Calpini, Valentin Simeonov, Alexander Haefele, Federal Office of Meteorology and Climatology, MeteoSwiss
Abstract Number: 861 Working Group: Aerosol Physics
Abstract The uncertainty in assessing total anthropogenic greenhouse gas and aerosol impacts on climate must be substantially reduced from its current level to allow meaningful predictions of future climate. This uncertainty is currently dominated by the aerosol component. Aerosol particles scatter and absorb radiation as well as change the microphysical properties of clouds. Evaluation of aerosol effects on climate must take into account high spatial and temporal variation of aerosol amounts and properties as well as the aerosol interactions with clouds and precipitation. During the last years a huge effort has been made in order to characterize vertically-resolved profiles of optical and microphysical properties for different kinds of particles. Raman lidars (light detection and ranging) have proven to be an essential tool to obtain profiles of these properties without modifying the environmental conditions. An important factor that can modify the role of aerosols in the global energy budget is the relative humidity (RH). Under high relative humidity conditions, aerosol particles size may increase due to water uptake (hygroscopic growth) altering their size distribution. Therefore, hygroscopic growth affects the direct scattering of radiation and especially the indirect effects, as the affinity of atmospheric aerosols for water vapour is highly related to their ability to act as cloud condensation nuclei (CCN). Thus, understanding aerosol hygroscopic growth is of high importance to quantify the influence of atmospheric aerosol in climate models.
Despite its importance, aerosol hygroscopic properties have not been properly characterized yet using remote sensing techniques (non-invasive method) and it is an open issue that needs to be addressed. The number of aerosol hygroscopic studies is modest and most of them were limited to few case studies during specific field campaigns. The major limitation of most of these studies is due to the lack of simultaneous observations of vertically resolved profiles of relative humidity and aerosol properties.
The Swiss RAman Lidar for Meteorological Observations (RALMO) can overcome these difficulties since it is able to provide continuous daytime and nighttime profiles of aerosol properties (backscatter and extinction) and relative humidity. RALMO is a state-of-art humidity, temperature and aerosol profiler capable to measure the rotational-vibrational Raman signals of nitrogen and water vapour (wavelengths of 386.7 and 407.5 nm, respectively) along with the pure rotational Raman (PRR) signal around the Rayleigh line at 355 nm. RALMO is operated at the aerological station of MeteoSwiss at Payerne (46º48’ N, 6º56’ E, 491 m asl) since beginning 2008 and provides one of the longest time-series of vertical profiles of humidity, temperature and aerosol properties in Europe. The presented study shows several case studies where the capability of this lidar system to detect vertically and temporally resolved aerosol hygroscopicity is proved. In addition, a methodology to exploit the 10-year data set and to produce a solid statistical analysis of aerosol hygroscopic properties is presented. The results show the potential of RALMO dataset for future statistical analysis of hygroscopic properties for a large variety of particles that reach our station (e.g. volcanic particles, Saharan dust, pollution, biomass burning aerosols, etc).