Air Toxics Emissions Inventory Protocol for the Great Lakes States

4.5 Activity Data Generation Methods

Most of the EET categories discussed above require the generation of activity data. The EET for on-road motor vehicles includes a discussion of activity data. Activity data for the other EETs are any data that quantify a source, device, or process for purposes of emission calculation. Most activity data quantify processes; examples of process activity include fuel burned and hours of operation. Some activity data quantify devices; examples include the storage volume of a tank, the area of a pond and, for area sources, the number of devices. In a few cases, activity data quantify sources; examples include population and number of dwelling units in a county for an area source, and number of employees at a facility for facility sources.

Activity data are either:

• Obtained directly from a facility operator (e.g., tons of solvent used) or from an organization that develops or collects data useful for emissions calculation (e.g., population and national fuel use statistics); or
• Calculated from other activity data that were directly obtained.

4.5.1 Direct Acquisition of Readily Available Activity Data

Table 4-12 lists organizations that gather and distribute data that can be used for developing the regional inventory to determine activity data profiles (as identified in Table 4-2).

DOT = Department of Transportation
USDA - U.S. Department of Agriculture

Some of the available data are facility-specific, and other data are aggregated to different reporting areas, usually counties. As a practical matter, state-specific data for the data items listed should be obtained early in the emission inventory process and stored by each state. This eliminates the need for multiple persons to query the same organization for the same data item, and provides the needed backup documentation in a single reference source.

It is not feasible to present a complete list of information sources in this volume. State and local agencies vary widely in the amount and type of data that they can provide. The U.S. Bureau of the Census, the Energy Information Agency (EIA), and other federal agencies are valuable sources of information.

Table 4-13 contains a work breakdown describing the steps involved in acquiring activity data.

4.5.2 Acquisition of Activity Data by Survey

In addition to obtaining data readily available from other organizations, some activity data can only be obtained by making specific data requests to organizations with access or the ability to generate a needed activity data item. Often the data are available from a local organization that has information for the specific area of interest. For example, local trade associations may have data on the amount and types of architectural surface coatings, or the amount and types of dry cleaning solvents used in an area. Tax, highway, energy, and other state or local agency records may provide collective activity level estimates for other area source categories, including gasoline sales and cutback asphalt use. Railroads may have data on ton-miles of freight hauled. The state should survey various local associations and other state agencies to determine what information is maintained for the area that can be used in the area source inventory.

For some area source categories, surveys of a representative sample of facilities within the source category may be necessary. It is beyond the scope of this discussion to provide a thorough treatment of survey and sample design. The correct number of samples must be determined based on the priority given to the category and the resources available. However, unless a particular industry is represented by one facility in the area, information from only one company is generally not sufficient.

If not already done as part of the facility source inventory development effort, a list of sources may be identified from state permits or enforcement files, business directories, or lists supplied by state agencies. Surveys may be conducted either over the telephone or by mail. The nature of the survey form will depend on the type of inventory being prepared.

Table 4-14 contains a work breakdown describing the steps involved in developing a survey to obtain activity data.

4.5.3 Calculation of Activity Data

Often, activity data are available at the state or national level, but not at the county or similar local level needed to calculate emissions. In this situation, state or national totals may be apportioned to approximate the county or local activity. A surrogate variable such as population, employment, number of households, or other readily available information is used to apportion the activity. Residential, commercial, and industrial fuel consumption data are commonly handled this way. In any case, a critical factor is choosing the appropriate surrogate so that it correlates with the activity data of concern.

Table 4-15 contains a work breakdown describing the steps involved in using surrogate data to obtain desired activity data.

4.6 Documentation Requirements

This section discusses the documentation requirements for data included in the regional inventory. Additional documentation requirements are included in the QA/QC Plan in Appendix A.

All inventory documentation should be reproducible; that is, it should be possible for anyone reading the document to reproduce the results. All sources of data and assumptions must be fully documented. The essential components of the inventory documentation are described briefly below.

4.6.1 Completeness

Sufficient information needs to be given to document the completeness of the area source inventory. Categories excluded need to be named, and the reasons for their exclusion given. Some explanation of the process used to identify source categories needs to be provided.

4.6.2 Methods

For each area source category, the rationale for the method used should be given. This can be very simple, such as stating that the preferred method from Volume III of the Encyclopedia of Methods (U.S. EPA, 1993b) was used. More explanation is warranted if the method used deviates from the preferred method. If alternative emission factors or activity data are available, the reason for using the factors or data chosen should be stated. Similarly, any assumptions used to develop the activity data or emission factors also should be clearly stated.

