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7 Equipment Calibration and Maintenance

7.1 Overview

Instrument calibration and maintenance are an integral part of operating an air quality monitoring site and are vital for data quality assurance. Accurate and reliable monitoring results are crucial for data analysis, particularly when the monitoring results are to be compared with the relevant standards or guidelines for compliance purposes, or for population exposure and health risk assessments. Where such analyses lead to air quality policy formulation and air pollution mitigation strategies, the quality of the original data is especially important.

This chapter outlines the basic requirements for the calibration and maintenance of air quality monitoring instruments based primarily on standard monitoring methods. Precedence is given to Australian / New Zealand Standards for ambient air quality monitoring, where relevant, as these are the methods recommended by the AAQG and the methods required by the NES for air quality.

Monitoring agencies should develop their own detailed calibration and maintenance programmes appropriate to their data quality assurance goals. Guidance is provided on various associated technical topics, including calibration frequency and a framework for compiling operating procedures manuals. Specific guidance on data quality assurance is given in chapter 8, which should be read in conjunction with this chapter.

Recommendation 16: Monitoring records

Agencies operating monitoring instruments need to keep detailed records of visits and maintenance, preferably in electronic form.

7.2 Equipment calibration

The calibration of an analyser establishes the relationship between instrument response (such as output voltage) and known contaminant concentrations. This response/contaminant concentration relationship is then used to convert analyser response to corresponding ambient pollution concentrations. To meet data quality objectives, most air quality monitoring equipment has to be calibrated at regular intervals to:

  • compensate for baseline and span drift

  • check the linearity of instrument response.

Note that meteorological instruments also require calibration. Calibration requirements vary depending on instrument type and manufacturer. Detailed operation and service manuals should be requested and supplied with any instrument purchase.

As a general rule, instrument calibration and maintenance should follow the recommendations and requirements of the appropriate standard method and the manufacturer’s instructions. The use of Australian / New Zealand standards (AS/NZS) is recommended. In the absence of an AS/NZS, other appropriate standards may be used, such as the USEPA or British Standards. For the purposes of compliance monitoring, the use of specified standard monitoring methods is a statutory obligation.

7.2.1 Use of standard monitoring methods

A range of standard methods for the sampling and analysis of ambient air are available from various agencies such as Standards Australia, Standards New Zealand, USEPA, British Standards and the International Organisation for Standardisation (ISO). Standard monitoring methods set out the basic principles of operation, instrument performance requirements, apparatus and set-up, calibration procedures, and the calculation and expression of results. It is essential that the equipment is then operated according to that standard at all times.

Monitoring instruments that are designated as reference methods or equivalent by organisations such as the USEPA are usually accompanied by detailed calibration and service manuals produced by the instrument manufacturer, which describe how a particular instrument is to be operated to meet the requirements of that designation. Checking whether a particular instrument complies with a standard monitoring method should be made at the time of purchase.

7.2.2 Calibration of gas analysers

The calibration of monitoring instruments for gaseous contaminants requires a calibration gas, a ‘zero’ air supply and some means of delivering a known calibration gas concentration to the instrument being calibrated, as well as calibration of flow, temperature and pressure sensors. Calibration gas mixtures should be traceable back to standard reference materials.

A gas analyser is only calibrated when the instrument response settings are actually physically changed to agree with a known concentration of supplied analyte gas. During the calibration process, zero air is produced by scrubbing any traces of the contaminant gas (as well as interfering species and moisture) from a stream of atmospheric gas. An analyser is ‘zeroed’ by adjusting the instrument’s response (contaminant concentration output) to read zero while this scrubbed zero air is fed through the system. The instrument is ‘spanned’ by supplying a known concentration of gas (at the ‘span’ concentration of around 75 to 80 per cent of the full scale range) and altering the instrument response to read the correct concentration. This procedure establishes the instrument’s response/concentration relationship and in most cases will be a straight-line equation.

