Standard Operating Procedure for Generating a 

Quantitative Multi-Metals Reference Aerosol with 

the CES QAG 

June 9, 2005

DRAFT 

Submitted to: 

The Environmental Protection Agency 

Research Triangle Park, NC 

Prepared by: 

Cooper Environmental Services, LLC 

10180 SW Nimbus Blvd Suite J6 

Portland, Oregon 97223
Standard Operating Procedure for Generating a 

Quantitative Multi-Metals Reference Aerosol with 

the CES QAG 

June 9, 2005

DRAFT 

Submitted to: 

The Environmental Protection Agency 

Research Triangle Park, NC 

Prepared by: 

J.A. Cooper, B.E. Johnsen, K. Petterson, 

C. A. Yanca, M. Nakanishi, D. Barth 

Cooper Environmental Services 

10180 SW Nimbus Blvd Suite J6 

Portland, Oregon 97223
Standard Operating Procedure for Generating a 

Quantitative Multi-Metals Reference Aerosol with 

the CES QAG

Prepared by:___________________________________ Date:_________

 Catherine A. Yanca, Environmental Scientist 

Reviewed by: ___________________________________ Date:_________ 

 Krag A. Petterson, Environmental Scientist 

Reviewed by: ___________________________________ Date:_________ 

 Bruce E. Johnson, QA Manger 

Approved by: ___________________________________ Date:________ 

 John A. Cooper, Director 
Instrumental Method for a QAG: V1.0 Page i of vi

Executive Summary 

The QAG is a reference aerosol generator that produces a NIST-traceable aerosol of known 

analyte concentration. In the QAG, a NIST-traceable or equivalent solution containing an 

analyte or analytes of interest is conveyed to an aspirator where it is combined with a gas and 

nebulized to form an aerosol of liquid droplets. The smaller droplets continue through the 

system and are dried. The resulting salt particles and/or vapors are then emitted from the 

system as a reference aerosol of known concentration. Specifically, the QAG is used to 

generate a NIST-traceable reference aerosol that contains a known concentration of metal. 

This method can be used to spike controlled and uncontrolled emissions as well as laboratory 

air for the purpose of evaluating the accuracy and precision of aerosol measurement methods 

and/or calibration of methods. 

The QAG’s generated aerosol concentration ( a-QAG Ci ) is process traceable to NIST through 

the traceability of its components. The generated concentration is a function of the 

concentration of the solution standard ( s-QAG Ci ), total flow rate (Ft), rate of mass loss of the 

solution (Rm), and rate of vapor loss (Rv). Process traceability to NIST is established by using 

instruments that are NIST-traceable (e.g., calibrated with NIST standards) to measure these 

parameters. One exception is the standard solution used to generate the aerosol; solutions 

with NIST-traceable accuracies are either prepared in the laboratory or purchased from an 

outside vendor. 

There are five major components of a nebulizer-based QAG, as described below: 

1. The standard solution control system is required to transport the analyte-containing 

solution to the point of nebulization. This system is needed to regulate the flow of the 

solution from the reservoir to the nebulization cup and determine the solution mass 

loss rate. A peristaltic pump is included for cycling the NIST-traceable solution 

through the nebulizer cup as well as a laptop connected to a balance for measuring the 

mass loss of the solution. 

2. The nebulizer air control system is used to establish and measure the flow, 

temperature, pressure and saturation of the air used in the nebulization process (i.e., 

nebulizer air). This section of the QAG uses filtered and saturated compressed air to 

create the initial solution droplet aerosol. 

3. An ice bath for is needed to maintain the temperature of the nebulizer air at or near 

32°F. 

4. The nebulizer and vapor size control system is used for creation of the aerosol. It 

consists of three major components: the nebulizer cup, the nebulizer and nebulizer 

nozzle and the nebulizer settling-equilibrating chamber. 

The nebulizer cup contains the standard solution. This solution is continuously 

circulated from the nebulizer cup to an external reservoir in order to minimize the 

impact of vapor loss on solution concentration and allow for determination of the 

solution mass loss rate. The standard solution is aerosolized by a nebulizer, located 

inside the nebulizer cup. The nebulization process creates a droplet spray containing 
Instrumental Method for a QAG: V1.0 Page ii of vi

a wide range of droplet sizes. The largest droplets impact on the walls of the 

nebulizer cup and are recycled. The smaller droplets are entrained in the nebulizer air 

flow and pass into the settling-equilibration chamber. The function of the nebulizer 

settling-equilibration chamber is to remove and recycle all droplets greater than 30 

μm in diameter as well as to assure droplet-vapor equilibrium at 32°F. Thus, the only 

droplets emitted into the drying chamber have diameters less than 30 μm and have 

been equilibrated with water vapor at 32°F. 

5. The drying air and drying chamber with temperature and flow control is needed for 

drying the liquid aerosol into salt particles. Heated CDA (termed “drying air”) is 

introduced into the drying chamber for this purpose. 

The final product of the QAG is an aerosol containing dried salt particles of the analyte or 

analytes. The concentration of the analytes in the aerosol and the concentration uncertainty 

are calculated from the QAG’s recorded parameters. The uncertainty of the generated 

aerosol concentration is determined using standard propagation of error techniques relevant 

to those parameters. The uncertainty values for the parameters are those listed as certified 

uncertainties by the manufacturers and/or NIST. 
Instrumental Method for a QAG: V1.0 Page iii of vi

Table of Contents 

Executive Summary................................................................................................................. i 

List of Symbols .........................................................................................................................v 

List of Figures......................................................................................................................... vi 

1.0 Principle and Applicability ........................................................................................ 1 

1.1 Principle ................................................................................................................ 1 

1.2 Applicability ......................................................................................................... 1 

2.0 Range of Emission Characteristics............................................................................ 1 

2.1 Concentration........................................................................................................ 1 

2.2 Flow ...................................................................................................................... 1

2.3 Particle Size .......................................................................................................... 1 

2.4 Temperature .......................................................................................................... 1 

2.5 Species .................................................................................................................. 1 

3.0 Definitions.................................................................................................................... 2 

4.0 Operational Specifications ......................................................................................... 4 

