Unraveling the structural features of organic aerosols by NMR spectroscopy: a review.

Our limited understanding of the effect of organic aerosols (OAs) on the climate and human health is largely because of the vast array of formation processes and sources that produce a multitude of molecular structures and physical properties. The need to unravel the enormous complexity and heterogeneity of OAs and thus understand their effects on the climate and human health has led to the development of different off-line methods based on the use of advanced analytical techniques. Within this context, nuclear magnetic resonance (NMR) spectroscopy has become essential for acquiring detailed structural characterization of the complex natural organic matter contained in atmospheric aerosols. In this article, we present a critical review on the application of NMR spectroscopy in OAs (primary and secondary) studies, focusing mainly on the water-soluble organic fraction, and how NMR has impacted our knowledge on atmospheric organic matter. A major emphasis is given on the wealth of chemical information that solid-state and multi-dimensional solution-state NMR can provide, including the sources, formation pathways, seasonal, and regional characterization of atmospheric OAs. Finally, major challenges are discussed and recommendations for future research directions are proposed.