Emission factors of air toxics from semiconductor manufacturing in Korea

The development of local, accurate emission factors is very important for the estimation of reliable national emissions and air quality management. For that, this study is performed for pollutants released to the atmosphere with source-specific emission tests from the semiconductor manufacturing industry. The semiconductor manufacturing industry is one of the major sources of air toxics or hazardous air pollutants (HAPs); thus, understanding the emission characteristics of the emission source is a very important factor in the development of a control strategy. However, in Korea, there is a general lack of information available on air emissions from the semiconductor industry. The major emission sources of air toxics examined from the semiconductor manufacturing industry were wet chemical stations, coating applications, gaseous operations, photolithography, and miscellaneous devices in the wafer fabrication and semiconductor packaging processes. In this study, analyses of emission characteristics, and the estimations of emission data and factors for air toxics, such as acids, bases, heavy metals, and volatile organic compounds from the semiconductor manufacturing process have been performed. The concentration of hydrogen chloride from the packaging process was the highest among all of the processes. In addition, the emission factor of total volatile organic compounds (TVOCs) for the packaging process was higher than that of the wafer fabrication process. Emission factors estimated in this study were compared with those of Taiwan for evaluation, and they were found to be of similar level in the case of TVOCs and fluorine compounds.     

Estimation of the rate of VOC emissions from solvent-based indoor coating materials based on product formulation

Two computational methods are proposed for estimation of the emission rate of volatile organic compounds (VOCs) from solvent-based indoor coating materials based on the knowledge of product formulation. The first method utilizes two previously developed mass transfer models with two key parameters – the total vapor pressure and the average molecular weight for total volatile organic compounds (TVOCs) – being estimated based on the VOC contents in the product. The second method is based on a simple, first-order decay model with its parameters being estimated from the properties of both the source and the environment. All the model parameters can be readily obtained. Detailed procedures for computing the key parameters are described by using examples. The predictive errors were evaluated with small chamber data, and the results were satisfactory. Thus, the proposed methods provide a way to predict the VOC emissions in the indoor environment without having to conduct costly chamber testing. The two proposed methods work for both TVOCs and individual VOCs. Pros and cons for each method are discussed.     

Emission Factors of Air Toxics from Semiconductor Manufacturing in Korea

Abstract

The development of local, accurate emission factors is very important for the estimation of reliable national emissions and air quality management. For that, this study is performed for pollutants released to the atmosphere with source-specific emission tests from the semiconductor manufacturing industry. The semiconductor manufacturing industry is one of the major sources of air toxics or hazardous air pollutants (HAPs); thus, understanding the emission characteristics of the emission source is a very important factor in the development of a control strategy. However, in Korea, there is a general lack of information available on air emissions from the semiconductor industry. The major emission sources of air toxics examined from the semiconductor manufacturing industry were wet chemical stations, coating applications, gaseous operations, photolithography, and miscellaneous devices in the wafer fabrication and semiconductor packaging processes. In this study, analyses of emission characteristics, and the estimations of emission data and factors for air toxics, such as acids, bases, heavy metals, and volatile organic compounds from the semiconductor manufacturing process have been performed. The concentration of hydrogen chloride from the packaging process was the highest among all of the processes. In addition, the emission factor of total volatile organic compounds (TVOCs) for the packaging process was higher than that of the wafer fabrication process. Emission factors estimated in this study were compared with those of Taiwan for evaluation, and they were found to be of similar level in the case of TVOCs and fluorine compounds.     

Emission of air pollutants from burning candles with different composition in indoor environments

Candle composition is expected to influence the air pollutants emissions, possibly leading to important differences in the emissions of volatile organic compounds and polycyclic aromatic hydrocarbons. In this regard, the purity of the raw materials and additives used can play a key role. Consequently, in this work emission factors for some polycyclic aromatic hydrocarbons, aromatic species, short-chain aldehydes and particulate matter have been determined for container candles constituted by different paraffin waxes burning in a test chamber. It has been found that wax quality strongly influences the air pollutant emissions. These results could be used, at least at a first glance, to foresee the expected pollutant concentration in a given indoor environment with respect to health safety standards, while the test chamber used for performing the reported results could be useful to estimate the emission factors of any other candle in an easy-to-build standardised environment.     

