Evaluating Sources of Indoor Air Pollution

Evaluation of Indoor air pollution problems requires an understanding of the relationship between sources, air movement, and outdoor air exchange. Research is underway to investigate these relationships. A three-phase program is being implemented: 1) Environmental chambers are used to provide source emission factors for specific indoor pollutants; 2) An IAQ (Indoor Air Quality) model has been developed to calculate indoor pollutant concentrations based on chamber emissions data and the air exchange and air movement within the indoor environment; and 3) An IAQ test house is used to conduct experiments to evaluate the model results. Examples are provided to show how this coordinated approach can be used to evaluate specific sources of indoor air pollution. Two sources are examined: 1) para-dichlorobenzene emissions from solid moth repellant; and 2) particle emissions from unvented kerosene heaters.

The evaluation process for both sources followed the three-phase approach discussed above. Para-dichlorobenzene emission factors were determined by small chamber testing at EPA’s Air and Energy Engineering Research Laboratory. Particle emission factors for the kerosene heaters were developed In large chambers at the J. B. Pierce Foundation Laboratory. Both sources were subsequently evaluated in EPA’s IAQ test house. The IAQ model predictions showed good agreement with the test house measurements when appropriate values were provided for source emissions, outside air exchange, in-house air movement, and deposition on “sink” surfaces.     

The Effects of Infiltration and Insulation on the Source Strengths and Indoor Air Pollution from Combustion Space Heating Appliances

Many energy conservation strategies for residences involve reducing house air exchange rates. Reducing the air exchange rate of a house can cause an increase in pollutant levels if there is an indoor pollution source and if the indoor pollutant source strength remains constant. However, if the indoor pollutant source strength can also be reduced, then it is possible to maintain or even improve indoor air quality. Increasing the insulation level of a house is a means of achieving energy conservation goals and, in addition, can reduce the need for space heating and thereby reduce the pollutant source strengths of combustion space heaters such as unvented kerosene space heaters, unvented gas space heaters, and wood stoves. In this paper, the indoor air quality trade-off between reduced infiltration and increased insulation in residences is investigated for combustion space heaters. Two similar residences were used for the experiment. One residence was used as a control and the other residence had infiltration and insulation levels modified. An unvented propane space heater was used as the source in this study. A model was developed to describe the dependence of both indoor air pollution levels and the appliance source strengths on house air exchange rates and house insulation levels. Model parameters were estimated by applying regression techniques to the data. Results show that indoor air pollution levels in houses with indoor combustion space heating pollution sources can be held constant (or lowered) by reducing the thermal conductance by an amount proportional to (or greater than) the reduction of the air exchange rate.     

Emission rates from range-top burners—Assessment of measurement methods

Unvented combustion sources in indoor environments generate emissions that contribute to indoor air pollution. Both the direct and mass-balance methods have been used to measure emission rates from these sources in field houses, test houses and chambers. In particular, emission rates have been obtained for pollutants from kerosene space heaters and from unvented gas appliances such as range-top burners, ovens, dryers and gas space heaters.Most studies have focused on the emission rates of the inorganic air constituents (NO, NO₂, CO and a few others). This paper compares the two methods of emission rate measurement, and summarizes the emission rates of NO, NO₂ and CO from range-top burners.The emission rates of NO, NO₂ and CO from range-top burners are well quantified, but vary widely as a function of the source condition. The experiments described herein found that the two methods provide comparable emission rates. Consequently, in support of the research needed to establish the distribution of emission rates from range-top burners in the U.S. housing stock, the method to be employed should be the one that provides the required information cost effectively.     

Field monitoring design considerations for assessing indoor exposures to combustion pollutants

Laboratory and controlled field studies of indoor air quality (IAQ) have characterized pollutant emission rates from combustion sources and have measured other key indoor air pollution parameters such as air exchange rates and indoor reactivity rates for the houses investigated. In addition, several field studies have attempted to measure, with varying degrees of success, pollutant exposures, indoor pollutant concentrations, and other parameters in large populations. To date, there exists no comprehensive strategy for assessing distributions of exposures to combustion pollutants and distributions of factors that affect such exposures in large populations. This paper outlines important parameters that affect combustion-related indoor air pollution concentrations and exposures, delineates weaknesses in our current understanding of exposures and field sampling methodologies, and mentions important considerations in planning appropriate field sampling strategies.     

