###### Abstract  
Water-soluble organic aerosols (OA) are an important component of air particles and one of the key drivers that impact both climate and human health. Understanding the processes involving water-soluble OA depends on how well the chemical composition of this aerosol component is decoded. Yet, obtaining detailed information faces several challenges, including water-soluble OA collection, extraction, and chemical complexity. This review highlights the multidimensional non-targeted analytical strategies that have been developed and employed for providing new insights into the structural and molecular features of water-soluble organic components present in air particles. First, the most prominent high-resolution mass spectrometric methods for near real-time measurements of water-soluble OA and their limitations are discussed. Afterward, a special emphasis is given to the degree of compositional information provided by offline multidimensional analytical techniques, namely excitation-emission (EEM) fluorescence spectroscopy, high-resolution mass spectrometry and two-dimensional nuclear magnetic resonance (NMR) spectroscopy and their hyphenation with chromatographic systems. The major challenges ahead on the application of these multidimensional analytical strategies for OA research are also addressed so that they can be used advantageously in future studies. organic aerosols; air particles; water-soluble organic matter; 2D NMR spectroscopy; high-resolution mass spectrometry; EEM fluorescence spectroscopy; 2D chromatographic separation 2021 11 2539 2021 10 March 2021 12 March 2021 11 2539 10 March 2021 12 February 2021 10 March 2021 12 March 2021 10 March 2021 10 March 2021 10 March 2021 10 March 2021 10 March  
more difficult to achieve due to the structural diversity and complexity of this aerosol component. The organic aerosols (OA) fraction can be the predominant component of suspended PM mass, accounting for ~20-50% of the total fine particulate mass at continental mid-latitudes and reach 90% in tropical forested areas [5; 6]. The interest of the atmospheric research community on this OA component has been fueled by the realization that an important fraction of the OA is water-soluble. In Northern Hemisphere midlatitudes, the ubiquitous water-soluble organic matter (WSOM) represents 10% to 80% of the total particulate organics [7; 8; 9; 10], whereas lower percentage values (up to 13%) have been reported for Southern Hemisphere locations [11]. The aerosol WSOM plays a key role in cloud formation and properties [12; 13], Earth's radiative balance [14; 15], and atmospheric chemistry [14; 16]. Atmospheric deposition of aerosol WSOM can also affect carbon and nitrogen biogeochemical cycles in aquatic ecosystems [17; 18; 19]. Aerosol WSOM in fine inhalable air particles may also exert adverse health effects by generating reactive oxygen and nitrogen species [20; 21] or by promoting a moderate pro-inflammatory status [7]. Understanding these dynamic processes involving aerosol WSOM depends on how well one can identify its organic constituents. It is now well established that the atmospheric aerosol WSOM comprises a multitude of molecular structures, physical properties, and sources (primary and secondary formation) [14; 15; 22; 23]. However, coping with aerosol WSOM complexity still is a major impairment in advancing our understanding of its molecular composition, as well as its physical properties, sources, transformation, fate, as well as climatic and health impacts. Understanding aerosol WSOM composition and significance is, therefore, a focus of major scientific and policy concern. This review aims at highlighting the use of high-resolution multidimensional analytical techniques for assessing the molecular- and bulk-level structural features of the water-soluble fraction of OA.