Atmospheric transport of soil-derived dicarboxylic acids over the North Pacific Ocean

Revealing the Reactivity of Individual Chemical Entities in Complex Mixtures: the Chemistry Behind Bio-Oil Upgrading

Bio-oils are precursors for biofuels but are highly corrosive necessitating further upgrading. Furthermore, bio-oil samples are highly complex and represent a broad range of chemistries. They are complex mixtures not simply because of the large number of poly-oxygenated compounds but because each composition can comprise many isomers with multiple functional groups. The use of hyphenated ultrahigh-resolution mass spectrometry affords the ability to separate isomeric species of complex mixtures. Here, we present for the first time, the use of this powerful analytical technique combined with chemical reactivity to gain greater insights into the reactivity of the individual isomeric species of bio-oils. A pyrolysis bio-oils and its esterified bio-oil were analyzed using gas chromatography coupled to Fourier transform ion cyclotron resonance mass spectrometry, and in-house software (KairosMS) was used for fast comparison of the hyphenated data sets. The data revealed a total of 10,368 isomers in the pyrolysis bio-oil and an increase to 18,827 isomers after esterification conditions. Furthermore, the comparison of the isomeric distribution before and after esterification provide new light on the reactivities within these complex mixtures; these reactivities would be expected to correspond with carboxylic acid, aldehyde, and ketone functional groups. Using this approach, it was possible to reveal the increased chemical complexity of bio-oils after upgrading and target detection of valuable compounds within the bio-oils. The combination of chemical reactions alongside with in-depth molecular characterization opens a new window for the understanding of the chemistry and reactivity of complex mixtures.

Terrestrial lipid biomarkers in marine aerosols over the western North Pacific during 1990-1993 and 2006-2009

Terrestrial lipid biomarkers are one of the key tracers in the studies of atmospheric aerosols. Here, we investigated such organic compounds in marine aerosols collected at Chichijima Island, the western North Pacific for two 4-year periods: 1990-1993 and 2006-2009. A homologous series of lipid biomarkers including C₁₈-C₃₇n-alkanes, C₉-C₃₄ fatty acids, and C₁₄-C₃₅ fatty alcohols were determined by gas chromatography/mass spectrometry (GC/MS). The atmospheric levels of these tracers increased from 1990-1993 to 2006-2009. Their seasonal trends were clearly characterized by winter-spring maxima and summer-fall minima. The relative abundance of the high-molecular-weight (HMW) n-alkanes (C₂₅-C₃₇) and n-alcohols (C₂₀-C₃₅) in total HMW lipids peaked in winter and winter/fall, respectively, whereas those of HMW fatty acids (C₂₀-C₃₄) peaked in summer. Air-mass backward trajectory analyses suggest that the Asian continent, Southeast Asia including tropical regions, and the Central Pacific are the main source regions. The seasonal shift and distribution of the carbon preference index and average chain length for the HMW lipids were controlled by the changes in climatic factors and source regions. The higher abundance of terrestrial lipids during 2006-2009 than 1990-1993 indicates a higher emission from terrestrial plantation in the 2000s than in the early 1990s in upwind regions of East Asia. Furthermore, HMW lipid compounds exhibited much stronger positive correlations with levoglucosan, a biomass-burning tracer, during 2006-2009 than 1990-1993, suggesting that biomass-burning emissions contributed more significantly in this century.

Carbonaceous aerosol tracers in ice-cores record multi-decadal climate oscillations

Carbonaceous aerosols influence the climate via direct and indirect effects on radiative balance. However, the factors controlling the emissions, transport and role of carbonaceous aerosols in the climate system are highly uncertain. Here we investigate organic tracers in ice cores from Greenland and Kamchatka and find that, throughout the period covered by the records (1550 to 2000 CE), the concentrations and composition of biomass burning-, soil bacterial- and plant wax- tracers correspond to Arctic and regional temperatures as well as the warm season Arctic Oscillation (AO) over multi-decadal time-scales. Specifically, order of magnitude decreases (increases) in abundances of ice-core organic tracers, likely representing significant decreases (increases) in the atmospheric loading of carbonaceous aerosols, occur during colder (warmer) phases in the high latitudinal Northern Hemisphere. This raises questions about causality and possible carbonaceous aerosol feedback mechanisms. Our work opens new avenues for ice core research. Translating concentrations of organic tracers (μg/kg-ice or TOC) from ice-cores, into estimates of the atmospheric loading of carbonaceous aerosols (μg/m³) combined with new model constraints on the strength and sign of climate forcing by carbonaceous aerosols should be a priority for future research.

Biogenic and anthropogenic organic components of Saharan sands

Till now, the Sahara desert sands have scarcely characterized for their organic contents, despite they are known to heavily affect Europe and America when transported by winds. In this study, the composition of sands collected in ten oasis lying in two regions of the Algerian Sahara during 2011 was investigated with regards to organic fraction. Attention was paid to anthropogenic and biogenic sources of organics associated to sands, through the characterization of n-alkanes, n-alkanoic and n-alkanedioic acids, n-alkanols, sterols, PAHs and caffeine. The organic fraction load on sands associable to natural sources was higher in the Region of Biskra than in that of Ouargla. The biogenic contribution to the total amount of organics in sands exceeded that of the anthropogenic sources. The composition of sands from Hassi Messaoud, compared to that observed there in 2006, showed that the anthropic impact over the region was not changed.