Persistence of urban organic aerosols composition: Decoding their structural complexity and seasonal variability

• Published in: Environmental pollution (1987) 2017-12, Vol.231 (Pt 1), p.281-290
• Main Authors: Matos, João T.V., Duarte, Regina M.B.O., Lopes, Sónia P., Silva, Artur M.S., Duarte, Armando C.
• Format: Article
• Language: English
• Subjects: Aerosols - analysis; Air Pollutants - analysis; Biomass; Environmental Monitoring; Hydrophobic and Hydrophilic Interactions; Magnetic Resonance Spectroscopy - methods; Molecular diversity; Particulate Matter - analysis; Seasons; Smoke; Sources signatures; Two-dimensional NMR spectroscopy; Urban organic aerosols; Water - chemistry; Water- and alkaline-soluble organic matter
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2017.08.022

Organic Aerosols (OAs) are typically defined as highly complex matrices whose composition changes in time and space. Focusing on time vector, this work uses two-dimensional nuclear magnetic resonance (2D NMR) techniques to examine the structural features of water-soluble (WSOM) and alkaline-soluble organic matter (ASOM) sequentially extracted from fine atmospheric aerosols collected in an urban setting during cold and warm seasons. This study reveals molecular signatures not previously decoded in NMR-related studies of OAs as meaningful source markers. Although the ASOM is less hydrophilic and structurally diverse than its WSOM counterpart, both fractions feature a core with heteroatom-rich branched aliphatics from both primary (natural and anthropogenic) and secondary origin, aromatic secondary organics originated from anthropogenic aromatic precursors, as well as primary saccharides and amino sugar derivatives from biogenic emissions. These common structures represent those 2D NMR spectral signatures that are present in both seasons and can thus be seen as an “annual background” profile of the structural composition of OAs at the urban location. Lignin-derived structures, nitroaromatics, disaccharides, and anhydrosaccharides signatures were also identified in the WSOM samples only from periods identified as smoke impacted, which reflects the influence of biomass-burning sources. The NMR dataset on the H–C molecules backbone was also used to propose a semi-quantitative structural model of urban WSOM, which will aid efforts for more realistic studies relating the chemical properties of OAs with their atmospheric behavior. [Display omitted] •2D NMR spectroscopy was used to decode urban organic aerosols.•Water and alkaline soluble components of urban organic aerosols have been compared.•Persistence of urban organic aerosols composition across different seasons.•Annual background profile of the structural features of urban organic aerosols.•Semi-quantitative structural model of water soluble urban organic aerosols. Persistence of water- and alkaline-soluble organic matter composition in urban aerosols related to its molecular characteristics.