Emission of non-methane volatile organic compounds (VOCs) from boreal peatland microcosms—effects of ozone exposure

Non-methane volatile organic compounds (VOCs) emitted from boreal peatland microcosms were semiquantitatively determined using gas chromatography–mass spectrometry techniques in a growth chamber experiment. Furthermore, effects of vegetation composition and different ozone concentrations on these emissions were estimated by multivariate data analyses. The study concentrated on the less-studied VOCs, and isoprene was not analyzed. The analyses suggest that a sedge Eriophorum vaginatum is associated with emissions of the four most-emitted VOC groups (cyclic, aromatic, carbonyl and aliphatic hydrocarbon compounds) and also with VOCs emitted in smaller amounts (terpenoids and N-containing compounds). A woody dwarf shrub Andromeda polifolia was strongly associated with emissions of aromatic, carbonyl and terpenoid compounds. Results suggest that exposure to an ozone concentration of 150 ppb leads to an increased emission of most VOC groups. Emission of aromatic compounds seems to increase linearly with increasing ozone concentration. These observations indicate that peatlands may be a source of a vast range of volatile compounds to the atmosphere. For more accurate assessment of the impact of elevated tropospheric ozone on the terpenoid and non-terpenoid VOC emissions from peatlands, well-replicated open-air ozone-exposure experiments should be conducted.     

Approaches for quantifying reactive and low-volatility biogenic organic compound emissions by vegetation enclosure techniques - part B: applications

The focus of the studies presented in the preceding companion paper (Part A: Review) and here (Part B: Applications) is on defining representative emission rates from vegetation for determining the roles of biogenic volatile organic compound (BVOC) emissions in atmospheric chemistry and aerosol processes. The review of previously published procedures for identifying and quantifying BVOC emissions has revealed a wide variety of experimental methods used by various researchers. Experimental details become increasingly critical for quantitative emission measurements of low volatility monoterpenes (MT) and sesquiterpenes (SQT). These compounds are prone to be lost inadvertently by uptake to materials in contact with the sample air or by reactions with atmospheric oxidants. These losses become more prominent with higher molecular weight compounds, potentially leading to an underestimation of their emission rates. We present MT and SQT emission rate data from numerous experiments that include 23 deciduous tree species, 14 coniferous tree species, 8 crops, and 2 shrubs. These data indicate total, normalized (30 degrees C) basal emission rates from <10 to 5600ngCg(-1)h(-1) for MT, and from <10 to 1150ngCg(-1)h(-1) for SQT compounds. Both MT and SQT emissions have exponential dependencies on temperature (i.e. rates are proportional to e(betaT)). The inter-quartile range of beta-values for MT was between 0.12 and 0.17K(-1), which is higher than the value commonly used in models (0.09K(-1)). However many of the MT emissions also exhibited light dependencies, making it difficult to separate light and temperature influences. The primary light-dependent MT was ocimene, whose emissions were up to a factor of 10 higher than light-independent MT emissions. The inner-quartile range of beta-values for SQT was between 0.15 and 0.21K(-1).     

Development of emission factors for polycarbonate processing

Emission factors for selected volatile organic compounds (VOCs) and particulate emissions were developed while processing eight commercial grades of polycarbonate (PC) and one grade of a PC/acrylonitrile-butadiene-styrene (ABS) blend. A small commercial-type extruder was used, and the extrusion temperature was held constant at 304 degrees C. An emission factor was calculated for each substance measured and is reported as pounds released to the atmosphere/million pounds of polymer resin processed [ppm (wt/wt)]. Scaled to production volumes, these emission factors can be used by processors to estimate emission quantities from similar PC processing operations.     