It is crucial that the zero air supply is as free of analyte (and interfering species) as possible and that the supply of span gas is known accurately and delivered with precision. During the calibration process, zero air and span gases must be treated in exactly the same manner as the ambient sample air flow, and this is usually achieved by passing calibration gases through the sample inlet.

All other types of calibration, such as multi-point calibrations and auto-calibrations, can be regarded as checks to see if the instrument response is performing within defined parameters. The instrument may or may not need adjusting following these checks depending on the specifications contained in the relevant standard or manufacturer’s instructions.

Calibration frequency

Calibration frequency is a key consideration for a calibration and maintenance programme. There are three types of standard method calibration requirements for gaseous contaminants.

  1. Initial calibration: where zero air and calibration gas atmospheres are supplied and any necessary adjustments are made to the analyser. Once this is done, calibration gas concentrations are required at approximately 20, 40, 60 and 80 per cent of the full measurement range of the instrument, and the instrument response is required to agree within 2 per cent of the calculated reference value. Alternatively, when actual concentration is plotted against expected concentration, the slope of the best-fit line should be within 1.00 ± 0.01, with a correlation coefficient of at least 0.999. This is also referred to as a linearity or multi-point check.
  2. Operational precision checks: where the zero and span responses of the instrument are checked for drift on a regular basis. The recommended frequency is daily, but in any case it is recommended that precision checks be undertaken at least weekly to adjust or correct for zero and span drift. The drift tolerances given by the standards vary with each contaminant. In some standards this is also called an operational recalibration.
  3. Operational recalibration: where zero and span gases are supplied, as for an initial calibration. It should be done when the analyser drift exceeds the instrument performance requirements, or after six months since the last calibration. Multi-point checks should be carried out every six months.

It is recommended that gas analysers be calibrated (or recalibrated):

  • upon initial installation

  • following relocation

  • after any repairs or service that might affect its calibration

  • following an interruption in operation of more than a few days

  • upon any indication of analyser malfunction or change in calibration

  • at some routine interval (see below).

The routine periodic calibrations should be balanced against a number of other considerations, including the:

  • inherent stability of the analyser under prevailing conditions of humidity, temperature, pressure, mains voltage stability and the like

  • costs and time involved in carrying out calibrations

  • amount of ambient data lost during calibrations

  • data quality goals

  • risk of collecting invalid data due to a problem with the analyser not discovered until the calibration is performed.

The periodicity of regular calibrations can be set operationally by noting the adjustments (if any) required after each calibration and by monitoring span and zero drift performance for each analyser. The requirement for routine instrument servicing and maintenance plus any unforeseen outages generally makes multi-point calibrations a reasonably regular necessity.

Note that routine maintenance and calibrations should be scheduled in such a way that any associated data loss is evenly distributed throughout the year, avoiding critical monitoring times.

Tracking the results of the calibrations on a spreadsheet can help determine the frequency of calibrations and also draws attention to the trend in the drift. Figure 7.1 shows an example. It should be noted that some analysers will take a couple of months to settle down when they are first installed.

Figure 7.1: Example of calibration results tracking for a CO analyser

Figure 7.1: Example of calibration results tracking for a CO analyser

See text description for figure 7.1

Multi-point calibrations

Multi-point calibrations are the key criteria by which the instrument’s accuracy and linearity of response to a range of known concentrations of a contaminant are assessed (USEPA, 1998). The multi-point calibration results are also used for preparing calibration curves for the data quality assurance process (data adjustments – see section 8.4). While a multi-point calibration is referred to as being only part of an initial calibration by some of the standards (more recent Australian standards include it with operational recalibration), it is interpreted to include the following situations:

  • instrument commissioning

  • following any maintenance and servicing where the instrument is turned off or settings changed

  • at regular operational intervals of not less than six months.

Zero and span checks

Zero and span checks are performed by introducing zero air and a span gas concentration through the system but not making any actual adjustments. Recording the instrument response at zero and span concentrations provides a way to determine instrument reliability and drift over time, and to assist with the data quality assurance process. The checks can also be used to help set calibration frequency. In some standards, this type of check is called an ‘operational precision check’.

