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Comprehensive characterization and health assessment of occupational exposures to volatile organic compounds (VOCs) in Xi'an, a major city of northwestern China
No full textThe personal exposure to volatile organic compounds (VOCs) was determined in five occupational groups (including printing shop employees, office workers, furniture store employees, bus and taxi drivers) in the capital city of Xi'an in northwest China. The highest personal exposure concentration (258.7 +/- 10.0 mu gm3) to the 64 Air Toxics VOCs classified by the United States Environmental Protection Agency (U.S.EPA), as well as associated health risk potential, were seen in the furniture store employees. These could be attributed to off-gassing from brand new furniture and volatiles from cleaning reagents. Aromatic species were the dominant class in the personal exposure samples collected from the groups of printing shop employees, office workers, and bus and taxi drivers, with the concentrations of 49.8-74.4 mu g m(-3) and mass compositions of 34.8-43.2% of the sum of the 64 Air Toxics for the cases studied. The highest personal exposure to carbonyls (C >= 3) of 100.4 +/- 25.6 mu g m(-3) and composition of 38.8% were again seen in the furniture store employees. The unique VOC composition profiles represented potential indoor or in-vehicle sources in each workplace. Moreover, environmental tobacco smoke (ETS) contributed to the personal exposure to many of the Air Toxics species, especially methyl butyl ketone and 1,2-dibromoethane. The cancer risks of Class 1 carcinogens of vinyl chloride, 1,3-butadiene, and benzene, were 1.4, 12, and 5.2 times, respectively, of the threshold of carcinogenicity (1 x 10(-6)). Acrolein showed the highest non-cancer risk which was similar to 150 times the acceptable level (1.0). The results could offer a scientific basis for the government to establish the occupational air quality standards to the toxic VOCs in China
Development of the Leeuwin Current on the northwest shelf of Australia through the Pliocene-Pleistocene period
No full textAlthough the Leeuwin Current (LC) is thought to play a pivotal role in climatic and oceanic systems of the western Australian region, how the LC developed through the Pliocene-Pleistocene period remains elusive. Here we used biomarker records to reconstruct variations of temperatures and primary productivity on the northwest shelf of Australia over the last 6 million years. Since similar to 1.2 million years ago (Ma), our sea surface temperature record indicates progressive warming, with temperature values comparable to those in the Indo-Pacific Warm Pool, in contrast with the long-term global cooling trend. The regional surface warming was accompanied by suppressed primary productivity, together indicating prevailing warm, low-salinity, nutrient-deficient surface water, and thus a stronger LC since the Mid-Pleistocene Transition. During 4-1.2 Ma, greater surface temperature gradient between the Indo-Pacific Warm Pool and the northwest shelf of Australia and higher primary productivity seem to suggest a generally weaker LC. Warmer temperatures and lower productivity suggest a plausible existence of the LC during 6-4 Ma, but more work is required to confirm this. Impact of sea level and the Indonesian Throughflow on the LC strength may exist, but did not dominate through the Pliocene-Pleistocene period, considering different variation patterns among them. We propose the stronger LC after similar to 1.2 Ma was more likely triggered by enhanced atmospheric circulation. Although the increased LC after similar to 1.2 Ma may have potentially brought additional moisture to the Australian continent during the interglacial periods, it has not overturned the long-term drying trend through the Pliocene-Pleistocene period. (C) 2021 Elsevier B.V. All rights reserved
Indian summer monsoon variability in northeastern India during the last two millennia
No full textHigh-resolution proxy records help to understand natural forcing of climate variability and improving our capability to predict climate variability on decadal to centennial time scales. Present study from the Mawmluh cave, northeastern India shows sudden shifts in speleothem oxygen isotope values, indicating several abrupt changes in the Indian summer monsoon (ISM) during-212 BCE to 1986 CE. Moderate ISM conditions prevailed during-212 BCE to 400 CE punctuated with weak intervals, strong ISM during 400 and 500 CE and from 640 to 1060 CE, whereas weak ISM conditions prevailed during 520-540 CE, 820-850 CE and 940-980 CE and after 1060 CE. The interval from 1060 to 1986 CE witnessed decreased precipitation than the previous millennium. The latter phase of the Medieval Climate Anomaly (MCA; 1060 to 1200 CE) was quite drier in contrast to the earlier intervals. The ISM was generally weak during the Little Ice Age (LIA; 1350 to 1850 CE) with short-term pulses of high precipitation when sun-spot activity was high. The data shows the weakest ISM condition during 1640-1740 CE (Maunder Minimum) of the last two millennia. Variations in extra-tropical northern hemisphere temperatures due to volcanic activity and solar insolation, and accompanying northward/southward shifting of the Inter-Tropical Convergence Zone played a pivotal role in modulating the strength of the ISM during the past two millennia