4.6.3 References

The sources of all data, methods, and assumptions should be fully documented. If the source is a person at a government agency, trade group, or other organization, that person's name, affiliation, and the date of the contact should be documented, at a minimum. Reports and other documents should be referenced by author (if known), year, title of report, publishing agency, and location. Documents published by most government agencies usually have an identifying number that should be included.

4.6.4 Sample Calculations

In addition to text explaining the process used to develop the inventory, sample calculations should be provided. This is particularly important for complicated calculations or if several steps were required to develop the estimates.

4.6.5 Supporting Data

The data used to develop the input variables should be supplied if at all possible. For example, where employment in several SIC's is summed to produce the activity parameter, the original employment data by SIC should be included in the documentation unless prohibited by the size of the data set or confidentiality issues. Alternatively, if the data were derived from a published data set, the source should be unambiguously referenced (supplying page and table numbers, if necessary). All conversion factors used should be explicitly stated.

If models are used in any part of the calculations, the input data used for the model should be provided. Any statistical analyses should also be clearly documented; the complete data set used and the output from the statistical analysis should be provided. Similarly, survey results should be provided in as much detail as possible along with, at a minimum, the number of facilities surveyed, the percent responding, and some descriptive statistics of the results.

4.7 Temporal Variation Data

Emissions for some categories vary by day of the week and by season. Seasonal activity is very important for some source categories, such as agricultural pesticide use and residential fuel combustion. The volatility of the VOC is partially dependent on temperature. This relationship is factored into the emission factor equations for gasolineevaporative losses, among others. (For this category, Reid vapor pressure [RVP] is also dependent on the season, with lower RVP's in the summer than in the winter).

Most emissions data and estimates developed for and stored in the regional air toxics inventory will be for a specified calendar year. Some users of these data are expected to need emissions data by month. In order to support these users, the monthly variation data need to be identified for each source/device/process.

The data needed to specify seasonal variation are 12 values quantifying the relative variation in monthly emissions over a calendar year. These data are entered into the inventory repository along with other emissions data. Absence of such data will be taken as an indication of uniform monthly variation (i.e., each month has the same relative emissions).

To ensure that important temporal variation data are not missing, certain source/ device/ process types that are known to have significant monthly variation have been identified in Table 4-16. Source/device/process types in this table are required to have monthly variation included in the regional repository.

4.8 Examples of Calculations Using the EETs

The following discussion provides specific examples of the general estimation methods to calculate annual average emissions. Each example presents emission estimates from one process for a compound of interest. Annual average emissions are defined as the total emissions (expressed in pounds) of listed substances released under normal operating conditions during the reporting calendar year.

4.8.1 Examples Using Mass Balance

1.	Estimating Emissions Using Mass Balance with a Single Component

In one process, facility "Z" uses a solvent bath to clean its product, widgets. The solvent density is 7.7 pounds per gallon. (The density of the solvent is used to convert from gallons of solvent to pounds of solvent in the emissions calculation.) Substance A is the only substance in the solvent for which emissions must be quantified, and it constitutes 87% of the solvent by weight. At the beginning of 1989, the facility had 7,500 pounds of this solvent in storage and purchased another nine tons over the year. At the end of 1989, the facility has 10,000 pounds in storage.

Assumptions:

1. Solvents are typically volatile, and the total volume is usually emitted to the atmosphere. Thus, emissions equal amount of solvent used.
2. No control device is used to reduce the emissions of solvent.

EMS

=

(SB + SI - SE) x F

where:

EMS	=	Annual emissions of substance A, lbs/yr;
SB	=	Amount of solvent in storage at the beginning of the year, lbs;
SI	=	Amount of solvent purchased during 1993, lbs;
SE	=	Amount of solvent left in storage at the end of 1993, lbs;
F	=	Fraction of substance A in the solvent, lbs A/lb solvent; and
EMS	=	[7,500 lbs + (9 tons x 2,000 lbs/ton) - 10,000 lbs] x 0.87 lb A/lb solvent
	=	15,500 lbs x 0.87 lb A/lb solvent
	=	13,485 lbs of substance A emitted in 1989

2.	Estimating Emissions Using Mass Balance With Multiple Components

A facility uses a solvent "B" that is 16% perchloroethylene (PERC), 28% methyl chloroform (1,1,1-trichloroethane [TCA]), and 45% xylenes by weight. The remaining 11% consists of components not found on the list of substances to be quantified. The facility began 1989 with 1,250 pounds of solvent "B" in storage. The facility purchased 1,500 pounds that year, and when 1989 ended had 875 pounds of solvent "B" in storage.

