Control of exhaled SARS-CoV-2-laden aerosols in the interpersonal breathing microenvironment in a ventilated room with limited space air stability

The Coronavirus Disease 2019 (COVID-19) highlights the importance of understanding and controlling the spread of the coronavirus between persons. We experimentally and numerically investigated an advanced engineering and environmental method on controlling the transmission of airborne SARS-CoV-2-laden aerosols in the breathing microenvironment between two persons during interactive breathing process by combining the limited space air stability and a ventilation method. Experiments were carried out in a full-scale ventilated room with different limited space air stability conditions, i.e., stable condition, neutral condition and unstable condition. Two real humans were involved to conducted normal breathing process in the room and the exhaled carbon dioxide was used as the surrogate of infectious airborne SARS-CoV-2-laden aerosols from respiratory activities. A correspondent numerical model was established to visualize the temperature field and contaminated field in the test room. Results show that the performance of a ventilation system on removing infectious airborne SARS-CoV-2-laden aerosols from the interpersonal breathing microenvironment is dependent on the limited space air stability conditions. Appropriate ventilation method should be implemented based on an evaluation of the air condition. It is recommended that total volume ventilation methods are suitable for unstable and neutral conditions and local ventilation methods are preferable for stable conditions. This study provides an insight into the transmission of airborne SARS-CoV-2-laden aerosols between persons in ventilated rooms with different limited space air stability conditions. Useful guidance has been provided to cope with COVID-19 in limited spaces.     

北京冬季PM2.5中有机气溶胶的化学特征和来源解析

为探讨北京冬季大气细颗粒物（PM_2.5）中有机气溶胶的浓度水平、分布特征和来源变化,对2016年11月10日~12月10日采集的北京大气PM_2.5样品进行气相色谱-质谱测定,定量了129种颗粒有机物（POM）,约占有机物总量的（9.3±1.2）%.其中含量最高的是糖类,仅左旋葡聚糖即可占到定量有机物的18%,其次是正构烷酸、正构烷烃、二元羧酸和多环芳烃.根据POM示踪物的变化特征,分析了供暖和生物质燃烧传输对北京冬季有机气溶胶的影响.相比于非供暖期间,供暖期间化石燃料示踪物藿烷的质量浓度及在有机物中的占比都明显升高,各组分间的分布也更加趋向于燃煤排放的特征.正构烷烃主峰碳数和奇偶分布的变化,反映了化石燃料贡献增强的影响.生物质燃烧示踪物左旋葡聚糖的浓度权重轨迹（CWT）模型结果表明,北京周围区域的秸秆燃烧污染会通过传输影响北京的有机气溶胶组成.利用分子示踪-化学质量平衡（MM-CMB）模型对2016年北京冬季有机碳（OC）进行了来源解析,并与2006年的结果进行比较,以定量10年间各污染来源贡献发生的变化.2016年与2006年相比,机动车对有机气溶胶贡献明显增加,燃煤和木材燃烧的贡献则大幅度降低,餐饮排放的贡献也不容忽视.因此,控制机动车和餐饮源的排放对改善北京冬季PM_2.5污染问题至关重要.     

基于排放清单和实地测试的工业VOCs排放特征:以郑州市高新区为例

基于本地污染源调查,同时对重点工业行业进行实地采样测试,建立了郑州市高新区工业VOCs排放清单及组分清单,并评估了 VOCs各组分的臭氧生成潜势(OFP)和二次有机气溶胶生成潜势(SOAp).结果表明,2017年郑州市高新区工业源VOCs排放总量为4 566.0 t,橡胶和塑料制品业、设备制造业和有色金属业是排放量最大的3个行业,排放量分别为1 924.2、1 396.3和813.4 t;各VOCs组分中,烷烃占比最大(40.9％),其次是含氧VOCs(32.2％)和芳香烃(20.3％);异丙醇、正十二烷、甲苯、甲基环己烷和丙酮是排放量最大的5种物质;OFP总量为8 753.8 t,最大贡献源和VOCs种类分别为设备制造业和芳香烃;SOAp总量为643.0 t,贡献较大的排放源为设备制造业和铝箔制造业,烷烃和芳香烃是两种主要贡献组分.     

