From July to September 2008, air samples were collected aboard the research expedition icebreaker XueLong (Snow Dragon) as part of the 2008 Chinese Arctic Research Expedition Program. Hexachlorocyclohexane (HCH) concentrations were analyzed in all of the samples. The average concentrations (? standard deviation) over the entire period were 33 ? 16, 5.4 ? 3.0, and 13 ? 7.5 pg m?? for a-, ?- and ?-HCH, respectively. Compared to previous studies in the same areas, total HCH (SHCH, the sum of a-, ?-, and ?-HCH) levels declined by more than 10 ? compared to those observed in the 1990s, but were approximately 4 ? higher than those measured by the 2003 China Arctic Research Expedition, suggesting the increase of atmospheric SHCH recently. Because of the continuing use of lindane, ratios of a/?-HCH showed an obvious decrease in North Pacific and Arctic region compared with those for 2003 Chinese Arctic Research Expedition. In Arctic, the level of a-HCH was found to be linked to sea ice distribution. Geographically, the average concentration of a-HCH in air samples from the Chukchi and Beaufort Seas, neither of which contain sea ice, was 23 ? 4.4 pg m??, while samples from the area covered by seasonal ice (~75?N to ~83?N), the so-called "floating sea ice region", contained the highest average levels of a-HCH at 48 ? 12 pg m??, likely due to emission from sea ice and strong air-sea exchange. The lowest concentrations of a-HCH were observed in the pack ice region in the high Arctic covered by multiyear sea ice (~83?N to ~86?N). This phenomenon implies that the re-emission of HCH trapped in ice sheets and Arctic Ocean may accelerate during the summer as ice coverage in the Arctic Ocean decreases in response to global climate change.
The biogeochemical cycles of CH4 over oceans are poorly understood, especially over the Arctic Ocean. Here we report atmospheric CH4 levels together with d(13)C-CH4 from offshore China (31°N) to the central Arctic Ocean (up to 87°N) from July to September 2012. CH4 concentrations and d(13)C-CH4 displayed temporal and spatial variation ranging from 1.65 to 2.63 ppm, and from -50.34% to -44.94% (mean value: -48.55?±?0.84%), respectively. Changes in CH4 with latitude were linked to the decreasing input of enriched d(13)C and chemical oxidation by both OH and Cl radicals as indicated by variation of d(13)C. There were complex mixing sources outside and inside the Arctic Ocean. A keeling plot showed the dominant influence by hydrate gas in the Nordic Sea region, while the long range transport of wetland emissions were one of potentially important sources in the central Arctic Ocean. Experiments comparing sunlight and darkness indicate that microbes may also play an important role in regional variations.
Organic acids are major components in marine organic aerosols. Many studies on the occurrence, sources and sinks of organic acids over oceans in the low and middle latitudes have been conducted. However, the understanding of relative contributions of specific sources to organic acids over oceans, especially in the high latitudes, is still inadequate. This study measured organic acids, including C14:0 - C32:0 saturated monocarboxylic acids (MCAs), C16:1, C18:1 and C18:2 unsaturated MCAs, and di-C4 - di-C10 dicarboxylic acids (DCAs), in the marine boundary layer from the East China Sea to the Arctic Ocean during the 3rd Chinese Arctic Research Expedition (CHINARE 08). The average concentrations were 18?±?16?ng/m3 and 11?±?5.4?ng/m3 for SMCA and SDCA, respectively. The levels of saturated MCAs were much higher than those of unsaturated DCAs, with peaks at C16:0, C18:0 and C14:0. DCAs peaked at di-C4, followed by di-C9 and di-C8. Concentrations of MCAs and DCAs generally decreased with increasing latitudes. Sources of MCAs and DCAs were further investigated using principal component analysis with a multiple linear regression (PCA-MLR) model. Overall, carboxylic acids originated from ocean emissions, continental input (including biomass burning, anthropogenic emissions and terrestrial plant emissions), and secondary formation. All the five sources contributed to MCAs with ocean emissions as the predominant source (48%), followed by biomass burning (20%). In contrast, only 3 sources (i.e., secondary formation (50%), anthropogenic emissions (41%) and biomass burning (9%)) contributed to DCAs. Furthermore, the sources varied with regions. Over the Arctic Ocean, only secondary formation and anthropogenic emissions contributed to MCAs and DCAs.
Institute of Polar Environment & Anhui Key Laboratory of Polar Environment and Global Change, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026, PR China; Anhui Provincial Engineering Laboratory of Water and Soil Pollution Control and Remediation, School of Ecology and Environment, Anhui Normal University, Wuhu, Anhui, 241002, PR China.
Air and seawater samples were collected in 2016 over the North Pacific Ocean (NPO) and adjacent Arctic Ocean (AO), and Polycyclic Aromatic Hydrocarbons (PAHs) were quantified in them. Atmospheric concentrations of ?15 PAHs (gas + particle phase) were 0.44-7.0 ng m-3 (mean = 2.3 ng m-3), and concentrations of aqueous ?15 PAHs (dissolved phase) were 0.82-3.7 ng L-1 (mean = 1.9 ng L-1). Decreasing latitudinal trends were observed for atmospheric and aqueous PAHs. Results of diagnostic ratios suggested that gaseous and aqueous PAHs were most likely to be related to the pyrogenic and petrogenic sources, respectively. Three sources, volatilization, coal and fuel oil combustion, and biomass burning, were determined by the PMF model for gaseous PAHs, with percent contributions of 10%, 44%, and 46%, respectively. The 4- ring PAHs underwent net deposition during the cruise, while some 3- ring PAHs were strongly dominated by net volatilization, even in the high latitude Arctic region. Offshore oil/gas production activities might result in the sustained input of low molecular weight 3- ring PAHs to the survey region, and further lead to the volatilization of them. Compared to the gaseous exchange fluxes, fluxes of atmospheric dry deposition and gaseous degradation were negligible. According to the extrapolated results, the gaseous exchange of semivolatile aromatic-like compounds (SALCs) may have a significant influence on the carbon cycling in the low latitude oceans, but not for the high latitude oceans.