Secondary organic aerosol (SOA) plays a critical role in sustained haze pollution in megacities. Traditional observation of atmospheric aerosols usually analyzes the ambient organic aerosol (OA) but neglects the SOA formation potential (SOAFP) of precursors remaining in ambient air. Knowledge on SOAFP is still limited, especially in megacities suffering from frequent haze. In this study, the SOAFP of ambient air in urban Beijing was characterized at different pollution levels based on a two-year field observation using an oxidation flow reactor (OFR) system. Both OA and SOAFP increased as a function of ambient pollution level, in which increasing concentrations of precursor volatile organic compounds (VOCs) and decreasing atmospheric oxidation capacity were found to be the two main influencing factors. To address the role of the atmospheric oxidation capacity in SOAFP, a relative OA enhancement ratio (EROA = 1 + SOAFP/OA) and the elemental composition of the OA were investigated in this study. The results indicated that the atmospheric oxidation capacity was weakened and resulted in higher SOAFP on more polluted days. The relationship found between SOAFP and the atmospheric oxidation capacity could be helpful in understanding changes in SOA pollution with improving air quality in the megacities of developing countries.
Abstract The high‐temperature solid oxide electrolysis cell (SOEC) is one of the most promising devices for hydrogen mass production. To make SOEC suitable from an economical point of view, each component of the SOEC has to be optimized. At this level, the optimization of the oxygen electrode is of particular interest since it contributes to a large extent to the cell polarization resistance. The present paper is focused on an alternative oxygen electrode of Zr 0.84 Y 0.16 O 2– δ ‐Sr 2 Fe 1.5 Mo 0.5 O 6– δ (YSZ‐SFM). YSZ‐SFM composite oxygen electrodes were fabricated by impregnating the YSZ matrix with SFM, and the ion‐impregnated YSZ‐SFM composite oxygen electrodes showed excellent performance. For a voltage of 1.2 V, the electrolysis current was 223 mA cm −2 , 327 mA cm −2 and 310 mA cm −2 at 750 °C for the YSZ‐SFM10, YSZ‐SFM20, and YSZ‐SFM30 oxygen electrode, respectively. A hydrogen production rate as high as 11.46 NL h −1 has been achieved for the SOEC with the YSZ‐SFM20 electrode at 750 °C. The results demonstrate that YSZ‐SFM fabricated by impregnating the YSZ matrix with SFM is a promising composite electrode for the SOEC.
Abstract. Hygroscopicity largely affects environmental and climatic impacts of pollen grains, one important type of primary biological aerosol particles in the troposphere. However, our knowledge of pollen hygroscopicity is rather limited, and the effect of temperature in particular has rarely been explored before. In this work three different techniques, including a vapor sorption analyzer, diffusion reflectance infrared Fourier transform spectroscopy (DRIFTS) and transmission Fourier transform infrared spectroscopy (transmission FTIR) were employed to characterize six anemophilous pollen species and to investigate their hygroscopic properties as a function of relative humidity (RH, up to 95 %) and temperature (5 or 15, 25 and 37 ∘C). Substantial mass increase due to water uptake was observed for all the six pollen species, and at 25 ∘C the relative mass increase at 90 % RH, when compared to that at <1 % RH, ranged from ∼30 % to ∼50 %, varying with pollen species. It was found that the modified κ-Köhler equation can well approximate mass hygroscopic growth of all the six pollen species, and the single hygroscopicity parameter (κ) was determined to be in the range of 0.034±0.001 to 0.061±0.007 at 25 ∘C. In situ DRIFTS measurements suggested that water adsorption by pollen species was mainly contributed to by OH groups of organic compounds they contained, and good correlations were indeed found between hygroscopicity of pollen species and the number of OH groups, as determined using transmission FTIR. An increase in temperature would in general lead to a decrease in hygroscopicity, except for pecan pollen. For example, κ values decreased from 0.073±0.006 at 5 ∘C to 0.061±0.007 at 25 ∘C and to 0.057±0.004 at 37 ∘C for Populus tremuloides pollen, and decreased from 0.060±0.001 at 15 ∘C to 0.054±0.001 at 25 ∘C and 0.050±0.002 at 37 ∘C for paper mulberry pollen.
