Title of Example

Example

Running air quality monitoring stations is more then just watching the numbers rolling in. To produce results of known and sufficient quality there is a whole range of tasks to be performed such as periodic status checking, maintenance, calibrations, data evaluation and so on. Failing to perform all or some of these tasks will reduce the data quality. To ensure unified operation both within a monitoring network and across several networks a documented quality system is necessary. All operations must be described in written procedures and documented for later reference. Only then will it be possible to assess the quality of the measured data as required in the EU Air Quality Framework Directive.

Based on the above and article 3 of the AQ Framework directive which calls for the designation of bodies responsible for ensuring accuracy of measurements etc., the Norwegian Pollution Control Agency appointed NILU as National Reference Laboratory for Air Quality in Norway (NRL) in 2001. NRL’s first task was to introduce a common quality system for all network operators in Norway.

The Quality Manual was written for non-experts. It aims at guiding the operators towards a unified way of operating their measurement networks by explaining in detail how maintenance, calibrations, data validation, etc. is performed and documented.

The main documentation at a site is:

• Standard Operations Procedure (SOP) for each instrument at the site
• A format for each SOP to document the procedure
• Performance Acceptance Criteria specific to the instrumentation at the site

The results from periodic testing of instruments, typically once a week, e.g. zero/span checks on gas monitors, are compared to the Performance Acceptance Criteria. If the results fall outside the prescribed limits, certain actions have to be taken, e.g. recalibration, troubleshooting or service of the instrument. By using common action criteria across and between measurement networks, it is more probable that the operators will evaluate test results equally.

A typical weekly maintenance procedure for a gas monitor would be:

1. Record time and date of arrival to the station, serial number of instrument and working gas standard and working gas concentration.
2. Record selected status parameters, such as sample flow rate, sample temperature, reaction chamber temperature, light intensity.
3. Compare status parameters with last few weeks of status parameters to detect trends, e.g. falling light intensity in an ozone monitor. The objective is to change consumables and spare parts before they reduce the quality of the data or brake down.
4. Disconnect the inlet tube from the inlet and connect it to the zero/span check unit.
5. Test the instrument by feeding zero and span gas to it.
6. Compare the results with the results from last few weeks of zero/span checks to detect trends. Normally there would be a linear decrease in the response. A sudden drop may indicate a problem.
7. Compare the results with the performance acceptance criteria and perform necessary actions if the test results fall outside the performance limits. The instrument response is changed only if it is outside the action limits.
8. Perform regular maintenance as required, such as changing inlet filter.
9. Remember to reconnect the inlet tube to the inlet!
10. Record time of end of operation.
11. Sign the maintenance form.
12. Record the visit in the visit log.

Once the operator is back at the office he/she immediately calculates scale factors (slope and offset) based on the results from the zero/span check. The scale factors are entered into the data acquisition system and used by the system to mathematically correct the acquired data. Data is collected every hour from all stations, scaled and transferred directly for display on the internet web page (in this case: http://www.luftkvalitet.info/ ).

Even if the instruments are maintained in a proper order they may break down. In order to detect malfunctions as soon as possible, validation of collected data is required. Continuous display of data on the internet requires some automatic validation, re. e.g. spikes, too high values, too negative values. In addition a manual data validation is performed as well to cover other kinds of invalid data.

Manual data validation is performed as follows:

1. Every day the operator goes onto the internet and looks at charts from his/her stations. The operator looks for indications of instrument malfunctions, such as constant levels, spikes and negative values.
2. If any measurement data looks suspicious the operator will connect to the station and run a check on the instrument and inspect on-line or one-minute averages for details.
3. Every week the operator enters the scale factors into the system.
4. After the end of the month the last month of data is evaluated. The operator looks for trends in measurement data and scale factors, invalid measurement data, e.g. from zero/span checks and periods of instrument malfunctions are flagged.
5. The monthly data is finally approved and transferred to the central database. They are now ready for use.

