EPA \ TAQMN \ Quality Assurance \ Performance Audit

Performance Audit

Performance audits are used to assess the monitoring system (including the on site monitoring station and laboratory) and the quality at which it is functioning. Auditing personnel will test and grade the monitoring instruments, standard gases, sample analysis techniques, and data processing procedures. This is a quantitative assessment task and auditing methods will differ with various instruments and equipment.

1. Auditing of air pollution gases analysis

Standard gases of various densities will be injected into the analysis instrument during audit with density range being three to four different densities between zero and the maximum range on the instrument. After the standard gases are diluted they will be injected into the analysis instrument and compared to the numbers of the known densities to calculate the deviation percentage.

Also, the standard gas ozone during audit is taken from the O3 generator in the calibrator which produces ozones of various densities which are injected into a certified analyzer used as a transfer standard which is taken to the audited monitoring station and compared to the ozone analysis instrument in the station to assess the precision of the ozone analysis instrument in the station.

The standard gases used by this administration during audits include CO, NO, SO2, C3H8 in high density gas cylinders which are diluted through calibrators into standard gases of various densities. The standard gases listed above must follow the highest standards such as those listed by America's National Institute of Standards and Technology (NIST) and their standard reference materials (SRM) or the their EPA's national traceable reference materials (NTRM). Also, gases produced by the gas manufacturers intermediate standard (GMIS) can also be used as standard materials.

Our testing stations include analysis instruments for sulfur nitrate (SO2), nitrogen oxides (Nox, NO, NO2), ozone (O3), carbon monoxide (CO), and hydrocarbons (HC) and performance audits are held once annually (table 1). Table 2 shows the accepted audit result standards of the administration --- automatic monitoring facilities data quality goals have been amended according to foreign standards, our monitoring instrument specifications, and opinions from scholars and specialists.

Audited Item Ozone analyzer (O3) Nitrogen oxide analysis instrument (Nox, NO, NO2) Carbon monoxide analysis instrument (CO) Sulfur nitrate analysis instrument (SO2) Hydrocarbon analysis instrument (HC)
Monitor frequency Continuous automatic monitoring (hourly average value) Continuous automatic monitoring (hourly average value) Continuous automatic monitoring (hourly average value) Continuous automatic monitoring (hourly average value) Continuous automatic monitoring (hourly average value)
Monitored stations 78 80 79 80 39
Monitor method Absorption of UV rays Chemiluminescence Non-scattering and infrared absorption method Ultraviolet fluorescence method Flame ionization detection method
Usable figures R.O.C. Air quality monitoring report (for specific information contact quality assurance at 07-776-1190)
[Table 1 Auditing categories in air pollution gas analysis]

Monitored Item Precision Linear Slope Intercept
Gas dilution calibration system (air) ±5% ≧0.9950 N/A ±3%F.S.
Gas dilution calibration system (gas) ±5% ≧0.9950 N/A ±3%F.S.
Sulfur nitrate (SO2) ±15% ≧0.9950 0.85-1.15 ±3%F.S.
Nitrogen oxide (Nox) ±15% ≧0.9950 0.85-1.15 ±3%F.S.
Nitrogen conversion rate ≧96% N/A N/A N/A
Carbon monoxide (CO) ±15% ≧0.9950 0.85-1.15 ±3%F.S.
Ozone (O3) ±15% ≧0.9950 0.85-1.15 ±3%F.S.
Total hydrocarbons (THC) ±15% ≧0.9950 0.85-1.15 ±3%F.S.
PM10 flow ±10% N/A N/A N/A
Wind speed ±0.25m/s WS <5m/s ±2% WS ≧5m/s N/A N/A N/A N/A
Wind direction ±5 degrees N/A N/A N/A
Thermometer ±0.5℃ N/A N/A N/A
Dew point thermometer ±2.0℃ N/A N/A N/A
Rain fall meter (RFL) ±0.2mm N/A N/A N/A
Barometer ≦5mmhg N/A N/A N/A
Solar radiation meter (total radiation, net radiation, ultraviolet rays) ±5% Full scale N/A N/A N/A
Acid rain (pH) ±0.2pH N/A N/A N/A
Acid rain (conductivity) ±5% N/A N/A
Acid rain (amount) ±0.5mm N/A N/A N/A
[Table 2 Quality assurance standards for automatic monitoring facilities in performance audits]

△The second and fourth volumes of America's air pollutant monitoring system quality assurance manuals and sky net simulation plan were referenced, as were 1990's “Execution Plans for the Quality Assurance of Air Quality Monitoring Networks” and 1990's “Establishing Management Standards and Operation Systems for National Air Quality Monitoring Networks Volume 1”
△N/A: Currently not regulated

2. Audit of particle sampling flow meter

The auditing of suspended micro particle samplers (including TSP, highvol PM10, continuous PM10) includes two audits: one is the audit of actual flow value and its deviation with the value displayed on the instrument, and the other is an audit of how close the actual flow values are to the designed flow values in the instruments. Average commercial PM10 highvol and TSP samplers have a flow design of 40.0 CFM (cubic feet per minute), but actual flow allowed is 40.0± 10%CFM. Continuous automatic monitor PM10 samplers are designed with a flow amount of 18.9LPM (Wedding) or 16.7LPM (Anderson). Thus, the standard value when auditing is either 18.9± 10%LPM or 16.7± 10%LPM.

The main audit instrument for non-automatic monitoring PM10 highvol and TSPs are the root meter, orifice, and the difference in pressure of the water pillar in correcting curve graphs to find true flow which is then compared to the recorded flow on the sampler to calculate the deviation percentage. As automatic monitoring PM10 analysis instruments use foam flow as their transfer standard, the true flow is obtained from the station to calculate the deviation percentage with displayed flow.

3. Audit of meteorological instruments

Meteorological instruments include wind speed, wind direction, temperature, dew point, atmospheric pressure, daylight meter, and UV radiation meter. The sensors are retrospectively compared to the NIST standard instruments to calculate the deviation between the displayed value and true value. (Standard of audit data quality, see table 2)

4. Audit of acid rain meters (RFL)

Using known pH values and conductivity, the meter is tested for deviation between the displayed and true value of the pH and conductivity meters. (Standard of audit data quality, see table 2)

last update : 2019/11/27