A substance is not normally identified as an air contaminant until its presence and concentration actually or potentially produce or contribute to development of a deleterious effect. The composition of an unpolluted dry air is shown in Table 4.1.
Sources of air contaminants may be classified as stationary, mobile, or fugitive. Mobile sources are at- tributed to transportation activities, such as automobile exhausts, and are not included per se in this text. This chapter focuses on emissions from stationary sources. Special sections are provided on fugitive emis- sions and related “air” topics of odor, indoor air quality, and noise pollution. These sections address source, effect, and control of pollutants.
The effects of an air pollution problem range in scope from a single type of contaminant to a multifaceted problem resulting from multiple contaminants complexed by atmospheric interactions.
Sources of Air Contaminants
Air contaminants originate in a wide variety of chemical compositions and different physical states and are emitted from a diversity of sources. Discussions follow that identify primary air contaminants and their prin- cipal sources. The term “primary” is used to denote direct emissions of a contaminant. In some cases, sec- ondary air contaminants are formed in the atmosphere by chemical interactions among primary contami- nants under normal atmospheric constituents.
Carbon Monoxide. Carbon monoxide (CO) is a colorless, odorless, tasteless gas formed primarily by the incomplete combustion of carbonaceous fuels. Important variables affecting its emission concentration in- clude combustion chamber residence time and turbulence (physical characteristics), flame temperature, and oxygen concentration.
By far, the major source of carbon monoxide is fuel combustion in the internal combustion engine of mo- bile sources. Miscellaneous combustion sources and industrial processes contribute to a much lesser extent. A companion gas emission from fuel combustion is carbon dioxide (CO2), which is also a secondary con-
taminant formed by the oxidation (very slow reaction rate) of carbon monoxide in the atmosphere.
Hydrocarbons. Compounds of carbon and hydrogen constitute primary hydrocarbon contaminants, such as aromatics, olefins, and paraffins, which originate with the processing and use of petroleum and its prod- ucts. Derivatives or secondary contaminants, such as aldehydes, ketones, and organic acids, are formed when hydrogen is replaced with oxygen, halogens, or other substituent groups.
Like carbon monoxide, the most significant source of hydrocarbons is the use of petroleum products to fuel motor vehicles. Petroleum processing, solvent use, and related uses of petroleum products in commer- cial and industrial operations contribute to air pollution by hydrocarbons.
Lead. Unlike other toxic heavy metals, lead is relatively abundant throughout the world and, thus, has many potential pathways into the human body via inhalation and ingestion. The potential for lead in air pol- lution is greatest in the vicinity of sources and in densely populated areas.
TABLE 4.1 Composition of Dry Air
Component Concentration, ppm Nitrogen 780,800 Oxygen 209,500 Argon 9,300 Carbon dioxide 315 Neon 18 Helium 5.2 Methane 1.0+ Krypton 1.0 Nitrous oxide 0.5 Hydrogen 0.5 Xenon 0.08 Nitrogen dioxide 0.02 Ozone 0.01+
Historically, the primary source of lead emissions has been the result of tetraethyl lead additives to gaso- line. Legislative controls have done much to lessen the impact of this source in the United States. Stationary sources include mining, smelting, waste incineration, iron and steel production, lead alkyl manufacturing, and battery manufacturing, where the lead is released in stack and fugitive emissions.
Nitrogen Oxides. Of the numerous forms of nitrogen oxide possible, nitric oxide (NO) and nitrogen diox- ide (NO2) are the most significant air contaminants. Nitric oxide is the primary contaminant and is formed by all high-temperature, atmospheric combustion through the direct combination of nitrogen and oxygen. In the presence of sunlight, nitric oxide combines with atmospheric oxygen to form nitrogen dioxide as a sec- ondary contaminant.
The major source of nitrogen oxides is from fuel combustion, where the quantity of nitrogen oxides is a function of the available nitrogen and oxygen concentrations, reaction time, and temperature. The chemical processing industry is another notable source of localized emissions.
Ozone. Photochemical oxidants, mostly as ozone, are the product of atmospheric reactions of such certain contaminants (precursors), such as hydrocarbons and nitrogen oxides, in the presence of sunlight. The for- mation of ozone also involves the physical processes of dispersion and transport of precursors.
Particulate Matter. The term “particulate matter” (or “aerosols”) is used to denote solid and liquid matter of organic or inorganic composition that is suspended as the result of a stack or fugitive emission. The mat- ter may be individual elements and/or compounds and may or may not be emitted along with gaseous conta- minants.
