Ambient aerosol sampling: Problems,goals and wind tunnel test results of hi-volume samplers

The area of ambient air sampling and its inherent problems and current goals are discussed in general. In particular, recently completed tests of the collection effectiveness of the Rocky Flats Hi-Volume Sampler are compared to previously completed tests of the Standard EPA Hi-Volume Sampler for a variety of field realistic conditions. Collection effectiveness is defined as the ratio of the aerosol collected on the collection substrates of the sampler to that collected by an isokinetic sampling system.The collection effectiveness of the Standard EPA Hi-Volume Sampler was determined as a function of particle size (5–50 μm) and sampler orientation (0° and 45°) at a base condition wind speed of 4.6 m/s and 8% relative turbulence intensity. The results indicated a strong effect of orientation on collection effectiveness at a sampling rate of 1416 l/min. Wind speed over the range of 1.5–4.6 m/s does not greatly influence the collection effectiveness of 15 μm particles. Free stream turbulence levels of 1 and 8% relative intensity has no effect upon collection characteristics.The collection effectiveness of the Rocky Flats Hi-Volume Sampler was determined as a function of particle size (1–34 μm), wind speed (1.52–12.19 m/s) and sampler orientation to the mean flow (0°, 45°, 180°). The results show the sampler, with an inlet flow rate of 880 l/min, has an inlet effectiveness that was a slight function of orientation angle for particles 1–10 μm with a larger effect seen for 20–34 μm; a strong effect of velocity was seen up to 5 m/s where a further increase showed only a slight decrease in effectiveness.The Microsorban-98 filter that is presently used in the Rocky Flats Sampler was tested for efficiency over the size range of particles from 0.01–1 μm and with three different face velocities using the sampler flow rates of 600, 800 and 1 000 l/min corresponding to pressure drops of 20–24 in. of water (3.74–4.49 cm HaG). The filter paper, which was of the fiber type, was found to be 99.9% efficient over the range of particle sizes and pressure drops tested.     

湖北省丘陵山区风能资源特征分析

利用分布在湖北省丘陵山区的12个70 m（80 m）高测风塔一整年的资料，对我省丘陵山区风能资源的若干特征进行了较为详尽的对比分析，找出其中普遍的规律。结果表明：（1）我省山区风速季节变化为春季大，夏季和秋季较小；风速日变化为夜间大白天小，且变化幅度相对较大的测风塔主要分布在低山和中山区域；（2）有效风速频率在79%～92%，破坏性风速出现少；（3）风向频率较为集中，主要分布在偏南和偏北两个相反的方位；（4）风速随高度变化较复杂，10～30 m高度风速增加幅度较大，部分地区30～80 m高度存在等风层或风速随高度减小的情况；（5）有效风速段、大风及主导风向下的湍流强度均为中等。研究成果对湖北省，甚至是南方山区风能资源的合理开发利用将有所裨益     

Measurements of major ion concentration in settled coarse particles and aerosols at a semiarid rural site in India

Deposition rates and deposition velocities of water-soluble ions (F, Cl, NO3, SO4, NH4, Ca, Mg, Na and K) were measured at a rural site (Gopalpura, Agra). Dry deposition samples were collected throughout the year from December 1995 to August 1997, while the aerosol samples were collected only during the winter season of 1996. Surrogate technique was used to collect the dry deposition samples, while aerosol samples were collected on PTFE membrane filter. Deposition velocities (Vd) of SO4 and NO3 are < or = 0.01 m s(-1) while Ca, Mg, Na, K, NH4, F and Cl exhibit greater than 0.01 m s(-1) Equivalent concentration ratios of K/Na, Ca/Na and Mg/Na conform with the corresponding ratios of local soil, indicating the dominant contribution of local sources. Deposition rates are maximum in winter, followed by summer and monsoon. No significant differences are found in dry deposition rates of all ions or in atmospheric concentrations of soil-derived elements with respect to wind direction. However, in aerosols, concentrations of F, Cl, NO3 and SO4 are higher with winds from southwesterly and westerly directions corresponding to pollution sources located in these directions. Deposition data have been used to calculate the critical load of S and N for soil with respect to Triticum vulgaris. The critical load of actual acidity was found to be 622.4 eq ha(-1) year(-1) within the range of 500-1,000 eq ha(-1) year(-1) as assessed by the RAINS-Asia model for this region. The present load of S and N (77.4 and 86.4 eq ha(-1) year(-1)) was much lower than the critical load of S and N (622.4 and 2,000 eq ha(-1) year(-1)), indicating that at present there is no harmful effect on ecosystem structure and function.     

