Human breath emissions of VOCs.

The medical community has long recognized that humans exhale volatile organic compounds (VOCs). Several studies have quantified emissions of VOCs from human breath, with values ranging widely due to variation between and within individuals. The authors have measured human breath concentrations of isoprene and pentane. The major VOCs in the breath of healthy individuals are isoprene (12-580 ppb), acetone (1.2-1,880 ppb), ethanol (13-1,000 ppb), methanol (160-2,000 ppb) and other alcohols. In this study, we give a brief summary of VOC measurements in human breath and discuss their implications for indoor concentrations of these compounds, their contributions to regional and global emissions budgets, and potential ambient air sampling artifacts. Though human breath emissions are a negligible source of VOCs on regional and global scales (less than 4% and 0.3%, respectively), simple box model calculations indicate that they may become an important (and sometimes major) indoor source of VOCs under crowded conditions. Human breath emissions are generally not taken into account in indoor air studies, and results from this study suggest that they should be.     

光催化降解模拟室内挥发性有机污染物研究

用浸渍-提拉法制备玻璃弹簧负载型TiO2薄膜催化剂,在自制的反应器中进行光催化降解由丙酮、甲苯、对二甲苯组成的模拟室内挥发性有机污染物VOCs研究.研究发现:催化剂中掺杂金属离子能影响催化剂的降解效果,降解效果依次为掺铈TiO2＞纯TiO2＞掺银TiO2;气体流量显著影响降解效果,丙酮、甲苯和对二甲苯的最佳降解流量分别为3、5、7 L/min;混合气体中非对称性的极性分子的降解效率高于对称性分子,导致丙酮、对二甲苯组分降解率降低,甲苯降解率增高.     

VOCs in representative canadian residences

Stored extracts of passive samplers exposed in 757 randomly selected Canadian residences provided a unique opportunity for retrospective determination of the occurrence of airborne volatile organic compounds (VOCs). Aliquots of the individual extracts were pooled to form a composite exposure sample and a corresponding blank sample. To identify and quantitate potentially hazardous organics in the samples, GC-MS analyses were conducted by several approaches. The amounts of 52 target compounds in the the composite sample were estimated based on selected ion monitoring (SIM) results, extraction recoveries, average air volume sampled, and 3M OVM 3500 passive sampling rates. Forty of the organics were detected and were present in amounts equivalent to airborne concentrations ranging from <1 to 104 μg m⁻³. Several other compounds were also tentatively identified by full scan analysis. Many of the detected organics have been reported to be associated with activities such as tobacco smoking and the presence of consumer products and plastic materials indoors. The analytical results have been useful in risk assessments and establishment of a new Canadian priority substances list (PSL).     

Significance of Participate Emissions

The advancement of technology relating to participate emissions is pointed out as a significant aspect of this nation’s air pollution control efforts. Important factors include the ability of particulates: to cause poor visibility, to constitute a health hazard, to act as transport vehicles for gaseous pollutants, and (for some) to be highly active both chemically and catalytically. Attention is drawn to fine particulates (those with diameters less than about 3 microns) as an object of special attention within the general problem area. Recent EPA evaluations have indicated the effectiveness, under proper conditions, of advanced precipitators for fine particulate control.     

Modeling VOCs adsorption onto activated carbon

The activated carbon adsorption process is affected by the characteristics of adsorbent, adsorbate and environmental conditions. In this study, both adsorption and desorption processes are assumed to occur simultaneously and a numerical model was developed with a non-linear driving force in conjunction with the Langmuir model for predicting the overall adsorption process. The numerical model provides both adsorption and desorption rate constants and activation energies. The resultant equilibrium constants are of the same order of magnitude as reported by other studies. Results show that the model could well predict the adsorption isotherms and breakthrough curves under various conditions.     

Effects of Operating Variables on PAH Emissions and Mutagenicity of Emissions from Woodstoves

As part of the Integrated Air Cancer Project, the U.S. Environmental Protection Agency (EPA) has conducted field emission measurement programs in Raleigh, North Carolina, and Boise, Idaho, to identify the potential mutagenic Impact of residential wood burning and motor vehicles on ambient and indoor air. These studies included the collection of emission samples from chimneys serving wood burning appliances. Parallel projects were undertaken in Instrumented woodstove test laboratories to quantify woodstove emissions during operations typical of in-house usage but under more controlled conditions.

