Henry's law constant and overall mass transfer coefficient for formaldehyde emission from small water pools under simulated indoor environmental conditions.

The Henry's law constant (HLC) and the overall mass transfer coefficient are both important parameters for modeling formaldehyde emissions from aqueous solutions. In this work, the apparent HLCs for formaldehyde aqueous solutions were determined in the concentration range from 0.01% to 1% (w/w) and at different temperatures (23, 40, and 55 °C) by a static headspace extraction method. The aqueous solutions tested included formaldehyde in water, formaldehyde-water with nonionic surfactant Tergitol NP-9, and formaldehyde-water with anionic surfactant sodium dodecyl sulfate. Overall, the measured HLCs ranged from 8.33 × 10(-6) to 1.12 × 10(-4) (gas-concentration/aqueous-concentration, dimensionless). Fourteen small-chamber tests were conducted with formaldehyde solutions in small pools. By applying the measured HLCs, the formaldehyde overall liquid-phase mass transfer coefficients (KOLs) were determined to be in the range of 8.12 × 10(-5) to 2.30 × 10(-4) m/h, and the overall gas-phase mass transfer coefficients were between 2.84 and 13.4 m/h. The influences of the formaldehyde concentration, temperature, agitation rate, and surfactant on HLC and KOL were investigated. This study provides useful data to support source modeling for indoor formaldehyde originating from the use of household products that contain formaldehyde-releasing biocides.

Modeling small-scale spills of aqueous solutions in the indoor environment.

A mass transfer model is proposed to estimate the rates of chemical emissions from aqueous solutions spilled on hard surfaces inside buildings. The model is presented in two forms: a set of four ordinary differential equations and a simplified exact solution. The latter can be implemented in a spreadsheet. User input includes ten parameters, which represent either the properties of the source or those of the building. All of them can be readily obtained. The proposed model is tested against and in good agreement with the measurements of simulated spill events in a room-sized environmental chamber. This model can be used by emergency response planners to estimate the time history of contaminant concentrations in indoor air.

Laboratory study of PCB transport from primary sources to settled dust.

Dust is an important sink for indoor air pollutants, such as polychlorinated biphenyls (PCBs) that were used in building materials and products. In this study, two types of dust, house dust and Arizona Test Dust, were tested in a 30-m(3) stainless steel chamber with two types of panels. The PCB-containing panels were aluminum sheets coated with a PCB-spiked primer or caulk. The PCB-free panels were coated with the same materials but without PCBs. The dust evenly spread on each panel was collected at different times to determine its PCB content. The data from the PCB panels were used to evaluate the PCB migration from the source to the dust through direct contact, and the data from the PCB-free panels were used to evaluate the sorption of PCBs through the dust/air partition. Settled dust can adsorb PCBs from air. The sorption concentration was dependent on the congener concentration in the air and favored less volatile congeners. When the house dust was in direct contact with the PCB-containing panel, PCBs migrated into the dust at a much faster rate than the PCB transfer rate due to the dust/air partition. The dust/source partition was not significantly affected by the congener's volatility. For a given congener, the ratio between its concentration in the dust and in the source was used to estimate the dust/source partition coefficient. The estimated values ranged from 0.04 to 0.16. These values are indicative of the sink strength of the tested house dust being in the middle or lower-middle range.

Determination of fluorotelomer alcohols in selected consumer products and preliminary investigation of their fate in the indoor environment.

The U.S. Environmental Protection Agency (EPA) has established an ongoing effort to identify the major perfluorocarboxylic acid (PFCA) sources in nonoccupational indoor environments and characterize their transport and fate. This study determined the concentrations of fluorotelomer alcohols (FTOHs), which are the precursors to PFCAs, in fifty-four consumer products collected from the U.S. open market in the years of 2011 and 2013. The products included carpet, commercial carpet-care liquids, household carpet/fabric-care liquids, treated apparel, treated home textiles, treated non-woven medical garments, floor waxes, food-contact paper, membranes for apparel, and thread-sealant tapes. The FTOHs quantified were 1H,1H,2H,2H-perfluoro-1-octanol (6:2 FTOH), 1H,1H,2H,2H-perfluoro-1-decanol (8:2 FTOH), and 1H,1H,2H,2H-perfluoro-1-dodecanol (10:2 FTOH). The content of 6:2 FTOH ranged from non-delectable to 331µgg(-1), 8:2 FTOH from non-delectable to 92µgg(-1), and 10:2 FTOH from non-detectable to 24µgg(-1). In addition, two consumer products from the home textile category were tested in the washing-drying process. One product from the treated apparel category and one from the home textile category were tested in the micro-scale chamber under elevated temperatures. The experimental data show that the washing-drying process with one cycle did not significantly reduce the FTOH concentrations in the tested consumer products. FTOH off-gassing was observed under accelerated aging conditions. Future tests should include air sampling to allow determination of the absolute emission rates at different temperatures. The results of this study should be informative to exposure assessment and risk management.

