Abstract
This study investigates the structural composition and major sources of water-soluble organic matter (WSOM) from PM2.5 collected, in parallel, during summer and winter, in two contrasting suburban sites at Iberian Peninsula Coast: Aveiro (Portugal) and Coruña (Spain). PM10 samples were also collected at Coruña for comparison. Ambient concentrations of PM2.5, total nitrogen (TN), and WSOM were higher in Aveiro than in Coruña, with the highest levels found in winter at both locations. In Coruña, concentrations of PM10, TN, and WSOM were higher than those from PM2.5. Regardless of the season, stable isotopic δ13C and δ15N in PM2.5 suggested important contributions of anthropogenic fresh organic aerosols (OAs) at Aveiro. In Coruña, δ13C and δ15N of PM2.5 and PM10 suggests decreased anthropogenic input during summer. Although excitation-emission fluorescence profiles were similar for all WSOM samples, multi-dimensional nuclear magnetic resonance (NMR) spectroscopy confirmed differences in their structural composition, reflecting differences in aging processes and/or local sources between the two locations. In PM2.5 WSOM in Aveiro, the relative distribution of non-exchangeable proton functional groups was in the order: HC (40–43%) > HCC (31–39%) > HCO (12–15%) > Ar-H (5.0–13%). However, in PM2.5 and PM10 WSOM in Coruña, the relative contribution of HCO groups (24–30% and 23–29%, respectively) equals and/or surpasses that of HCC (25–26% and 25–29%, respectively), being also higher than those of Aveiro. In both locations, the highest aromatic contents were observed during winter due to biomass burning emissions. The structural composition of PM2.5 and PM10 WSOM in Coruña is dominated by oxygenated aliphatic compounds, reflecting the contribution of secondary OAs from biogenic, soil dust, and minor influence of anthropogenic emissions. In contrast, the composition of PM2.5 WSOM in Aveiro appears to be significantly impacted by fresh and secondary anthropogenic OAs. Marine and biomass burning OAs are important contributors, common to both sites.
Highlights
The study of the water-soluble fraction of organic aerosols (OAs) has been in the spotlight of atmospheric research community due to its effects on aerosol optical depth (Andreae and Gelencsér, 2006; Mladenov et al, 2010; Moise et al, 2015), cloud formation and properties (Martin et al, 2013; Padró et al, 2010; Sun and Ariya, 2006; Wonaschütz et al, 2013), radiation balance (Bond et al, 2013; Laskin et al, 2015; Moise et al, 2015), and atmospheric chemistry (George et al, 2015; Laskin et al, 2015; Mellouki et al, 2015)
Important questions still remain: (i) how the levels of ambient OAs, in particular of the water-soluble organic fraction, distribute along this region located at the land-sea interface, (ii) how they compare in terms of their structural composition and sources, and (iii) whether would be possible to potentially complement existing OAs source profiles within this region
Three major questions have guided this study: (i) how the levels of ambient water-soluble OAs distribute along this region, (ii) how they compare in terms of their structural composition and sources, and (iii) whether would be possible to complement existing OAs source profiles within this region
Summary
The study of the water-soluble fraction of organic aerosols (OAs) has been in the spotlight of atmospheric research community due to its effects on aerosol optical depth (Andreae and Gelencsér, 2006; Mladenov et al, 2010; Moise et al, 2015), cloud formation and properties (Martin et al, 2013; Padró et al, 2010; Sun and Ariya, 2006; Wonaschütz et al, 2013), radiation balance (Bond et al, 2013; Laskin et al, 2015; Moise et al, 2015), and atmospheric chemistry (George et al, 2015; Laskin et al, 2015; Mellouki et al, 2015). In Southern European regional background and suburban sites, the total carbonaceous fraction [organic matter plus elemental carbon (EC)] is an important aerosol component, contributing to 28-41% of PM2.5 (Duarte et al, 2017a; Pio et al, 2007; Querol et al, 2013, 2009). Notwithstanding these relatively high proportions in ambient PM, the molecular features and source contributions of OAs, including their water-soluble organic component, are still not fully understood. Stable isotopic (δ13C and δ15N) and water-soluble trace metals compositions of the bulk PM2.5 and PM10 samples were assessed to better understand the contribution of various sources to OAs at the studied locations
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