The Altitude: A Fundamental Parameter in the Use of Air Quality Standards

Organic vapors are emitted to the indoor air from a variety of consumer products and building materials. The U.S. EPA Is evaluating the emission characteristics from such sources using small environmental test chambers. Emission rate data are presented, and the effect of temperature and air exchange rate are discussed. Models are used to account for the Impact of chamber concentration and “wall effects” on emission rates. Indoor concentrations of specific organlcs emitted from a silicone caulk are estimated from the chamber test data.     

Quantification of emission factor uncertainty

Emissions factors are important for estimating and characterizing emissions from sources of air pollution. There is no quantitative indication of uncertainty for these emission factors, most factors do not have an adequate data set to compute uncertainty, and it is very difficult to locate the data for those that do. The objectives are to compare the current emission factors of Electric Generating Unit NOx sources with currently available continuous emission monitoring data, develop quantitative uncertainty indicators for the Environmental Protection Agency (EPA) data quality rated emission factors, and determine the possible ranges of uncertainty associated with EPA's data quality rating of emission factors. EPA's data letter rating represents a general indication of the robustness of the emission factor and is assigned based on the estimated reliability of the tests used to develop the factor and on the quantity and representativeness of the data. Different sources and pollutants that have the same robustness in the measured emission factor and in the representativeness of the measured values are assumed to have a similar quantifiable uncertainty. For the purposes of comparison, we assume that the emission factor estimates from source categories with the same letter rating have enough robustness and consistency that we can quantify the uncertainty of these common emission factors based on the qualitative indication of data quality which is known for almost all factors. The results showed that EPA's current emission factor values for NOx emissions from combustion sources were found to be reasonably representative for some sources; however AP-42 values should be updated for over half of the sources to reflect current data. The quantified uncertainty ranges were found to be 25-62% for A rated emission factors, 45-75% for B rated emission factors, 60-82% for C rated emission factors, and 69-86% for D rated emission factors, and 82-92% for E rated emission factors.     

Effect of Gas and Kerosene Space Heaters on Indoor Air Quality: A Study in Homes of Santiago,Chile

Abstract

The impact of outdoor and indoor pollution sources on indoor air quality in Santiago, Chile was investigated. Toward this end, 16 homes were sampled in four sessions. Each session included an outdoor site and four homes using different unvented space heaters (electric or central heating, compressed natural gas, liquefied petroleum gas, and kerosene). Average outdoor fine particulate matter (PM_2.5) concentrations were very high (55.9 μg·m^-3), and a large fraction of these particles penetrated indoors. PM_2.5 and several PM_2.5 components (including sulfate, elemental carbon, organic carbon, metals, and polycyclic aromatic hydrocarbons) were elevated in homes using kerosene heaters. Nitrogen dioxide (NO₂) and ultrafine particles (UFPs) were higher in homes with combustion heaters as compared with those with electric heaters or central heating. A regression model was used to assess the effect of heater use on continuous indoor PM_2.5 concentrations when windows were closed. The model found an impact only for kerosene heaters (45.8 μg m^-3).     

Environmental chamber test methodology for characterizing organic vapors from solid emission sources

Environmental test chambers are an important tool in the characterization of organic emissions from solid consumer and construction products and in the evaluation of their potential impact on indoor air quality. The results of extensive research concerning formaldehyde (CH₂O) emissions from such products strongly support this application of environmental chambers to measure product emissions and provide useful input for the design of environmental chamber studies. The physical design and test methodology for environmental chambers are strongly influenced by several elements in a comprehensive project plan for source characterization, including the selection process for test samples and the mathematical models used to interpret the organic emissions data. The protocol for environmental chamber testing extends broadly from the acquisition, preparation and conditioning of test specimens, to the selection and control of environmental test conditions, and to the calibration and measurement of system parameters and organic emissions. The requirements for environmental control inside the test chamber can be estimated from the sensitivity of the organic emission rates of the test products (e.g. CH₂O emissions from pressed-wood products) to variation in environmental parameters. The cost of the numerous, multiple-organic analyses required for environmental chamber testing of solid emitters is seen as a strong limitation to product selection strategies and modeling efforts. The modeling of organic emissions from solid emitters can be both a planning tool for development of chamber test methodology and a means to interpret test chamber results.     

