黄渤海悬浮颗粒物密度的空间分布及其对固有光学特性的影响

【目的】研究悬浮颗粒物密度在黄渤海的空间分布特征及其对水体固有光学特性的影响。【方法】利用2014年11月以及2015年8月现场实测数据,计算得到黄渤海悬浮颗粒物密度,绘制出黄渤海悬浮颗粒物密度的空间分布图。将研究区域悬浮颗粒物密度与固有光学特性进行拟合分析。【结果】两个航次悬浮颗粒物密度的空间分布比较复杂,但整体趋势显示中层密度要小于表层和底层。在表层、中层和底层的密度分布图中,黄河口附近均有密度小值区域,山东半岛附近有密度大值区域,随着深度增加该大值区域有南移趋势。悬浮颗粒物密度与比固有光学特性cp＊、bp＊、bbp＊拟合所得到的P值绝大部分小于0.05,与固有光学特性cp、bp、bbp拟合得到的P值全部大于0.05,而与Qce、Qbe、Qbbe拟合得到的P值多数大于0.05。【结论】悬浮颗粒物密度对比固有光学特性变化影响较大,尤其对cp＊影响达到51%;对Qce、Qbe、Qbbe的变化影响一般;对cp、bp、bbp变化影响较小。

北京市春季天气状况对针叶树叶面颗粒物附着密度的影响

对北京市侧柏、圆柏、油松和云杉冲洗与未冲洗植株春季1个月内叶面颗粒物附着密度进行了观测,并对照逐日气象数据和测试树种叶表面微形态,分析了天气状况对叶面颗粒物附着密度的影响。结果表明,春季降雨、大风、沙尘等天气状况交替出现导致叶面颗粒物附着密度随之变化,大多数时间低于冬季。测试树种叶面部分颗粒物附着牢固,不能被中等强度15 mm降雨冲掉。5~6级大风不会使叶面颗粒物附着密度减少。与本地扬尘相比,外来入侵沙尘可使叶面颗粒物附着密度较大增加。侧柏和圆柏叶表面密集脊状突起间的沟槽可深藏许多颗粒物,且颗粒物固着牢固,不易被降雨和大风去除。油松叶表面光滑、粘性大,易于小颗粒物的附着,但颗粒物容量较低,附着不牢固。云杉气孔周围较宽凹槽利于牢固滞留较大颗粒物,能有效捕获粒径较大的外来沙尘。

机动车排放细微/超细颗粒物消光特性的Mie理论研究

机动车等燃烧源排放颗粒物离散系统的消光特性主要取决于颗粒群的物理化学组分和粒径分布特征.利用内部混合模型,确定典型机动车排放颗粒物的密度和光学复折射系数(m),通过Mie理论模型研究不同粒径下单体颗粒物的光学特性,从而研究机动车排放的nm/μm级粒径下细微/超细颗粒物的无量纲光散射率(Qscat)、无量纲光吸收率(Qabs)以及无量纲消光率(Qext).结果表明,不同国家的轻型柴油车(LDV)排放超细颗粒物的化学组分差异较大,而重型柴油车(HDV)则没有显著差别.相关性分析表明,机动车排放颗粒物的EC组分所占比例与复折射系数的实部(n)和虚部(k)均有极强相关性,相关系数(R2)分别为0.995 6和0.993 8.通过Mie理论计算4种复折射系数下典型机动车排放颗粒物Qscat,Qabs和Qext随粒径的变化特征发现,粒径为400～600 nm范围的单体颗粒物消光作用最大.当颗粒物粒径>1μm时,Qscat,Qabs和Qext逐渐稳定为常数1.2,1.0和2.2,此时消光率与复折射系数无关.

北京市11种园林植物滞留大气颗粒物能力研究

测定了北京市11种园林植物叶面颗粒物附着密度,利用环境扫描电镜观察比较了各测试树种叶表面微形态,测量统计了滞留颗粒物的粒径分布.结果表明,植物主要通过叶片上表面滞留大气颗粒物,上表面滞留的大气颗粒物数量约为下表面的5倍;叶片上表面滞留大气颗粒物能力由高到低的微形态结构依次是沟槽>叶脉+小室>小室>条状突起,并且结构越密集、深浅差别越大,越有利于滞留大气颗粒物;测试树种叶片上、下表面PM2.5和PM10平均百分含量分别为66.7%和98.3%与43.4%和92.9%.

北京市六种针叶树叶面附着颗粒物的理化特征

对北京市6种针叶树叶面颗粒物附着密度、叶表面微形态、颗粒物矿物与元素组成的研究结果表明：同一树种叶面颗粒物附着密度随大气颗粒物浓度增加而增大；同一地点不同树种叶面颗粒物附着密度存在很大差异，圆柏、侧柏颗粒物附着密度最高，其次为雪松、白皮松，油松、云杉最低；受地面扬尘影响，低矮叶片较高处叶片颗粒物附着密度大；受降雨和新生叶片稀释影响，夏季颗粒物附着密度小于冬季．叶表面粗糙程度越大，颗粒物附着密度越高．SiO2、CaCO3、CaMg（CO3）2、NaCl、2CaSO4·H2O、CaSO4·2H2O、Fe2O3 7种主要矿物占叶面颗粒物总质量的10％～30％，其中，SiO2含量最高，其次为CaMg（CO3）2、CaSO4·2H2O和CaCO3．此外，还含有蒙脱石、伊利石、高岭石等粘土矿物及长石．21种测定元素占叶面颗粒物总质量的16％～37％，其中Ca、Al、Fe、Mg、K、Na、S7种元素占测定元素总质量的97％以上。其它痕量污染元素含量很少，并且受采样地点和树种影响较小．