Calibrating the instruments and the working gas standard at the site is done once every three months, by bringing a travelling standard to the site.

The instruments are brought to the lab at NILU once a year for major service, adjustments and calibration. The calibration includes a test for linearity (dynamic calibration).

To test the actual performance of the networks, NRL performs an annual audit. The audit includes a performance audit and a system audit. The performance audit is conducted in every measurement network at a minimum of one measurement site selected at random. It tests the actual performance of an instrument by using an independent calibration standard brought to the site by NRL. The system audit is performed to document if the network operator is operating in accordance with the quality system and that the documentation and archives are in proper order.

NRL maintains the national reference gas standards and provides the networks with trace-ability to these standards. To assure the quality of the standards and other calibration equipment, NRL participates in international inter-comparisons.

Attached is an example of a SOP for weekly maintenance of a SO2 monitor.

ANNEX: Extract from NILU AQ Data Quality Manual

(see pages below)

Purpose of SOP

To maintain the gas monitor in a good order.

The monitor needs periodical maintenance and status checking to provide reliable results. The maintenance and status checking includes changing of consumables, cleaning, performance check, manual zero/ span check, leak checking and registration of status parameters.

Applicability and description of equipment

This SOP applies to the maintenance of gas monitors.

At the station the monitor is connected to the sample air intake system. During zero/span checks the monitor is connected to an external zero/ span check unit. The monitor is connected to the data logger by electrical wires.

Responsibilities

Personnel performing routine maintenance on gas monitors will be thoroughly knowledgeable of the contents of this SOP and will comply with its requirements when performing routine maintenance on gas monitors.

Instrumentation

This SOP assumes the following instrumentation:

· TEI 145 permeation tube zero/ span check calibrator

· TEI model 42C SO2 monitor

Documentation

This SOP is documented in the form:

Routine maintenance, TEI model 43C SO2 monitor

Maintenance procedure

1. Enter todays date and the time you entered the station in the Date and Start time fields respectively.

2. On the monitor press the RUN pushbutton to enter the continuous display. Enter the displayed SO2 concentration in the Ambient - Monitor - SO2 field.

3. On the monitor press the MENU pushbutton to enter the monitor menu and choose ALARM. Enter the INTERNAL TEMP, CHAMBER TEMP, PRESSURE, FLOW, INTENSITY, LAMP VOLTAGE and SO2 CONC status values in their respective fields in the Alarm section. Press RUN to return to the Run screen.

Manual zero/ span check

A manual zero/ span check is performed to validate the monitor response.

Registration of general information:

1. Enter the span gas cylinder pressure in the Z/S check monitor – Wrk. std. – Pressure field.

2. Enter the gas cylinder’s certified concentration in the Cert. conc. field.

3. On the monitor press the MENU pushbutton to enter the monitor menu and select RANGE using the arrow buttons. Press ENTER to enter the RANGE menu. Enter the RANGE values in the Z/S check monitor - Response - Range field in the form. Press RUN to return to the Run screen.

Zero check:

1. Disconnect the inlet tube from the inlet and connect it to the zero air generator.

2. Adjust the flow to 1 l/min.

3. Let the monitor sample zero air for 20 minutes. Enter the 1 Minute Average value from the datalogger in the Z/S check Monitor - Response - Zero field in the form.

Span check using a gas cylinder connected directly to the monitor:

1. Disconnect the inlet tube from the zero air generator and connect it to the span gas cyinder.

2. Adjust the flow to 1 l/min.

3. Let the monitor sample span gas for 20 minutes. Enter the 1 Minute Average value from the datalogger in the Z/S check monitor - Response - Span field in the form.

4. Reconnect the inlet tube to the inlet.

Do not forget:

1. Tick off the items in their respective fields in the NB! section in the form.

2. The monitor is sampling air from the intake.

3. Gas cylinder regulators are closed.

4. The zero/ span check unit and solenoids are not activated.

5. Sign the form

Last Updated

13th January 2005