Hazardous air pollutant emissions from gas-fired combustion sources: emissions and the effects of design and fuel type

Air emissions from gas-fired combustion devices such as boilers, process heaters, gas turbines and stationary reciprocating engines contain hazardous air pollutants (HAPs) subjected to consideration under the federal clean air act (CAA). This work presents a recently completed major research project to develop an understanding of HAP emissions from gas-fired boilers and process heaters and new HAP emission factors based on field emission tests of gas-fired external combustion devices used in the petroleum industry. The effect of combustion system design and operating parameters on HAP emissions determined by both field and research tests are discussed. Data from field tests of gas-fired petroleum industry boilers and heaters generally show very low emission levels of organic HAPs. A comparison of the emission data for boilers and process heaters, including units with and without various forms of NOx emission controls, showed no significant difference in organic HAP emission characteristics due to process or burner design. This conclusion is also supported by the results of research tests with different burner designs. Based on field tests of units fired with natural gas and various petroleum industry process gases and research tests in which gas composition was intentionally varied, organic HAP emissions were not determined to be significantly affected by the gas composition. Research data indicate that elevated organic HAP emission levels are found only under extreme operating conditions (starved air or high excess air combustion) associated with poor combustion.     

Evaluation of a Test Method for Measuring Indoor Air Emissions from Dry-Process Photocopiers

ABSTRACT

A large chamber test method for measuring indoor air emissions from office equipment was developed, evaluated, and revised based on the initial testing of four dry-process photocopiers. Because all chambers may not necessarily produce similar results (e.g., due to differences in sink effects, temperature and humidity control, air exchange, pollutant monitoring, and measurement biases), a preliminary four-laboratory evaluation of the revised test method was conducted. To minimize variability, the evaluation used a single dry-process photocopier that was shipped to each of the four laboratories along with supplies (i.e., toner and paper).

The results of this preliminary four-laboratory evaluation demonstrate that the test method was used successfully in the different chambers to measure emissions from dry-process photocopiers. Differences in chamber design and construction appeared to have had minimal effect on the results for the volatile organic compounds (VOCs). Perhaps more important than the chamber itself is the sample analysis as identified by duplicate samples that were analyzed by a different laboratory. Percent relative standard deviation (%RSD) was used to provide a simplistic view of interlaboratory precision for this evaluation. Excluding problems with suspected analytical bias observed from one of the laboratories, the precision was excellent for the VOCs with RSDs of less than 10% in most cases. Less precision was observed among the laboratories for aldehydes/ketones (RSD of 23.2% for formaldehyde). The precision for ozone emission rates among three of the laboratories was excellent (RSD of 7.9%), but emission rates measured at the fourth laboratory were much higher.     

Multiple comparisons of organic,microbial, and fine particulate pollutants in typical indoor environments: Diurnal and seasonal variations

This study was performed to investigate the possible sources as well as seasonal and diurnal variations of indoor air pollutants in widely used four different environments (house, office, kindergarten, and primary school) in which people spend most of their time. Bioaerosol levels and species, volatile organic compound (VOC) levels, and PM_2.5 (particulate matter with an aerodynamic diameter ≤2.5 μm) levels were determined in different parts of these environments in parallel with outdoor sampling. Air pollution samplings were carried out in each microenvironment during five subsequent days in both winter and summer in Ankara, Turkey. The results indicated that bioaerosol, VOC, and PM_2.5 levels were higher in the winter than in the summer. Moreover, PM_2.5 and bioaerosol levels showed remarkable daily and diurnal variations, whereas a good correlation was found between the VOC levels measured in the morning and in the afternoon. Bacteria levels were, in general, higher than fungi levels. Among the VOCs, toluene was the most predominant, whereas elevated n-hexane levels were also observed in the kindergarten and the primary school, probably due to the frequent wet cleaning during school days. According to factor analysis, several factors were found to be significantly influencing the indoor air quality (IAQ), and amongst them, VOC-based products used indoors ranked first. The overall results indicate that grab sampling in naturally ventilated places may overestimate or underestimate the IAQ due to the inhomogeneous composition of indoor air caused by irregular exchanges with the outdoor air according to the season and/or occupants' habits.