Three woodstoves were operated In test laboratories over a range of burnrates, burning eastern oak, southern yellow pine, or western white pine. Two conventional stoves were tested at an altitude of 90 m. One of the conventional stoves and a catalytic stove were tested at an altitude of 825 m.

Decreasing burnrate increased total paniculate emissions from the conventional stoves while the catalytic stove's total particulate emissions were unaffected. There was no correlation of total particulate emissions with altitude whereas total polynuclear aromatic hydrocarbon (PAH) emissions were higher at the lower altitude. Mutagenicity of the catalytic stove emissions was higher than emissions from the conventional stove. Emissions from burning pine were more mutagenic than emissions from oak.     

The Impact of Particulate Emissions Control On the Control of Other MWC Air Emissions

On December 20, 1989, the Environmental Protection Agency (EPA) proposed revised new source performance standards for new municipal waste combustion (MWC) units and guidelines for existing sources. The proposed national regulations require tighter particulate matter control and address pre-combustion, combustion, and post-combustion controls, the latter two depending on capacity and age of the facility.

The air pollutants of concern when municipal solid waste (MSW) is burned will be discussed. Generally, particulate control is an inherent part of the systems used to limit the emissions of these air pollutants. The relationships between MWC air emissions (acid gases, trace organics, and trace heavy metals) control and particulate control will be discussed. Test results to quantify air pollutant emissions from MWC units and their control will be presented and compared with the proposed regulations.     

The Significance of Particulate Emissions

Fine participates are the subject of increasing concern as one of the major air pollutants. They contribute to smog formation. They are a health hazard because they bypass the respiratory filters and penetrate deep into the lungs, and because they may act synergistically with other pollutants. The sources of submicron particle size pollutants are discussed.     

Quench Tower Particulate Emissions

Particulate emission sampling was conducted at Dofasco’s No. 2 Coke Want Quench Tower in August 1977. The sampling was performed by York Research Corporation using EPA developed quench tower sampling techniques. Particulate emissions averaged 0.245 lb/ton of coal over 17 tests. The mist eliminator in the tower consists of two rows of zig-zag baffles inclined at 20° from the vertical. Particle size data indicated that the majority of the particulate emissions were less than 10 microns in diameter. A mathematical model was used to predict the effect of particle size and gas velocity on collection efficiency. Pressure drop and re-entrainment are two restrictions which are considered in baffle design. Quench towers are the largest contributor to Dofasco’s allowable off-the-property suspended particulate impingement concentration.     

Continuous Measurement of Diesel Particulate Emissions

Evaluation of emerging diesel particulate emissions control technology will require analytical procedures capable of continuous or “real-time” measurement of transient organic and elemental carbon emissions. Procedures based on the flame ionlzation properties of organic carbon and the opacity or light extinction properties of elemental carbon are described, and applied for measurement of particulate emissions from diesel engines. The Instrumentation provided adequate sensitivity and time resolution for observation of the transient emissions associated with typical automobile urban driving conditions. Analytical accuracy is evaluated by comparing Integrated average results to measurements using classical gravimetric filtration and solvent extraction procedures. Mass specifc extinction coefficients are evaluated using the Beer-Lambert law. A simplified linear model relating elemental carbon concentration to opacity is also evaluated.     

NaY沸石分子筛在VOCs处理中的应用

为深入研究分子筛吸附VOCs的性能,采用固定床动态吸附法,对NaY分子筛吸附3种典型VOCs的性能进行了探究,考察了吸附温度、湿度、进气浓度和吸附质物理性质对吸附容量的影响,并探讨了NaY分子筛的循环使用性能;通过Yoon-Nelson模型,从吸附动力学角度,对单组分VOCs吸附穿透曲线进行了拟合。结果表明：NaY分子筛对3种VOCs的吸附饱和时间分别为丙酮355 min,邻二甲苯320 min,乙酸乙酯220 min;相对应的平衡吸附容量分别为丙酮176 mg·g⁻¹,邻二甲苯196 mg·g⁻¹,乙酸乙酯185 mg·g⁻¹。NaY分子筛对VOCs吸附能力排序为邻二甲苯>乙酸乙酯>丙酮。温度由303 K升至328 K时,3种VOCs吸附容量均分别下降,邻二甲苯下降3.66%,乙酸乙酯下降2.87%,丙酮下降10.0%;VOCs相对湿度为30%时,吸附容量显著降低;进气浓度为660 mg·m⁻³时,出现吸附交叉的现象;NaY分子筛具有较好的循环使用性;吸附容量与沸点、分子质量存在正相关关系;3种VOCs在NaY分子筛固定床的吸附速率排序为乙酸乙酯>邻二甲苯>丙酮。Yoon-Nelson模型能够较好地模拟NaY分子筛吸附不同VOCs的过程,为分子筛的工业应用提供了参考。     

