Use of natural basement ventilation to control radon in single family dwellings

Natural basement ventilation has always been recommended as a means of reducing radon levels in houses. However, its efficacy has never been documented. In these experiments, natural ventilation has for the first time been studied systematically in two research houses during both the summer cooling season and the winter heating season. Ventilation rates, environmental and house operating parameters, as well as radon levels, have been monitored.It can be definitively concluded from radon entry rate calculations that natural ventilation can reduce radon levels two ways. The first is by simple dilution. The second is by reducing basement depressurization and thus the amount of radon-contaminated soil gas drawn into the structure.Therefore, basement ventilation can be an effective mitigation strategy under some circumstances. It might be especially useful in houses with low radon concentrations (of the order of 370 Bq m ⁻¹) or those with low levels and which cannot be mitigated cost-effectively with conventional technology.     

Unusually high indoor radon concentrations

Measurements of indoor radon concentrations in the village Umhausen (2600 inhabitants, Ötztal valley, Tyrol, Austria) revealed unusually high indoor radon concentrations up to 274,000 Bq m⁻³. The medians measured on the basements were 3750 Bq m⁻³ in winter and 361 Bq m⁻³ in summer, those on the ground floors were 1180 Bq m⁻³ and 210 Bq m⁻³, respectively. Seventy-one per cent of the houses showed basement radon concentrations above the Austrian action level of 400 Bq m⁻³ in winter, 33% in summer. There are indications that the high radon concentrations are due to a giant rock slide about 8700 years ago. The unusually high radon concentrations in Umhausen coincide with a statistically significant increase in lung cancer mortality. For the period 1970–1991 the age and sex standardized mortality rate is 3.85 (95% confidence interval: 2.9 to 5.1). The control population is the total population of Tyrol (630,000 inhabitants).     

室内氡污染的控制方法

介绍了消除氡源、控制氡源、通风和空气净化等现有房屋室内氡污染的防治方法,以及控制未来房屋内氡污染的方法。     

Radon at the Mauna Loa observatory: Transport from distant continents

Continuous measurements of radon have been made at an altitude of 3400 m at the Mauna Loa Observatory, Hawaii. Concentrations ranged from about 20 to more than 700 mBq m⁻³. These were similar to values at remote Macquarie I., some 2000 km south of Australia in the Southern Ocean. At Mauna Loa, the radon concentrations could usually be separated into free tropospheric and island influenced categories on the basis of local meteorological observations. On one occasion a long range transport event from Asia brought relatively high radon concentrations to Mauna Loa and persisted for several days. The Asian origin of this event was supported by wind trajectories. This measurement program demonstrates the value of radon data in evaluating air transport models and the influence of transport from distant continents on baseline atmospheric measurements.     

地下工程中空气离子环境和氡害

近年来国内外大量研究资料表明:环境中空气离子和氡是两个与人舒适感及人体健康密切相关的环境因素。地下工程中空气离子和氡问题比地面室内环境更为突出。随着地下空间广为开发利用,如何改善地下工程中空气离子环境及防氡害问题正在引起人们的极大关注。我们对我国五个地区的37个     

个旧地区环境中氡水平及其与地质特点的关系

为了研究个旧地区环境中氡的浓度及分布、运移规律,采用ＳＳＮＴＤ方法,于１９９０－１９９２年间在个旧地区进行了氡的环境地质野外考察和土壤、居室内布点监测,共获４７９个数据。结果表明,尽管在个旧地区未发现铀、钍矿物,土壤氡水平普遍超过世界地壳土壤氡水平均值。居民室内氡水平均值高达４７１．９Ｂｑ·ｍ－３,远高于我国部分省、市近年来所测氡水平值,位于断裂带的居室氡水平高于远离断裂带的居室。个旧地区室内氡夏季高,冬季低,与一些国内、外有关报道结果相反。氡水平与楼层高度呈正相关,顶层为底层的２．７０倍。调查结果可能与个旧地区的环境地质因素有关。建议采取远离地质断裂带建房和防止上升气流逸入室内的防氡辐射进而防癌的措施。     

