The distributions, correlations, and source apportionment of aromatic acids, aromatic ketones, polycyclic aromatic hydrocarbons (PAHs), and trace metals were studied in Canadian high Arctic aerosols. Nineteen PAHs including minor sulfur-containing heterocyclic PAH (dibenzothiophene) and major 6 carcinogenic PAHs were detected with a high proportion of fluoranthene followed by benzo[k]fluoranthene, pyrene, and chrysene. However, in the sunlit period of spring, their concentrations significantly declined likely due to photochemical decomposition. During the polar sunrise from mid-March to mid-April, benzo[a]pyrene to benzo[e]pyrene ratios significantly dropped, and the ratios diminished further from late April to May onward. These results suggest that PAHs transported over the Arctic are subjected to strong photochemical degradation at polar sunrise. Although aromatic ketones decreased in spring, concentrations of some aromatic acids such as benzoic and phthalic acids increased during the course of polar sunrise, suggesting that aromatic hydrocarbons are oxidized to result in aromatic acids. However, PAHs do not act as the major source for low molecular weight (LMW) diacids such as oxalic acid that are largely formed at polar sunrise in the arctic atmosphere because PAHs are 1 to 2 orders of magnitude less abundant than LMW diacids. Correlations of trace metals with organics, their sources, and the possible role of trace transition metals are explained.
Arctic aerosol samples collected from Alert (82.5°N) have been studied using a capillary GC and GC/MS for long chain α,ω‐dicarboxylic acids that are produced in soils by bacterial ω and ω‐1 oxidations of plant‐derived fatty acids. Here, we report the discovery that one month after sunrise in the Arctic, atmospheric concentrations of the soil derived, long chain dicarboxylic acids are significantly (ca. 10 times) enhanced in the high Arctic. Relative abundances of long chain diacids in aerosol total carbon contents also increased in late April to early May. In March to May during peak concentrations, the relative distribution of C20–C26 diacids in the Arctic aerosols was similar to those of Chinese loess samples, suggesting atmospheric transport of Asian dusts over distances of three to five thousand kilometers into the Arctic. This conclusion is supported by air parcel trajectory analyses which showed stronger transport from southern desert regions during peaks in long chain dicarboxylic acids in the Arctic.
Chemical composition and in situ degradation profiles were analyzed for 27 samples of dried distillers grains with solubles (DDGS) distributed in Japan, and a wide variation was found in neutral detergent fiber (NDF) content, which had positive relationships to detergent-insoluble crude proteins such as neutral detergent-insoluble crude protein (NDICP) and acid detergent-insoluble CP (ADICP). Samples with lower NDF (< 35% on dry matter (DM)) showed higher soluble fractions of protein, but the degradation rate of microbially degradable protein in the rumen was not different in comparison with the samples with higher NDF, and no difference was shown between samples with higher and lower NDF after 24 and 48 h of in situ incubation for DM and CP degradation, respectively. The NDICP content in the digestion residue decreased with time of incubation, especially for samples with higher NDF, while the ADICP content increased. These results suggest that a part of the soluble fraction of CP in DDGS would be incorporated into NDICP by the heating process in bio-ethanol production, which is still highly degradable, whereas another part of the fraction incorporated into ADICP would proceed to the advanced steps of irreversible amino-carbonyl reaction.
Temporal variations and correlation
statistics of major inorganic
and organic species and carbonaceous components of the total suspended
particulate matter (TSPM) at Alert were concurrently studied. Organic
carbon (OC) and water-soluble organic carbon (WSOC) declined from
February to mid-March together with elemental carbon (EC), but OC
and WSOC increased in April while EC stayed low, suggesting photochemical
production of organic aerosols. WSOC/OC ratios peaked in mid-April
(89%). The ammonium availability index (AAI) increases from 31% (before
sunrise) to 58% (after sunrise). Strong correlations of NH4
+ with WSOC and dicarboxylic acids (DCAs) were found,
implying the formation of organic salts at polar sunrise. K+ is substantially correlated (R
2 = 0.96; p = 0.03) with levoglucosan before sunrise; however, the
correlation decreases after. Significant correlations were found for
5 cations (NH4
+, Na+, K+, Mg2+, and Ca2+), 2-alkaline earth metals
(Ca and Mg), and 3 transition metals (Fe, Cu, and Mn) with DCAs and
WSOC during both periods. Fe and Cu are strongly correlated (up to R
2 = 0.80; p < 0.05) with
DCAs before and after polar sunrise, implying the Fenton reaction
both in dark and light periods. On the basis of the significant correlation,
we found the plausibility of Fenton chemistry of Fe and Cu with oxalic
acid. In the multiple linear regression model, Mn is the most significant
predictor of WSOC followed by Cu and Fe after sunrise. This study
demonstrates the importance of the photochemical processing of Arctic
aerosols that are carried by long-range transport to the Arctic at
Alert, and bridges and answers the research gap and some questions
raised in our previous study (regarding, for example, the impacts
of inorganic species, primarily NH4
+ and transition
metals on organic aerosols).
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