Note that ‘as is’ zero and span checks should be performed immediately before any maintenance, instrument servicing or other shut-down for later quality assurance of the data.

Automated checks and calibrations

Some air monitoring analysers are capable of periodically carrying out automatic zero and span calibrations and making their own zero and span self-adjustments to predetermined readings. However, this requires permanent connection to a span gas supply, usually through a different inlet from the sample inlet and, in the strictest sense, does not meet the requirement that the calibration gas be treated in the same manner as the sample gas stream. It also requires that instrument parameters before and after calibration are recorded and that the span and zero are discernible from data-logger records for subsequent quality assurance assessment. For these reasons, it is recommended that the auto-calibration function only be used as a zero and span check, as described in the previous section.

Automatic zero and span checks can be useful for remote sites or large networks as they reduce the need for weekly inspections by staff. Automated systems generally allow for any user-defined frequency. While daily checks are possible, consideration must be given to the usefulness of this in terms of data quality assurance, the time of day it is performed (eg, not during peak pollution periods), and the amount of data loss, as most systems require some time to stabilise between concentration ranges and after a calibration process. It is likely that at least one hour’s worth (or 4 per cent of a 24-hour period) of data can be lost through this process.

Equipment configuration for automated systems requires a dedicated supply of span gas, such as a certified concentration in a cylinder or permeation tubes, dedicated zero air supply (some instruments include their own scrubber systems), plus the means to switch between different inputs (usually solenoid valves). This usually adds extra cost to the system set-up for each site.

Concentrations to use for calibration points

The concentrations selected for calibrations and checks should be determined from the requirements of the analyser (zero and 80 per cent span) and also from the data. For example, if it is necessary to have a CO analyser range set at 50 ppm to cover an occasional spike but the usual data maximum is only 15 ppm, then consider doing an additional point at the 15 ppm level.

A secondary reason for selecting additional points is that the calibration equation is normally a straight line (as only the zero and span values are used), but some analysers may not be truly linear. This is why multi-point or linearity checks may be needed.

7.2.3 Calibration of PM10 monitoring instruments

Manual gravimetric methods for PM10 require air flow calibration, while methods such as beta attenuation, nephelometry or TEOM technology require calibration of flows (and flow sensors), as well as other components specific to the method.

The calibration frequency for PM10 monitoring equipment varies depending on instrument type and the manufacturer’s recommendations. As indicated previously, calibration of air flows (and sensors) is important due to the requirement of maintaining a critical sample flow to achieve the design cut-point of the size-selective inlet.

Instruments that are more sophisticated require calibration of temperature and pressure sensors, along with specific items associated with a method (eg, beta particle attenuation checks use calibrated foils for BAMs and the mass verification is needed for TEOMs). Further discussion of standard PM10 monitoring methods is provided in chapter 5.

7.2.4 Calibration of meteorological instruments

Meteorological instruments such as cup anemometers, wind vanes, and temperature and relative humidity sensors generally require more specialised calibration and servicing, such as wind-tunnel testing, laboratory test atmospheres or calibration against primary standards. This should not prevent checks against calibrated instruments being done on a regular basis.

Sonic anemometers that measure both wind speed and direction involve a solid state technology, and they are calibrated and set at the time of manufacture for the lifetime of the instrument. While they do not require further calibration, they still need regular checks.

7.2.5 Use of traceable standards and equipment in calibration

Calibration is the primary means by which to verify that a gas analyser or particle sampler is performing as required, so it is important that the equipment or gases used to perform the calibrations are also certified to be accurate. This includes instruments to measure the following parameters:

  • temperature

  • pressure

  • flow rates

  • barometric pressure

  • gravimetric balances

  • standard gas mixtures (and their delivery regulators).

Calibration equipment should be purchased on the basis that it is accompanied by a certificate indicating calibration against a primary standard, or against other standards traceable to a primary standard. The most common is through the United States National Institutes of Standards and Technology traceable standards. The calibration equipment is also likely to require recalibration from time to time, and an expiry date is usually given on the accompanying calibration certificate.