4.1 Nebulizing Air Flow Rate (Fe) ............................................................................. 4 

4.2 Nebulizing Air Pressure (Pc)................................................................................. 4 

4.3 Nebulizing Air Temperature................................................................................. 4 

4.4 Nebulizer Cup Temperature.................................................................................. 4 

4.5 Ice Bath Temperature............................................................................................ 4 

4.6 Drying Air Flow Rate ........................................................................................... 4 

4.7 Drying Air Temperature ....................................................................................... 4 

5.0 NIST-Traceable Specifications .................................................................................. 4 

5.1 Mass Loss.............................................................................................................. 5 

5.2 Flow Rate.............................................................................................................. 5 

5.3 Rate of Vapor Loss ............................................................................................... 5 

5.4 Solution................................................................................................................. 5 

6.0 Apparatus .................................................................................................................... 6 

6.1 Quantitative Aerosol Generator ............................................................................ 6 

6.2 Standard Solution Control System........................................................................ 6 

6.3 Nebulizer Air Control System .............................................................................. 7 

6.4 Ice Bath ................................................................................................................. 8 
Instrumental Method for a QAG: V1.0 Page iv of vi

6.5 Nebulizer and Vapor Size Control System ........................................................... 8 

6.6 Drying Air and Drying Chamber System ............................................................. 9 

7.0 Supplies ...................................................................................................................... 10 

7.1 Standard Solutions .............................................................................................. 10 

7.2 Compressed Air .................................................................................................. 11 

7.3 Ice Bath ............................................................................................................... 11 

8.0 Pre-Test Performance Evaluation Procedures....................................................... 11 

8.1 Pre-Test Laboratory Preparation......................................................................... 11 

8.2 Pre-Test Field Preparation .................................................................................. 12 

8.3 Solution Concentration and Flow Rate Determination....................................... 13 

8.4 Solution Sample.................................................................................................. 13 

9.0 Generation of a Reference Aerosol with NIST-Traceable Accuracy ................... 13 

9.1 System Preparation ............................................................................................. 13 

9.2 Solution Exchange .............................................................................................. 14 

9.3 Flow Rate and Temperature Adjustments........................................................... 14 

9.4 Aerosol Generation and Performance Monitoring.............................................. 14 

9.5 Documentation of Performance .......................................................................... 14 

9.6 Shut-down........................................................................................................... 15 

9.7 Post-Test Procedures........................................................................................... 15 

10.0 Calculations ............................................................................................................... 15 

10.1 Generated Aerosol Concentration....................................................................... 15 

10.2 Generated Aerosol Concentration Uncertainty................................................... 16 

10.3 Solution Concentration and Flow Rate Set Points.............................................. 17 

10.4 Aerosol Emission Size ........................................................................................ 17 

11.0 Documentation of Quality Control and Assurance ............................................... 18 

11.1 Certifications....................................................................................................... 18 

11.2 Field Data Records.............................................................................................. 18 

12.0 Pollution Prevention ................................................................................................. 18 

13.0 Waste Management .................................................................................................. 18 

14.0 Figures and Tables.................................................................................................... 19 

15.0 References.................................................................................................................. 23 
Instrumental Method for a QAG: V1.0 Page v of vi

List of Symbols 

a QAG Ci− = Concentration of the ith element in the reference aerosol generated by the QAG. 

s QAG Ci− = Concentration of the ith element in the standard solution used for the QAG. 

Dliq = Diameter of the liquid droplets in the aerosol. 

Dsalt = Diameter of the salt particles in the aerosol. 

Fe = Flow of expanded nebulizer air in the QAG. 

Ft = Total combined flow of the nebulizer air and drying air in the QAG. 

M v = Mass of water vapor in a liter of saturated air. 

Pc = Absolute pressure of the compressed nebulizer air in the QAG. 

Pe = Pressure of the expanded nebulizer air in the QAG. 

Rm = Total rate of solution mass loss for the QAG. 

Rv = Rate of vapor loss of the QAG standard solution. 

ρ salt = Density of the analyte salt in the QAG. 

ρliq = The density of the liquid droplet in the QAG.

σ = One standard deviation. 
Instrumental Method for a QAG: V1.0 Page vi of vi

List of Figures 

Figure 1: A. Schematic of flow through QAG components. B. Overview of the set-up of the 

CES QAG.............................................................................................................. 19 

Figure 2: Schematic of the CES QAG standard solution control system. .............................. 19 

Figure 3: Schematic of the CES QAG nebulizer air control system....................................... 20 

Figure 4: Schematic of the CES QAG nebulizer and droplet size control system. ................ 20 

Figure 5: Schematic of the CES QAG drying air and drying chamber system. ..................... 21 
Instrumental Method for a QAG: V1.0 Page 1 of 1

1.0 Principle and Applicability 

1.1 Principle 

A solution containing an analyte or analytes of interest is conveyed to an aspirator where it is 

combined with a gas and nebulized to form an aerosol of liquid droplets. The smaller 

droplets continue through the system and are dried. The resulting salt particles and/or vapors 

are then emitted from the system as a reference aerosol of NIST-traceable concentration. 

1.2 Applicability 

This method is applicable to spiking controlled and uncontrolled emissions as well as 

laboratory air for the purpose of evaluating the accuracy and precision of aerosol 

measurement methods and/or calibration of methods. 

2.0 Range of Emission Characteristics 

2.1 Concentration 

The concentration of an analyte in the generator emissions can range between 0.001 and 

1000μg/m3 depending on the solution concentration, nebulizer configuration and the total 

flow of air through the Cooper Environmental Services (CES) quantitative aerosol generator 

(QAG). 

2.2 Flow 

The total flow of emissions can range from 10 to 1000 slpm. Total flow is dependent on the 

nebulizer configuration, nebulizer air flow and the flow of drying air. 

2.3 Particle Size 

The size of the dried salt particles is determined by the solution concentration and the liquid 

droplet size. The QAG should be operated such that the estimated physical diameter of the 

salt particles is less than 3-4μm (Section 10.4). 

2.4 Temperature 

The output temperature of the QAG emissions can be set between 200 and 400°F. 