Particle size may be used to classify the types of sources. For example, particles less than 1 m (in diam- eter) are mostly products of condensation and combustion. Large particles, above 10 m, result from physi- cal actions, such as wind erosion and grinding or spraying operations. Those particles between 1 and 10 m tend to be fugitive dusts, process dusts, and combustion products.
Sulfur Oxides. The air contaminants categorized as sulfur oxides are sulfur dioxide (SO2), which is pre-
dominant, and sulfur trioxide (SO3). The primary source for both is the combustion of fuels, mainly coal, containing sulfur in the presence of air (oxygen). The most significant secondary contaminant is sulfuric acid.
Effects of Air Contaminants
Impacts on public health, vegetation, materials, and/or visibility are used to describe the effects of air conta- minants. In the United States, the Environmental Protection Agency (EPA) develops and administers emis- sion source criteria and ambient air quality standards (Chapter 3) intended to control negative effects. Dis- cussions follow on the effects of the contaminants included in the ambient air quality standards.
Carbon Monoxide. The significance of carbon monoxide is its effects on human and other animal health; plants are relatively insensitive, and other deleterious effects are not notable.
Carbon monoxide is absorbed by the lungs and is associated with a decrease of oxygen-carrying capacity of the bloodstream and of available oxygen for body tissue. As a function of concentrations and exposure time, effects may include physiologic stress and impaired motor skills, visual discrimination, and time inter- val recognition.
Hydrocarbons. The effects of hydrocarbons vary according to the individual compounds and derivatives. Generally, hydrocarbons are recognized as components and promoters of photochemical smog. The associ- ated effects are eye irritation and other manifestations, injury to sensitive plants, and reduced visibility.
Lead. The multitude of sources and exposures to lead make it more than an air contaminant. Primary ex- posure occurs from direct inhalation, and secondary exposure comes from various routes to produce inges- tion of lead. Furthermore, lead affects human health at the subcellular, cellular, and organ system levels. Some specific effects of higher blood levels of lead include anemia, cognitive deficits, peripheral neu- ropathies, and encephalopathy symptoms.
Nitrogen Oxides. The effects of nitrogen oxides are often referenced as NO, NO2, and NOx; however, the most deleterious effects tend to be from NO2. For example, since nitrogen dioxide absorbs the full visible
spectrum of light energy, it can reduce visibility even in the absence of particulate matter.
Other effects include a number of respiratory disorders, depending on concentration, time of exposure, and affected age group. Material effects include fading of certain dyes, deterioration of selected fabrics, and cases of metal corrosion. Also, extended exposures can cause leaf or other damage to vegetation.
Ozone. The effects of ozone are widespread and are the result of its characteristics as a high-strength oxi- dizing chemical. Human health, materials, and vegetation are all subject to adverse impact as a function of ozone concentration and contact time.
Particulate Matter. Some effects of particulate matter are very evident to the affected general public. Problems of reduced visibility, eye irritation, and soiling of clothes are readily noticeable.
Other effects, such as interactions with other contaminants, are less obvious. For example, the adverse ef- fects of sulfur oxides are increased in the presence of particulate matter, and human respiratory problems may be accelerated due to contaminants associated with inhaled particulates.
Sulfur Oxides. The effects of sulfur oxides are manifested in the presence of particulate matter. This is shown by case studies and research investigations with respect to health impacts related to irritation of the respiratory system, to reduced visibility, to corrosion of materials, and to varying sensitivity of plant species.
An effect widely publicized is the formation of acid (H2S04) rain by the reaction of sulfur oxides and at-
mospheric moisture. Acid rain has a pH of 2 or less and is responsible for acidifying streams and lakes and, thus, not only killing fish but leaving waterways too acidic to be reinhabited. European and North American countries are confronted with not only air pollution control problems but also political issues due to the mi- gration of acid rain across political boundaries.
CHARACTERIZATION
The characterization of an emission stream begins with a survey of facility operations and a determination of emission locations. The stack emissions must be quantified through a sampling and measurement pro- gram, and, in some cases, ambient air monitoring is required or desirable. The following discussion focuses on procedures for an industrial installation (4), but largely applies to other facilities, such as a solid waste in- cinerator.
Emission Survey
The first step in characterizing air pollution from an industrial facility is the emission survey, which locates sources and defines quantities for all air contaminants.
Source Identification. The identification of emission sources begins with an in-depth review of process flow sheets and associated data. This data base is then tested and verified by a tour of plant operations.
