• Energy Research

Multiple PM2.5 samples collected through different seasons from October 2011 to August 2012 at an urban site in Shanghai, China were analyzed for carbonaceous pollutants. Data from this site, a 'super' air quality monitoring station at Fudan University, has been used by researchers to investigate the formation mechanism of haze episodes. The characteristics and concentrations of organic carbon (OC), elemental carbon (EC), n-alkanes, as well as relative abundances of hopanes, in these samples were determined. The concentrations showed a pronounced annual cycle with higher values in cold seasons (spring and winter, mean: 8.6 μg/m(3), 3.3 μg/m(3) and 136.4 ng/m(3) for OC, EC and n-alkanes, respectively) and lower values in warm seasons (fall and summer, mean: 6.6 μg/m(3), 2.6 μg/m(3) and 73.8 ng/m(3) for OC, EC and n-alkanes, respectively). EC generally displayed a common source with that of OC in all seasons. Petroleum residue was the major source of n-alkanes, contributing 71.4% to the targeted C14-C33n-alkanes over four seasons. Principal components analysis and the composition of hopanes showed that emissions from vehicle exhaust contributed more carbonaceous aerosols than coal combustion. These data could provide important information for measures to reduce carbonaceous pollutant emissions and improve air quality in Shanghai, and other urban centers across China.

AbstractAimDetermine the extent to which remote, high‐altitude (Afroalpine) aquatic ecosystems in tropical Africa have been impacted by global and regional‐scale environmental change processes.LocationTwo volcanic crater lakes (Bisoke and Muhavura) in the Afroalpine zone, Albertine (Western) Rift, central Africa.MethodsSediment cores were collected from Bisoke and Muhavura lakes and dated using radiometric techniques. A range of sediment‐based proxies was extracted from the cores and quantified. Sedimentary data were subjected to statistical analyses that contributed to the identification of influential environmental variables and their effects on diatom assemblages, the determination of variations in spatial beta diversity and estimates of the rate of compositional turnover over the last c. 1,200 years.ResultsSediments from the two sites provide evidence of the sensitivity of remote, Afroalpine aquatic ecosystems to perturbation. Climate variability has been a major driver of ecological change, particularly at Bisoke Lake, throughout the c. 1,200‐year‐long record, while Muhavura Lake has been directly impacted by and recovered from at least one volcanic eruption during this time. The effects of climatic warming from the mid‐ to late 19th century and especially from the late 20th century, possibly accentuated by atmospheric deposition‐driven nutrient enrichment, appear increasingly in lockstep. Effects include changes in diatom community composition, increased productivity and compositional turnover, and biotic homogenization (reduced spatial beta diversity) between the two sites.Main conclusionsThe two Afroalpine sites record changes in atmospheric conditions and their effects on diatom assemblage composition, particularly over the last c. 150 years. Drivers of these changes have the potential to disrupt ecosystems at lower altitudes in the Albertine Rift, including biodiverse areas of forest, and across tropical Africa more widely.

The Atlantic meridional overturning circulation (AMOC) is a system of ocean currents that has an essential role in Earth's climate, redistributing heat and influencing the carbon cycle1, 2. The AMOC has been shown to be weakening in recent years 1 ; this decline may reflect decadal-scale variability in convection in the Labrador Sea, but short observational datasets preclude a longer-term perspective on the modern state and variability of Labrador Sea convection and the AMOC1, 3-5. Here we provide several lines of palaeo-oceanographic evidence that Labrador Sea deep convection and the AMOC have been anomalously weak over the past 150 years or so (since the end of the Little Ice Age, LIA, approximately AD 1850) compared with the preceding 1,500 years. Our palaeoclimate reconstructions indicate that the transition occurred either as a predominantly abrupt shift towards the end of the LIA, or as a more gradual, continued decline over the past 150 years; this ambiguity probably arises from non-AMOC influences on the various proxies or from the different sensitivities of these proxies to individual components of the AMOC. We suggest that enhanced freshwater fluxes from the Arctic and Nordic seas towards the end of the LIA-sourced from melting glaciers and thickened sea ice that developed earlier in the LIA-weakened Labrador Sea convection and the AMOC. The lack of a subsequent recovery may have resulted from hysteresis or from twentieth-century melting of the Greenland Ice Sheet 6 . Our results suggest that recent decadal variability in Labrador Sea convection and the AMOC has occurred during an atypical, weak background state. Future work should aim to constrain the roles of internal climate variability and early anthropogenic forcing in the AMOC weakening described here.

We report a historical record of atmospheric deposition in dated sediment cores from Hasse Lake, ideally located near both currently and previously operational coal-fired power plants in Central Alberta, Canada. Accumulation rates of spheroidal carbonaceous particles (SCPs), an unambiguous marker of high-temperature fossil-fuel combustion, in the early part of the sediment record (pre-1955) compared well with historical emissions from one of North America's earliest coal-fired power plants (Rossdale) located ∼43 km to the east in the city of Edmonton. Accumulation rates in the latter part of the record (post-1955) suggested inputs from the Wabamun region's plants situated ∼17-25 km to the west. Increasing accumulation rates of SCPs, polycyclic aromatic hydrocarbons (PAHs) and Hg coincided with the previously documented period of peak pollution in the Wabamun region during the late 1960s to early 1970s, although Hg deposition trends were also similar to those found in western North American lakes not directly affected by point sources. A noticeable reduction in contaminant inputs during the 1970s is attributed in part to technological improvements and stricter emission controls. The over one hundred-year historical record of coal-fired power plant emissions documented in Hasse Lake sediments has provided insight into the impact that both environmental regulations and changes in electricity output have had over time. This information is crucial to assessing the current and future role of coal in the world's energy supply.