北京市16种树木吸附大气颗粒物的差异及颗粒物研究

为选择吸附颗粒物能力强的绿化树种修复大气颗粒物污染,以北京市西直门交通枢纽的16种常见绿化树种为材料,利用扫描电镜观察叶片表面的微观形貌和颗粒物的形态,并用Image J软件对颗粒物的粒径分布进行统计。研究发现,16种树叶表面形貌差异较大,阔叶树种叶片上表面形态比较复杂,有沟槽、褶皱、绒毛和蜡质等,下表面主要有气孔、腺毛、绒毛等,形态相对较单一。针叶树种叶表面形态相对简单,有少量褶皱,但是叶表面分泌大量油脂。叶片表面附着的大部分颗粒物表面粗糙且形态不规则,粒径小于2.5μm的颗粒物在3种粒径中占比最大。通过扫描电镜X射线能谱仪对颗粒物的元素进行分析发现,组成颗粒物的元素主要有C、N、O、Si、Ca、Fe,及少量的Na、Mg、Pb、Ni、Cd和Pd等元素。从颗粒物来源分析,主要含有C、N、O、Na、Mg、Si和Ca等元素的颗粒物,可能主要来自自然界,而Pb、Fe、Ni、Cd和Pd等元素含量较高的颗粒物可能主要来自人类活动的产物。叶表面颗粒物附着密度结果表明,圆柏和油松较其他树种叶片颗粒附着密度大,其余较大的树种依次是栾树、国槐和榆叶梅等。研究结果为揭示树木吸收大气颗粒物的机制及合理选择园林绿化树种提供了重要的理论科学依据。

Ultrasonic-Vibration-Assisted Pelleting of Switchgrass:Effects of Ultrasonic Vibration

Biofuels produced from cellulosic biomass can be used to replace petroleum-based transportation fuels. However, the manufacturing cost of cellulosic biofuels is still high, partly due to the low density of cellulosic feed-stocks. Pelleting of cellulosic feedstocks can increase their density, making their transportation and storage as well as biofuel conversion more efficient and, therefore, reducing the overall cost of biofuel manufacturing. It has been shown that ultrasonic-vibration-assisted (UV-A) pelleting, without using high-temperature steam and binder materials, can produce pellets with density comparable to that produced by conventional pelleting methods. Furthermore, the sugar yield of biomass (wheat straw) processed with UV-A pelleting is 20% higher than that of biomass pelleted without ultrasonic vibration. This paper reports an experimental investigation of UV-A pelleting of switchgrass. The influences of ultrasonic vibration on pellet density, stability, durability, and pelleting force are discussed. It is concluded that pellets processed with ultrasonic vibration had higher density and stability than those processed without ultrasonic vibration, they were more durable than those processed without ultrasonic vibration, and pelleting force with ultrasonic vibration was lower than that without ultrasonic vibration.

DMF/柴油混合燃料在柴油机上燃烧及排放特性

在1台改装过的4缸4冲程水冷增压直喷高压共轨柴油机上,以柴油与2,5-二甲基呋喃(DMF)的混合物为燃料进行试验,研究了柴油机的燃烧和排放性能.结果表明,当平均有效压力为0.13 MPa时,随着混合燃料中DMF质量分数的增加,缸内压力峰值显著降低,缸内放热率峰值却增加.然而,当平均有效压力为0.88 MPa时,随着混合燃料中DMF质量分数的增加,缸内压力峰值和放热率峰值都增加.随着发动机负荷的增加,1,3-丁二烯、乙醛和苯的排放减少,NO_x的排放增加.此外,柴油中加入DMF可以增加乙醛的排放,但1,3-丁二烯和苯的排放却减少.当平均有效压力为0.13 MPa时,D30的NO_x排放是最低的.对于每一种被测试的燃料,核模态粒子在颗粒物的尺寸分布中占主导地位.当平均有效压力为0.38 MPa时,混合燃料在每一种模态下的数密度都比纯柴油的小.然而,当平均有效压力为1.13 MPa的较高负荷时,柴油的颗粒物数密度在整个粒子半径范围内都是最低的.

Attribution of PM_(2.5) exposure in Beijing-Tianjin-Hebei region to emissions:implication to control strategies

The Beijing-Tianjin-Hebei （BTH） region is one of the most heavily polluted regions in China, with both high PM2.5 concentrations and a high population density. A quantitative source-receptor relationship can provide valuable insights that can inform effective emission control strategies. Both source appor- tionment （SA） and source sensitivity （SS） can provide such information from different perspectives. In this study, both methods are applied in northern China to identify the most significant emission cate- gories and source regions for PMz5 exposure in BTH in 2013. Despite their differences, both models show similar distribution patterns for population and simulated PM2.5 concentrations, resulting in overall high PM2.5 exposure values （approximately 110 Ixg/m3） and particularly high exposure values during the win- ter （approximately 200 ktg/m3）. Both methods show that local emissions play a dominant role （70%）, with some contribution from surrounding provinces （e.g., Shandong） via regional transport. The two methods also agree on the priority of local emission controls： both identify industrial, residential, and agricultural emissions as the top three categories that should be controlled locally. In addition, the effect of control- ling agricultural ammonia emissions is approximately doubled when the co-benefits of reducing nitrate are considered. The synthesis of SA and SS for addressing specific categories of emissions provides a quantitative basis for the development of emission control strategies and policies for controlling PM2.5 in China.