Chamber study of PCB emissions from caulking materials and light ballasts.

The emissions of polychlorinated biphenyl (PCB) congeners from thirteen caulk samples were tested in a micro-chamber system. Twelve samples were from PCB-contaminated buildings and one was prepared in the laboratory. Nineteen light ballasts collected from buildings that represent 13 different models from five manufacturers were tested in 53-L environmental chambers. The rates of PCB congener emissions from caulking materials and light ballasts were determined. Several factors that may have affected the emission rates were evaluated. The experimentally determined emission factors showed that, for a given PCB congener, there is a linear correlation between the emission factor and the concentration of the PCB congener in the source. Furthermore, the test results showed that an excellent log-linear correlation exists between the normalized emission factor and the vapor pressure (coefficient of determination, r(2)⩾0.8846). The PCB congener emissions from ballasts at or near room temperature were relatively low with or without electrical load. However, the PCB congener emission rates increased significantly as the temperature increased. The results of this research provide new data and models for ranking the primary sources of PCBs and supports the development and refinement of exposure assessment models for PCBs.

Review of indoor emission source models. Part 1. Overview.

Indoor emission source models are mainly used as a component in indoor air quality (IAQ) modeling, which, in turn, is part of exposure and risk modeling. They are also widely used to interpret the experimental data obtained from environmental chambers and buildings. This paper compiles 52 indoor emission source models found in the literature. Together, they represent the achievements that IAQ modelers have made in recent years. While most models have a certain degree of usefulness, genuine predictive models are still few, and there is undoubtedly much room for improvement. This review consists of two parts. Part 1--this paper-provides an overview of the 52 models, briefly discussing their validity, usefulness, limitations, and flaws (if any). Part 2 focuses on parameter estimation, a topic that is critically important to modelers but has not been systematically discussed.

Review of indoor emission source models. Part 2. Parameter estimation.

This review consists of two parts. Part 1 provides an overview of 52 indoor emission source models. Part 2--this paper-focuses on parameter estimation, a topic that is critical to modelers but has never been systematically discussed. A perfectly valid model may not be a useful one if some of its parameters are difficult to estimate in the absence of experimental data. This is true for both statistical and mass transfer models. Forty-eight methods are compiled and reviewed in this paper. Overall, developing methods for parameter estimation has fallen behind the development of models. Such imbalance is the main reason that many models have been left on the shelf since they were published.

Characterization of emissions from burning incense.

The primary objective of this study was to improve the characterization of particulate matter emissions from burning incense. Emissions of particulate matter were measured for 23 different types of incense using a cyclone/filter method. Emission rates for PM2.5 (particulate matter less than 2.5 microm in aerodynamic diameter) ranged from 7 to 202 mg/h, and PM2.5 emission factors ranged from 5 to 56 mg/g of incense burned. Emission rates were also determined using an electrical low pressure impactor (ELPI) and a small electrostatic precipitator (ESP), and emission rates were compared to those determined using the cyclone/filter method. Emission rates determined by the ELPI method were consistently lower than those determined by the cyclone/filter method, and a linear regression correlation was found between emission rates determined by the two methods. Emission rates determined by the ESP method were consistently higher than those determined by the cyclone/filter method, indicating that the ESP may be a more effective method for measuring semivolatile particle emissions. A linear regression correlation was also found between emission rates determined by the ESP and cyclone/filter methods. Particle size distributions were measured with the ELPI, and distributions were found to be similar for most types of incense that were tested. Size distributions by mass typically ranged from approximately 0.06 to 2.5 microm in aerodynamic diameter, with peak values between 0.26 and 0.65 microm. Results indicated that burning incense emits fine particulate matter in large quantities compared to other indoor sources. An indoor air quality model showed that indoor concentrations of PM25 can far exceed the outdoor concentrations specified by the US EPA's National Ambient Air Quality Standards (NAAQS), so incense smoke can pose a health risk to people due to inhalation exposure of particulate matter. Emissions of carbon monoxide (CO), nitric oxide (NO), and sulfur dioxide (SO2) were also measured for seven types of incense. Emission rates of the gaseous pollutants were sufficient to cause indoor concentrations, estimated using the indoor air quality model, to exceed the outdoor concentrations specified by the NAAQS under certain conditions. However, the incense samples that were tested would fill a room with thick smoke under these conditions.