The Atlantic meridional overturning circulation (AMOC) is a system of ocean currents that has an essential role in Earth's climate, redistributing heat and influencing the carbon cycle. The AMOC has been shown to be weakening in recent years1; this decline may reflect decadal-scale variability in convection in the Labrador Sea, but short observational datasets preclude a longer-term perspective on the modern state and variability of Labrador Sea convection and the AMOC. Here we provide several lines of palaeo-oceanographic evidence that Labrador Sea deep convection and the AMOC have been anomalously weak over the past 150 years or so (since the end of the Little Ice Age, LIA, approximately AD 1850) compared with the preceding 1,500 years. Our palaeoclimate reconstructions indicate that the transition occurred either as a predominantly abrupt shift towards the end of the LIA, or as a more gradual, continued decline over the past 150 years; this ambiguity probably arises from non-AMOC influences on the various proxies or from the different sensitivities of these proxies to individual components of the AMOC. We suggest that enhanced freshwater fluxes from the Arctic and Nordic seas towards the end of the LIA—sourced from melting glaciers and thickened sea ice that developed earlier in the LIA—weakened Labrador Sea convection and the AMOC. The lack of a subsequent recovery may have resulted from hysteresis or from twentieth-century melting of the Greenland Ice Sheet. Our results suggest that recent decadal variability in Labrador Sea convection and the AMOC has occurred during an atypical, weak background state. Future work should aim to constrain the roles of internal climate variability and early anthropogenic forcing in the AMOC weakening described here. The data presented here is the supporting data for Thornalley et al. 2018 (see details below) and is derived from cores KNR-178-56JPC and KNR-178-48JPC. It includes the mean sortable silt size, details of radiocarbon dating, the % nps and binned sub-surface temperature reconstructions. Supplement to: Thornalley, David J R; Oppo, Delia W; Ortega, Pablo; Robson, Jon I; Brierley, Chris M; Davis, Renee; Hall, Ian R; Moffa-Sanchez, Paola; Rose, Neil L; Spooner, Peter T; Yashayaev, Igor M; Keigwin, Lloyd D (2018): Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years. Nature, 556(7700), 227-230

Despite Australia's high reliance on coal for electricity generation, no study has addressed the extent to which mercury (Hg) deposition has increased since the commissioning of coal-fired power plants. We present stratigraphic data from lake sediments in the Hunter Valley (New South Wales) and Latrobe Valley (Victoria), where a significant proportion of Australia's electricity is generated via coal combustion. Mercury deposition in lake sediments increased in the 1970s with the commissioning of coal-fired power plants, by a factor of 2.9-times in sediments of Lake Glenbawn (Hunter Valley) and 14-times in Traralgon Reservoir (Latrobe Valley). Sediments deposited after the commissioning of power plants have distinct Hg isotope compositions, similar to those of combusted coals. Mercury emission, estimated using an atmospheric model (CALPUFF), was higher in the Latrobe Valley than in the Hunter Valley. This is a result of higher Hg concentrations in lignite coal, lax regulation and older pollution-control technologies adopted by coal-fired power plants in the Latrobe Valley. Near-source deposition of Hg in Australia is significantly higher than North America and Europe, where better emission controls (e.g. wet flue gas desulfurization) have been in effect for decades. The challenge for Australia in years to come will be to ratify the Minamata Convention and develop better regulation policies to reduce Hg emissions.

The major patterns of biostratigraphical and geochemical change detected in a multidisciplinary study on recent environmental change and atmospheric contamination on Svalbard are summarised and synthesised. The patterns discussed are changes in sediment accumulation rates, organic matter accumulation rates, atmospheric contaminants, and biological assemblages (diatoms, chrysophyte cysts, chironomids). Possible environmental factors that may have influenced these patterns are discussed, in particular, the role of atmospheric contamination (including the deposition of nitrogen-compounds), local human impact, and recent climatic change. The major conclusions are (1) sediment accumulation rates show consistent temporal and geographical patterns with rates increasing towards the present-day and highest in the south, (2) sediment organic-matter accumulation rates increase markedly in the last 50–100 years, (3) atmospheric contamination is a combination of local and regional sources, (4) sediment inorganic geochemistry suggests catchment and lake responses to climate change in the last 30–50 years, (5) all lakes show a marked increase in the rate of biotic compositional changes in the last 50–100 years, and (6) Svalbard lakes appear to be highly dynamic and show considerable biotic and sedimentary changes in recent decades. The most likely cause of many of the observed changes is recent climatic change, with some local human activity at one site. Detailed interpretation of the observed changes is problematic given current limited knowledge about high Arctic limnology, biology, and catchment processes.