RESIDENCE TIME FOR AIR MONITOIRNG STATIONS

Laura Niles Quality Assurance Section California Resources Board

May/June 2014

RESIDENCE TIME • It is how long the ambient air takes to go

from the inlet probe to the analyzer • Parameters Include: O3, NO2, CO, SO2,

H2S, NMHC etc. • Measured in seconds • Must be defensible in court

IMPORTANCE OF RESIDENCE TIME

• Reactivity of air pollutants in the probe line

CRITERIA LIMITS

• U.S. EPA criteria: less than 20 seconds • Reference: CFR Title 40 Part 58 Appendix E Section 9 under Probe

Material & Pollutant Sample Residence Time

FURTHERMORE

• Other studies indicate that a 10 second or less residence time is easily achievable.

• Therefore, sampling probes for reactive gas monitors at NCore and at NO2sites MUST have a sample residence time less than 20 seconds.

Internet/Phone Line

Measure Pressure Drop from line to Manifold

• Pressure drop should be < 1” of H2O • Measured at the manifold • Don’t want to overcome pump vacuum

in analyzers • Indicates you are sampling ambient air • Document your results anytime there is

a change • Defensible data

MEASURING TOOLS For Calculating Residence Time

• Vernier Caliper • Flow Meter (liters) • Measuring Tape (metric)

STEPS TO MEASURE RESIDENCE TIME

• Obtain internal diameters of probe tubing line, manifold and filter holders.

• Obtain probe, manifold and filter holder lengths.

• Obtain Flows from analyzer(s) – Obtain Flow from and of booster pump

(if any)

Probe

L = 4.7 m ID = 6.4 mm

6.40 4.70

Booster Pump

LPM = 9.15

6.40 4.70

9.15

Manifold Length = 0.3 m ID = 46 mm

6.40 4.70

9.15

46.00 0.30

O3 analyzer flow = 0.754 LPM

Length = 2.68 m ID = 3.2 mm

6.40 4.70

9.15

46.00 0.30

O3

3.20 2.68 0.754

As the numbers are added the flow (Q), time and total residence time cells begin to populate.

Length = 3.13 m ID = 3.2 mm

NO2 analyzer flow = 0.850 LPM

6.40 4.70

9.15

46.00 0.30

O3

3.20 2.68 0.754

3.13

NO/NOx/NO2

3.20

0.850

Add all the lengths, internal diameters and flows for all analyzers connected to the manifold.

6.40 4.70

9.15

46.00 0.30

O3

3.20 2.68 0.754

3.13

NO/NOx/NO2

3.20

0.850

THC

3.20 2.50 0.720

CO

3.20 2.50 0.730

SO2

3.20 2.50 0.900

6.40 4.70

9.15

46.00 0.30

O3

3.20 2.68 0.754

3.13

NO/NOx/NO2

3.20

0.850

THC

3.20 2.50 0.720

CO

3.20 2.50 0.730

SO2

3.20 2.50 0.900

1.71 1.78 1.67 1.65 1.34 4.69 4.75 4.65 4.63 4.31

13.104 13.104 0.69 2.28

The residence time for each analyzer.

Caution!!

• If you take analyzers offline it will change the residence time for the remaining analyzers.

• Will Residence Time INCREASE or DECREASE?

• Let’s See

6.40 4.70

9.15

46.00 0.30

O3

3.20 2.68 0.754

3.13

NO/NOx/NO2

3.20

0.850

THC

3.20 2.50 0.720

CO

3.20 2.50 0.730

SO2

3.20 2.50 0.900

1.71 1.78 1.67 1.65 1.34 4.69 4.75 4.65 4.63 4.31

13.104 13.104 0.69 2.28

You need to take the CO analyzer offline.

#DIV/0! #DIV/0!

6.40 4.70

9.15

46.00 0.30

O3

3.20 2.68 0.754

3.13

NO/NOx/NO2

3.20

0.850

THC

3.20 2.50 0.720

CO

3.20 2.50 0.730

SO2

3.20 2.50 0.900

1.71 1.78 1.67 1.34 4.86 4.93 4.82 4.49

12.374 12.374 0.73 2.42

Residence time changes for remaining analyzers because the total flow is altered.

#DIV/0! #DIV/0!

Multiple Diameter Tubing Residence Time

38.1

WHERE TO FIND HELP

• US EPA Quality Assurance Handbook for Air Pollution Measurement Systems Volume II

• Excel Spreadsheet from ARB QA

ACTION TAKEN IF RESIDENCE TIME EXCEEDS CRITERIA LIMITS

• A Corrective Action Notification (CAN) is issued

• Station Operator takes action

SUMMARY

• Residence Time is one of the most important requirements at an air monitoring station

• Determine the ID sizes, length, and flows

• Maintain the residence time below 20 seconds to restrict reactivity in the probe line

Contact Information: Laura Niles Air Pollution Specialist Quality Assurance Section California Air Resources Board (916) 322-9192 lniles@arb.ca.gov

QUESTIONS?