上海近海海域低层风特性分析

基于南汇和奉贤两个海上测风塔观测资料,采用数值统计分析方法,研究了上海近海海域低层风特征,包括风切变指数特征、风的阵性特征和湍流强度特征。结果表明,上海近海10~70 m高度风切变指数在0.09左右,阵风系数在1.20左右,均小于《建筑结构荷载规范》的推荐值。随着风速的增大,风切变指数和阵风系数均呈减小的变化。当风力等级在4级及以上时,切变指数可靠性较好,阵风系数变化较小,湍流强度基本相等。上海近海阵风系数和湍流强度均随着高度的增加而减小,在40 m以上时都趋于稳定。研究结果可为上海近海风资源评价、重大工程规划设计和施工建设以及区域防灾减灾实践提供科学依据和参考。     

Calculation of the depletion of airborne pollutant plumes through dry deposition processes

The depletion of airborne pollutant plumes resulting from dry deposition on ground surfaces should be taken into account when estimating pollutant concentrations in air at distances downwind from their sources. This can be done by using a reduced release rate instead of the actual release rate for the pollutant in atmospheric dispersion equations. The reduced release rate is the actual rate of release multiplied by a depletion fraction. Depletion fractions for use with the Gaussian atmospheric dispersion equation of Pasquill and Gifford were calculated by numerical integration for downwind distances ranging from 35 to 90 000 m for release heights from 1 to 400 m, and they are tabulated for convenient interpolation for intermediate values of distance and release height. Pasquill atmospheric stability categories A-G are included. The listed values are for a deposition velocity of 0.01 m/s and a wind speed of 1 m/s but can be easily converted to apply to other deposition velocities and wind speeds. The tabulated values may be applied for downwind distances close enough to the point of release that the Gaussian model may be assumed to be realistic and where the vertical dispersion of the plume has not yet been significantly affected by the overlying atmospheric lid.     

城、郊能量及辐射平衡特征观测分析

城市化发展导致城、郊能量平衡及辐射平衡存在明显差异。利用城、郊夏季涡度相关系统观测数据,分析了南京城、郊在晴天条件下的辐射平衡、能量平衡、反照率以及储热项变化特征。结果表明：（1）夏季晴天条件下,城、郊辐射收支分配有显著不同。城市辐射陷阱作用导致城区向上短波辐射日均值小于郊区,城、郊分别为246 W/m2和395 W/m2,城市辐射陷阱效应导致截留的短波辐射日平均值可达237 W/m2。同时城市地表向上长波辐射日均值大于郊区自然地表,城、郊分别为5051 W/m2和4883 W/m2,这与城、郊地区不同的地表温度直接相关;（2）城、郊能量平衡分配的方式有显著不同,城市地表储热及感热为能量分配的主要方式,感热全天为正,始终处于不稳定层结。郊区潜热为能量分配的主要方式,夜间存在稳定层结条件;（3）城区总体日平均反照率为011,郊区草地日平均反照率为017,城区水泥楼顶日平均反照率为023。城区铁塔上日均反照率代表整体城市下垫面反照率的特征,城市辐射陷阱作用导致其小于郊区反照率。而水泥楼顶的反照率代表水泥板单一下垫面城市特征,因此大于前2者的反照率日均值。另外,郊区日平均反照率的日变化比城区表现出更明显的不对称性;（4）白天城区储热项占净辐射的56%,而郊区仅占净辐射的7%,并与已有试验中夏季白天储热项数据进行了比较,城市储热项特征与观测所处站点的水泥（硬地）面积所占比重以及是否考虑人为热的影响密切相关     

