Reactivity of ambient volatile organic compounds （VOCs） in summer of 2004 in Beijing

Ambient volatile organic compounds （VOCs） were sampled at six sites in Beijing in the summer of 2004 and analyzed by GCMS. The chemical reactivities of 73 quantified VOCs species were evaluated by OH loss rates （LOH） and ozone formation potentials （OFPs）. Top 15 reactive species, mainly alkenes and aromatics, were identified by these two methods, and accounted for more than 70% of total reactivity of VOCs. In urban areas, isoprene was the most reactive species in term of OH loss rate, contributing 11.4% to the LOH of VOCs. While toluene, accounting for 9.4% of OFPs, appeared to have a long-time role in the photochemical processes. Tongzhou site is obviously influenced by local chemical industry, but the other five sites showed typical urban features influenced mainly by vehicular emissions.     

Rapid Ozone Decomposition over Water-activated Monolithic MoO3/Graphdiyne Nanowalls under High Humidity

Catalytic ozone (O₃) decomposition at high relative humidity (RH) remains a great challenge due to the catalysts poison and deactivation under high humidity. Here, we firstly elaborate the role of water activation and the corresponding mechanism of the promoted O₃ decomposition over the three-dimensional monolithic molybdenum oxide/graphdiyne (MoO₃/GDY) catalyst. The O₃ decomposition over MoO₃/GDY reaches up to 100 % under high humid condition (75 % RH) at room temperature, which is 4.0 times as high as that of dry conditions, significantly surpasses other carbon-based MoO₃ materials(≤7.1 %). The sp-hybridized carbon in GDY donates electrons to MoO₃ along the C−O−Mo bond, facilitating water activation to form hydroxyl species. As a result, hydroxyl species dissociated from water act as new active sites, promoting the adsorption of O₃ and the generation of new intermediate species (hydroxyl ⋅OH and superoxo ⋅O₂⁻), which significantly lowers the energy barriers of O₃ decomposition (0.57 eV lower than dry conditions).     

Ambient air monitoring with Auto-gas chromatography running in trigger mode

Speciated volatile organic compounds (VOC), either as ozone precursors or air toxics in the air, are commonly monitored by triggered canister method or continuous ozone precursor analyzer (commonly known as Auto-gas chromatography (GC)) method. In the triggered canister method, a canister sample is collected when a total non-methane organic compound (TNMOC) concentration exceeds a pre-determined trigger level. The canister sample is then analyzed in a lab in a later time. In the Auto-GC method, an online GC runs in a “continuous” mode with a sampling and analysis cycle of 1 h. Within the cycle hour, samples are collected only during the first 40 min.A new approach of Auto-GC running in trigger mode is developed in this study. This new approach uses Auto-GC but operates it in a trigger mode similar to the triggered canister sampling method. Compared to the triggered canister sample method, this system provides near real-time speciated VOC data, which are critical for responding to a high VOC concentration episode. Although the canister system generally costs less, its cost advantage may diminish if trigger events are frequent and the monitoring duration is long. Compared to continuous Auto-GC, triggered GC has its niche—it is better for capturing transient plumes with a small footprint. The continuous GC either misses a transient plume if the plume does not arrive at the sampling site during the sampling cycle or flattens the plume concentration peak by dilution with non-plume air sample.Field experience with this system for fenceline VOC monitoring is presented. The sampling and calibration strategy for trigger mode operation is described. The chromatograph retention time drift issues are discussed. The system performance is evaluated, including the method detection limit, precision and accuracy. The trigger mode configuration for VOC fenceline or near source monitoring in this work proved effective for local and transient plume identification.     

New insights about the electrochemical production of ozone

Ozone is a rather attractive oxidant, it is very efficient in the oxidation of pollutants and in the killing of pathogens and does not generate any hazardous waste during its use. Its generation has been constantly sought in an effective way, focusing on obtaining high concentrations of ozone at the lowest possible cost. Recently, electrochemical production of ozone show advantages over conventional corona discharge generation, since this technology do not need very high voltages, feeding oxygen or pure air or dissolving the ozone into wastewater to be treated. However, it is still at early development stage and there is still a long way to reach the high technology readiness levels needed to complete its value chain. Equipment considerations and operation conditions are the key points that need to be understood in order to increase efficiently. Recent novelties in the state of the art of research are summarized in this work.     

A recent progress of room–temperature airborne ozone decomposition catalysts

Ozone (O₃) plays essential roles in stratosphere and helps reduce the amount of harmful ultraviolet arriving the Earth’s surface. However, O₃ is also a strong oxidant and causes troubles to human health in troposphere, especially in the confined space, such as indoor environment. Recently, O₃ abatement materials have become research hotspots due to the urgent environmental demands. Catalysis is a facile strategy that can eliminate indoor airborne O₃ efficiently and economically. Thus, this review summarizes the recent progresses of O₃ decomposition catalysts. The catalysts covered here are categorized as follows: zeolite, metal organic frameworks (MOFs), metal oxides, noble metals. Manganese–based catalysts display higher efficiency and are mainly discussed. Generally, the active sites of O₃ decomposition catalysts are described as Lewis acid sites (e.g., zeolite), metal sites (e.g., MOFs), oxygen vacancy sites (e.g., MnO₂) in the previous work. In this review, we ascribe all the active sites to unsaturated metal sites and their Lewis acidity. Possible evidence from the experimental and theoretical perspectives are proposed. Furthermore, the strategy to circumvent deactivation caused by peroxides (O₂^2–) accumulation and water molecular competition are also elaborated. Finally, perspective is presented on the challenges and opportunities of exploring existing and new O₃ decomposition catalysts.     