Process Flow Sheets. Design, or preferably, “record” drawings of the facility’s processes will identify the location of emission sources. Typically, process flow sheets will provide sufficient information on input ma- terials and process functions to make a qualitative assessment of the emissions. Figure 4.1 illustrates the components of a simple, generic process flow sheet.
Design development reports, permit applications, historical process and emission records for the facility or a similar facility, and other such data will aid in the preliminary identification of emission sources.
This step of the emission survey concludes with the development of plant-specific survey data sheets pertaining to the process(es) and emission control(s) data and with the establishment of an appropriate filing or coding system for data management (4).
Plant Inspection. With the foregoing material in hand, an inspection tour is made of the plant to verify available records, to record undocumented changes, and to provide input (Table 4.2), to the design of control equipment. Candid interviews with plant operating personnel are a very important function during the tour.
Completing the plant inspections with accurate stack information is another important task. These data are needed for development of a testing program.
Emission Quantifications. Data from the records search and plant tour are next organized to formulate specific emission survey functions as part of the plant’s compliance schedule.
Compliance Program. Source testing is required to define needs to achieve compliance, to demonstrate effectiveness of new control techniques, or to provide records of continuing compliance based on quantita- tive field results from individual sources. Steps in achieving compliance are charted in Figure 4.2 (5).
Quantification Procedures. The emission survey is developed by applying a combination of procedures related to quantity measurements from existing files, ongoing record keeping and monitoring, and new data collection. These procedures include review of permit application and design data, analysis of fuel and raw material usage, calculation of mass balance, application of expected emission factors from the literature (6), and new testing of emission sources.
Emission Measurements
Measurement of plant emissions provides a data base for determination of needs for new control equipment, effectiveness of existing control equipment, compliance with emission regulations and/or permit require- ments, and losses of products or by-products via the emission. The process involves sampling and testing procedures and physical and chemical measurements.
Emission Testing. The planning and conduct of emission testing begins with development of the testing program, including definition of sampling point requirements. Finally, the test procedures are defined.
Testing Program Development. A first step in developing a compliance testing program is to define and coordinate with the participants. The participants normally include plant process and pollution control per- sonnel, the testing team, and the regulatory agency. The goal of this group is to agree on general and often very specific aspects of the testing program.
Using the applicable regulatory requirements, compliance schedule criteria, and the findings of the emis- sion survey, a written testing program is initiated. Contents include the location of sampling points, parame- ters to be tested, and the facility production operations for the test period.
Sampling Point Requirements. In addition to defining an emission for testing, sampling requirements must be refined to best obtain representative samples for analysis. Sampling ports, a work platform, and a power supply are the primary features of a stack sampling arrangement. Using U.S. customary units for di- mensioning, Figure 4.3 illustrates and denotes requirements for stack sampling.
Emission Measurements. In order to standardize procedures for obtaining representative samples, the EPA has published reference sampling methods for most parameters of interest. These methods are com- piled in Table 4.3. The following discussions and illustrations are used to highlight requirements for selected measurements.
Velocity. Reference method 2 is used for determining the velocity and volumetric flow rate of stack gases. At several sampling points with equal portions of the stack volume, the velocity and temperature are mea- sured with the system shown in Figure 4.4.
Moisture Content. Reference method 4 describes procedures for determining moisture content of a stack gas, and Figure 4.5 illustrates a moisture sampling train. This method is not applicable if liquid droplets are present.
When liquid droplets are in the emission stream, gas temperatures should be obtained at several designat- ed points in the stack. By assuming that the emission stream is saturated, the moisture content is determined from a psychrometric chart or saturated vapor pressure tables.
Particulates. Reference method 5 is designed for material collectible at 120°C (250°F) on a filtering TABLE 4.2 Plant Inspection Data Needed for Control Equipment Design (4)
Site characteristics Process characterization
1. Environmental conditions, such as ambient 1. Capacity and capability of existing control equipment temperatures and wind patterns
2. Proximity to sensitive areas, such as residential 2. Reuse/recycling of collected emissions and process or public access developments by-products and wastes
3. Availability of water and power 3. Status and future of control regulations
4. Availability of solid waste and waste-water 4. Anticipated changes in raw material and additives disposal facilities
5. Physical limitations, such as roof loads and space 5. Frequency of startups and shutdowns 6. Plant expansion plans
FIG.
4.2
Compliance schedule char
t (
4
medium. Alternate reference methods are published for special applications. In addition, some sampling system alterations may be required by other regulatory agencies.