Lead in candle emissions.

The candle-using public should be made aware that the core of candle wicks may contain lead. Used as a stiffening agent to keep the wick out of the molten wax, lead can be emitted as particulates to the air and then deposited on indoor surfaces. To define the problem, 100 sets of candles (two or more identical candles) were purchased locally. The criterion for purchase was that the candles must appear to contain a metal-cored wick or be covered by a metallic pigment. Of the candles purchased, 8% contained lead wicks. The wicks were 39-74% lead (the remainder was fabric or paper) and the lead cores (approx. 100% lead) had linear densities of 13-27 mg/cm. Candles were burned to completion in a closed chamber to capture the air emissions, and the candle residue was extracted to assess the lead mass balance. It was found that individual candles emitted lead to the air at average rates that ranged from 100 to 1700 microg/h. Assuming realistic indoor conditions, these emission rates were modeled to project room air concentration, child exposure by inhalation, and indoor deposition. Results showed that burning single candles can easily raise the source room concentration above the ambient air lead concentration limit of 1.5 microg/m3 set by EPA. Burning multiple candles can elevate it above OSHA permissible exposure limits of 50 microg/m3. Although blood lead levels have dropped precipitously in the United States since lead was phased out of gasoline in 1986, nearly 900,000 children still had levels above 10 microg/dl during NHANES III. Considering that candle sales in the US are estimated at $1-2 billion per year, and that children may spend as much as 88% of their time indoors, it is reasonable to suspect that some blood lead elevation in children arises from indoor micro-environments where lead-wick candles are burned.

Concentrations and trends of perfluorinated chemicals in potential indoor sources from 2007 through 2011 in the US.

Certain perfluorinated chemicals (PFCs) in consumer products used indoors are potential indoor PFCs sources and have been associated with developmental toxicity and other adverse health effects in laboratory animals (Lao et al., 2007). The concentrations of selected PFCs including perfluorooctanoic acid (PFOA) and other perfluorocarboxylic acids (PFCAs), in 35 selected consumer products that are commonly used in indoors were measured from the year of 2007 through 2011. The products collected included carpet, commercial carpet-care liquids, household carpet/fabric-care liquids, treated apparel, treated home textiles, treated non-woven medical garments, floor waxes, food-contact paper, membranes for apparel, and thread-sealant tapes. They were purchased from retail outlets in the United States between March 2007 and September 2011. The perfluorocarboxylic acid (PFCA) contents in the products have shown an overall downward trend. However, PFOA (C8) could still be detected in many products that we analyzed. Reductions of PFCAs were shown in both short-chain PFCAs (sum of C4 to C7) and long-chain PFCAs (sum of C8 to C12) over the study period. There were no significant changes observed between short-chain PFCAs and long-chain PFCAs. Fourteen products were analyzed to determine the amounts of perfluoroalkyl sulfonates (PFASs) they contained. These limited data show the pronounced increase of perfluoro-butane sulfonate (PFBS), an alternative to perfluorooctanoic sulfonate (PFOS), in the samples. A longer and wider range of study will be required to confirm this observed trend.

Method development for liquid chromatographic/triple quadrupole mass spectrometric analysis of trace level perfluorocarboxylic acids in articles of commerce.