甲醛等室内主要污染物分布特征与影响评价

现代人80%以上的时间是在室内度过的,室内实际上已成为越来越多的人最直接、最经常的生活环境。与此同时,室内空气质量的优劣也越来越受到人们的关注。本文在呼和浩特市选择不同时间装修的居室,对其室内空气中甲醛、氨、一氧化碳、氡的含量进行了实测,分析了居室装修后室内主要空气污染物的污染水平以及各污染物的分布特征。数据表明,目前新近装修的居室内存在严重的甲醛污染,其超标率达到55.81%,随装修后时间的推移室内甲醛含量逐渐减少,其超标率逐渐降低,说明室内甲醛含量与室内通风状况有明显的正相关性;在所测定的居室中,一氧化碳及氨均未超标,氡的超标率为20%。     

Subjective reactions to volatile organic compounds as air pollutants

Human subjective reactions to indoor air pollution in the form of volatile organic compounds in five concentrations ⩽ mg m⁻³ were examined in a climate chamber under controlled conditions in a balanced experimental design. The reactions of 25 subjects were registered in two questionnaires containing 25 and six questions and on a linear analogue rating scale. Each subject was tested for one day including four runs in each of the five treatments of 50 min duration. Dose effects were found for perceived odour intensity at 3 mgm⁻³. Air quality, need for ventilation, irritation of eye and nose showed significant effect at 8 mg m⁻³. Significant reduced well being was reported at 25 mgm⁻³. The analyses indicated that lower threshold for some of these effects would have been found if more subjects or longer exposure-times had been used. Gender, age, occupational education and smoking habits were co-factors for many of the symptoms reported.     

Transport and deposition of indoor radon decay products—I. Model development and validation

Commonly used mathematical models of indoor radon decay product behavior are based on macroscopic mass-balances, often referred to as ‘uniformly-mixed models’. The uniformly-mixed model's applicability is limited by its inability to track the movement of pollutants from their sources to other areas within the enclosure, to permit spatial- or time-dependent sources, or to take proper account of interactions with macroscopic surfaces. Although the uniformly-mixed model parameterizes the deposition process as a constant volumetric removal rate, in reality the deposition process is actually a surface phenomenon and is strongly affected by environmental conditions.This paper describes the development of RADTRAN, a two-dimensional radon progeny transport model that begins with the differential conservation equations describing the motion of air and the transport of reactive pollutants, introduces appropriate boundary conditions to represent surface deposition, and then calculates the concentration distribution of radon progeny throughout the entire region of interest. Knowing the concentration gradient near the surface, a local mass-transfer coefficient (the deposition velocity) can be determined as a function of environmental conditions. RADTRAN simulations have been based on several flow conditions: buoyancy-driven recirculating enclosure flows, free and forced-convection boundary layer flows, and one-dimensional diffusion. Free progeny diffusivity, D^f, and attachment rate, X, were varied over representative ranges. For these conditions, RADTRAN calculated free deposition velocities of u^f = 0.014–0.079 cm s⁻¹, for ²¹⁸Po. RADTRAN predictions are compared to a range of experimental measurements. It was found that the predicted range of deposition velocities is in rough agreement with findings from experiments conducted in flow conditions similar to the simplified flows used in RADTRAN.     

Rate constants for the gas-phase reactions of OH and NO3 radicals and O3 with sabinene and camphene at 296±2 K