Effect of vegetation removal and water table drawdown on the non-methane biogenic volatile organic compound emissions in boreal peatland microcosms

Biogenic volatile organic compound (BVOC) emissions are important in the global atmospheric chemistry and their feedbacks to global warming are uncertain. Global warming is expected to trigger vegetation changes and water table drawdown in boreal peatlands, such changes have only been investigated on isoprene emission but never on other BVOCs. We aimed at distinguishing the BVOCs released from vascular plants, mosses and peat in hummocks (dry microsites) and hollows (wet microsites) of boreal peatland microcosms maintained in growth chambers. We also assessed the effect of water table drawdown (?20 cm) on the BVOC emissions in hollow microcosms. BVOC emissions were measured from peat samples underneath the moss surface after the 7-week-long experiment to investigate whether the potential effects of vegetation and water table drawdown were shown. BVOCs were sampled using a conventional chamber method, collected on adsorbent and analyzed with GC–MS. In hummock microcosms, vascular plants increased the monoterpene emissions compared with the treatment where all above-ground vegetation was removed while no effect was detected on the sesquiterpenes, other reactive VOCs (ORVOCs) and other VOCs. Peat layer from underneath the surface with intact vegetation had the highest sesquiterpene emissions. In hollow microcosms, intact vegetation had the highest sesquiterpene emissions. Water table drawdown decreased monoterpene and other VOC emissions. Specific compounds could be closely associated to the natural/lowered water tables. Peat layer from underneath the surface of hollows with intact vegetation had the highest emissions of monoterpenes, sesquiterpenes and ORVOCs whereas water table drawdown decreased those emissions. The results suggest that global warming would change the BVOC emission mixtures from boreal peatlands following changes in vegetation composition and water table drawdown.     

Effect of bubble-induced surface turbulence on gas-liquid mass transfer in diffused aeration systems.

Models that predict volatilization of organic compounds from wastewater treatment basins may underestimate emission rates if the surfaces are considered as quiescent. In reality, the water surface may be agitated by subsurface aeration, increasing mass transfer across the tank surface air-water interface. This study investigated the effect of turbulence, induced by diffused bubble aeration, on mass transfer at the water surface of a pilot aeration basin. The mass transfer of ammonia from an enclosed headspace over the basin to acidified water was measured when different diffuser types and airflow rates were applied. Oxygen-transfer tests were conducted immediately following each ammonia-transfer test. Increasing airflow rates through fine- and coarse-bubble diffusers had a significant effect on the ammonia mass-transfer rate. Experimental mass-transfer parameters (K(L)a's) for surface volatilization derived with aeration present were up to 48% higher than the K(L)a values for quiescent conditions over the range of conditions tested. No effect of diffuser type on ammonia transfer could be determined. The study results infer an effect on oxygen transfer into the water at the surface and potential transfer of volatile organic compounds, if present, from the water. The results of the ammonia mass-transfer experiments suggest that adjustments to the existing mass transfer correlations for surface volatilization from aeration basins may be in order. Such adjustments will have the greatest effect on predictions for the less volatile compounds, under conditions of low airflow rates.     

Evaluation of total volatile organic compound emissions from adhesives based on chamber tests

