Multidimensional Analytical Characterization of Water-Soluble Organic Aerosols: Challenges and New Perspectives

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.

Advanced instrumental approaches for chemical characterization of indoor particulate matter

“…As recently reviewed by Duarte et al, [16] online or in situ methodologies are typically used in field observations to provide real-time (in the order of seconds/minutes) Figure 1. Levels of airborne PM components identification related to the research need on atmospheric behavior, properties, and sources of PM components (n is the number of PM constituents identified and/or measured).…”

“…However, it offers unparalleled rewards since determining the molecular composition and structure of aerosol WSOC is warranted to increase the current understanding of its role in various atmospheric processes and on human health. [161][162][163] Hence, the most promising analytical techniques in terms of molecular and structural elucidation include one-and two-dimensional nuclear magnetic resonance (1 D and 2 D NMR) spectroscopy [16,19,61,[65][66][67] and HR-MS [e.g., Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS)] (e.g., Willoughby et al, [164] Bao et al, [165] and Tang et al [166] ). While 1 D and 2 D NMR spectroscopy is particularly suitable for the untargeted analysis of the complex aerosol WSOC fraction, the HR-MS allows for a more reliable target analysis with reference standards as well as a screening for unknowns within the WSOC matrix.…”

“…As for the case of indoor aerosol WSOC, exploring the chemical composition of this complex mixture will require the use of complementary state-of-the-art analytical tools, such as HR-MS, 2 D NMR, and online or offline coupling between multidimensional LC and different detection systems (e.g., diode array detector, fluorescence detector, NMR, or HR-MS), assisted by chemometric tools [e.g., principal component analysis (PCA) or multivariate curve resolution-alternating least squares (MCR-ALS) methods]. [16] The combined use of multiple structural characterization techniques may prove indispensable to molecular-level identification of indoor aerosol WSOC. The structural information gleaned from the untargeted profiling of this indoor aerosol carbonaceous fraction will allow suggesting fruitful directions for resolving issues of aerosol WSOC effects on indoor air quality and human health.…”

“…[7] A comprehensive characterization of the complex mixture of organic and inorganic constituents within PM, to understand its origin and assess on abatement strategies, requires the application of multidimensional and complementary analytical methods, able to provide data ranging from bulk measurements such as mass loadings of specific PM components [e.g., BC/elemental carbon (EC), organic carbon (OC), major inorganic ions, organic speciation and major and trace elements] to in-depth properties of individual particles (e.g., elemental mapping of internally mixed air particles), [1,11] and molecular-level characterization of either specific organic constituents [e.g., PAHs, organophosphate flame retardants (OPFRs), and polychlorinated biphenyls (PCBs)] or other complex organic molecules. [12][13][14][15][16][17][18] Over the last two decades, the rapidly-evolving field of analytical instrumentation has produced sophisticated tools capable of meeting this challenge, either by providing field and real-time information on the chemical composition of atmospheric PM, or by affording a high chemical resolution, but at the expense of a low temporal resolution. In either way, when delving into the chemical analysis of PM, it is important to match the level of knowledge on the chemical species to the problem being addressed.…”

Special Issue on New Insights into Atmospheric Chemistry and Climate

“…Full characterization of organic aerosol fraction is particularly difficult to achieve due to the complexity of this aerosol component and its structural diversity. In the review, Duarte et al [7] highlighted 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.…”