Study of atmospheric desert dust and dust model evaluation through synergy and integration of different measurement techniques

The aim of this thesis is to study the desert dust aerosols and their transport in the atmosphere and in particular to gain insight into the desert dust distribution over North Africa, Middle East and Europe region during a ten-year period, using dust model reanalysis products of various optical and physical dust particle properties. Atmospheric desert dust is one of the major contributors to global aerosol loading and is the dominant component of atmospheric aerosols over large areas of Earth, strongly affecting Earth’s radiative budget and ecosystems. Mineral dust particles, suspended in the atmosphere from arid and semi-arid regions, can remain in the atmosphere from several days to about a week, depending on their size. Huge amounts of dust can be transported over great distances under favorable meteorological conditions, affecting regions hundreds to thousands of kilometers away. For countries in and downwind of arid regions, airborne sand and dust poses a serious threat to human and animal health and to various socio-economic sectors, such as aviation, ground transportation, agriculture, infrastructure, and the solar energy and other industries. An advanced regional model reanalysis for Northern Africa, Middle East and Europe was produced specifically for the desert dust component in the framework of the DustClim project using the MONARCH atmospheric chemistry model, based on the assimilation of dust retrievals obtained from aerosol satellite observations over a ten-year period 2007-2016. The reanalysis products cover a wide range of dust-related atmospheric parameters, including optical and physical dust properties, - such as dust optical depth, dust extinction coefficient and dust mass concentration - along with dust deposition and solar radiation variables. Such kind of reanalysis can be used as suitable tool for having a complete picture of the desert dust distribution, at high temporal and spatial resolution, overcoming the gap into observations and providing reliable climatological information on sand and dust storm trends and current conditions. Additionally, combined dust products can be investigated as suitable for quantifying the impact of desert dust on aviation (visibility), air quality (dust concentration exposure), solar energy plants (deposition and solar energy attenuation). The main objective of this thesis is to perform a thorough evaluation of the reanalysis performance using a wide variety of observations and data from experimental campaigns. The evaluation of the model simulations, performed by comparing the model-predicted values against selected observed values, is critical to assess the quality and uncertainty of the simulations and to establish the model’s reliability. In the most recent years, the advancement in observing techniques and the synergistic use of passive and active sensors and of satellite and ground based measurements are opening new possibilities like the identification of the dust particle contribution to measured optical properties through lidar measurements of particle depolarization ratio and estimation of the dust concentration through inversion methods when collocated lidar and photometer measurements are available. Moreover, a general overview of the desert dust climatology produced by the MONARCH reanalysis is provided in this work. Dust climatology aims to provide reliable reference values describing the spatial and temporal distribution of airborne dust, both near the Earth’s surface and in upper levels. In a later stage, the data analyzed and processed during this thesis, could be exploited for investigating the impact of the desert dust on different sectors. This kind of study could be of interest for developing mitigation and resilient actions to desert dust impacts. This thesis is structured in the following way: The 1st Chapter is an introduction to basic concepts revolving the atmospheric desert dust, its cycle – emission, transport, deposition – and its impacts on various socio-economic sectors. Moreover, datasets of observations and global and regional models, specifically for the desert dust component, are introduced. The 2nd Chapter provides a description of the MONARCH dust reanalysis, its novelties and its products. It also presents the approach used to evaluate the reanalysis products and describes in detail the main characteristics of the observational datasets used for the evaluation along with the assessment of satellite data quality. A description of the methodology which was applied in order to retrieve the dust component of the observations and the results from the evaluation procedure are presented for each variable separately. The 3rd Chapter provides an analysis of the inter- and intra-annual variability and climatology of the atmospheric dust load produced by the reanalysis. In addition, an assessment of dust climatological tendencies is attempted. In the final Chapter 4 the main findings and conclusions are summarized.