In 1997, Homeswest in western Australia and Murdoch University developed a project to construct low-allergen houses (LAHs) in a newly developed suburb. Before the construction of LAHs, all potential volatile organic compound (VOC) emission materials used in LAHs are required to be measured to ensure that they are low total VOC (TVOC) emission materials. This program was developed based on this purpose. In recent times, the number of complaints about indoor air pollution caused by VOCs has increased. A number of surveys of indoor VOCs have indicated that many indoor materials contribute to indoor air pollution. Although some studies have been conducted on the characteristics of VOC emissions from adhesives, most of them were focused on VOC emissions from floor adhesives. Few measurements of VOC emissions from adhesives used for wood, fabrics, and leather are available. Furthermore, most research on VOC emissions from adhesives has been done in countries with cool climates, where ventilation rates in the indoor environment are lower than those in Mediterranean climates, due to energy conservation. VOCs emitted from adhesives have not been sufficiently researched to prepare an emission inventory to predict indoor air quality and to determine both exposure levels for the Australian population and the most appropriate strategies to reduce exposure. An environmental test chamber with controlled temperature, relative humidity, and airflow rate was used to evaluate emissions of TVOCs from three adhesives used frequently in Australia. The quantity of TVOC emissions was measured by a gas chromatography/flame ionization detector. The primary VOCs emitted from each adhesive were detected by gas chromatography/mass spectrometry. The temporal change of TVOC concentrations emitted from each adhesive was tested. A double-exponential equation was then developed to evaluate the characteristics of TVOC emissions from these three adhesives. With this double-exponential model, the physical processes of TVOC emissions can be explained, and a variety of emission parameters can be calculated. These emission parameters could be used to estimate real indoor TVOC concentrations in Mediterranean climates.     

Development of Emission Factors for Polycarbonate Processing

Abstract

Emission factors for selected volatile organic compounds (VOCs) and particulate emissions were developed while processing eight commercial grades of polycarbonate (PC) and one grade of a PC/acrylonitrile-butadiene-styrene (ABS) blend. A small commercial-type extruder was used, and the extrusion temperature was held constant at 304 °C. An emission factor was calculated for each substance measured and is reported as pounds released to the atmosphere/million pounds of polymer resin processed [ppm (wt/wt)]. Scaled to production volumes, these emission factors can be used by processors to estimate emission quantities from similar PC processing operations.     

Indoor Emissions from Conversion Varnishes

ABSTRACT

Conversion varnishes are two-component, acid-catalyzed varnishes that are commonly used to finish cabinets. They are valued for their water and stain resistance, as well as their appearance. They have been found, however, to contribute to indoor emissions of organic compounds. For this project, three commercially available conversion varnish systems were selected. A U.S. Environmental Protection Agency (EPA) Method 24 analysis was performed to determine total volatile content, and a sodium sulfite titration method was used to determine uncombined (free) formaldehyde content of the varnish components. The resin component was also analyzed by gas chromatography/mass spectroscopy (GC/MS) (EPA Method 311 with an MS detector) to identify individual organic compounds. Dynamic small chamber tests were then performed to identify and quantify emissions following application to coupons of typical kitchen cabinet wood substrates, during both curing and aging. Because conversion varnishes cure by chemical reaction, the compounds emitted during curing and aging are not necessarily the same as those in the formulation. Results of small chamber tests showed that the amount of formaldehyde emitted from these coatings was 2.3–8.1 times the amount of free formaldehyde applied in the coatings. A long-term test showed a formaldehyde emission rate of 0.17 mg/m²/hr after 115 days.     

Improved land cover and emission factors for modeling biogenic volatile organic compounds emissions from Hong Kong

This paper describes a study of local biogenic volatile organic compounds (BVOC) emissions from the Hong Kong Special Administrative Region (HKSAR). An improved land cover and emission factor database was developed to estimate Hong Kong emissions using MEGAN, a BVOC emission model developed by Guenther et al. (2006). Field surveys of plant species composition and laboratory measurements of emission factors were combined with other data to improve existing land cover and emission factor data. The BVOC emissions from Hong Kong were calculated for 12 consecutive years from 1995 to 2006. For the year 2006, the total annual BVOC emissions were determined to be 12,400 metric tons or 9.82 × 10⁹ g C (BVOC carbon). Isoprene emission accounts for 72%, monoterpene emissions account for 8%, and other VOCs emissions account for the remaining 20%. As expected, seasonal variation results in a higher emission in the summer and a lower emission in the winter, with emission predominantly in day time. A high emission of isoprene occurs for regions, such as Lowest Forest-NT North, dominated by broadleaf trees. The spatial variation of total BVOC is similar to the isoprene spatial variation due to its high contribution. The year to year variability in emissions due to weather was small over the twelve-year period (?1.4%, 2006 to 1995 trendline), but an increasing trend in the annual variation due to an increase in forest land cover can be observed (+7%, 2006 to 1995 trendline). The results of this study demonstrate the importance of accurate land cover inputs for biogenic emission models and indicate that land cover change should be considered for these models.     