Relationship between deposition and attachment rates in Jacobi room model

It is shown in this work that parameters of the Jacobi model, which describes behavior of short-lived radon progeny, are not independent. The relationship between deposition rate of attached radon progeny and attachment rate of their unattached fraction was determined in this paper. It was found that deposition rate increases when the attachment rate is smaller; this effect is more pronounced for larger friction velocity. The deposition rate of attached radon progeny is presented here as a function of friction velocity, ventilation and attachment rate. Deposition rate of attached fraction was estimated in the range 0.012-0.46 h⁻¹, when attachment rate varies from 10 h⁻¹ to 100 h⁻¹.     

近期长江口南港河槽沉积地貌变异及其可能原因

南港是长江口两个主要入海通道之一,也是长江深水航道的必经之路。基于2012和1984年的地形资料,利用Arc GIS技术对南港进行冲淤分析;并用同一种方法(筛析法-移液管)对相应年份所采表层沉积物样品进行粒径测试对比。结果表明:近28年来南港地形发生了重大变化,复式河槽间的沙脊因刷深而趋于消亡,主航槽则淤浅数米;沉积物中值粒径均值从81μm下降为24μm,特别是原沙脊位置上的沉积物从砂变细为砂质粉砂或粘土质粉砂。分析认为,采砂是上述变化的主要原因:沙脊采砂使复式河槽"中脊"消失,水动力减弱,河槽中央过水断面增大、分流增多,两侧航槽流速减小导致淤浅;沉积物变细是较粗颗粒被采走、动力减弱和淤积发生的综合结果。     

基于底泥再悬浮试验的太湖水质模拟

为探索浅水湖泊水动力扰动作用对底泥再悬浮影响的规律,在室内矩形水槽内模拟了各种水动力条件下太湖底泥的起动规律,得到了太湖底泥在3种不同起动标准下的起动流速,通过考察上覆水中悬浮物浓度的变化,建立了底泥沉积物再悬浮通量与水体流速的定量化关系。结果表明:太湖底泥在个别动、少量动、普遍动3种标准下的起动流速分别为15、30和40 cm/s,且底泥沉积物再悬浮通量与流速呈现线性正相关关系,再悬浮通量随流速增大而增大,且相关性较好。将该试验结果应用于太湖的水量水质数学模型中,并和太湖实测资料进行了对比,取得了比较满意的效果。该模拟装置能够在室内可控条件下较好地反映太湖沉积物再悬浮特征,对太湖的富营养化治理具有重要意义。     

Air flow and concentration fields at urban road intersections for improved understanding of personal exposure

This paper reviews the state of knowledge on modelling air flow and concentration fields at road intersections. The first part covers the available literature from the past two decades on experimental (both field and wind tunnel) and modelling activities in order to provide insight into the physical basis of flow behaviour at a typical cross-street intersection. This is followed by a review of associated investigations of the impact of traffic-generated localised turbulence on the concentration fields due to emissions from vehicles. There is a discussion on the role of adequate characterisation of vehicle-induced turbulence in making predictions using hybrid models, combining the merits of conventional approaches with information obtained from more detailed modelling. This concludes that, despite advancements in computational techniques, there are crucial knowledge gaps affecting the parameterisations used in current models for individual exposure. This is specifically relevant to the growing impetus on walking and cycling activities on urban roads in the context of current drives for sustainable transport and healthy living. Due to inherently longer travel times involved during such trips, compared to automotive transport, pedestrians and cyclists are subjected to higher levels of exposure to emissions. Current modelling tools seem to under-predict this exposure because of limitations in their design and in the empirical parameters employed.     

