An inter-comparison of black-carbon-related instruments in a laboratory study of biomass burning aerosol

Black carbon (BC)-containing particles are the most strongly light absorbing aerosols in the atmosphere. Measurements of BC are challenging because of its semi-empirical definition based on physical properties and not chemical structure, the complex and continuously changing morphology of the corresponding particles, and the effects of other particulate components on its absorption. In this study, we compare six available commercial continuous instruments measuring BC using biomass burning aerosol. The comparison involves a Soot Particle Aerosol Mass Spectrometer (SP-AMS), a Single-Particle Soot Photometer (SP2), an aethalometer, a Multiangle Absorption Photometer (MAAP), and a blue and a green photoacoustic extinctiometer (PAX). An SP-AMS collection efficiency equal to 0.35 was measured for this aerosol system. The corrected SP-AMS BC mass measurements agreed within 6% with the SP2 refractory BC mass values. Two regimes of behavior were identified for the optical instruments corresponding to high and low organic/BC ratio. The mass absorption cross-sections (MAC) measured varied from 26% to two times the instrument default values depending on the instrument and the regime. The presence of high organic aerosol concentration in this system can lead to overestimation of the BC mass by the optical instruments by as much as a factor of 2.7. In general, the discrepancy among the BC measurements increased as the organic carbon content of the BC-containing particles increased.

© 2018 American Association for Aerosol Research     

Volume changes upon heating of aerosol particles from biomass burning using transmission electron microscopy

The responses of aerosol particles to heating are important for measurements of their chemical, physical, and optical properties, classification, and determination of origin. However, the thermal behavior of organic aerosol particles is largely unknown. We provide a method to analyze such thermal behavior through heating from room temperature to >600°C by using a heating holder within a transmission electron microscope (TEM). Here we describe in-situ shape and size changes and variations in the compositions of individual particles before and after heating. We use ambient samples from wildland and agricultural biomass fires in North America collected during the 2013 Biomass Burning Observation Project (BBOP). The results indicate that individual tar balls (TB; spherical organic material) from biomass burning retained, on average, up to 30% of their volume when heated to 600°C. Chemical analysis reveals that K and Na remain in the residues, whereas S and O were lost. In contrast to bulk sample measurements of carbonaceous particles using thermal/optical carbon analyzers, our single-particle results imply that many individual organic particles consist of multiple types of organic matter having different thermal stabilities. Beyond TBs, our results suggest that because of their thermal stability some organic particles may not be detectable by using aerosol mass spectrometry or thermal/optical carbon analyzers. This result can lead to an underestimate of the abundance of TBs and other organic particles, and therefore biomass burning may have more influence than currently recognized in regional and global climate models.

Copyright © 2018 American Association for Aerosol Research     

Coupled analysis on heterogeneous oxidative aging and viscoelastic performance of rubber based on multi-scale simulation

An oxidative aging-viscoelastic constitutive model was established to study the coupled heterogeneous oxidation and viscoelastic performance of rubber during aging process. The basic elasticity and viscoelasticity of rubber materials were comparatively considered as the function of ongoing aging. The dynamic compression process of natural rubber at different aging times was analyzed by the finite element method. And then the effects of oxygen uptake, diffusion, and oxidative reactions on the dynamic viscoelasticity of rubber were analyzed. The permeability of the oxygen in natural rubber was determined by means of molecular dynamics simulation. The results reveal that the heterogeneous degradation caused by diffusion-limited oxidation can lead to a complex stress distribution in the natural rubber specimen under dynamic loading condition; the relaxation time and the energy dissipation of the rubber specimen also increased after aging. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47452     

Novel nitrogen containing heterogeneous catalysts for oxidative dehydrogenation of light paraffins

Novel nitrogen contained catalyst CoN_x/Al₂O₃ yielded high performance in the oxidative dehydrogenation of propane and n-butane. 47.6 and 37.4 wt% yield of olefins at 82% butane and 76.7% propane conversion were measured at 600 °C. Ethylene and propylene were mainly formed at >400 °C via oxidative cracking of paraffins. XRD and XPS studies of the novel catalytic system indicate an essential modification of cobalt by nitrogen.     