Implications Seasonal and diurnal variations of VOCs, PM_2.5, bioaerosols in house, office, and schools were observed, in which PM_2.5 and bioaeorosols showed marked both intra- and interday variability, but VOCs did not. VOC-containing products were the most common source of air pollutants affecting the indoor air quality. External factors affecting the indoor air quality were season and indirectly ventilation. A grab sample cannot be representative in evaluating the air quality of a naturally ventilated environment precisely.     

Dissociation of sulfur hexafluoride tracer gas in the presence of an indoor combustion source

As an odorless, nontoxic, and inert compound, sulfur hexafluoride (SF6) is one of the most widely used tracer gases in indoor air quality studies in both controlled and uncontrolled environments. This compound may be subject to reactions with water vapor under elevated temperature to form acidic inorganic compounds such as HF and H2SO4. Thus, in the presence of unvented combustion sources such as kerosene heaters, natural gas heaters, gas log fireplaces, candles, and lamps, the SF6 dissociation may interfere with measurements of the emissions from these sources. Tests were conducted in a research house with a vent-free natural gas heater to investigate these potential interferences. It was observed that the heater operation caused about a 5% reduction of SF6 concentration, which can be an error source for the ventilation rate measurement and consequently the estimated pollutant emission rates. Further analysis indicates that this error can be much greater than the observed 5% under certain test conditions because it is a function of the ventilation flow rate. Reducing the tracer gas concentration has no effect on this error. A simple theoretical model is proposed to estimate the magnitude of this error. The second type of interference comes from the primary and secondary products of the SF6 dissociation, mainly H2SO4, SO2, HF, and fine particulate matter (PM). In the presence of approximately 5 ppm SF6, the total airborne concentrations of these species increased by a factor of 4-10. The tests were performed at relatively high SF6 concentrations, which is necessary to determine the interferences quantitatively. The second type of interference can be significantly reduced if the SF6 concentration is kept at a low ppb level.     

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.     

Gaseous Emissions from Unregulated Mobile Sources

The impact of gaseous exhaust emissions is determined for the following categories of mobile sources which are currently not covered by national emission regulations: 1) farm equipment, 2) merchant vessels, 3) locomotives, 4) lawn and garden implements, 5) snowmobiles, 6) outboard motors, 7) transport refrigeration units, and 8) helicopters. Mass emission rates of each category are tabulated and compared to other emissions from both mobile and stationary sources in selected Air Quality Control Regions. Also, projections are made as to the expected increase of emissions from each source category through 1990. The results show that in the near future some categories of mobile sources will be contributing substantial amounts of pollutants, on a mass basis, in regions with critical air pollution problems. As stricter emission standards on regulated sources continue to be implemented, the relative significance of these unregulated sources will increase. The major conclusion is that broad generalizations as to the amounts of air pollution contributed by these unregulated mobile sources nationwide may be grossly misleading. The only effective way to assess their impact is on a region-by-region basis. To this end, generalized computer programs are developed which permit the estimation of each category’s present and future mass emission rates in any Air Quality Control Region in the country     

Household wood heater usage and indoor leakage of BTEX in Launceston,Australia: A null result