2015年冬季苏州城市热岛特征研究

基于Landsat土地利用类型分类资料、夜间灯光影像资料、自动气象站资料以及大气边界层探测资料，划分出城市、郊区以及湖区代表站，分析了苏州2015年1月城市热岛日变化、昼夜差异特征以及城、湖温度差日变化特征，并对苏州城市热岛分布特征以及城、湖大气边界层结构差异进行分析。结果显示：(1)白天热岛强度小，09~17时热岛强度均小于1℃，最小值仅为02℃；夜间热岛强度大，19~05时热岛强度维持在12℃以上，最大值为17℃。(2)城、湖温差白天为正，夜间为负，市区变温速率比湖区快约02℃/h。(3) 苏州白天热中心形状不规则，范围大，城郊温差小，夜间形成单一封闭稳定热中心，热中心形状与市区有较好对应，城、郊温差维持在15℃左右。冬季地面盛行西北风，太湖湖陆风现象显著，湖陆风和盛行风向共同影响城市热羽向西南方向发展。（4）城、湖虚位温廓线在白天差异小，均有不稳定边界层形成，夜间市区仍维持不稳定边界层，而湖区有稳定边界层发展，近地层内干岛效应显著。(5)城市热岛影响范围有明显日变化特征，白天城市热岛影响范围小于40 m，夜间大于200 m。     

南京地区7Be沉降特征

7Be是研究大气科学与地球化学的核元素之一，对研究短期过程的地表土壤颗粒迁移具有较大价值。为了解南京地区利用7Be进行土壤侵蚀示踪研究的合适时机，于2010年1月~2011年12月收集南京地区各月的7Be沉降样品，经实验室化学实验处理和γ谱仪测量，计算7Be沉降通量，并分析7Be大气沉降的季节性变化趋势。结果表明：南京地区平均7Be沉降量为1 62178 Bq/（m2·a），沉降通量为066～1449 Bq/（m2·d），平均沉降通量为444 Bq/（m2·d）；7Be沉降通量的季节变化呈现双峰型趋势，冬末春初和夏季是两个高值区；7Be沉降的а值冬春季较大，夏季最低；降雨量大小与沉降量存在明显的正相关     

Deposition rates of unattached and attached radon progeny in room with turbulent airflow and ventilation

In this paper deposition rate coefficients for unattached and attached radon progeny were estimated according to a particle deposition model for turbulent indoor airflow described by Zhao and Wu [2006. Modeling particle deposition from fully developed turbulent flow in ventilation duct. Atmos. Environ. 40, 457–466]. The parameter which characterizes turbulent indoor airflow in this model is friction velocity, u*. Indoor ventilation changes indoor airflow and friction velocity and influences deposition rate coefficients. Correlation between deposition and ventilation rate coefficients in the room was determined. It was shown that deposition rate coefficient increases with ventilation rate coefficient and that these parameters of the Jacobi room model cannot be assumed to be independent. The values of deposition rate coefficients were presented as functions of friction velocity and ventilation rate coefficient. If ventilation rate coefficient varies from 0.1 up to 1 h⁻¹, deposition rate coefficients for unattached and attached fractions were estimated to be in the range 3–110 h⁻¹ and 0.015–0.35 h⁻¹, respectively.     

Electrical augmentation of granular bed filters

A study of the enhancement of the collection efficiency of granular bed filters by electrical means is reported. By applying electric fields of a few kV/cm (DC or AC) across a bed of insulating granules, the efficiency for submicron charged aerosol is greatly increased, to the point where the efficiency minimum normally observed with such filters in the size range 0.1–1 μm is removed. The performance of such filters is explored as a function of granule size, applied field, face velocity and charge state of the entering aerosol with both a bench-scale flow system (to 40 ft³/min; 1.1 m³/min) and a wind tunnel (to 600 ft³/min; 17 m³/min). Some theoretical estimates are made to identify the most likely physical mechanism of electrical enhancement, and a number of potential application possibilities are discussed.     