Thermal and Catalytic Incinerators for the Control of VOCs

Abstract

The emission of Volatile Organic Compounds (VOCs) is attracting increasing concern both from the public and by government agencies. Among the many available control technologies for the treatment of VOC containing waste streams, incineration offers an ultimate disposal strategy rather than a means for collecting or concentrating the offending compounds. This paper describes the major, commercially available thermal and catalytic incinerator systems that are designed to treat dilute, VOC containing gas streams. Qualitative guidelines are presented whereby the technologies can be compared. In addition, an example waste stream is used to illustrate a simplified procedure for calculating the material and energy balances for each of the incinerators. The resulting parameters will be used in a companion paper to estimate the capital and operating costs associated with each design. In this manner, a first estimate can be obtained of the costs of cleaning a waste stream containing low levels of VOCs.     

新型管状光催化反应器降解VOCs特性

以一种新型折流式管状光催化反应器为研究对象,选择甲醛、苯和甲苯为目标污染物,以紫外光源、催化剂负载量和反应器内循环流量为关键影响因素,利用非密闭型环境舱,分析了反应器降解室内VOCs特性。结果表明,在254 nm和365 nm紫外光源照射下,VOCs的总衰减系数随初始浓度的增加而增大,且254 nm紫外光源照射下的总衰减系数更大。365 nm紫外光源照射时,VOCs的反应有效度随催化剂负载量的增加而增大;254 nm紫外光源照射时,反应有效度受催化剂负载量变化的影响很小。VOCs的转化率随循环流量的增加而增大,而反应速率受循环流量的影响较小;相同的循环流量下,转化率和反应速率均随着VOCs初始浓度增加而增大。由于增设肋片,折流式管状反应器比传统无肋片管状反应器的洁净空气量提升60%,且反应有效度更接近0.5,说明前者的传质-反应速率更加匹配,降解性能明显更优。     

Kinetics of photocatalytic VOCs abatement in a standardized reactor

A standardized micro-pilot scale continuous flow apparatus has been built up, using two types of differential photoreactors, and equipped with a refined control of the working conditions in order to study the photocatalytic degradation as a way to abate VOCs in air. Kinetic measurements have been carried out on trichloroethylene (TCE), methanol and benzene as model pollutants. The absence of diffusional limitation and of reaction product effect on the kinetics have both been demonstrated under our working conditions. The influences of concentration, light flux and temperature on the initial degradation rate have been studied. A simple Langmuir-Hinshelwood kinetic model has been verified for TCE and methanol, whereas benzene degradation was more complex and did not follow this simple mechanism. The determined experimental data aim at being useful in the scaling-up of photocatalytic reactors.     

生物法处理挥发性有机废气的研究

生物法处理被污染的空气这一技术已经被德国和荷兰成功地运用了 2 0年之久 ,但是在国内还属于一种较新的空气污染治理技术。本文主要概述了有机废气生物处理的 3种主要形式 :生物滤池、生物滴滤塔和生物洗涤器的原理、流程和几种影响反应器性能的因素 ,并比较了以上 3种反应器及其不同支撑材料的优缺点。目前 ,气态生物反应器主要以通用的指导方针、试验性的研究和来自类似应用的经验为基础进行设计的。     

Thermal and catalytic incinerators for the control of VOCs

The emission of Volatile Organic Compounds (VOCs) is attracting increasing concern both from the public and by government agencies. Among the many available control technologies for the treatment of VOC containing waste streams, incineration offers an ultimate disposal strategy rather than a means for collecting or concentrating the offending compounds. This paper describes the major, commercially available thermal and catalytic incinerator systems that are designed to treat dilute, VOC containing gas streams. Qualitative guidelines are presented whereby the technologies can be compared. In addition, an example waste stream is used to illustrate a simplified procedure for calculating the material and energy balances for each of the incinerators. The resulting parameters will be used in a companion paper to estimate the capital and operating costs associated with each design. In this manner, a first estimate can be obtained of the costs of cleaning a waste stream containing low levels of VOCs.