臭氧催化氧化脱除低浓度甲醛的新方法

甲醛作为一种典型的室内挥发性有机污染物,对人体健康危害很大.目前,在可用于室内甲醛脱除的诸多方法之中,臭氧催化氧化法因可于室温下使用廉价的金属氧化物催化剂实现对甲醛的高效脱除,从而受到了科研工作者的广泛关注.然而,考虑到室内甲醛的浓度极低,且存在着长期缓慢释放的特点,传统的臭氧催化氧化法应用于实际的室内甲醛脱除不仅会造成能量的浪费,而且还易因未完全分解臭氧的连续释放带来二次污染问题.为了提高臭氧催化氧化脱除甲醛过程的臭氧利用率,降低能耗,并有效缓解未分解臭氧引起的二次污染,本文将一种循环的甲醛存储-臭氧催化氧化新方法应用于室内低浓度甲醛的脱除.该新方法包含甲醛存储与臭氧催化氧化两个过程,在存储阶段低浓度甲醛吸附存储于催化剂表面,而在臭氧催化氧化阶段臭氧将存储的甲醛氧化为CO2与H2O,并重新释放催化剂表面的吸附位.因负载型氧化锰具有优良的臭氧分解能力,本研究以Al2O3负载的MnOx为催化剂,通过研究前驱体及担载量对甲醛脱除反应的影响,筛选出了最优的MnOx/Al2O3催化剂,并对相对湿度的影响规律进行了考察,最后通过低浓度甲醛存储-臭氧催化氧化循环实验验证了该甲醛臭氧催化氧化新过程的可靠性.我们采用传统的等体积浸渍法,基于不同的前驱体制备MnOx/Al2O3催化剂.XRD表征结果表明,乙酸锰为前驱体制得的MA/Al2O3催化剂中MnOx相主要为Mn3O4(粒径约为6.0 nm);而硝酸锰前驱体所得MN/Al2O3催化剂中则含有MnO2与Mn2O3相,且其MnOx颗粒粒径较大,约为9.5 nm.XPS测试结果表明,MA/Al2O3催化剂含有Mn2+,Mn3+及Mn4+,其中Mn3+与Mn4+的含量分别为75%与12%;而MN/Al2O3催化剂则仅含有Mn3+与Mn4+,含量分别为35%与65%.上述XRD与XPS结果相一致,说明以乙酸锰为前驱体所得催化剂的分散度较高且易形成低氧化态的Mn.甲醛存储-臭氧催化氧化实验结果表明,与Al2O3及MN/Al2O3相比,MA/Al2O3催化剂具有更高的甲醛存储与催化氧化脱除性能.基于MA/Al2O3催化剂,不同Mn负载量下的甲醛存储与臭氧催化氧化实验结果表明,Mn负载量为10 wt%时MA/Al2O3的性能最佳.因而,进一步的实验中我们均选用最优的10 wt%MA/Al2O3为催化剂,其在50%相对湿度下的甲醛存储量为26.9μmol/mL,臭氧催化氧化阶段碳平衡为92%,CO2选择性为100%.相对湿度的影响结果(23℃)则表明,由于水分子与甲醛分子间存在着竞争吸附作用,甲醛存储容量随相对湿度的增加而降低;但因相对湿度增加可建立利于甲醛氧化的新途径,故臭氧催化氧化性能随相对湿度增加而增强.综合考虑,10 wt%MA/Al2O3上甲醛存储-臭氧催化氧化的最优相对湿度为50%.为验证所提出新方法的实用性,我们基于10 wt%MA/Al2O3开展了甲醛存储-臭氧催化氧化的4次循环实验.4次循环实验中的甲醛存储以及臭氧催化氧化处理的规律可基本保持一致.50%相对湿度下,低浓度甲醛(15×10-6)在空速为27000 h-1时的穿透时间为110 min,而在臭氧催化氧化阶段(150×10-6臭氧,空速15000 h-1)仅需约50 min即可实现对存储甲醛的氧化脱除(碳平衡大于92%,CO2选择性100%),表明该新方法较传统的臭氧催化氧化方法臭氧用量可节省60%.     