An analytical method to identify and quantify trace levels of C5-C12 perfluorocarboxylic acids (PFCAs) in articles of commerce (AOCs) was developed and rigorously validated. Solid samples were extracted in methanol, and liquid samples were diluted with a solvent consisting of 60:40 (v/v) methanol and 2 mM ammonium acetate (NH(4)Ac) aqueous solution. In both cases, the samples were spiked with an isotopically labeled recovery check standard. The samples were concentrated in a nitrogen atmosphere (solid samples only), filtered, and then analyzed by HPLC coupled with a tandem mass spectrometer. Method evaluation included selection of the extraction solvent and the sample preparation solvent used to facilitate sample injection into the analytical system, method comparison for extraction and sample concentration, determination of extraction efficiency, instrument and method detection limits, and determination of potential sample loss during filtration and sample storage. Results of consecutive extractions demonstrated that a single extraction step accounts for 70-100% of the "total" PFCAs in the AOCs with the exception of cookware. The instrument's detection limit was < or = 0.05 ng/mL, and the method detection limit were 1.0-3.9 ng/g for solid AOCs and 1.1-6.8 ng/g for liquid AOCs. The method has been used to determine the PFCA content in a wide range of AOCs containing or treated with fluoropolymers and fluorotelomers.

Characterization and reduction of formaldehyde emissions from a low-VOC latex paint.

The patterns of formaldehyde emission from a low volatile organic compound (VOC) latex paint applied to gypsum board were measured and analyzed by small environmental chamber tests. It was found that the formaldehyde emissions resulted in a sharp increase of chamber air formaldehyde concentration to a peak followed by transition to a long-term slow decay. A semi-empirical first-order decay in-series model was developed to interpret the chamber data. The model characterized the formaldehyde emissions from the paint in three stages: an initial "puff" of instant release, a fast decay, and a final stage of slow decay controlled by a solid-phase diffusion process that can last for more than a month. The model was also used to estimate the peak concentration and the amount of formaldehyde emitted during each stage. The formaldehyde sources were investigated by comparing emission patterns and modeling outcomes of different paint formulations. The biocide used to preserve the paint was found to be a major source of the formaldehyde. Chamber test results demonstrated that replacing the preservative with a different biocide for the particular paint tested resulted in an approximate reduction of 55% of formaldehyde emissions. But the reduction affected only the third-stage long-term emissions.

Evaluation of Sink Effects on VOCs from a Latex Paint.

The sink strength of two common indoor materials, a carpet and a gypsum board, was evaluated by environmental chamber tests with four volatile organic compounds (VOCs): propylene glycol, ethylene glycol, 2-(2-butoxyethoxy)ethanol (BEE), and Texanol. These oxygenated compounds represent the major VOCs emitted from a latex paint. Each chamber test included two phases. Phase 1 was the dosing/sorption period during which sink materials (pieces of carpet and gypsum board samples) were exposed to the four VOCs. The sink strength of each material tested was characterized by the amount of the VOCs adsorbed or absorbed. Phase 2 was the purging/de-sorption period during which the chambers with the dosed sink materials were flushed with purified air. The reemission rates of the adsorbed VOCs from the sinks were reflected by the amount of the VOCs being flushed. Phase 1 results indicated that the sink strength for the four target compounds is more than 1 order of magnitude higher than that for other VOCs previously tested by the U.S. Environmental Protection Agency (EPA). The high sink strength reflected the unusually high sorption capacity of common indoor materials for the four VOCs. Phase 2 results showed that reemission was an extremely slow process. If all the VOCs adsorbed were reemittable, it would take more than a year to completely flush out the VOCs from the sink materials tested. The long reemission process can result in chronic and low-level exposure to the VOCs after painting interior walls and surfaces.

Characterization of Curing Emissions from Conversion Varnishes.

Three commercially available conversion varnish coating "systems" (stain, sealer, and topcoat) were selected for an initial scoping study. The total volatile content of the catalyzed varnishes, as determined by U.S. Environmental Protection Agency (EPA) Method 24, ranged from 64 to 73 weight%. Uncombined (free) formaldehyde concentrations, determined by a sodium sulfite titration method, ranged from 0.15 to 0.58 weight% of the uncatalyzed varnishes. Each sealer and topcoat was also analyzed by gas chromatography (EPA Method 311). The primary volatile organic constituents included methyl ethyl ketone (MEK), isobutanol, n-butanol, methyl isobutyl ketone (MIBK), toluene, ethylbenzene, the xylenes, and 1,2,4-trimethylbenzene.