The rate constants for the gas-phase reactions of sabinene and camphene, two monoterpenes emitted from vegetation, with OH and NO₃ radicals and O₃ have been determined at 296±2 K and one atmosphere total pressure of air. The OH and NO₃ radical reaction rate constants were determined using relative rate techniques. Using rate constants of k(OH + isoprene) = 1.01 × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, k(NO₃ + trans-2-butene) = 3.87 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ and k(NO₃ + 2-methyl-2-butene) = 9.33 × 10⁻¹² cm³ molecule⁻¹ s⁻¹, the following OH and NO₃ radical reaction rate constants (in cm³ molecule⁻¹ s⁻¹ were obtained: OH radical reaction; sabinene, 1.17 × 10⁻¹⁰ and camphene, 5.33 × 10⁻¹¹; NO₃ radical reaction; sabinene, 1.01 × 10⁻¹¹, and camphene, 6.54 × 10⁻¹³. The absolute O₃ reaction rate constants determined were (in cm³ molecule⁻¹ s⁻¹ units): sabinene, 8.07 × 10⁻¹⁷, and camphene, 9.0 × 10⁻¹⁹. These rate constants are compared to literature data for other structural-related alkenes and monoterpenes.     

Spatial and temporal patterns in nitrogen dioxide concentrations in a hot desert region

This paper reports seasonal and spatial variations in the ambient air concentration of nitrogen dioxide throughout the State of Bahrain, from February to December 1992. Monitoring sites were chosen to include urban areas with high traffic density, suburban areas with low traffic density, commercial and industrial areas. Correlations between meteorological parameters and mean NO₂ concentrations were analysed, and NO₂ levels were only significantly correlated with temperature (r = 0.63). Only February, a winter month, showed a significantly lower concentration of NO₂ with an overall mean value of 23 μgm⁻³, whereas in August, a summer month, it was 33 μgm⁻³. The results revealed that in a hot region like Bahrain, NO₂ concentrations do not show significant monthly variations. Also summer-averaged NO₂ values exceeded corresponding spring and winter values. In cold regions opposite patterns were observed. Moreover, the results revealed significant spatial variations in NO₂ concentrations. In suburban areas with low traffic density, the overall mean NO₂ level was 15, with a range of 12–17 μg m⁻³, while in urban areas with high traffic density, the overall mean value was 52 with a range of 44–60 μg m⁻³. The mean NO₂ value in industrial sites with low traffic density was 21 with a range of 14–27 μg m⁻³, whereas in the same areas near major roads, it was 32 with a range of 31–32 μg m⁻³. These results indicate that automobiles exhaust are the dominant source of NO₂ in Bahrain. The highest NO₂ levels were found in roads with high traffic density, which are narrow, with several traffic lights and roundabouts, suggesting the effect of road geometry on NO₂ levels.     

Human reactions to a mixture of indoor air volatile organic compounds

A controlled experimental study of human reactions to a mixture of 22 volatile organic compounds often found in indoor air was performed in a climate chamber. Twenty-one healthy subjects were compared with a group of 14 subjects suffering from the ‘sick building syndrome’ (SBS subjects), i.e. having symptoms related to the indoor environment (irritated mucous membranes, headache, etc.) as defined by WHO in 1982. In groups of 4 these subjects were exposed during two successive periods to either 0 and 0 mg m⁻³, 25 and 0 mg m⁻³, or 0 and 25 mg m⁻³; 25 mg m⁻³ is equivalent to the highest concentrations expected in a new building. The study was double blinded, and a latin square design was used to balance out effects of day in the week and season. Both groups reacted subjectively to the air reporting worse odor, worse indoor air quality as defined by the subject, and more irritated mucous membranes in eye, throat and nose than in the clean environment. A tendency to a stronger response was seen among the SBS subjects. Objective measures indicated among others an exposure related reduction in lung function among SBS subjects. Both groups had an increased number of polymorphonuclear leucocytes in tear fluid as a result of exposure. This was not seen for nasal secretions. Psychological performance tests indicated an exposure related diminished ability to learn. In conclusion, the experiment indicates that exposure to volatile organic compounds in low concentrations as seen in new houses causes both subjective complaints and objective signs in normal healty subjects; but more so in subjects from the sick building syndrome.     