Understanding the synergy between N-doped ultra-microporous carbonaceous adsorbent and nitrogen functionalities for high performance of CO2 sorption
No full textPorous carbonaceous adsorbents are believed to encourage contenders to CO2 uptake however their high production cost has urged researchers towards cheap renewable. In this study, nitrogen-doped carbonaceous adsorbents with high ultra-microporous structure were synthesized by carbonization and activation of chitosan along with urea and KOH simultaneously at various temperatures (600-900 degrees C). The effects of temperature, urea modification, and chemical activation on nitrogen functionalities and development of porous structure were analyzed. Results showed that porous carbons synthesized with urea and KOH modification at 700 degrees C exhibit the highest CO2 adsorption value (5.92 mmol g(-1) at 0 degrees C and 4.45 mmol g(-1) at 25 degrees C). Enhanced adsorption by NCABC-700 was found due to synergistic effect of nitrogen as well as high specific surface area (1404 m(2) g(-1)) and micropore volume (0.68 cm(3) g(-1)), respectively. Furthermore, best fitting of Freundlich isotherm model explained heterogeneous nature of adsorbent. Isosteric heat of adsorption with a value of 42.2 kJ mol(-1), also indicated the presence of N containing functional groups and a high number of micropores that created a strong interaction between adsorbent and adsorbate, helping in high CO2 uptake
Decisive role of vacuum-assisted carbonization in valorization of lignin-enriched (Juglans regia-shell) biowaste
No full textBioenergy is considered a sustainable substitute to fossil-fuel resources and the development of a prudent combination of renewable and innovative conversion technologies are essential for the valorization and effective conversion of biowaste to value-added commodities. Here, a negative pressure-induced carbonization process was proposed for the valorization of lignin-enriched biowaste precursor to bio-oil and environmental materials (biochar) at various temperatures. The high heating values (HHV) of the as-prepared biochars from the lignin enriched precursor under negative pressure (low-medium vacuum) were within 25.9-31.5 MJ/kg, which matched satisfactorily to the commercial charcoal. Whereas, the bio-oils produced from the lignin enriched precursor under vacuum conditions was a blend of complex aromatic and straight-chain hydro-carbons, including aldehyde, ketone, phenol, and furans, exhibiting ability as potential heating-oil with HHV within 21.2-28.2 MJ/kg. Moreover, the biochars produced under vacuum environments at higher temperature showed greater stability (22.5-35.9%) than those produced under N-2 atmosphere
Correlation and anti-correlation of the Asian summer monsoon and westerlies during the Holocene
No full textThe relationship between the Asian summer monsoon (ASM) and westerlies at different timescales is still under discussion. In this paper, we present Holocene precipitation records derived from loess and lake sediment in the northeastern Tibetan Plateau and reconstruct changes in the strength of the ASM during the Holocene. Compared with other Eurasian paleohydroclimatic records, we find that precipitation variations between ASM- and westerlies-dominant regions are positively correlated (anti-correlated) at millennial (sub-orbital) timescales. Based on the analysis of the TraCE-21 results, we suggest that Atlantic meridional overturning circulation may be the primary reason for this in-phase pattern at millennial timescales whereas this anti-phased pattern at sub-orbital timescales is attributed to precessional changes. Due to different response mechanisms, the relationship between the ASM and westerlies may differ significantly at different timescales, which highlights the complex dynamic characteristics of atmospheric systems in the Northern Hemisphere and the challenges for future predictions. (C) 2020 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved
A new method for long-term source apportionment with time-dependent factor profiles and uncertainty assessment using SoFi Pro: application to 1 year of organic aerosol data
No full textA new methodology for performing long-term source apportionment (SA) using positive matrix factorization (PMF) is presented. The method is implemented within the SoFi Pro software package and uses the multilinear engine (ME-2) as a PMF solver. The technique is applied to a 1-year aerosol chemical speciation monitor (ACSM) dataset from downtown Zurich, Switzerland.
The measured organic aerosol mass spectra were analyzed by PMF using a small (14 d) and rolling PMF window to account for the temporal evolution of the sources. The rotational ambiguity is explored and the uncertainties of the PMF solutions were estimated. Factor-tracer correlations for averaged seasonal results from the rolling window analysis are higher than those retrieved from conventional PMF analyses of individual seasons, highlighting the improved performance of the rolling window algorithm for long-term data.