Temporal lobe epilepsy (TLE) is one of the most common drug-resistant forms of epilepsy in adults and usually originates in the hippocampal formations. However, both the network mechanisms that support the seizure spread and the exact directions of ictal propagation remain largely unknown. Here we report the dissection of ictal propagation in the hippocampal-entorhinal cortex (HP-EC) structures using optogenetic methods in multiple brain regions of a kainic acid-induced model of TLE in VGAT-ChR2 transgenic mice. We perform highly temporally precise cross-area analyses of epileptic neuronal networks and find a feed-forward propagation pathway of ictal discharges from the dentate gyrus/hilus (DGH) to the medial entorhinal cortex, instead of a re-entrant loop. We also demonstrate that activating DGH GABAergic interneurons can significantly inhibit the spread of ictal seizures and largely rescue behavioural deficits in kainate-exposed animals. These findings may shed light on future therapeutic treatments of TLE.
Abstract Heterogeneous reactions on mineral dust play pivotal roles in the removal/production of gaseous pollutants and the formation of secondary particles. However, the uptake coefficient ( γ ), a key kinetic parameter for a heterogeneous reaction, could vary by several orders of magnitude in different laboratory analyses and give rise to great uncertainties in modeling studies. Thus, a detailed understanding of heterogeneous uptake kinetics is vital to accurately evaluate the impacts of heterogeneous reactions on atmospheric chemistry. In order to reveal the key factors affecting uptake kinetics, heterogeneous reaction of NO 2 on surfaces of typical mineral component alumina ( α ‐Al 2 O 3 , γ ‐Al 2 O 3 , δ ‐Al 2 O 3 , and AlOOH) was comprehensively studied using two widely used methods, including diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and flow tube reactor. The discrepancy between the true uptake coefficients ( γ BET ) obtained via two techniques was within 1–2 orders of magnitude for alumina samples. The γ BET depended positively on NO 2 concentration in the DRIFTS measurements but negatively on NO 2 concentration in the flow tube experiments, and the discrepancy might be attributed to different calculation methods of γ BET , which was calculated based on nitrate formation kinetics in DRIFTS experiments while based on NO 2 consumption kinetics in flow tube experiments. The results implied that an accurate selection of the uptake coefficient for modeling studies should base on the consideration of factors such as the measurement method, the concentration range of the reaction gas, and the characteristics of the sample such as crystal structure and effective surface area.
Nitrates formed on mineral dust through heterogeneous reactions in high NOx areas can undergo photolysis to regenerate NOx and potentially interfere in the photochemistry in the downwind low NOx areas. However, little is known about such renoxification processes. In this study, photolysis of various nitrates on different mineral oxides was comprehensively investigated in a flow reactor and in situ diffuse reflectance Fourier-transform infrared spectroscopy (in situ DRIFTS). TiO2 was found much more reactive than Al2O3 and SiO2 with both NO2 and HONO as the two major photolysis products. The yields of NO2 and HONO depend on the cation basicity of the nitrate salts or the acidity of particles. As such, NH4NO3 is much more productive than other nitrates like Fe(NO3)3, Ca(NO3)2, and KNO3. SO2 and water vapor promote the photodegradation by increasing the surface acidity due to the photoinduced formation of H2SO4/sulfate and H+, respectively. O2 enables the photo-oxidation of NOx to regenerate nitrate and thus inhibits the NOx yield. Overall, our results demonstrated that the photolysis of nitrate can be accelerated under complex air pollution conditions, which are helpful for understanding the transformation of nitrate and the nitrogen cycle in the atmosphere.
The hygroscopic behavior of particles is important for assessing their environmental and climate effect. The hygroscopic behavior of individual particles has been widely investigated; however, the hygroscopic behavior of mixed particles is still not well-known. Although the Zdanovskii–Stokes–Robinson (ZSR) method could be applied to predict the hygroscopicity of some aerosol mixtures, it is invalid to describe the humidification process of mixed particles when chemical reactions take place. In the present study, the hygroscopic growth factors (GF) of individual oxalic acid (H2C2O4), nitrate (Ca(NO3)2, NaNO3, Zn(NO3)2), and the mixed H2C2O4/nitrate particles were measured using a hygroscopic tandem differential mobility analyzer (H-TDMA). The GFs of these mixtures are much smaller than those predicted by the ZSR method. The chemical composition of individual and mixed particles was characterized by Raman spectrometer. It was found that oxalate dominated the constituents of internal mixtures. Further comparison of the humidification of externally mixed oxalic acid and nitrate revealed that the solubility of oxalate plays a critical role in the replacement of nitrate by oxalate. These results could be helpful for understanding the occurrence of metal oxalate complex in the atmospheric aerosol.
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