Temperatures downstream of the QAG must be above the dew point of the emitted aerosol 

but can be as high as the required application. 

2.5 Species 

The QAG principles are generally applicable to a wide range of analytes and solvents 

(organic and inorganic). However, the application described in this method is for inorganic 
Instrumental Method for a QAG: V1.0 Page 2 of 2

metal salts in aqueous solutions. This can include soluble salts of elements ranging from 

atomic number 3 (Li) to 92 (U). 

3.0 Definitions 

Aerosol Generator System: System in which analytes contained within a solution are 

aerosolized, separated based on size, dried, and emitted. 

Aerosol: A suspension of solids and/or liquids in a gas at various relative concentrations. 

Analyte: A species (element, metal, etc.) of interest in an analytical method. 

Analytically NIST Traceable Parameter: A parameter whose value is traceable to NIST 

through a measurement that is NIST traceable1

. 

Applicable Concentration Range: The range of concentrations over which a QRAG must 

be able to produce an aerosol of NIST-traceable or equivalent analyte concentration to be 

used for a given application. 

Aspiration: The process by which a liquid is drawn from a reservoir through a narrow tube 

by creating a vacuum above the tube with fast moving air. 

Atomization: The process of converting a liquid into small suspended droplets. 

Certified Concentration Range: Range of concentrations for which the QAG is certified. 

Drying Air: Air added to the QAG at the point of the drying chamber that is used to help dry 

the aerosolized liquid droplets into salt particles. 

Generated Aerosol Concentration: The concentration of the aerosolized metal at the point 

of emission from the QAG. This concentration is a function of the solution concentration, 

total flow, rate of mass loss and rate of vapor loss; it can be calculated using Equation 1. 

Key Component: A piece of equipment or instrument that measures any parameter used to 

determine the generated aerosol concentration. 

Linearity: The degree to which two parameters are linearly related as determined by the 

value of the slope and correlation coefficient of a least squares regression analysis. 

Main Flow: Flow of gas through the aerosol generator, transport/interface, and sampling 

system. 

Make Up Flow (Air or Stack Gas): Flow of air and/or stack gas added after the aerosol is 

emitted from the QAG either before or as part of the transport/interface system. 
Instrumental Method for a QAG: V1.0 Page 3 of 3

Nebulization: A size-limiting atomization process in which larger droplets are removed from 

the aerosol through impaction or sedimentation prior to being emitted from a nebulizer. 

Nebulizer Air: Air flowing into the nebulizer that is combined with the NIST-traceable 

solution to create the aerosolized metals. 

NIST: The National Institute of Standards and Technology, Gaithersburg, MD. 

Particulate: A particle of solid or liquid matter. 

Process NIST Traceable: A parameter whose value is traceable to NIST through a 

procedure, the steps of which are each NIST traceable1. 

Quantitative Aerosol Generator (QAG): An aerosol generator system that uses analytes of 

known concentrations in aqueous solution to create aerosol emissions of known metal 

concentrations. 

Quantitative Reference Aerosol Generator (QRAG): An aerosol generator which emits an 

aerosol of known analyte concentration that is NIST or equivalent traceable. 

Sampling System: A collection of integrated components designed to collect a portion of an 

aerosol that accurately represents an analyte concentration. 

Stability: Percent relative standard deviation of a value measured over an extended period of 

time. 

Standard: Something established by authority, custom, or agreement for use as a rule or 

basis for comparison in measurement. 

Standard deviation: A parameter that indicates the way in which a probability function or a 

probability density function is centered around its mean and that is equal to the square root of 

the moment in which the deviation from the mean is squared. 

Total Flow: The combined flow of nebulizer air and drying air within the aerosol generation 

system. Total flow does not include air added to the transport system after the aerosol exits 

the QAG. 

Traceability to NIST: A documented procedure by which a measured response is related to 

a standard with an accuracy defined by and certified by the National Institute of Standards 

Technology (NIST). 

Traceability: A property of the result of a measurement or the value of a standard whereby it 

can be related to stated references, usually national or international standards, through an 

unbroken chain of comparisons all having stated uncertainties2

. 

Transport/Interface Component: That portion of a test arrangement that connects the 

QRAG to the point where the aerosol will be evaluated. 
Instrumental Method for a QAG: V1.0 Page 4 of 4

Uncertainty: An indication of the degree of reliability of a value usually expressed 

statistically (probability) as a multiple of the standard deviation of a set of measurements. 

Unless otherwise stated, the uncertainty in a mean value of a series of measurements will be 

the standard deviation. In the case of values based on calculations, the uncertainty in the 

value is equal to the propagated uncertainty based on the uncertainties in the parameters used 

in the calculations. 

4.0 Operational Specifications 

The following operational specifications must be met to ensure the QAG is functioning 

properly and the generated aerosol concentration can be accurately determined. 

4.1 Nebulizing Air Flow Rate (Fe) 

The flow must be set between 10 and 11 liters per minute corrected to 32°F. 

4.2 Nebulizing Air Pressure (Pc) 

The pressure must fall in the range of 15 to 20 psi-gauge. 

4.3 Nebulizing Air Temperature 

The temperature of the nebulizing air must be between 32 and 33°F. 

4.4 Nebulizer Cup Temperature 

The nebulizer cup temperature must fall in the range of 30 to 34°F. 

4.5 Ice Bath Temperature 

The ice bath must be kept between 32 and 33°F. 

4.6 Drying Air Flow Rate 

The flow rate must be between 25 and 75 slpm. 

4.7 Drying Air Temperature 

The drying air temperature must be between 220 and 400°F. 

5.0 NIST-Traceable Specifications 

In addition to meeting the above operational specifications (Section 0), the QAG’s 

parameters must be confirmed as NIST-traceable. The generated aerosol concentration is 
Instrumental Method for a QAG: V1.0 Page 5 of 5

process traceable to NIST through the traceability of the QAG’s key components1,

2

. The 

aerosol concentration is a function of the concentration of the solution standard, total flow 

rate, rate of mass loss of the solution, and rate of vapor loss (Equation 1 and Equation 2). 