Seasonality of cooling tower drift in vegetation at ORGDP

Cooling tower operation at the Oak Ridge Gaseous Diffusion Plant (ORGDP) requires the addition of a chromated corrosion inhibitor to the recirculating cooling water (RCW) system. Fluctuations in the RCW flow rates of the ORGDP cooling towers correlates with operational levels of the enrichment plant. Drift fraction is a function of the RCW flow rate, with variations in chromium deposition reflected in vegetation contamination. Fescue grass and litter were collected in the plant environs along a distance gradient, during different seasons, and analyzed for chromium. Foliar chromium concentrations were maximum (1390 μg/g) during the winter months, decreasing in spring and summer months (190 and 173 μg/g, respectively) at 13 m as the demand for cooling decreased with lower plant operations. In contrast, concentrations in litter increased with time, ranging from 894 μg/g at 13 m during the winter to 1890 and 2140 μg/g during the summer and fall months. The accumulation of chromium in the litter component was likely related to more exchange sites associated with increased litter biomass due to the seasonal senescence of foliage, whereas decreased accumulations on foliage reflected high mobility of the drift residue due to leaching and a short lifespan of individual leaves. In addition to operational considerations, the data illustrate the importance of seasonal considerations in the use of biological materials in a monitoring program.     

Influence of rainfall characteristics on elimination of aerosols of cesium, strontium, barium and tellurium deposited on grassland

This work is aimed at quantifying foliar transfer of cesium, strontium, barium and tellurium under the influence of rainfall characteristics (intensity, frequency and time elapsed between contamination and first rainfall). Grassland boxes were contaminated by dry deposition of multi-element aerosols of (137)Cs, (85)Sr, (133)Ba and (123m)Te. They were grown in a greenhouse under controlled conditions. The treatments consisted of mowing and applying rainfalls (8 and 30 mmh(-1)) at different times after the contamination. At a leaf area index of 5.9+/-1.9, interception of the aerosols was similar for the 4 radionuclides (83.8+/-5.9%). Dew produced significant radionuclide accumulation in the base of the vegetation and transfer to the soil. For moderate intensity, an early (2 days after contamination) first rainfall was as efficient, in terms of leaf wash-off, as a longer rainfall occurring later (6 days after contamination). For early rainfalls, eliminated activities were comparable because the influence of rain intensity was compensated by rain duration. However, for late rainfalls, wash-off efficiency increased with rainfall intensity. Total transfer factors (TTF) were determined on whole grass immediately after 4 rainfalls and at harvest. After 4 medium intensity rainfalls, rain frequency did not influence total transfer factors (TTF) of strontium, barium and tellurium (about 0.2, 0.3 and 0.35 Bq kg(fresh weight)(-1) by Bq m(-2), respectively). Cesium TTF value was lower in the case of a weekly rain (0.1 against 0.2 Bq kg(fresh weight)(-1) by Bqm(-2)). TTF values were similar for twice-a-week rainfalls, whatever their intensity. They were higher for weekly rains of high intensity (between 0.3 and 0.75 Bq kg(fresh weight)(-1) by Bqm(-2) against 0.1-0.35 Bq kg(fresh weight)(-1) by Bq m(-2), depending on the radionuclides). TTF values attested that wash-off was more efficient when rainfalls lasted longer. Field loss on the top of the leaves was well described by an offset exponential model. The half-lives varied with rainfall characteristics from 4 days for cesium, strontium and barium to 20 days for tellurium. The offset value varied between 0% for tellurium (high intensity rainfalls) and 14% for cesium (medium intensity rainfalls).     

Resuspension of coarse fuel hot particles in the Chernobyl area

Measurements of resuspended aerosol in the Chernobyl 30-km exclusion zone have shown coarse fuel hot particles in the activity range 1-12 Bq 137Cs per particle. The particles were sampled with newly designed rotating arm impactors which simultaneously collect during the same experiment three samples with fuel particles in the size ranges larger than 3 microns, larger than 6 microns and larger than 9 microns in geometric diameter. The radionuclide ratios, determined after gamma-spectrometry, were in good agreement with the theoretical calculations for the radionuclide-composition of the Chernobyl Nuclear Power Plant at the moment of the accident and the measured hot particles in soil in the early years after the accident. The number concentrations of airborne hot particles were derived from digital autoradiography. For wind resuspension, maximal concentrations of 2.6 coarse hot particles per 1000 m3 and during agricultural activities 36 coarse hot particles per 1000 m3 were measured. The geometric diameter of single hot particles was estimated to be between 6 and 12 microns.     

