Combining rigid twisted spirobifluorene with two strongly electron-withdrawing terpyridine moieties to form a ``(A)(n)-D-(A)(n)'' structure is an effective way to achieve electron transport materials (ETMs) with high triplet energy, suitable frontier orbital levels, excellent thermal stability and electrochemical stability for long-lived and highly efficient organic light-emitting diodes (OLEDs), 2,2'-di([2,2':6',2 `'-terpyridin]-4'-yl)-9,9'-spirobi[fluorene] (22-TPSF) and 2,7-di([2,2':6',2 `'-terpyridin]-4'-yl)-9,9'-spirobifluorene (27-TPSF), both of which are better than the conventional ETM 1,3,5-tris(N-phenylbenzimidazol-2-yl-benzene (TPBi). In addition, the crystal packing mode in their single crystals undergoes a significant transformation from the sandwich arrangement of 22-TPSF into the brick wall arrangement of 27-TPSF, causing a big difference in electron transport mobility, which changes from 0.012 to 0.104 cm(2) V-1 s(-1) as calculated through density functional theory. This variation leads to a phenomenon where the 22-TPSF based devices display a lower maximum external quantum efficiency of 22.9% and a shorter half-life (T-50) of 173925 hours at an initial luminance of 100 cd m(-2) than the 27-TPSF based devices. These findings highlight the great potential of the ETM structured as ``(A)(n)-D-(A)(n)'' using the terpyridine and spirobifluorene moieties; moreover, the positional isomerism effect allows remarkable tuning of the electron transport mobility and makes an obvious influence on OLED performance and lifetime.
Light-duty gasoline vehicles have drawn public attention in China due to their significant primary emissions of particulate matter and volatile organic compounds (VOCs). However, little information on secondary aerosol formation from exhaust for Chinese vehicles and fuel conditions is available. In this study, chamber experiments were conducted to quantify the potential of secondary aerosol formation from the exhaust of a port fuel injection gasoline engine. The engine and fuel used are common in the Chinese market, and the fuel satisfies the China V gasoline fuel standard. Substantial secondary aerosol formation was observed during a 4-5 hr simulation, which was estimated to represent more than 10 days of equivalent atmospheric photo-oxidation in Beijing. As a consequence, the extreme case secondary organic aerosol (SOA) production was 426 +/- 85 mg/kg-fuel, with high levels of precursors and OH exposure. The low hygroscopicity of the aerosols formed inside the chamber suggests that SOA was the dominant chemical composition. Fourteen percent of SOA measured in the chamber experiments could be explained through the oxidation of speciated single-ring aromatics. Unspeciated precursors, such as intermediate-volatility organic compounds and semi-volatile organic compounds, might be significant for SOA formation from gasoline VOCs. We concluded that reductions of emissions of aerosol precursor gases from vehicles are essential to mediate pollution in China. (C) 2017 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.
In this paper, measurements of air pollutants made at a ground site near Fort McKay in the Athabasca oil sands region as part of a multi-platform campaign in the summer of 2013 are presented. The observations included measurements of selected volatile organic compounds (VOCs) by a gas chromatograph-ion trap mass spectrometer (GC-ITMS). This instrument observed a large, analytically unresolved hydrocarbon peak (with a retention index between 1100 and 1700) associated with intermediate-volatility organic compounds (IVOCs). However, the activities or processes that contribute to the release of these IVOCs in the oil sands region remain unclear. Principal component analysis (PCA) with varimax rotation was applied to elucidate major source types impacting the sampling site in the summer of 2013. The analysis included 28 variables, including concentrations of total odd nitrogen (NOy), carbon dioxide (CO2), methane (CH4), ammonia (NH3), carbon monoxide (CO), sulfur dioxide (SO2), total reduced-sulfur compounds (TRSs), speciated monoterpenes (including alpha- and beta-pinene and limonene), particle volume calculated from measured size distributions of particles less than 10 and 1 mu m in diameter (PM10-1 and PM1), particle-surface-bound polycyclic aromatic hydrocarbons (pPAHs), and aerosol mass spectrometer composition measurements, including refractory black carbon (rBC) and organic aerosol components. The PCA was complemented by bivariate polar plots showing the joint wind speed and direction dependence of air pollutant concentrations to illustrate the spatial distribution of sources in the area. Using the 95% cumulative percentage of variance criterion, 10 components were identified and categorized by source type. These included emissions by wet tailing ponds, vegetation, open pit mining operations, upgrader facilities, and surface dust. Three components correlated with IVOCs, with the largest associated with surface mining and likely caused by the unearthing and processing of raw bitumen.
Determination of the limiting nutrient of phytoplankton is critical to the lake eutrophication management. The average value of total nitrogen/total phosphorus (TN/TP) ratio is widely used to determine the limiting nutrient; while it suffers from the risk of the incorrect description of data and neglecting dynamics of the nutrient limitation. A probabilistic method was thereby proposed in this study to explore dynamics of nutrient limitation, including (a) indicator definition as the probability of TN/TP ratio failing in Redfield ratio line (PFR), indicating the possibility of TN limitation, to improve a probabilistic measure for the nutrient limitation; (b) Bayesian ANOVA analysis for posterior distributions of different treatments; and (c) dynamics determination as PFRs to show dynamics of nutrient limitation. Lake Xingyun in Southwestern China was taken as a case to explore the interannual and seasonal dynamics of the nutrient limitation. According to modeling results, we deducted that (a) for the interannual dynamics, the limiting nutrient shifted from TP to TN; and (b) for the seasonal dynamics, TN and TP were co-limiting. Deductions were further confirmed by the observed data. With the proposed probabilistic method, the co-limitation of TN and TP was identified for the seasonal dynamics; while using the average ratio solely denied the possibility of co-limitation. The current study also revealed that, due to neglecting the interannual and seasonal dynamics of nutrient limitation, the average ratio might mislead the eutrophication management strategy by recommending reducing TN and TP concentration together. The proposed probabilistic method demonstrated that TN was the limiting nutrient during the growing season of the phytoplankton in recent years and actions should focus on the TN concentration reduction. (C) 2017 Elsevier B.V. All rights reserved.
Methacrolein (MACR) is an abundant multifunctional carbonyl compound with highreactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiatedoxidation of MACR at various NO/MACR ratios (0 to 4.04) and relative humidities (< 3% to80%) using a flow tube. Meanwhile, a box model based on the Master Chemical Mechanismwas performed to test our current understanding of the mechanism. In contrast to thereasonable predictions for hydroxyacetone production, the modeled yields of formaldehyde(HCHO) were twice higher than the experimental results. The discrepancy was ascribed tothe existence of unconsidered non-HCHO forming channels in the chemistry of CH3C(=CH2)OO., which account for approx. 50%. In addition, the production of hydroxyacetoneand HCHO were affected by water vapor as well as the initial NO/MACR ratio. The yields ofHCHO were higher under humid conditions than that under dry condition. The yields ofhydroxyacetone were higher under humid conditions at low-NOx level, while lower athigh-NOx level. The reasonable explanation for the lower hydroxyacetone yield underhumid conditions at high-NOx level is that water vapor promotes the production ofmethacrolein nitrate in the reaction of HOCH2C(CH3)(OO.)CHO with NO due to the peroxyradical-water complex formation, which was evidenced by calculational results. And theminimum equilibrium constant of this water complex formation was estimated to be1.89 × 10−18 cm3/molecule. These results provide new insights into the MACR oxidationmechanismand the effects of water vapor.