Phase separation and regrowth of aerosol matter collected after size fractionation in an impactor

Aerosol matter in the size range <2 μm was collected in a Berner impactor and subsequently analysed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectrometry. Owing to the low electron beam energy of 5 keV (occasionally 10 keV), analysis was restricted to elements with atomic numbers 20 (Ca). Sub-micrometer aerosol matter was found to contain mostly S, O, and C as well as some K and Ca. Nitrogen appeared to escape detection, probably due to bombardment-induced sublimation of NO₃ and NH₄. During sampling at low to moderate relative humidity (<60%) the sulphur-rich fraction of the aerosol matter (most likely sulphates) regrew in the form of microcrystals with sizes up to 10 times larger than the mean aerodynamic diameter of the respective impactor stage. By contrast, when sampling during periods in course of which the relative humidity exceeded 70%, the aerosol matter regrew in the form of extended amorphous agglomerates. The aerosol deposits also contained large numbers of carbon nanoparticles, well separated from the regrown sulphate-rich matter. The nanoparticles were similar in size (20–40 nm), much smaller than the equivalent aerodynamic diameter of the impacting particles (63 nm–2 μm). Presumably, the carbon nanoparticles constituted the core of larger air-borne particles covered with sulphates (as well as with nitrates and organic carbon). The regrown microcrystals disappeared rapidly under electron bombardment at high current density, an observation that indicates high volatility at elevated temperatures. Aerosol matter collected in the size range between 1 and 2 μm contained large fractions of particles made of O, Si, P, K, and Ca (oxides). These particles were highly resistant to electron bombardment (hard) and showed little or no evidence for agglomeration or regrowth. After removing the soluble (acidic) material from the collected aerosol matter, only carbon nanoparticles and hard coarse particles were left behind. The observation of agglomerated or crystallized “soft” aerosol matter in combination with phase separation of carbon nanoparticles lends further support to the assertion that it is not possible to collect useful quantities of fine and ultrafine aerosol particles with as-suspended morphology. Some implications for health-related research are discussed.     

A Screening Procedure for Prioritizing Riparian Management

A spatially explicit linear, additive model was developed for quantifying site characteristics of riparian areas of the lower Cedar River, Washington, USA. The spatial complexity and distribution of combined habitat and anthropogenic landscape features were used to define habitat indices that indicate the relative quality of riparian habitats. Patches of contiguous grid cells were measured in terms of their locations, sizes, and relative degree of fragmentation. Additionally, intrapatch heterogeneity was measured to identify unique combinations of habitat and anthropogenic factors for individual grid cells within patches. Model verification indicated that existing floodplain riparian habitats received positive indices more than 90% of the time. Mean patch sizes and fragmentation indices were similar for all positive indices throughout the reaches in the valley floor. Among all reaches, reach 7 had the highest number of positive patches due to a higher degree of meandering in this reach. This procedure and model outputs provide unique screening opportunities for prioritizing management of riparian areas (e.g., conservation, restoration and enhancement).     

Features in Number Concentration-Size Distributions of Aerosols in the Free Atmosphere over the Desert Areas in the Asian Continent: Balloon-Borne Measurements at Dunhuang,China

Vertical changes of aerosol concentration and size in the freetroposphere over the Asian desert areas were firstly observed using a balloon-borne optical particle counter at DunHuang, China (40°00N, 94°30E) (17 August and 17 October 2001, and 11 January 2002). In the free troposphere highly concentrated aerosol layers were frequentlyobserved, suggesting the importance of regional scale particletransportation over the Asian continent. Concentration ofparticles with a diameter larger than 0.15 m was about 5–10particles cm^-3 in the free troposphere.Particle number-size distribution in the free troposphereshows important contribution of super micron particles. Regionalscale transportation, in addition to diffusion of soil particlesfrom the lower atmosphere to the free troposphere through localand small scale air motions, is suggested by backward trajectoryanalysis of air masses containing super micron particles. The importance of horizontal transport of coarse size particles in the free troposphere was strongly suggested.Thickness of the boundary mixing layer, from distributions ofparticle concentration, was about 4 km in summer (17 August 2001)and apparently higher than the height of layers in fall (17 October2001) and in winter (11 January 2002), which suggest an active mixingof particles near the boundary in summer. In winter measurement(11 January 2002), strong inversion was found in the vertical profile of temperature, suggesting cold ground surface and vertically stable atmosphere near the ground.     