A study has been conducted in Launceston, Australia, to determine within households with wood heaters the effect of leakage from the heater and flue on the indoor air concentrations of the pollutants: benzene, toluene, ethylbenzene and xylene (BTEX). The study involved three classes: 28 households without wood heaters, 19 households with wood heaters compliant with the relevant Australian Standard and 30 households with non-compliant wood heaters. Outdoor and indoor BTEX concentrations were measured in each household for 7 days during summer when there was little or no wood heater usage, and for 7 days during winter when there was widespread wood heater usage. Each participant kept a household activity diary throughout their sampling periods. For wintertime, there were no significant differences of the indoor BTEX concentrations between the three classes of households. Also there were no significant relationships between BTEX indoor concentrations within houses and several measures of the amount of wood heater use within these houses. For the households sampled in this study, the use of a wood heater within a house did not lead to BTEX release within that house and had no direct detectable influence on the concentrations of BTEX within the house. We propose that the pressure differences associated with the both the leakiness or permeability of the building envelope and the draught of the wood heater have key roles in determining whether there will be backflow of smoke from the wood heater into the house. For a leaky house with a well maintained wood heater there should be no backflow of smoke from the wood heater into the house. However backflow of smoke may occur in well sealed houses.The study also found that wood heater emissions raise the outdoor concentrations of BTEX in winter in Launceston and through the mixing of outdoor air through the building envelopes into the houses, these emissions contribute to increases in the indoor concentrations of BTEX in winter in all houses in Launceston.     

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.     

Effects of Operational Factors on Pollutant Emission Rates from Residential Gas Appliances

The NO, NO₂, and CO emissions from residential gas combustion appliances contribute to indoor air pollution. The work described investigated the impact of various unvented gas appliances designs and/or operational factors on pollutant emission rates. All experiments were performed in a 1150 ft³ (32.56 m³) all aluminum chamber under controlled conditions. Results are presented for the effect of the following factors on emission rates: 1) appliance type and/or design, 2) primary aeration level, 3) firing rate (fuel input rate), 4) chamber humidity, and 5) time dependence of emission rates. It is concluded that primary aeration level has the largest impact on pollutant emission rates of range-top burners, followed in turn by firing rate, appliance type, chamber humidity, and time dependence of emission rate.     

Combustion sources of particles: 2. Emission factors and measurement methods

Emissions from the combustion of biomass and fossil fuels are a significant source of particulate matter (PM) in ambient outdoor and/or indoor air. It is important to quantify PM emissions from combustion sources for regulatory and control purposes in relation to air quality. In this paper, we review emission factors for several types of important combustion sources: road transport, industrial facilities, small household combustion devices, environmental tobacco smoke, and vegetation burning. We also review current methods for measuring particle physical characteristics (mass and number concentrations) and principles of methodologies for measuring emission factors. The emission factors can be measured on a fuel-mass basis and/or a task basis. Fuel-mass based emission factors (e.g., g/kg of fuel) can be readily used for the development of emission inventories when the amount of fuels consumed are known. Task-based emission factors (g/mile driven, g/MJ generated) are more appropriate when used to conduct comparisons of air pollution potentials of different combustion devices. Finally, we discuss major shortcomings and limitations of current methods for measuring particle emissions and present recommendations for development of future measurement techniques.     

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.     

Indoor pollution and burning practices in wood stove management

This study evaluates effects of good burning practice and correct installation and management of wood heaters on indoor air pollution in an Italian rural area. The same study attests the role of education in mitigating wood smoke pollution. In August 2007 and winters of 2007 and 2008, in a little mountain village of Liguria Apennines (Italy), indoor and outdoor benzene, toluene, ethylbenzene, and xylene (BTEX) concentrations were measured in nine wood-heated houses. During the first sampling, several mistakes in heating plant installations and management were found in all houses. Indoor BTEX concentrations increased during use of wood burning. Low toluene/benzene ratios were in agreement with wood smoke as main indoor and outdoor pollution source. Other BTEX sources were identified as the indoor use of solvents and paints and incense burning. Results obtained during 2007 were presented and discussed with homeowners. Following this preventive intervention, in the second winter sampling all indoor BTEX concentrations decreased, in spite of the colder outdoor air temperatures. Information provided to families has induced the adoption of effective good practices in stoves and fire management. These results highlight the importance of education, supported by reliable data on air pollution, as an effective method to reduce wood smoke exposures.

Implications:Information about burning practices and correct installation and management of wood heaters, supported by reliable data on indoor and outdoor pollution, may help to identify and remove indoor pollution sources. This can be an effective strategy in mitigate wood smoke pollution.