In this study four to five factors were tested for every PMF window. Factor profiles for primary organic aerosol from traffic (HOA), cooking (COA) and biomass burning (BBOA) were constrained. Secondary organic aerosol was represented by either the combination of semi-volatile and low-volatility organic aerosol (SV-OOA and LV-OOA, respectively) or by a single OOA when this separation was not robust. This scheme led to roughly 40 000 PMF runs. Full visual inspection of all these PMF runs is unrealistic and is replaced by predefined user-selected criteria, which allow factor sorting and PMF run acceptance/rejection. The selected criteria for traffic (HOA) and BBOA were the correlation with equivalent black carbon from traffic (eBC(tr)) and the explained variation of m/z 60, respectively. COA was assessed by the prominence of a lunchtime concentration peak within the diurnal cycle. SV-OOA and LV-OOA were evaluated based on the fractions of m/z 43 and 44 in their respective factor profiles. Seasonal pre-tests revealed a noncontinuous separation of OOA into SV-OOA and LV-OOA, in particular during the warm seasons. Therefore, a differentiation between four-factor solutions (HOA, COA, BBOA and OOA) and five-factor solutions (HOA, COA, BBOA, SVOOA and LV-OOA) was also conducted based on the criterion for SV-OOA.
HOA and COA contribute between 0.4-0.7 mu g m(-3) (7.8 %-9.0 %) and 0.7-1.2 mu g m(-3) (12.2 %-15.7 %) on average throughout the year, respectively. BBOA shows a strong yearly cycle with the lowest mean concentrations in summer (0.6 mu g m(-3), 12.0 %), slightly higher mean concentrations during spring and fall (1.0 and 1.5 mu g m(-3), or 15.6% and 18.6 %, respectively), and the highest mean concentrations during winter (1.9 mu g m(-3), 25.0 %). In summer, OOA is separated into SV-OOA and LV-OOA, with mean concentrations of 1.4 mu g m(-3) (26.5 %) and 2.2 mu g m(-3) (40.3 %), respectively. For the remaining seasons the seasonal concentrations of SV-OOA, LV-OOA and OOA range from 0.3 to 1.1 mu g m(-3) (3.4 %-15.9 %), from 0.6 to 2.2 mu g m(-3) (7.7 %33.7 %) and from 0.9 to 3.1 mu g m(-3) (13.7 %-39.9 %), respectively. The relative PMF errors modeled for this study for HOA, COA, BBOA, LV-OOA, SV-OOA and OOA are on average +/- 34 %, +/- 27 %, +/- 30 %, +/- 11 %, +/- 25 % and +/- 12 %, respectively
Impacts of natural and socioeconomic factors on PM2.5 from 2014 to 2017
No full textThe State Council of China had issued the Air Pollution Prevention and Control Action Plan (abbreviated as "Clean Air Actions"), which ended in 2017. To evaluate the implementation effect of the clean air actions and provide the scientific basis on the future control policy, a Geographical Detector was used to quantify the impact of natural and socioeconomic factors on the PM2.5 concentration and its reductions in China from the years of 2014-2017. In terms of the impact on PM2.5 reduction, the industrial sulfur dioxide (SO2) and industrial soot emissions are the only two factors shown significant influences. So the controls of industrial emission were the major policies during the implementation of the Clean Air Actions. In terms of the impact on the PM2.5 concentrations, industrial emission was the strongest socioeconomic factor in the beginning of the Clean Air Actions, but its dominance was then declining. In contrast, the influences of population density had been enhancing and became the greatest factor in the final year. So the new control measures should focus on the urbanization regulation. In addition, the interactions between different socioeconomic factors are proved to bivariate enhance the influences on the PM2.5 concentration levels. Multiple factors should thus be taken into account when any new control policies are going to be established
Accurate Determination of Plutonium in Soil by Tandem Quadrupole ICP-MS with Different Sample Preparation Methods
No full textIn this work, three commonly used digestion techniques, such as acid leaching with 8 M HNO3, aqua regia and lithium metaborate fusion, were employed to extract Pu from different types of soil samples widely found across China, and to establish the influence of the major interference elements (U, Hg, Pb, Tl, and Bi) on the accurate measurement of Pu by tandem quadrupole ICP-MS. The three sample digestion techniques yielded good results for the analysis of Pu isotopes originating from global atmospheric fallout. The U and Pb contributions to m/z=239 (2.38 and 0.3 cps) in samples digested by the fusion method using AGMP-1M resin were higher than those digested by the acid leaching methods (0.55 cps for U and < 0.03 cps for Pb), which implies that additional purification with TEVA resin would be required for low-level Pu determination in soil samples. By taking advantage of tandem quadrupole ICP-MS in the NH3/He mode, the count rates of Hg, Tl and Bi at m/z=239 (<0.01 cps) in the samples purified by using AGMP-1M resin and/or TEVA resin were found to be negligible for the different sample digestion methods