Comparison of the Chemical Composition of Mineral Particles Collected in Dunhuang,China and those Collected in the Free Troposphere over Japan: Possible Chemical Modification during Long-Range Transport

The Asian continent is recognized as one of the most important sources of mineral (or soil) particles. These particles have a large potential to effect global changes through the biogeochemical cycle of particulates and through radiative balance (IPCC Third Assessment Report, 2001). Therefore, comparison of particle compositions near the source region and those after long-range transport is important in understanding the long-range particle transport phenomenon. Individual aerosolparticles were collected in Dunhuang (40°09N; 94°41E), China. Particles were collected at the campus of the Meteorological Bureau of Dunhuang City (17 August 2001) and near the Mogao Grots, located approximately 30 km from Dunhuang (18 August 2001, 18 October 2001 and 13 January 2002) using a two-stage low-volume impactor. The morphology of individual aerosol particles and their elemental compositions were examined via a scanning electron microscope (Hitachi, S-3000N) equipped with an energy dispersive X-ray (EDX) analyzer (Horiba, EMAX-500). The particles collected at these locations were comprised primarily of minerals, with the exception of sulphateparticles in the submicron range that were contained in thesample collected on 18 October 2001 (likely, ammonium sulphate). The most abundant elements were found to be Si and Al. Approximately 46–77% of the collected particles were Si-richparticles (composed primarily of quartz and aluminosilicate),and 13–41% of the collected particles were Ca-rich particles,such as calcite (CaCO₃), dolomite (CaMg(CO₃)₂),and gypsum (CaSO₄2H₂O). The fractions of Fe-rich, Mg-rich, Ti-rich, K-rich, and Cl-rich were 3–10, 0–7, 0–3, 0–1, and 0–1%, respectively. Similar types of mineral particles were found in the free troposphere over Japan(Trochkine et al., 2002). A number of differences were found to exist between the particles collected in China and thosecollected in Japan, and these differences can be explained bychemical modification of the particles during transport fromChina to Japan.     

防御城市高温灾害、减低夏季热岛强度的途径

以上海市气象观测资料为基础,探讨了在区域性高温背景下,叠加上城市热岛效应所导致的高温灾害的成因及危害,提出了减低危害的对策及途径。     

大气气溶胶无机组成的FTIR测定及与离子色谱分析的比较

利用傅立叶变换红外光谱仪，固体制样方式，对北京市中关村地区的气溶胶样品中的无机组成进行了分析，并对气溶胶样品中的ＳＯ４＾２－，ＮＨ４＾＋和ＮＯ３＾－进行了定量测定，为检验ＦＴＩＲ测定法的可靠性，将ＦＴＩＲ法与离子色谱的测定结果进行了对照分析，结果表明，ＳＯ４＾２－和ＮＨ４＾的ＦＴＩＲ测定结果与离子色谱有较好的相关性。     

Tree-ring analysis for the assessment of anthropogenic changes and trends

Investigation of Pine (Pinus sylvestris L.)annual radial increment (width of annual tree rings) was carriedout in the surroundings of one of the largest pollution sources inLithuania – Jonava Nitrogen Fertilizers Plant. The main objectiveof investigation was to analyse different sides of anthropogenictransformations of tree-ring series in the polluted environment:changes in tree growth intensity; variance changes in tree-ringseries; changes in the relations with natural external factors.Three different periods of tree reaction to the environmentalpollution were singled out – fertilization period, depressionperiod and recovery period since annual emissions were essentiallyreduced. The variance of tree-ring series has increased severaltimes in the polluted environment. Reaction of trees to the impactof climatic factors (temperature, precipitation) has changedsignificantly in the polluted environment and their sensitivity hasalso increased.