Assumptions:

1. No solvent is reclaimed.
2. All solvent used is eventually emitted to the atmosphere.

EMS

=

(SB + SI - SE) x F

where:

EMS	=	Annual emissions of listed substance, lbs;
SB	=	Amount of solvent in storage in the beginning of the year, lbs;
SI	=	Amount of solvent purchased during the year, lbs;
SE	=	Amount of solvent left in storage at the end of the year, lbs; and
F	=	Fraction of listed substance in the solvent, lbs of listed substance/lb of solvent

Emissions of PERC

EMS	=	(1,250 lbs + 1,500 lbs - 875 lbs) x (0.16 lb PERC/lb solvent "B")
	=	1,875 lbs x 0.16 lb/lb = 300 lbs of PERC emitted in 1989

Emissions of TCA

EMS	=	(1,250 lbs + 1,500 lbs - 875 lbs) x (0.28 lb methyl chloroform/lb solvent "B")
	=	1,875 lbs x 0.28 lb/lb = 525 lbs of methyl chloroform emitted in 1989

Emissions of Xylenes

EMS	=	(1,250 lbs + 1,500 lbs - 875 lbs) x (0.45 lb xylene/lb solvent "B")
	=	1,875 lbs x 0.45 lb/lb = 844 lbs of xylenes emitted in 1989

For a quick check on whether the annual average calculations are correct, add the individual quantities of each listed substance emitted to determine whether the total equals the percentage of listed substances to be quantified. In this example, the individual quantities of substances emitted are:

300 lbs + 525 lbs + 844 lbs	=	1,669 lbs of three quantified substances in solvent "B" emitted in 1989
1,875 lbs x .89 lb to quantify/lb "B"	=	1,669 lbs of PERC, TCA, and Xylenes emitted in 1989

The calculation is correct.

4.8.2 Examples Using Emission Factors

The following discussions, based on California Air Resources Board (CARB) reports, presents some example emission calculations using emission factors.

1.	Estimating Emissions of Chloroform From a Pulp and Paper Mill Using An Emission Factor

A mill used wood chips and recycled paper to produce approximately 35,000 tons of bleached kraft pulp and 52,500 tons of tissue paper pulp in 1993 by chemical pulping process. The mill operates 10 hours per day, 350 days a year. Other days are reserved for maintenance.

The uncontrolled emission factor for bleached kraft pulp is 0.00022 pound of chloroform per pound of pulp produced (or 0.00022 ton of chloroform per ton of pulp produced), and the uncontrolled emission factor for tissue paper pulp is 0.00016 pound chloroform per pound of pulp produced.

Using these emission factors and the calculated process rates, the estimated chloroform emissions are:

EMS

=

PR x EF

where:

EMS	=	Chloroform emissions, tons;
PR	=	Annual production, tons; and
EF	=	Emission factor, ton chloroform emitted/ton pulp produced.
For bleached kraft pulp:
EMS	=	35,000 tons x 0.00022 ton chloroform/ton pulp produced;
	=	7.7 tons of chloroform emitted per year; and
	=	15,400 lbs chloroform emitted per year.
For tissue paper pulp:
EMS	=	52,500 tons x 0.00016 ton chloroform/ton pulp produced
	=	8.4 tons of chloroform
	=	16,800 lbs chloroform

Total annual chloroform emissions from the pulping process for the facility:

	=	15,400 lbs + 16,800 lb
	=	32,200 lbs

2.	Estimating Emissions of Nitrobenzene From Nitrobenzene Production Using An Emission Factor

Facility "P" produced 5,000 gallons of nitrobenzene in 1993 for use in manufacturing benzidine and quinoline. The facility operator reports that nitrobenzene weighs approximately 10 pounds per gallon. (The density of the solvent is used to convert from gallons of solvent to pounds of solvent in the emissions calculation.) The nitrobenzene emitted during this process is calcualted as follows:

Calculate the activity level or process-related parameter:

PR

=

PRV x DN

where:

PR	=	Amount of nitrobenzene produced through the wash and neutralization phase in mass units, lbs;
PRV	=	Amount of nitrobenzene produced through the wash and neutralization phase in volumetric units, gallons;
DN	=	Density of nitrobenzene, lbs/gallon; and
PR	=	5,000 gallons produced/year x 10 lbs/gallon
	=	50,000 lbs of nitrobenzene produced