恒电流模式下污泥电渗透的脱水性能及能耗分析

对传统机械脱水后的污泥采用电渗透技术进行二次脱水,在恒电流模式下研究了电流密度、机械压力、污泥厚度、初始含水率对脱水效率及能耗的影响.结果表明:在恒电流模式下,增加电流密度和初始含水率及降低污泥厚度对污泥电渗透脱水速率有促进作用.脱水后的最终含水率随着机械压力和初始含水率的增加及污泥厚度的降低而降低.电渗透脱水的最佳工艺参数为:电流密度为178.3 A·m~(-2),机械压力为31.4k Pa,污泥厚度为0.8 cm,初始含水率为81.5%,脱水后污泥的含水率可降至51. 3%.恒电流模式下污泥电渗透脱水单位能耗为0. 135～0. 269kW·h·kg~(-1),初始含水率对能耗影响最大,初始含水率每增加2%,单位能耗平均降低0.05 kW·h·kg~(-1).     

泉州湾洛阳江河口潮间带柱状沉积物铅同位素组成的变化与来源

不同源区铅同位素的组成不同,可以利用铅同位素的这种“指纹”特征来示踪铅的不同来源.泉州湾洛阳江河口潮间带柱状沉积物中,从底层到表层其铅同位素组成呈现出一定的变化规律,其中207 pb/204Pb呈上升趋势,206 Pb/2077 Pb和208 Pb/(2066pb+207 Pb)呈下降趋势.铅污染的来源主要与工业生产、污水排放和燃油尾气排放有关,受燃煤的影响很少,从底层到表层铅同位素组成的演化趋势为:由工业及污水排放逐渐向汽车尾气方向飘移结合定年分析,推断出油铅的污染起源于20世纪80年代中期,其污染呈不断加重趋势;其中表层沉积物中铅的污染受汽车尾气排放的影响最为严重.对不同时期沉积物中铅污染的来源及其相对贡献率研究表明,1973年到1984年间,沉积物受燃油铅的影响较少,其污染来源主要以工业污染为主,其贡献率占70％以上;1984到1994年间汽车尾气铅的贡献率迅速上升,占到了50％;而1996年到2008年汽车尾气铅的贡献率逐渐增加,由50％上升到了66％.     

垂直发射装置排气道极限承压性能分析

目的研究导弹在意外点火时排气道的力学性能及导弹发射的安全性,对排气道的极限承压性能进行研究。方法建立排气道的极限承压的仿真模型,通过水压试验及发射试验,获取排气道不同种试验方式下的极限承压数据。结果排气道在导弹正常发射时承压设计值为0.3 MPa。极限承压仿真试验过程中,排气道在受到0.5 MPa压强时,所受应力超过材料最大抗拉极限。水压试验过程中,排气道受0.58 MPa压强时,其结构发生破坏。意外点火试验过程中,排气道所受最大压强值为0.24 MPa。结论排气道的极限承压能力可以满足正常发射及意外点火的发射要求,排气道的设计裕量充足。     

Polynuclear aromatic hydrocarbon degradation by heterogeneous reactions with N2O5 on atmospheric particles

The degradation of particulate polynuclear aromatic hydrocarbons (PAH) on atmospheric soot particles in the presence of gas phase dinitrogen pentoxide (N₂O₅) was explored. Dilute diesel and wood soot particles containing PAH were reacted with∼10ppm of N₂O₅ in a 200 ℓ continuous stirred tank reactor (CSTR). To provide a stable source of particles for reaction in the CSTR, diesel or wood soot particles were injected at night into a 25 m³ Teflon outdoor chamber. The large chamber served as a reservoir for the feed aerosol, and the aerosol could then be introduced at a constant flow rate into the CSTR. PAH-N₂O₅ heterogeneous rate constants for wood soot at 15°C ranged from2 × 10⁻¹⁸to5 × 10⁻¹⁸ cm³ molecules⁻¹ s⁻¹. For diesel soot the rate constants at 16°C were higher and ranged from5 × 10⁻¹⁸to30 × 10⁻¹⁸ cm³ molecules⁻¹ s⁻¹. Comparisons with other studies suggest that sunlight is the most important factor which influences PAH decay. This is followed by ozone, NO₂, N₂O₅ and nitric acid. The rate constants of nitro-PAH formation from a parent PAH and N₂O₅ were of the order of1 × 10⁻¹⁹−1 × 10⁻¹⁸ molecules⁻¹s⁻¹. The uncertainty associated with all of these rate constants is± a factor of 3. Given, however, the small magnitude of the rate constants and the low levels of N₂O₅ present in the atmosphere, we concluded that PAH heterogeneous reactions with gas phase N₂O₅ degrade particle-bound PAH or to form nitro-PAH from PAH arenot very important. (Direct application of the specific rate constants derived in this study to ambient atmospheres should not be undertaken unless the ambient particle size distributions and chemical composition of the particles are similar to the ones reported in this study.)     