Effect of nonequilibrium absorption on gas transport in heterogeneous systems

A mathematical model is suggested for nonequilibrium gas absorption by a condensed medium through a free surface or a membrane. Surface reactions describe by first-and second-order rate equations are taken into account. Gas transport through membranes and nonequilibrium gas sorption by liquids through a membrane are considered by way of examples. The effect of the sorption rate can be accounted for by introducing an efficient permeability of the gas-liquid interface.     

Evidence in biomass burning smoke for a light-absorbing aerosol with properties intermediate between brown and black carbon

Biomass combustion produces black carbon (BC) and brown carbon (BrC) aerosols that contribute substantially to warming the Earth’s atmosphere. Accurate knowledge of their emissions and absorption per unit mass (mass absorption cross-section; MAC) can be used to quantify the radiative impact of these combustion products. We isolated particles generated from laboratory biomass burning fires by morphology and found that some particles from biomass burning do not correspond to either BC or BrC according to common operational definitions. Unlike BrC, these particles strongly absorb red light, with a MAC and spectral dependence of absorption between that of BrC and BC. They also have intermediate volatility: they survive thermodenuding at 250?°C but do not heat to incandescence in a single particle soot photometer (SP2) instrument. We also found evidence for intermediate properties in ambient wildfire smoke from the 2013 Rim Fire in California. More work is needed to understand how much this intermediate material contributes to atmospheric light absorption from typical combustion, whether or not it corresponds to “tar balls,” and how it may affect previous MAC measurements that were attributed to enhanced absorption by transparent coatings.

Copyright © 2019 American Association for Aerosol Research     

Effect of activity coefficient models on predictions of secondary organic aerosol partitioning

Several available models for predicting organic aerosol activity coefficients are compared by examining their effect on predictions of secondary organic aerosol (SOA) concentrations and aerosol water uptake in laboratory and atmospheric systems. Activity coefficient models studied include Ideal behavior, the Wilson and NRTL equations, and UNIFAC in standard form, with revised interaction parameters, and with no temperature dependence. Wilson and NRTL binary interaction parameters were fit from UNIFAC predictions of activity coefficients. SOA model simulations were performed for different combinations of primary organic aerosol (POA) composition, SOA composition, and relative humidity. All of the activity coefficient methods predict similar results for mixtures of similar components, but for highly dissimilar aerosol mixtures, the Ideal, Wilson and NRTL models tend to predict higher SOA concentrations and aerosol water uptake compared to UNIFAC. Different versions of UNIFAC gave nearly identical results for most scenarios. Computational requirements are lowest for Ideal, followed by Wilson, and then NRTL and UNIFAC models.     

天然橡胶光/热氧老化及抗老化性能研究进展

对天然橡胶的老化失效行为,特别是光/热氧老化机理进行了总结,同时综述了自然老化和人工加速老化等常见老化方法及天然橡胶的防老化技术,并展望了天然橡胶防老化技术未来的发展趋势。     

Ambient measurements of light-absorption by agricultural waste burning organic aerosols

Absorption properties (absorption Ångstrom exponent and mass absorption efficiency) of agricultural waste burning organic aerosols (AWB-OA) and their impact on total absorption were investigated in Cairo (Egypt) during the post-harvest rice straw burning autumn season. At 370 nm, AWB-OA were found to account for more than 25% of total absorption on average for the period of study (and for ～50% during intense biomass burning events), pointing out the major role potentially played by such particles on light absorption at short wavelengths. The absorption exponent obtained for AWB-OA (～3.5) is consistent with values previously reported for biomass burning brown carbon. In addition, AWB-OA were found to exhibit high mass absorption efficiencies at the near ultraviolet/mid-visible regions (e.g. 3.2±1.6 m² g^?1 at 370 nm and 0.8±0.4 m² g^?1 at 520 nm). Such findings clearly illustrate the need to take light absorption by organic aerosols into account for a better estimate of the radiative impact of biomass burning aerosols.     