The emission factor for nitrobenzene during its production is 8.0 x 10^-6 pound of nitrobenzene per 1.0 pound of nitrobenzene produced, which represents uncontrolled fugitive emissions. Thus, the estimated nitrobenzene emissions are as follows:

Using the first equation again:

EMS

=

PR x EF

where:

EMS	=	Annual nitrobenzene emissions, lbs;
PR	=	Amount of nitrobenzene produced during the wash and neutralization phase in mass units, lbs;
EF	=	Emission factor, lbs nitrobenzene/lbs of nitrobenzene produced; and
EMS	=	50,000 lbs/yr x (8.0 x 10-6) lb nitrobenzene/lbs nitrobenzene produced
	=	0.4 lb nitrobenzene emitted per year

4.8.3 Examples Using Engineering Calculations

The following discussions presents some example emission calculations using engineering calculations.

1. Estimating Releases From a Process Vent
A facility withdraws liquid from a process tank to feed a reactor. The mixture in the tank contains 5% by weight of substance A, 15% by weight of substance B, and 80% by weight of substance C. To prevent possible explosion, the vessel is vented at the top of the tank under a hood. A fan is used to draw the vapor to the atmosphere at the rate of 0.5 cubic feet per minute (measured at 70 F). This fan is operated continuously for 200 days per year. The process is simplified in this figure:

Assumptions:

1. Vapor above the liquid in the tank is continuously emitted to the atmosphere at the exhaust rate of the vent.
2. The substance content vapor is constant in composition.

The estimated emissions of any species from the tank are as follows (any component in the mixture is denoted the "ith" species):

EMSi

=

[ER x Yi x (Kv)-1] x MWi

where:

EMSi	=	Emissions of the ith species, lbs;
ER	=	Exhaust rate, ft3;
Yi	=	Mole fraction or volume fraction of the ith species in vapor phase, dimensionless;
Kv	=	Conversion factor from molar unit to volumetric unit, ft3/lb-mole; and
MW	=	Molecular weight of the ith species, lb/lb-mole

The exhaust rate, ER, from the vent rate and the operation rate is calculated as follows:

ER	=	0.5 ft3/min x 60 min/hr x 24 hr/day x 200 days
	=	1.44 x 105 ft3

Assume equilibrium exists between vapor and liquid in the tank. For an ideal solution, the relationship (Raoult's Law) among the partial pressure, the liquid mole fraction, and the vapor pressure of any component in the mixture is:

pi

=

Xi x poi

where:

pi	=	Partial pressure of component i, atmosphere;
Xi	=	Mole fraction of the ith species in the liquid, dimensionless; and
poi	=	Vapor pressure of pure component i, atmosphere

For an ideal gas, partial pressure of any component (also known as Dalton's Law) is expressed as:

pi

=

Yi x PT

where:

Yi	=	Mole fraction of component i in the gas, dimensionless; and
PT	=	Total pressure of the vapor, atmosphere.

Setting the above two equations as equal yields the mole fraction in the vapor.

Yi

=

(Poi x Xi)/PT

Assume the vapor is exposed to air; therefore, the total pressure is equal to 1.0 atmosphere.

Raoult's Law works best if the liquid and the gas are ideal solutions. For ideal solutions, the components in the liquid mixture are very similar chemically and physically, and the pressure of the gas is relatively low (approximately less than 3 atm). A more rigorous approach to estimating the gaseous mole fraction requires the Henry's Law constants in place of the pressure ratios. Henry's Law is applicable to non-ideal solutions, and these constants must be determined experimentally for each substance.

Only weight percents of the liquid components are provided; therefore, the liquid mole fraction, X, is estimated as follows:

Xi	=	[(Wti / MWi)] / E [(Wti ö MWi)]

Where:

Wti	=	Fraction by weight, dimensionless; and
MWi	=	Molecular weight, lb/lb-mole.

As an example, the calculated the liquid mole fraction of A in the mixture as follows:

To calculate the liquid mole fraction, X_i, and the vapor mole fraction, Y_i, the facility operator needs the physical properties of the substances A, B, and C are needed. The CRC Handbook of Chemistry and Physics is one source. Some other sources that provide information on the physical properties of substances include the Perry's Chemical Engineer's Handbook and the Handbook of Environmental Data on Organic Chemicals (Vershueren, 1983). In this example, the data for A, B, and C are:

Substances	Molecular Weight	Vapor Pressure (atm)
A	78	0.10
B	92	0.03
C	106	0.01

From the above properties, the facility operator uses the liquid mole fraction equation to calculate the liquid mole fraction of X_A, of substance A:

XA	=	[.05 / 78] / [(.05 / 78) + (.15 / 92) + (.80 / 106)]
	=	0.065

Similarly, the calculated X_B and X_C are 0.166 and 0.769, respectively.