This process traceability to NIST is established by meeting the following specifications: 

5.1 Mass Loss

The QAG solution rate of mass loss (Rm) is determined by the balance, which must be 

calibrated in the field with NIST-traceable mass standards. Balance readings must be ± 1% 

of the standard value and certification of the mass standards must be current. 

5.2 Flow Rate 

The QAG’s flow parameters, total flow rate (Ft) and flow rate of the expanded nebulizer air 

(Fe, used to calculate the rate of vapor loss (Rv); Equation 2), are measured by flow meters. 

The flow meters must be calibrated to ± 2% in the field with a primary flow calibrator such 

as the DryCal®3. The NIST standard certification must be current. 

5.3 Rate of Vapor Loss 

The rate of vapor loss (Rv) is dependent on the temperature and pressure of the expanded 

nebulizing air (Pe) as well as the pressure of the compressed nebulizing air (Pc; Equation 2). 

In addition, the vapor loss rate requires that the nebulizing air be saturated with water vapor 

at 32°F. This is assured by measuring the temperature of the nebulizing air with a NISTtraceable thermometer to confirm that it is 32 ± 1°F. The condition of saturation is assured 

by first passing the nebulizer air through a bubbler at room temperature and then through a 

condenser at 32°F. 

5.3.1 Temperature 

The mass of water vapor in one liter of saturated air is a referenced value at 32°F4

. The 

operator must confirm that the temperature of the nebulizing air is measured using a 

NIST-standardized thermometer with current certification. 

5.3.2 Pressure 

The operator must confirm that the ambient pressure and the absolute pressure of the 

compressed nebulizing air upstream of the nebulizer are measured using a NISTtraceable pressure gauge with current certification. 

5.4 Solution 

The analyte solution must be prepared using a NIST-traceable standard of the analyte(s). 

The operator must confirm that the standard certification has not expired. 
Instrumental Method for a QAG: V1.0 Page 6 of 6

6.0 Apparatus 

6.1 Quantitative Aerosol Generator 

Use any aerosol generator to generate a reference aerosol that meets the specifications of this 

method. A schematic of the CES QAG is shown in Figure 1. The five major components of 

a nebulizer-based QAG include: 

1. A standard solution control component required to regulate the flow of solution from 

the reservoir to the nebulization cup and determination of the solution mass loss rate. 

2. A nebulizer air control component that establishes and measures the flow, 

temperature, pressure and saturation of the nebulizer air. 

3. An ice bath for maintaining temperature of the nebulizer air at or near 32°F. 

4. A nebulizer and vapor size control and equilibration. 

5. A drying air and drying chamber with temperature and flow control. 

6.2 Standard Solution Control System 

This section of the QAG includes a peristaltic pump to cycle the NIST-traceable solution 

through the nebulizer cup and a laptop connected to a balance for measuring the mass loss of 

the solution (Figure 2). 

6.2.1 Solution Reservoir 

The solution reservoir must be large enough to hold a minimum of 1 liter of solution 

and small enough to fit completely and securely on the balance. It must be insulated 

with foam to prevent moisture from condensing on the outside of the reservoir. Note: 

it is important that the extraction and return of solution tubing not touch any part of the 

reservoir. 

6.2.2 Solution Transport Line 

Noroprene or equivalent tubing is used to transport the solution through the solution 

system. 

6.2.3 Peristaltic Pump 

A two-headed peristaltic pump is used to circulate the NIST-traceable solution between 

the solution reservoir and the nebulizer cup. The solution is pushed into the chamber at 

a rate of 15 ml/min and pulled out of the chamber at a rate of 17 ml/min. 

6.2.4 Balance 

The NIST-traceable solution and its reservoir are placed on a balance located next to 

the nebulizer/drying chamber assembly. The balance is used to measure the mass of 

the solution being condensed by the QAG. 
Instrumental Method for a QAG: V1.0 Page 7 of 7

6.2.5 Computer 

A computer is connected to the balance and is used to record the changing mass of the 

NIST-traceable solution continuously with custom software. These data are used to 

determine the rate of reservoir mass loss (Rm), which is the slope of the recorded 

reservoir mass over time. 

6.3 Nebulizer Air Control System 

This section of the QAG uses compressed air to create the initial solution droplet aerosol 

(Figure 3). 

6.3.1 Nebulizing Air Lines 

Stainless steel, PFA or equivalent tubing is used to transport the nebulizing air through 

the saturator, impinger, and nebulizer. 

6.3.2 Filter Units 

Filter units are used to remove oil and other particles from the nebulizing air. 

6.3.3 Pressure Regulator 

Downstream of the filter units, a precision pressure regulator is needed to control the 

pressure of air flowing into the QAG system to a nominal pressure of about 18 psi that 

is regulated to ± 0.5 psi-gauge. 

6.3.4 Flow Meter 

A flow meter is required for determining the flow rate of the compressed air which is 

used to calculate the flow rate of the expanded nebulization air (Fe). This flow rate 

which must be set to a pre-determined value based on the desired concentration of the 

aerosol emission (Section 10.3). 

6.3.5 Ball Valve 

A manual two-way ball valve is used to shut-off the flow of air to the nebulizer. 

6.3.6 Ambient Temperature Saturator 

The ambient temperature saturator is a bubbler half-filled with water. The nebulizer air 

is pushed through a PFA-coated stainless steel chamber and is bubbled through water 

to assure saturation with water vapor at room temperature. The saturator should be 

checked and refilled at least once a day. 
Instrumental Method for a QAG: V1.0 Page 8 of 8

6.3.7 Condenser 

Nebulizing air passing through the condenser is cooled to and saturated at 

approximately 32oF. The condenser should be checked and emptied at least once a 

day. 

6.3.8 Pressure Gauge 

A NIST-traceable pressure gauge is used to measure the pressure of the compressed air 

flowing into the nebulizer (Pc). 

6.4 Ice Bath 

Downstream of the ambient temperature saturator, the nebulizer air is pushed into a container 

filled with ice and water maintained at approximately 32o F. The condenser, nebulizer cup 

(which contains the nebulizer), and nebulizer settling-equilibration chamber are all housed 

within this container. The container should have a thermocouple and thermometer for 

monitoring the temperature of the ice bath and a drain to remove water. 