有机转光剂在EVA光伏胶膜中的应用及耐老化性能研究

以EVA(乙烯-醋酸乙烯共聚物)为基体,通过引入适量的交联剂、抗氧剂和转光剂(即含饱和C—H键的有机转光剂O),制得转光型EVA光伏胶膜。研究结果表明:当w(有机转光剂O)=0.03%(相对于胶膜质量而言)、挤出机温度为95℃和胶膜厚度为(0.5±0.01)mm时,所得胶膜透明性良好(280~380 nm透光率占30.8%、380~1 100 nm透光率占92.5%)、对光伏发电功率增益较高(功率增益为0.67%)且耐UV黄变性较佳(经155℃层压25 min后,耐老化性符合光伏组件封装用EVA胶膜的国家标准)。     

Effect of vinyl acetate on aging mechanism of polyacrylate under UV light

Diversity of aging behaviors of polyacrylate and poly(vinyl acetate‐acrylate) with the ultraviolet light radiation was studied. The aging degree was evaluated and the mechanism dominated the behaviors was investigated by color aberration, the degree of cross‐linking, molecular weight and its distribution by gel permeation chromatography (GPC), ultraviolet absorption spectroscopy (UV–vis), and fourier transform infrared spectrometer (FTIR). These studies found that although photodegradation mechanism of poly(vinyl acetate‐acrylate) still preserves three main steps of the scission of main chain, formation of double bond and the generation of cross‐linking reaction, introducing structural units of vinyl acetate to polyacrylate cause the rules various. The structural units can aggravate the aging of polyacrylate, through increasing formation of double bonds and generating cross‐linking reaction. However, what is interesting is that the structural units can strikingly restrain main chain from scission. It is significant for modifying the photodegradation behaviors of polyacrylate coatings. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thresholds of secondary organic aerosol formation by ozonolysis of monoterpenes measured in a laminar flow aerosol reactor

The reactions of ozone with a series of monoterpenes (α-pinene, sabinene, limonene and myrcene) were investigated in a novel flow reactor dedicated to the investigation of secondary organic aerosol (SOA) formation. Rate constants for the gas phase reactions and nucleation thresholds were determined at T～296 K, P～764 Torr under dry conditions (dew point ≤?33 °C) and in absence of OH radicals scavenger and seed particles. Comparison with the literature as well as data from a simulation chamber showed good agreement. The experiments also show that the novel flow reactor improves the accuracy in evaluating the nucleation thresholds during the ozonolysis of monoterpenes and show that aerosol flow reactor is a useful tool to study the SOA nucleation step. Given as an upper limit, the nucleation thresholds obtained are (in molecule cm^?3/ppb): α-pinene, 3.9×10¹⁰/1.56; sabinene, 6.2×10⁹/0.26; limonene, 1.1×10¹⁰/0.43 and myrcene 2.1×10¹⁰/0.83.     

抗氧剂和浓缩液含量对尼龙6耐热氧老化性能的影响

采用原位聚合和共混改性的方式制备了不同配方的尼龙6(PA 6),研究了热稳定剂的加入量及其加入方式、己内酰胺(CPL)回收液的加入量对PA 6耐热氧老化性能的影响。结果表明:复合抗氧剂168/抗氧剂1098的加入可以提高PA 6的长期高温下的耐热氧老化性能,加入复合抗氧剂质量分数为0.1%可以达到理想的效果;相比于共混,采用原位聚合的方法加入复合抗氧剂,其耐热氧老化效果更加明显;当CPL回收液加入质量分数小于等于30%时,PA 6的力学性能随着CPL回收液含量的提高而提高,但CPL回收液的加入对PA 6的耐老化性能有不利的影响,CPL回收液加入量越高,在长期高温下的老化速度越快,力学性能损失越大,黄变指数越高;当CPL回收液质量分数为30%,复合抗氧剂加入质量分数为0.1%时,PA 6的力学性能和耐热氧老化性能达到最优,且均优于纯PA 6。