Using the mole fraction in vapor equation and the calculated liquid mole fraction of A, X_A, the calculated the vapor mole fraction of A, Y_A, are follows:

YA	=	(0.10 / 1.0) x 0.065
	=	0.0065

The vapor mole fractions Y_B and Y_C are 0.005 and 0.00769, respectively. Because the total of vapor mole fractions equals 1.0, the balance of 0.922 is air.

To estimate the conversion factor, K_V, from molar unit to volumetric unit, use the following equation:

Kv

=

359 ft3/lb-mole x [(Ta + 460) oR / (32 + 460) oR]

where:

Ta

=

Measured temperature of the vent exhaust, oF.

Assume the vapor follows the ideal gas relationship. Therefore, one lb/mole of gas at standard temperature and pressure (32 F and 1 atmosphere) occupies 359 ft³/lb-mole. In this case, T is 70 F; therefore the conversion factor is corrected to the actual temperature T_a. In this example, K_v is calculated as follows:

Kv	=	359 ft3/lb-mole x (70 + 460) oR / (32 + 460) oR
	=	387 ft33/lb-mole

With all the available data, the following equation is used to estimate emissions of any substance as follows:

EMSA	=	1.44 x 105 ft3 x 0.0065 x (387 ft3/lb-mole)-1 x 78 lb/lb-mole
	=	189 lbs

Emissions of species B are 171 lbs and emissions of species C are 303 lbs.

2. Estimating Emissions of Trace Metals Using Engineering Calculations, with a Control Efficiency

Facility A burns 5 million gallons of distillate oil a year in its boilers. The average trace metal composition from all the storage tanks in the facility is reported as follows:

The ppmw is the part per million by weight, or one unit mass of the substance per million unit masses of the fluid. Assume all metals in the oil are emitted upon combustion.

The estimated trace metal emissions resulting from burning the oil as follows:

EMSi

=

(1 - CNTLi) x PR x D x Ci

where:

EMSi	=	Annual emissions of the ith trace metal, lbs;
CNTLi	=	Control efficiency for the ith substance (expressed as fraction), dimensionless;
PR	=	Amount of distillate oil burned, gals;
D	=	Density of distillate oil, lbs/gallon; and
Ci	=	Concentration of the ith element in distillate oil, ppmw or lb/106 lbs.

Facility A uses a baghouse (fabric filter) with an 85% control efficiency for trace metals except mercury. Assume the average density of distillate oil equals 7.2 lb/gal.

Using the nickel concentration of distillate oil, the estimated annual average and maximum hourly emissions of nickel as follows: Using the above equation:

EMSi	=	(1 -.85) x 5 x 106 gals x 7.2 lb/gal x 5.2 lb/106 lb
	=	28 lb of nickel emitted

Similarly, emissions for other trace contaminants are estimated by substituting their concentrations in distillate oil as reported. Since mercury behaves like a gas under these conditions and escapes through the baghouse, the control efficiency of the baghouse is zero.

3. Estimating Emissions of Carbon Tetrachloride Using Engineering Calculations Based on the Conversion of a Chemical Reaction

A facility manufactures a specific drug which used 5,000 pounds in 1993 of carbon tetrachloride as an intermediate. Ninety percent of carbon tetrachloride is converted to the manufacturer's product, and only 10% of carbon tetrachloride is lost at the end of the process. The effluent of this process is 85% liquid and 15% gas by weight. The gas is vented to the atmosphere and the liquid is drained into the sewer. (The publicly owned treatment works [POTW] accounts for the emissions from the sewer.) The weight ratio between carbon tetrachloride and other processed materials is 1:4.

To simplify the emission estimation, the process is diagrammed:

Using the available information, the estimated carbon tetrachloride emissions are as follows.

The calculation for emissions vented directly to the atmosphere at the plant is:

EMSi

=

[(R x PR) x (1 - Xc)] x (1 - L)

where:

EMS1	=	Emissions of carbon tetrachloride from exhaust, lbs;
R	=	Weight ratio of carbon tetrachloride to feed material, dimensionless;
PR	=	Amount of feed materials, lbs/year;
Xc	=	Fraction of conversion, carbon tetrachloride, dimensionless; and
L	=	Fraction of liquid discharged into the sewage, dimensionless.