6.5 Nebulizer Droplet Size Control System 

This section of the QAG consists of three major components (Figure 4): 

1. Nebulizer and nebulizer nozzle 

2. Nebulizer cup 

3. Nebulizer settling-equilibrating chamber 

6.5.1 Nebulizer and Nebulizer Nozzle 

A NIST-traceable solution of known metal concentration is aerosolized by a nebulizer, 

such as a Collison nebulizer2

, located inside the nebulizer cup (see Figure XX-2). The 

cooled and saturated nebulizing air leaves the condenser and is pushed through the 

nebulizer nozzles. The bottom of the nebulizer nozzle is located about 3/8 of an inch 

below the surface of the solution. The nebulizing air is forced across the surface of the 

capillary tube causing the solution to be drawn into the high velocity air stream. This 

process creates a droplet spray containing a wide range of droplet sizes. The largest 

droplets impact on the walls of the nebulizer cup and are recycled. The smaller 

droplets are entrained in the nebulizer air flow and pass into the settling-equilibration 

chamber. 

6.5.2 Nebulizer Cup 

The nebulizer cup contains the standard solution. This solution is continuously 

circulated from the nebulizer cup to the external reservoir in order to minimize the 

impact of vapor loss on solution concentration and allow for determination of the 

solution mass loss rate. 
Instrumental Method for a QAG: V1.0 Page 9 of 9

A thermocouple attached to the nebulizer cup is connected to a NIST-traceable 

thermometer in order to measure the temperature of the cup. The temperature of the 

cup must be kept at 32°F, which is the effective temperature of Mv, the term for the 

mass of water vapor in one liter of saturated air. 

6.5.3 Nebulizer Settling-Equilibration Chamber 

The function of the nebulizer settling-equilibration chamber is to remove and recycle 

all droplets greater than 30 μm in diameter as well as to assure droplet-vapor 

equilibrium at 32°F. Thus, the only droplets emitted into the drying chamber have 

diameters less than 30 μm and have been equilibrated with water vapor at 32°F. 

6.6 Drying Air and Drying Chamber System 

The drying air is heated and used for drying the liquid aerosol into salt particles. In this part 

of the QAG, clean dry air (CDA) air is required (Figure 5). 

6.6.1 Drying Air Lines 

Stainless steel, PFA or equivalent tubing is used to transport the CDA through the tube 

heaters and into the drying chamber. 

6.6.2 Filter Units 

Filter units are used to remove oil and other particles from the drying air. 

6.6.3 Pressure Regulator 

The pressure regulator on the drying air line is used to adjust the flow of drying air to 

the desired flow rate. 

6.6.4 Drying Air Flow Meter 

The drying air flow meter is used to measure the drying air flow for the purpose of 

adjusting the pressure regulator. 

6.6.5 Tube Heaters 

The drying air is split into two lines downstream of the flow meter and each line is 

passed through a tube heater just before the air enters the drying chamber. Both heaters 

are maintained at 300 ± 20oF. 

6.6.6 Drying Air Ring 

After being heated by the tube heaters, the drying air enters the drying chamber 

through a series of holes in the drying air ring. The air increases the drying rate of 

liquid droplets and acts as an air curtain that keeps the droplets from impacting the 

chamber walls.
Instrumental Method for a QAG: V1.0 Page 10 of 10

6.6.7 Drying Chamber 

The nebulized liquid droplets from the nebulizer settling-equilibration chamber are 

combined with the drying air in the drying chamber, which is heated to approximately 

250oF. The droplets are dried in the chamber and the resulting aerosolized metals are 

emitted into the transport system. 

6.6.8 Drying Chamber Heaters 

The drying chamber is heated by a tape heater or a blanket heater maintained at 

approximately 250oF. 

6.6.9 Flow Meter 

A flow meter is required for determining the total flow rate (Ft). The user can 

determine the total flow by either (1) measuring the drying air flow rate with a flow 

meter and adding this to the nebulizer air flow rate, or (2) measuring the main flow rate 

with a flow meter and subtracting all flows except the total flow. 

7.0 Supplies 

7.1 Standard Solutions 

The QAG generates an aerosol with NIST-traceable accuracy based on the NIST-traceable 

accuracy of the standard solutions used. These solutions are consumed at a rate of about 5 to 

10 ml/hour. An adequate supply of solutions at various concentrations required by a test plan 

should be prepared prior to the testing. The primary requirements of these solutions are that 

(1) the accuracy of the analyte concentrations be NIST-traceable (2) the solutions be stable 

over the period of their use and (3) the calculated diameter of the resulting dried salt particles 

be less than 4μm (Section 10.4). 

7.1.1 NIST-Traceable Accuracy 

Solutions with NIST-traceable accuracies can be prepared in the laboratory or 

purchased from an outside vendor. Solution accuracies are generally expected to be 

better than 0.5% at the 95% confidence level. At these accuracies, uncertainties in 

standard solution concentrations are insignificant contributors to the uncertainty of the 

generated aerosol concentration. 

7.1.2 Standard Solution Stability 

The stability of the standard solution over a period of months is generally assured if the 

metal analytes are prepared as nitrates in 1% nitric acid solutions. Other metal analyte 

salts and acids may be used, but stability needs to be documented either by laboratory 

testing or by vendor certification. Particular care should be taken when using standard 

solutions with multiple analytes to assure analyte stability. 
Instrumental Method for a QAG: V1.0 Page 11 of 11

7.1.3 Solution Volume 

The volume of standard solution prepared should generally be at least 2 liters or more. 

Although only a fraction of this volume might be used, the larger volume is required by 

the solution reservoir to minimize solution concentration increases due to evaporation 

over the test period. Under normal operating conditions, the solution concentration 

increase is less than 1% over test periods of about 10 hours, or about 0.1% per hour, 

which is usually insignificant for test periods of a few hours. 