乌鲁木齐市民用住宅室内氡浓度水平调查研究

对乌鲁木齐市具有代表性的民用住宅室内氡浓度进行了连续一年的监测调查,调查结果显示室内氡浓度平均值55.4 Bq／m3,低于国标的“200 Bq／m3”,并据此估算出其所致居民的年均有效剂量为1.400 mSv,以及所致居民支气管上皮组织、肺、性腺、骨髓及骨表面细胞等关键组织的年吸收剂量分别为1886．49,378.96,2.80,3.20,3.20μGy／a,大于UNSCEAR2000年报告的世界平均值1.008 mSv,结合室内氡的主要来源,提出了对建筑材料进行放射性监测、控制装修、工程竣工后开展室内环境监测、加强室内通风以及开展室内氡污染治理等措施控制室内氡浓度水平。     

室内氡的危害及防氡降氡措施

氡及其子体是铀、钍等放射性元素产物，是引发肺癌的重要致病因子。居室高氡浓度易造成氡危害。不同地段房间的氡有不同的来源途径，它包括了氡的产生、向地表运移和进入室内的过程。本文将从室内氡的危害、致癌机理、氡的来源及防氡降氡等几个方面探讨居室氡的危害及其防治措施。     

Levels of airborne man-made mineral fibres in U.K. dwellings. I—Fibre levels during and after installation of insulation

This paper gives the details of airborne levels of man-made mineral fibres (MMMF) found during installation of loft insulation in 12 dwellings. About 250 samples of air were collected and analyzed by transmission electron microscopy (TEM).Respirable fibre levels measured in static samples collected in the lofts during installation generally were < 0.1 f ml⁻¹. In living spaces respirable fibre levels were< 0.006 f ml⁻¹. Personal samples on the installers gave < 1 f ml⁻¹, with the exception of a fine glass fibre blanket. A few selected samples were also analyzed by phase contrast optical microscopy (PCOM) which showed lower values than those recorded by TEM. Static gravimetric concentrations in the lofts were in the 0.3–6.5 mg m⁻³ range, and in the living spaces 0.11–0.44 mg m⁻³, but in both environments most of this dust was not MMMF.     

Wind tunnel experiments on the resuspension of particulate material

A programme of wind tunnel experiments has been carried out in which the resuspension of particulate material of four sizes (4, 10, 18 and 22 μm diameter) from concrete and grass surfaces has been studied. The importance of wind speed has been investigated and the time dependence of the resuspension rate has been evaluated for periods shortly after the onset of resuspension. The results indicate rapidly falling values of the resuspension rate which are approximately related to 1/time. The increase in the resuspension rate with increasing wind speed was most pronounced for large particles, leading to the conclusion that resuspension can be dominated by short-duration episodes which coincide with conditions that favour resuspension. Resuspension rates, averaged over approximately 1 h after the onset of conditions leading to resuspension, were in the range 1 × 10⁻⁶ to 5 × 10⁻⁶ s⁻¹, at moderate wind speeds (less than 5 m s⁻¹), with little difference between the grass and concrete surfaces. For high wind speeds (greater than 6.5 m s⁻¹), several per cent of the total surface deposit of 22 μ diameter particles was removed from both the concrete and grass surfaces within 10 s of the onset of wind.