Aerosol filtration by a cocurrent moving granular bed: Penetration mechanisms

An experimental apparatus has been constructed to investigate aerosol filtration by a cocurrent moving granular bed filter (CMGBF). In a CMGBF, aerosol passes downward through a descending bed of dirty granules while clean granules are added continously at the bed top. The effect of an intergranular dust deposit on penetration in a CMGBF was investigated in a 2⁴ factorial experiment in which the control variables were superficial gas velocity (100 and 250 mm/s), bed depth (130 and 230 mm), granule size (2.1 and 2.7 mm), and the intergranular dust deposit expressed as percent by weight of collected dust in the bed (1% and 5%). All tests were conducted at ambient temperature and pressure using resuspended utility boiler fly ash as the test aerosol.Mass penetration data identified two major penetration mechanisms: (1) straight through penetration and (2) reentrainment due to granular motion. A static, intergranular dust deposit produced high filtration efficiency (>99%) at the low superficial velocity. When the bed was moving, reentrainment of collected dust was significant and accounted for about three-quarters of the penetrating dust. Particle size analyses reveal that the two penetration mechanisms are size dependent. Most particles larger than about one micrometer in diameter that penetrate the CMGBF do so by reentrainment after being collected initially. Virtually no particles smaller than about 0.3 μm in diameter penetrate by reentrainment; when these small particles penetrate, they pass straight through without being collected.     

利用CFSR数据开展海上风电场长年代风能资源评估

开展长年代风能资源评估可为海上风电场的可行性研究和风险评估提供依据和支撑。创新性地引入了气候预测系统再分析(CFSR)数据,以江苏响水海上风电场为例开展了长年代风能资源评估,结果表明:CFSR数据10 m高度风速与海上气象塔10 m高度风速的平均偏差为-0.2 m·s~(-1),均方根误差为1.9 m·s~(-1);CFSR数据10 m高度风速与海上气象塔90 m高度风速的相关系数范围在0.359~0.619,相比气象站的相关系数提高了40%~90%;长年代订正得到海上气象塔90 m高度近30 a的风数据,多年平均风速为6.9 m·s~(-1),标准差为0.2 m·s~(-1)(2.9%);测算出海上风电场近30年的等效满负荷小时数,多年平均值为2 423 h,标准差为112 h(4.6%);评估出25 a一遇(海上风电场的寿命期)、10 a一遇、5 a一遇的最小年平均风速分别为6.6、6.7和6.8 m·s~(-1),最小年等效满负荷小时数分别为2 227、2 280和2 329 h。利用CFSR数据开展海上风电场长年代风能资源评估在技术上是可行的。     

长三角城市群臭氧浓度的时空分异及驱动因素

运用克里金插值、空间自相关分析、冷热点分析和地理探测等定量分析方法，对长三角城市群2015~2017年O3浓度的时空分异特征及驱动因素进行了探讨。结果表明：（1）2015~2017年长三角城市群O3浓度呈上升趋势，O3日最大8 h滑动平均值第90百分位数平均浓度由149 μg/m3上升到166 μg/m3，平均超标率由9.3%上升到12.1%，以O3为首要污染物的天数占超标总天数的比例由32.3%上升到46.4%。（2）受气温和降水量年际波动的影响，各年份O3月均浓度变化曲线形状不同。但O3超标都主要发生在4~9月，超标天数分别占2015、2016、2017年的88.3%、98.2%和97.0%。（3）由于安徽O3浓度快速上升，长三角城市群O3浓度空间分布格局由东高西低演变为北高南低，且同质化增强、异质性减弱。（4）随着O3浓度的上升，O3浓度热点区由环太湖地区向南京都市圈扩展，冷点区在安徽有明显收缩。（5）地理探测表明，长三角城市群O3浓度空间分异主要受经济规模、城市化和排放源等社会经济因素驱动，且均呈正向影响。自然因素中的降水量和风速呈负向影响，分别对O3有显著的清除和扩散作用。