7.1.4 Analyte Concentration 

The concentration of analytes in the standard solution is controlled so as to be less than 

the concentration that would result in dried salt particles with diameters greater than 

about 4μm (Section 10.4). With nitrates in nitric acid solutions, this will generally be 

the case if the dissolved solids are less than about 500 to 1000 ppm. A single metal 

analyte concentration of about 100 ppm will result in an aerosol concentration of about 

100 μg/m3

 if the typical QAG operating conditions are used with a total flow of about 

100 slpm. Thus, the QAG can be used to generate aerosols with multiple analytes in 

range of EPA emission standards without generating salt particles greater than about 

4μm in diameter that might otherwise have significant transport issues. 

7.2 Compressed Air 

The QAG requires at least 40 psi and 80 slpm (approximately 2 cfm) of instrument air. 

Between 10-12 lpm are needed to maintain the flow of nebulizing air and between 25 and 75 

slpm are needed for the drying air flow, depending on the desired emission concentration. 

The selected compressed air source should be sufficient to meet the flow requirements for the 

desired tests runs. 

7.3 Ice Bath 

The QAG requires ice sufficient for filling the ice bath container and maintaining the 

temperature of the nebulizer air at 32°F for the duration of the test. 

8.0 Pre-Test Performance Evaluation Procedures 

8.1 Pre-Test Laboratory Preparation 

The following system checks and preparations must be conducted in the laboratory prior to 

shipping and assembling the QAG at a test site. 

8.1.1 Certification Check 

Confirm that all required NIST-traceable certificates are valid. 
Instrumental Method for a QAG: V1.0 Page 12 of 12

8.1.2 Operations Check 

Confirm that the general operation of the QAG meets the manufacturer’s 

specifications. 

8.1.3 Analyte Solution Preparation 

Prepare a sufficient amount of analyte solution for the length of the test; for example, 

two liters of solution is sufficient for a 12-hour run. 

8.2 Pre-Test Field Preparation 

The following procedures must be conducted after receiving the QAG at the test site and 

prior to operating it in the field. 

8.2.1 Physical Integrity Check 

Check the QAG’s physical components to ensure no parts were damaged in shipping. 

8.2.2 Assembly 

Assemble the QAG per manufacturer’s instructions. 

8.2.3 Operations Check and Calibration 

Check the QAG’s operations to ensure that it meets the manufacturer’s specifications. 

Confirm that the pressure gauges used to measure the ambient air and nebulizing air 

pressures are NIST-certified and the certifications are current. Confirm that the 

thermometer used to measure the temperature of the nebulizing air is NIST-certified 

and the certificate is valid. In addition, calibrate the following components prior to 

installation and document all pre-test check results and readings: 

Balance Calibration: Calibrate the balance using NIST-traceable masses; confirm that 

the readings are ±1% of the standard and the NIST certificates are current. 

Flow Meter Calibration. Calibrate flow meter with a primary flow calibrator such as 

a DryCal®3

; confirm that the readings are within 2% of the NIST-traceable certificate 

values. 

8.2.4 Installation. 

Install the QAG in the test facility per test plan requirements. 

8.2.5 Pressure and Leak Check 

The QAG system uses positive pressure, and the nebulizer air flow line must be leak 

checked before testing. Cap off the nebulizer air line just before the nebulizer, 
Instrumental Method for a QAG: V1.0 Page 13 of 13

pressurize the line, and check for leaks using an appropriate leak indicator. Tighten 

any sections of the line where leaks are indicated. 

8.2.6 Mass-Loss Evaluation 

Before running the QAG with NIST-traceable solution, the operator must conduct a 

mass loss rate evaluation test. Follow the instructions below for starting and running 

the QAG with a NIST-traceable solution, and substitute a blank solution of 5% nitric 

acid and distilled water. Run the QAG for 3 to 5 hours using the blank; this also allows 

the QAG to thermally equilibrate. Calculate the slope and correlation coefficient for 

the decrease in the weight of the reservoir over the run period. The QAG is 

functioning properly if the slope is between 0.1 and 0.2 and the correlation coefficient 

is better than 0.99. 

8.3 Solution Concentration and Flow Rate Determination 

Using the equation for generated aerosol concentration (Equation 1), determine the necessary 

solution concentration and flow rates set points for the desired emission concentrations (see 

section 10.3). 

8.4 Solution Sample 

Collect and store a 50 ml sample of the analyte solution for possible quality assurance checks 

at a later time if necessary. 

9.0 Generation of a Reference Aerosol with NIST-Traceable Accuracy 

9.1 System Preparation 

Connect the thermometers for the ice bath and nebulizer cup. Fill the ice bath container with 

ice, making sure it surrounds the impinger and nebulizer cup. If an ice bath is left from a 

previous run, drain the water and add enough ice to ensure that the temperature of the bath 

remains at 32 ± 1°F during the test run. While the ice bath is stabilizing, turn on the main 

flow pump. Adjust the flow to the rate specified in the test plan. Next, turn on the drying air 

flow and adjust the pressure regulator until the flow reaches the desired rate. Periodically 

check the drying air flow and readjust as necessary as it will tend to drop after the initial 

adjustment. Turn on the tube heaters and adjust the set point to 300°F. Switch on the drying 

chamber heaters to 125°F and start increasing the temperatures by 50°F increments to the set 

point. At this time, turn on any heaters associated with the transport system. When the 

cooler is full of ice, add water to 1” below the top of the cooler wall and insulate any gaps at 

the top of the cooler with foam. Continue to increase the temperature of the heaters 

throughout the solution exchange process described below until they reach their set points. 

Continue to monitor and adjust QAG operating parameters as necessary. 
Instrumental Method for a QAG: V1.0 Page 14 of 14

9.2 Solution Exchange 

The 5% nitric acid solution left in the bottom of the nebulizer cup after the mass loss 

evaluation must be cycled out of the system and replaced with the analyte solution. Using 

the tubes connecting the peristaltic pump to the reservoir, pump the distilled water out of the 

nebulizer cup and into an empty beaker while simultaneously pumping 300 ml of the analyte 

solution from another beaker into the chamber. When all of the analyte solution has been 

pumped through the chamber, place the remaining analyte solution in an empty reservoir, 

swirl gently, center the reservoir on the balance, and replace the peristaltic pump tubes. 