Sampling for particulates is performed at several designated points, representing equal areas, in the stack. The most widely used sampling apparatus is illustrated in Figure 4.6. Selection of the sampling points must be sensitive to potential stratification of particulates; common problems are shown in Figure 4.7.
Sulfur Dioxide. Reference method 6 uses the sample train presented in Figure 4.8 and is applicable to all stationary sources of sulfur dioxide except sulfuric acid plants.
Sampling for sulfur dioxide requires only a single collection point located at the center of the stack or at least 1 m (3.28 ft) from the inner wall. In addition, the sample must be extracted at a constant rate, which re- quires adjustments for any changes in stack gas velocity.
Continuous Emission Monitoring. Continuous emission monitoring (CEM) consists of two steps: extract- ing or locating a representative sample, and analyzing the sample. The types of CEM methods are:
앫 Extractive method, in which gas is withdrawn from the stack, conditioned, and analyzed 앫 In-situ method, in which gas is not extracted but is monitored in the stack by the analyzer
TABLE 4.3 Reference Sampling Methods (7) Method 1—Sample and velocity traverses for stationary
sources
Method 2—Determination of stack gas velocity and volumetric flow rate (Type S Pitot tube) Method 2A—Direct measurement of gas volume
through pipes and small ducts
Method 2B—Determination of exhaust gas volume flow rate from gasoline vapor incinerators
Method 3—Gas analysis for carbon dioxide, oxygen, excess air, and dry molecular weight
Method 3A—Determination of oxygen and carbon dioxide concentrations in emissions from stationary sources (instrumental analyzer procedure)
Method 4—Determination of moisture content in stack gases
Method 5—Determination of particulate emissions from stationary sources
Method 5A—Determination of particulate emissions from the asphalt processing and asphalt roofing industry
Method 5B—Determination of nonsulfuric acid particulate matter from stationary sources Method 5D—Determination of particulate matter
emissions from positive pressure fabric filters Method 5E—Determination of particulate emissions
from the wool fiberglass insulation manufacturing industry
Method 5F—Determination of nonsulfate particulate matter from stationary sources
Method 6—Determination of sulfur dioxide emissions from stationary sources
Method 6A—Determination of sulfur dioxide, moisture, and carbon dioxide emissions from fossil fuel combustion sources
Method 6B—Determination of sulfur dioxide and carbon dioxide daily average emissions from fossil fuel combustion sources
Method 6C—Determination of sulfur dioxide emissions from stationary sources (instrumental analyzer procedure)
Method 7—Determination of nitrogen oxide emissions from stationary sources
Method 7A—Determination of nitrogen oxide emissions from stationary sources Method 7B—Determination of nitrogen oxide
emissions from stationary sources (ultraviolet spectrophotometry)
Method 7C—Determination of nitrogen oxide emissions from stationary sources
Method 7D—Determination of nitrogen oxide emission from stationary sources
Method 7E—Determination of nitrogen oxides emissions from stationary sources (instrumental analyzer procedure)
Method 8—Determination of sulfuric acid mist and sulfur dioxide emissions from stationary sources Method 9—Visual determination of the opacity of
emissions from stationary sources
Method 10—Determination of carbon monoxide emissions from stationary sources
Method l0A—Determination of carbon monoxide emissions in certifying continuous emission monitoring systems at petroleum refineries
Method 11—Determination of hydrogen sulfide content of fuel gas streams in petroleum refineries
Method 12—Determination of inorganic lead emissions from stationary sources
Method 13A—Determination of total fluoride emissions from stationary sources—SPADNS zirconium lake method
Method 13B—Determination of total fluoride emissions from stationary sources—specific ion electrode method
Method 14—Determination of fluoride emissions from potroom roof monitors of primary aluminum plants
Method 15—Determination of hydrogen sulfide, carbonyl sulfide, and carbon disulfide emissions from stationary sources
Method ISA—Determination of total reduced sulfur emissions from sulfur recovery plants in petroleum refineries
Method 16—Semicontinuous determination of sulfur emissions from stationary sources
Method l6A—Determination of total reduced sulfur emissions from stationary sources (impinger technique)
Method 16B—Determination of total reduced sulfur emissions from stationary sources
Method 17—Determination of particulate emissions from stationary sources (instack filtration method)
Method 18—Measurement of gaseous organic compound emissions by gas chromatography Method 19—Determination of sulfur dioxide removal
efficiency and particulate matter, sulfur dioxide and