Measurement of Indoor Air Emissions from Dry-Process Photocopy Machines

Abstract

Presently, no standard test method exists to evaluate the various emissions from office equipment (e.g., ozone, volatile organic compounds, inorganic gases, and particulates) so it is difficult to compare data from different studies.1 As a result, the authors are developing a standardized guidance document for measuring indoor air emissions from office equipment. The ultimate goal is to apply the test method to better understand emissions from office equipment and to develop lower emitting machines. This paper provides background information on indoor air emissions from office equipment with an emphasis on dry-process photocopy machines. The test method is described in detail, along with the results of a study to evaluate the test method using four dry-process photocopy machines.

The results from this study indicate that the test method provides acceptable performance for characterizing emissions; that it can adequately identify differences in emissions between machines both in compounds emitted and their emission rates; and that it is capable of measuring both intra- and inter-machine variability in emissions. Challenges and complications were encountered in developing and implementing the test method. These included heat generation, which can cause large increases in chamber temperature; finite paper supplies for photocopy machines, which limit test duration; varying power requirements that may require changes in chamber electrical supply; and remote starting of the machines, which is necessary to maintain chamber integrity.

Results show that dry-process photocopy machines can produce emissions of ozone and volatile organic compounds that can potentially have a significant impact on indoor air quality. For the four machines tested in this study, the compounds with the highest emission rates overall were ethylbenzene (28,000 µg/hour), m,p-xylenes (29,000 µg/hour), o-xylene (17,000 µg/hour), 2-ethyl-lhexanol (14,000 µg/hour), and styrene (12,000 fig/hour). Although many of the same compounds tended to be detected in emissions from each of the four photocopiers, the relative contribution of individual compounds varied considerably between machines, with differences greater than an order of magnitude for some compounds.     

The Role of Viscosity in Fabric Filtration

Abstract

An approach for measuring point-source emissions of volatile organic compounds (VOCs), acidic vapors, and other species is presented. The amount emitted is determined by directly measuring the actual weight gain of an adsorbent bed over a period of time, which is a cumulative rather than a grabbed sample. As a result, wide fluctuations of concentration and erratic flow behavior during sampling are accommodated with no apparent effect on the accuracy of the measured emission rate. The emission rate is determined by a mass balance including the mass change of the sorbent, as well as the influent and effluent humidities.

Validation tests used a known mass flow rate of vapor in a carrier gas, which was compared with the amount measured. The vapor was a single VOC, a mixture of VOCs, or a mixture of a VOC with water. Conditions studied were the compound or mixture of compounds, concentration, carrier gas, flow rate, and adsorbent. In some tests the VOC was admitted intermittently. The VOCs included n-hexane, acetone, toluene, vinyl acetate, and 1,1,1 trichloroethane. For 105 tests, the average absolute discrepancy of the delivered and measured emission rates was 6.8% and the standard deviation was 3.4%.     

Aerostat-lofted instrument and sampling method for determination of emissions from open area sources

An aerostat-borne instrument and sampling method was developed to characterize air samples from area sources, such as emissions from open burning. The 10 kg battery-powered instrument system, termed “the Flyer”, is lofted with a helium-filled aerostat of 4 m nominal diameter and maneuvered by means of one or two tethers. The Flyer can be configured variously for continuous CO₂ monitoring, batch sampling of semi-volatile organic compounds (SVOCs), volatile organic compounds (VOCs), black carbon, metals, and PM by size. The samplers are controlled by a trigger circuit to avoid unnecessary dilution from background sampling when not within the source plume. The aerostat/Flyer method was demonstrated by sampling emissions from open burning (OB) and open detonation (OD) of military ordnance. A carbon balance approach was used to derive emission factors that showed excellent agreement with published values.     