On the action of ozone at high concentration on various grades of polyethylene and certain straight chain paraffins

The surface functionalisation of UHMWPE (ultra high molecular weight polyethylene) was successfully achieved by the action of ozone (10% by weight in oxygen) under mild conditions. The kinetics of the gas-solid reaction between O₃ and UHMWPE in powder form were measured in an IR gas cell and the pseudo-first-order rate constant was k′_UHMWPE = 1.9 × 10⁻⁴ s⁻¹. The resulting surface-oxidized UHMWPE was studied by FT-IR spectroscopy and the nature of the surface functionalities was determined. Furthermore, the surface-oxidized UHMWPE was studied by DSC (differential scanning calorimetry). It was evident that ozone attacks and oxidizes the amorphous phase of UHMWPE preserving the crystalline phase because after the ozone treatment there was an increase in the % of crystallinity. Two other polyethylene grades having respectively M_w = 15,000 Da (defined as LMWPE = low molecular weight polyethylene) and M_w = 4000 Da (defined as VLMWPE = very low molecular weight polyethylene) were studied as model compounds in comparison to UHMWPE in their reaction with ozone. Commercial liquid paraffin and n-dodecane were used as model compounds to study the reaction between high ozone concentration and alkanes.     

星光掩星剥洋葱法反演臭氧密度

星光掩星技术探测恒星光经大气层消光、折射等作用后的恒星光光谱,利用大气中不同成分对不同波长的光吸收的差异反演得到大气密度信息。低轨卫星与恒星分别位于地球两侧,低轨卫星接收到不同切线高度上光谱,即构成星光掩星观测。光谱探测高度可从平流层至低热层,其中不同波段可用于不同大气痕量成分密度反演。星光掩星技术具有探测参数多、全球覆盖、垂直分辨率高、无需定标等优点。GOMOS(global ozone monitoring by occultation of stars)是搭载在欧洲航天局ENVISAT卫星上的平流层臭氧检测仪器。GOMOS利用星光掩星技术进行探测,设计精密,分辨率高,在轨稳定运行十年（2002年-2012年）,探测波长跨越紫外到可见光波段,采用光谱反演和垂直反演迭代的方法反演大气成分密度,得到了大量关于临近空间区域大气资料,对长期监测平流层至低热层区域变化提供了可靠的数据支持。利用GOMOS掩星数据,提出一种简单的反演方法--剥洋葱法,反演临近空间高度上臭氧数密度。剥洋葱法假设地球大气对称且水平分层,利用单个波段光谱进行反演,假设在此波长上光谱的大气吸收效应全部由臭氧造成,即选择臭氧吸收占据绝对优势的波长。经分析,在50～100 km高度上可以利用290 nm波段进行反演,在15～50 km高度上可以利用600 nm波段进行反演。根据Beer-Lambert定律,随切点高度自上而下,对恒星光光谱透过率利用剥洋葱法进行反演得到臭氧数密度。将剥洋葱法反演结果与GOMOS官方发布结果相对比,两者符合得很好。     

格尔木地区整层大气臭氧浓度激光外差测量与反演研究

搭建了便于外场观测的3.3μm激光外差光谱仪,实测其光谱分辨率为0.004 cm^-1。利用该设备测量了青海格尔木地区整层大气臭氧的吸收光谱,并结合最优估算法反演了该地区的臭氧浓度。测量期间,格尔木地区臭氧柱浓度均值约241.7 DU,且浓度随观测时间呈上升趋势,上升速度约4 DU/h。结果表明,该激光外差光谱仪结合最优估算法能够实现高海拔地区整层大气臭氧浓度的测量,在环境、气象及激光大气传输等研究领域具有重要的应用前景。     

温度对CrIS热红外卫星资料反演臭氧廓线的影响分析

臭氧是地球大气中一种重要的痕量气体,在光化学反应和气候变化中都扮演着非常重要的角色。高光谱红外卫星可以观测到较高垂直分辨率的大气臭氧信息,但是由于热红外受大气温度影响较大,臭氧反演精度会有所下降。为此详细讨论和分析了温度对臭氧吸收光谱和权重函数的敏感性,以及对臭氧反演精度的影响。首先利用逐线积分辐射传输模型LBLRTM,分别模拟计算了六种不同标准大气模式下,1K的随机温度误差对大气透过率和辐射值的影响,发现1 K温度随机误差和臭氧浓度5%～6%的变化引起的辐射值变化量一致。接着利用CRTM辐射传输模型,针对搭载于美国对地观测卫星Suomi NPP(National Polar-orbiting Partnership)平台上的CrIS(Cross-track Infrared Sounder)红外高光谱观测数据,计算了1K的随机温度误差对大气臭氧权重函数的影响,并计算了由1K温度误差所导致的热红外高光谱资料大气臭氧廓线反演误差,结果显示CrIS对于臭氧的敏感区位于10～100 hPa之间,且1 K的温度误差和6%的臭氧浓度变化引起的权重函数变化量相当。最后以CrIS作为实验数据,在最优估计法框架下,通过特征向量统计法获取臭氧廓线的先验知识,并将大气温度廓线和大气臭氧廓线都作为未知量,进行同步迭代反演。将反演结果和配对的世界臭氧紫外数据中心WOUDC的站点数据进行比较,发现在反演中加入大气温度廓线进行同步迭代后,反演结果有显著提高,尤其在平流层与真值几乎一致,最大相对误差不超过20%,在对流层反演结果相对较差,最大相对误差不超过50%,优于欧洲中期天气预报中心ECMWF(European Center for Medium-range Weather Forecasting)臭氧模式数据集ERA-Interim。