Using this equation and the information provided about the process, the estimated carbon tetrachloride emissions directly at the plant in 1993 is:

EMS1	=	(.20) x 5,000 lbs x (1 - .90) x (1 - 0.85)
	=	15 lbs

4.9 Example Calculations Using Ideal Gas Relationships

The engineering calculations discussed in the previous section utilize ideal gas relations to generate emissions estimates. This section presents in condensed format a collection of eight of the the most commonly-used ideal gas calculations. Example calculations presented in this section are:

1. Parts per million by volume (ppmv) to parts per million by weight (ppmw) conversion;
2. ppmw to lb/hr calculation;
3. ppmv to lb/hr calculation;
4. ppmv to æg/m³ conversion;
5. Temperature correction: actual cubic feet per minute (acfm) to standard cubic feet per minute (scfm);
6. Water vapor correction: acfm to dscfm;
7. Oxygen in flue gas correction; and
8. CO₂ in flue gas correction.

NOTE: Examples #5 and #6 are adjustments of reported stack gas flow, while examples #7 and #8 are examples of adjustment of reported pollutant concentration. These two operations are the mathematical inverses of each other. Hence, any of these conversion equations can be switched from a pollutant concentration conversion to a stack gas flow rate conversion by simply inverting the conversion term in the equation.

Example #1: ppmv to ppmw conversion

Given:

Benzene measured at 4 ppmv in stack gas
(stack gas mostly air)

Required:

ppmw benzene in stack gas

Data:

Benzene molecular weight (MW) = 78.11

Air molecular weight = 29.0

MM = million

Example #2: ppmw to lb/hr calculation

Given:

10.77 ppmw benzene in stack gas (stack gas mostly air)

Stack flow of 1,200 scfm

Molar volume = 379 ft³ @ 59 F 1 ATM

MM = million

Required:

lb/hr benzene emitted in stack gas

Example #3: ppmv to lb/hr calculation

Given:

Benzene measured at 4 ppmv in stack gas

Stack flow of 1,200 scfm

Required:

lb/hr benzene emitted in stack gas

Data:

Benzene MW = 78.11

Molar volume = 379 ft3/lbmol (@ 60 F)

MM = million

Notes: This is a combination of Examples #1 and #2 but we don't need to know the composition or molecular weight of the stack gas (it cancels out).

When computing mass emissions of NO_x, use the molecular weight of NO₂ (MW = 46) in the calculation. This is the standard convention, even though most NO_x is actually emitted from combustion sources as NO.

Example #4: ppmv to æg/m³ conversion

Given:

Benzene measured at 4 ppmv in stack gas

Required:

æg/m³ benzene concentration in stack gas
(@ 25 ^oC reference temperature)

Data:

Benzene MW = 78.11

Molar volume = 24.45 m³/kgmol @ 25 ^oC

Conversion:

(where standard temperature = 25 ^oC)

Example #5: Temperature correction: acfm to scfm (stack gas flow rate correction)

Given:

Stack gas flow rate measured at 26 ft/sec

Stack diameter = 2.5 ft

Stack temperature = 175 ^oF

Required:

Stack gas flow in scfm (68 ^oF reference temperature)

Conversion:

Note: For elevated temperature stack gas flows, it is generally necessary to correct for both temperature and water content.

Example #6: Water Vapor correction: acfm to dscfm (stack gas flow rate correction)

Given:

Wet stack gas flow rate from Example #5 = 6367 scfm

Stack gas water vapor content = 2.1% (volume)

Required:

Dry stack gas flow (dscfm)

Conversion:

Flow_dry = Flow_wet [100% - %H₂0]

6367 scfm [1 - 0.021] = 6234 dscfm

Example #7: Oxygen in flue gas correction (pollutant concentration correction)

Given:

Particulate in stack gas = 0.045 grains/dscf
NO_x concentration in stack gas = 48 ppmv
Stack gas oxygen concentration = 4% (vol)

Required:

Stack gas particulate and NO_x concentrations corrected to 7% oxygen.

Conversion:

Conc_7% = Conc_X% [21% - 7% / 21% - X %]

Example #8: CO₂ in flue gas correction (pollutant concentration correction)

Given:

Particulate in stack gas = 0.05 gr/dscf

Stack gas CO₂ concentration = 9.5% (vol)

Required:

Stack gas particulate concentration corrected to 12% CO₂.

Conversion:

Conc_12% = Conc_X% [12% / X%]