Gently lift the reservoir off the balance, zero the balance, and place the reservoir back down, 

taking care to ensure that the peristaltic pump tubes are not touching any part of the reservoir 

itself. Once the solution is pumping in and out of the reservoir, turn on the laptop and the 

balance software. Monitor the mass of the reservoir until it begins to fluctuate around a 

constant mean. 

9.3 Flow Rate and Temperature Adjustments 

At this point, the flow rates and heaters must be checked and adjusted again if necessary. 

During this process, turn on the sample system and bring it into equilibrium. The QAG 

system is in equilibrium when the operational specifications are met (Section 0), the total 

flow is stable, the flow of drying air is stable, and the heaters are operating at their set points. 

9.4 Aerosol Generation and Performance Monitoring 

When the QAG is in equilibrium, turn on the nebulizer flow by slowly opening the manual 

ball valve. Check to make sure the pressure regulator is controlling the flow at the flow set 

point (between 10 and 11 slpm) and adjust if necessary. When the nebulizer flow is on, the 

QAG is functioning as an aerosol generator. Check to ensure the pressure regulator and flow 

meter are stable at the desired set point. Monitor the performance of the QAG for the next 30 

minutes, making minor adjustments if necessary. During this time, the sampling system 

results should also be monitored to ensure that system is functioning properly. The QAG 

should be checked again after 90 minutes of running time and any necessary minor 

adjustments should be made. Before leaving the QAG for any overnight runs, the operator 

should pack fresh ice into the cooler. 

9.5 Documentation of Performance 

The QAG’s performance must be documented using a data sheet such as Figure 6. Before 

beginning a test, fill out the top of the data sheet with the appropriate test information. Take 

a reading of the atmospheric pressure with a NIST-traceable pressure gauge and record this 

value, which is equivalent to the pressure of the expanded nebulizer air (Pe). After the QAG 

reaches equilibrium, the nebulizer flow is on, and the system is generating an aerosol, record 

the time and the following parameters: the temperature of the ice bath, the temperature of the 

nebulizer cup (for Mv), the nebulizer flow rate (Fe), the pressure of the nebulizer compressed 

air (Pc), the flow rate of the drying air, the pressure of the drying air, the temperature of the 

drying air (i.e., tube heater temperature), the total flow rate (Ft), room temperature, room 
Instrumental Method for a QAG: V1.0 Section 10.0 Calculations Page 15 of 15

humidity, and the weight of the solution. Document new readings for these parameters every 

1 hour. Also record bags of ice added and time as well as any necessary notes. 

9.6 Shut-down 

To turn the QAG off after testing, first close the manual ball valve on the nebulizing air line 

and shut off the flow. Turn off all of the heaters. Next, turn off the drying air flow and shut 

down the sampling system. Pump as much of the solution out of the droplet generating 

chamber as possible and turn off the peristaltic pump, balance, and laptop. Finally, shut off 

the main flow. 

9.7 Post-Test Procedures 

9.7.1 Balance Check 

Check the balance calibration following the procedure described in Section 8.2.3. 

9.7.2 Flow Meter Check 

Check the flow meters calibrations following the procedure described in Section 8.2.3. 

9.7.3 Ambient Pressure Reading 

Take a final reading of the ambient pressure with a NIST-traceable pressure gauge. 

9.7.4 Solution Sample 

Collect and store an additional 50 ml sample of the analyte solution for possible quality 

assurance checks at a later time if necessary. 

10.0 Calculations 

10.1 Generated Aerosol Concentration 

The following equation is used to calculate the generated aerosol concentration of the ith 

element ( a-QAG Ci ) from the QAG’s recorded parameters:

(R R ) F

C C m v

t

s QAG

a QAG i

i = −

−

−

Equation 1

Where: 

s-QAG Ci = Concentration of the ith element in the QAG’s NIST 

 traceable solution. 
Instrumental Method for a QAG: V1.0 Page 16 of 16

Ft = Total flow, i.e., the combined flow of nebulizer air and drying air 

 added within the aerosol generation system, determined by the 

 flow meter located between the QAG and the transport system. 

Rm = Measured rate of reservoir mass loss, determined as the slope of a 

 linear least squares fit of the reservoir mass data over the period of 

 a test or series of tests. 

Rv = Rate of vapor loss is a calculated value based on the following 

 equation: 

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = −

c

e

v e v P

P R F M 1 Equation 2

Where: 

Fe = Flow rate of the expanded nebulization air as measured by the flow 

 meter on the nebulizing air line. 

Mv = Mass of water vapor in a liter of saturated air at 32 °F. This value 

 has been well defined and documented3: 

 Mv (32°F) = 4.847 mg/liter 

Pe = Pressure of the expanded gas outside the nebulizer nozzle. Since 

 the droplet generating chamber and the droplet size selector are 

 open to the atmosphere, Pe is the atmospheric pressure recorded 

 from the field barometer reading. 

Pc = Absolute pressure of the compressed air upstream of the nebulizer 

 nozzle, calculated by adding the atmospheric pressure to the gauge 

 pressure. 

10.2 Generated Aerosol Concentration Uncertainty. 

The uncertainty of the generated aerosol concentration ( a-QAG Ci

σ ) is determined using standard 

propagation of error techniques5

 relevant to the parameters of Equation 1. The uncertainty 

values for the parameters are those listed as certified uncertainties by the manufacturers 

and/or NIST. This procedure is consistent with those used at NIST6,7,8. 

