1. Research project objectives/Research hypothesis
A number of techniques have been developed for measuring atmospheric aerosols that constitute of solid and liquid particles suspended in air. These may be divided into two main categories: in situ and remote. Remote techniques typically use visible light which wavelengths are close to aerosol size to measure so called optical aerosol parameters. LIDARs vary significantly in design and laser power but a typical system may retrieve aerosol backscattering and extinction coefficient profiles between approximately 0.5 km and 20 km. Consequently it is often impossible or impractical to obtain continuous information on aerosols above ground level, in the first few hundred meters of the atmosphere. A usual approach is to assume averaged aerosol parameters based on columnar measurements. This often leads to significant mismatch between concentrations and size distributions assumed above the surface and those measured at the ground level. In this project we postulate that it is possible to approximate a complete vertical profile of aerosol size distribution with the use of a synergy of in situ and remote measurements (synergy of LIDAR and sunphotometer) and propose an analytic scheme to achieve this objective.
2. Research project methodology
The proposed project will use aerosol size distribution profiles obtained with the use of a recently developed GRASP algorithm that is being utilized in IGP PAS as a part of the works associated with NCN OPUS project No. 2017/25/B/ST10/01650. The algorithm utilizes sunphotometer and LIDAR measurements to retrieve aerosol microphysical parameters within the LIDAR’s operating range. Approximately 20 one-hour-long cases will be selected from the results of the OPUS project for the further analysis within this project. A tandem of scanning mobility particle sizer (SMPS) and aerodynamic particle sizer (APS) will be collocated with the aforementioned optical instruments to provide in situ measurements of aerosol particle size distribution at the ground level in a wide range of sizes (2.5nm – 20μm). A fitting function will be developed to merge concentrations and size distributions between ground level and minimal LIDAR data range. Finally the reconstructed profiles of size distribution will be used to calculate profile of optical properties which will be validated based on extinction closure, i.e. equality between sunphotometer derived aerosol optical depth (AOD) and integrated extinction profile.
3. Expected impact of the research project on the development of science
In this project we propose a method for obtaining complete profiles of microphysical aerosol properties, especially in the planetary boundary layer (PBL), close to the ground. The common assumption of a constant vertical aerosol concentration in PBL is often insufficient and may lead to large errors. Approximation of complete profiles of aerosol microphysical parameters should prove useful for atmospheric modeling, especially in the scope of cloud formation and pollution forecasting that is sensitive to aerosol distribution in the vicinity of the surface. Moreover this reconstructed microphysical parameter profiles may be used to calculate optical extinction profiles for full range of altitudes. That is crucial to understand smog formed during winter season close to the ground when remote profiling techniques, like LIDARs, used alone seems to be insufficient
Szkop, A., Fernandes, A.R., Pietruczuk, A. (2020), Closing of LIDAR profiles using in-situ measurements at the surface Poland, Poster, EAC2020, Aachen, Germany.