Testing VOC emission measurement techniques in wood-coating industrial processes and developing a cost-effective measurement methodology

Availability of reliable emission measurements of concentrated volatile organic compounds (VOCs) bear great significance in facilitating the selection of a feasible emission abatement technique. There are numerous methods, which can be used to measure VOC emissions, however, there is no single method that would allow sampling of the whole range of volatile organics. In addition, research efforts are usually directed to the development of measuring VOCs in diluted concentrations. Therefore, there is a need for a novel measurement method, which can give reliable results while entailing simple operations and low costs. This paper represents a development effort of finding a reliable measurement procedure. A methodology is proposed and used to measure solvent emissions from coating processes.     

Attitudes and Responses Towards Air Pollution in Medieval England

ABSTRACT

The concentrations of contaminants in the supply air of mechanically ventilated buildings may be altered by pollutant emissions from and interactions with duct materials. We measured the emission rate of volatile organic compounds (VOCs) and aldehydes from materials typically found in ventilation ducts. The emission rate of VOCs per exposed surface area of materials was found to be low for some duct liners, but high for duct sealing caulk and a neo-prene gasket. For a typical duct, the contribution to VOC concentrations is predicted to be only a few percent of common indoor levels. We exposed selected materials to ~100-ppb ozone and measured VOC emissions. Exposure to ozone increased the emission rates of aldehydes from a duct liner, duct sealing caulk, and neoprene gasket. The emission of aldehydes from these materials could increase indoor air concentrations by amounts that are as much as 20% of odor thresholds. We also measured the rate of ozone uptake on duct liners and galvanized sheet metal to predict how much ozone might be removed by a typical duct in ventilation systems. For exposure to a constant ozone mol fraction of 37 ppb, a lined duct would initially remove ~9% of the ozone, but over a period of 10 days the ozone removal efficiency would diminish to less than 4%. In an unlined duct, in which only galvanized sheet metal is exposed to the air-stream, the removal efficiency would be much lower, ~0.02%. Therefore, ducts in ventilation systems are unlikely to be a major sink for ozone.     

Determination of 5-ethylidene-2-norbornene in industrial emission

A method to measure the emissive concentration of 5-ethylidene-2-norbornene (ENB), a reactive compound used in industrial synthesis of terpolymers, has been developed. The starting points for the development of the presented method are European and Italian reference methods for the quantification of nonreactive volatile organic compounds in industrial emission. In this study, sampling conditions and desorption solvent have been optimized in laboratory and the method was applied in an industrial plant. The laboratory tests showed a good recovery (88–95 %). The concentrations of ENB in industrial emission obtained with the developed method were compared with an online gas chromatography–flame ionization results (R ²?>?0.97). In addition, several manual measurements were performed in parallel, and the resulting %RSD repeatability was <9 %. The developed method provides a discontinuous technique to measure reactive volatile organic compounds using easy-to-use instruments and assures a very good accuracy and precision even with high-humidity gas flows. The method could be extended to other reactive compounds of the same class.     

Volatile organic compounds from leaves litter

Qualitative composition of volatile emissions of litter of five species of deciduous trees was investigated by GC-MS. The list of identified substances contains more than 70 organic compounds of various classes. It was established that the composition of components emitted by the litter into the gas phase greatly differs from that of essential oils extracted by hydrodistillation from turned leaves collected from trees during fall. It is suggested that most compounds found in litter emissions are products of vital activity of microorganisms decomposing it. The reported data indicate that after the vegetative period is over the decomposition processes of litter are important seasonal sources of reactive organic compounds under the forest canopy.