The uncertainty of the generated aerosol concentration ( a-QAG Ci ) is calculated using the 

following equation: 

2

m v

(R R )

2

t

F

2

s-QAG

i

a QAG C

C i (R R )

σ

F

σ

C

σ

σ C t m v s-QAG

i

a-QAG

i ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

− + ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = − − Equation 3
Instrumental Method for a QAG: V1.0 Section 10.0 Calculations Page 17 of 17

Where: ( ) ( )

2

R

2

(Rm Rv ) Rm v σ = σ + σ −

 Equation 4

and 

2

c

e

P

P 1 2

v

M

2

e

F

R v

P

P 1

σ

M

σ

F

σ

σ R c

e

e v

v

⎟

⎟

⎟

⎟

⎟

⎠

⎞

⎜

⎜

⎜

⎜

⎜

⎝

⎛

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ −

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ −

 Equation 5

and 

2

c

P

2

e

P

c

e

c

e

P

P

P P P

P

P

P 1

c e c

e

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ =

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ −

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ − σ σ

σ

1 Equation 6

10.3 Solution Concentration and Flow Rate Set Points 

To determine the required solution concentration and flow rate set points for given test run, 

select a desired concentration of the QAG’s aerosol emissions ( a-QAG Ci ). Use the expanded 

form of Equation 1:

 ⎥

⎦

⎤ ⎢

⎣

⎡

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = − −

−

−

c

e

m e v

t

s QAG

a QAG i

i P

P R F M 1

F

C C

Plug in the desired concentration ( a-QAG Ci ), the estimated rate of mass loss (Rm; see also 

section 8.3), the mass of water vapor in a liter of saturated air at 32 °F (Mv, 32 °F = 4.847 

mg/liter), the pressure of the expanded nebulization air (Pe), and the absolute pressure of the 

compressed nebulizing air (Pc). Solve for an appropriate combination of solution 

concentration ( s-QAG Ci ) and flow rates, bearing in mind that total flow (Ft) equals the 

expanded flow of nebulizing air (Fe; which must be between 10 and 12 lpm) plus the drying 

air flow (which can range from 28 to 1990 lpm). 

10.4 Aerosol Emission Size 

Use the following equation to determine the size of the salt particles emitted by the QAG: 
Instrumental Method for a QAG: V1.0 Section 13.0 Waste Management Page 18 of 18

3

salt

liq

s-QAG

i

salt liq

C

D D ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = ρ

ρ

Equation 7

Where: 

Dsalt = The diameter of the salt in μm. 

Dliq = The diameter of the liquid droplets in μm as specified by the 

 nebulizer manufacturer in μm. 

s-QAG Ci = The concentration of the analyte standard in the NIST-traceable 

 solution in grams of analyte salt per gram of solution 

ρsalt = The density of the analyte salt in g/m3

. 

ρliq = The density of the liquid droplet in g/m3

. 

11.0 Documentation of Quality Control and Assurance 

11.1 Certifications 

Prepare a check list and confirm the certifications of NIST-traceable components. Assemble 

the certifications of NIST traceability for each component. 

11.2 Field Data Records 

Create and use a data sheet for the calibration the balance and flow meters in the field. 

12.0 Pollution Prevention 

The excess aerosol generated by the QAG should be trapped in a filter and disposed of 

according to the appropriate regulations. The unused solution should also be disposed of 

according to regulation. 

13.0 Waste Management 

The solution standards should be handled according to their Material Safety Data Sheets. 
Instrumental Method for a QAG: V1.0 Page 19 of 19

14.0 Figures and Tables 

 

 A. B. 

Figure 1: A. Schematic of flow through QAG components. B. Overview of the set-up of 

the CES QAG. 

Figure 2: Schematic of the CES QAG standard solution control system. 
Instrumental Method for a QAG: V1.0 Page 20 of 20

Figure 3: Schematic of the CES QAG nebulizer air control system. 

Figure 4: Schematic of the CES QAG nebulizer and droplet size control system. 
Instrumental Method for a QAG: V1.0 Page 21 of 21

Figure 5: Schematic of the CES QAG drying air and drying chamber system. 
Instrumental Method for a QAG: V1.0 Page 22 of 22 Operator: Soln. Conc: Location: Spiking: Notes: # Bags Neb. Pres. (psi) Make-Up Air Pressure (in. H2O) Transport Temp (°F) Make-Up Air Temp (°F) Neb. Cold Bath (°F) Neb. Air (°F) Added Ice Spike Soln. Mass (g) Make-Up Air Flow (slpm) Room Temp (°F) Room (RH) Stack Gas Flow (lpm) Main Flow (slpm) Neb. Cup (°F) Time Data Sheet QAG M-301 Tests Date: Start Date/Time: Stop Date/Time: Time of Record Neb. Flow (lpm) Figure 6: Sample data sheet for the QAG. 
Instrumental Method for a QAG: V1.0 Page 23 of 23

15.0 References

1. Scott Specialty Gases. Scott Gas Mixtures Data: Gas and Liquid Mixture Basics. 

Plumsteadville, PA: Scott Specialty Gases; 2004. 

2. Bureau International des Poids et Mesures, International Electrotechnical 

Commission, International Federation of Clinical Chemistry and Laboratory 

Medicine, International Organization for Standardization, International Union of Pure 

and Applied Chemistry International Union of Pure and Applied Physics, 

International Organization of Legal Metrology [BIPM, IEC, IFCC, ISO, IUPAC, 

IUPAP, OIML]. International Vocabulary of Basic and General Terms in Metrology 

(VIM). Geneva, Switzerland: BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML; 1993. 

Available from: ISO, Geneva, Switzerland; ISBN 92-67-01075-1. 

3. Smithsonian Physical Tables, 9th Rev. Ed. Washington D.C.: Smithsonian Institution 

Press; 1954. 

4. Scace, G.E. and J.T. Hodges. Uncertainty of the NIST Low Frost-Point Humidity 

Generator. Gaithersburg, MD: National Institute of Standards and Technology; 2004. 

5. McClave, J.T., F.H. Dietrich, II, and T. Sincich. Statistics, 7th Ed. Upper Saddle 

River, NJ: Prentice Hall; 1997. 

6. Taylor, B.N. and C.E. Kuyatt. Guidelines for Evaluating and Expressing the 

Uncertainty of NIST Measurement Results. Gaithersburg, MD: National Institute of 

Standards and Technology [NIST]; 1994. Available from: NIST, Gaithersburg, MD; 

TN 1297. 

7. American National Standards Institute/National Conference of Standards 

Laboratories [ANSI/NCSL]. U.S. Guide to the Expression of Uncertainty in 

Measurement. Washington, D.C: ANSI/NCSL; 1997. Available from: NCSL 

International, Washington, D.C; Z540-2-1996. 

8. May, K.R. The Collison nebulizer: description, performance and application. Aerosol 

Science 1973; 4: 253-243.