Gas cylinders should be checked on purchase to ensure the correct concentration has been supplied and again if contamination is suspected during their use. This can be done by running gas from comparable cylinders against each other through a calibrated analyser and comparing the results. Any variation should be within the acceptable tolerances for the supplied gas and equipment. It may be possible to get gas cylinders recertified once they have reached the end of their expiry dates to prevent having to waste unused gas.

7.2.6 Calibration of data acquisition systems

Data acquisition systems such as external dataloggers may need calibration periodically if analogue outputs and inputs are used, because the voltages can vary over time. This can usually be avoided if digital interfaces are used.

Recommendation 17: Calibration

Calibrations should be carried out in accordance with the manufacturer’s specifications and the requirements of the standard method.

Span and zero checks are recommended on a daily basis.

Multi-point calibrations should be performed not less than six months apart.

7.3 Equipment maintenance

Maintenance refers to the regular inspection and servicing of monitoring instruments and ancillary equipment, through to general site maintenance. The efficient and smooth operation of an air quality monitoring station (along with the reliability and quality of data obtained) is entirely dependent on the manner in which it is maintained, and a critical element of this is preventive maintenance.

The following examples highlight some of the types of preventive maintenance and systems checks to ensure good data quality, but they by no-means constitute an exhaustive list:

  • conduct regular site inspections, including a check of air-conditioning systems and security

  • check instrument diagnostics for normal operation of pneumatics and electronics

  • check sample inlets and filters (service or change as required)

  • check vacuum pumps and pump filters (service as required)

  • ensure datalogger and instrument times are correct (they should be maintained within ± 1 minute of New Zealand Standard Time).

Maintenance is an ongoing process so it is usually incorporated into daily routines, and there are also monthly, quarterly, six-monthly and annually scheduled activities that must be performed. The physico-chemical properties measured by air quality monitoring instruments to infer ambient concentrations are different for each contaminant, so the specific maintenance requirements for each will also be different. Monitoring agencies should follow the routine maintenance and service requirements outlined and recommended by the instrument manufacturer and incorporate these procedures into their own detailed schedules, with sufficient time allocated accordingly. Note that time allocated for preventive maintenance is separate to the time that may be required for instrument breakdowns and repairs, but sufficient attention paid to the former is likely to reduce the time spent on the latter and, most importantly, avoid instrument down-time and loss of data.

A good preventive maintenance programme should be well documented and include:

  • a short description of each procedure

  • a frequency and schedule for performing each procedure

  • a supply of vital spare parts and consumables in stock

  • documentation showing that the maintenance has been carried out.

Much of this information can be summarised in tabulated form with a check-sheet format. This can be done for most activities such as site inspections, instrument diagnostics checklists and (preventive) maintenance schedules.

Recommendation 18: Equipment maintenance

The routine maintenance and service requirement outlined and recommended by the instrument manufacturer should be followed.

7.4 Procedures and documentation

The measurement of atmospheric gaseous and aerosol contaminants using instrumental methods is an analytical process that requires careful attention to accuracy and precision. This is generally assured by following standardised calibration and maintenance procedures specific to each type of instrument. Monitoring agencies should establish their own detailed procedures manuals and schedules for instrument maintenance and calibration as a fundamental part of their air quality monitoring activities. The importance of this for data quality assurance cannot be overemphasised, particularly where data may be used for assessing compliance with the NES for air quality, examining trends in air pollution over time, or determining strategies for emissions reduction.

Following standardised and documented procedures allows for a transparent process that can be easily audited and provides a level of confidence for end users of the data. Several different aspects of documentation need to be considered for an operational air quality monitoring site:

  • routine site inspections – schedules and checklists for appropriate parameters

  • instrument calibrations – schedules and procedures for carrying out routine calibrations

  • routine maintenance – schedules and procedures for carrying out routine (preventive) maintenance on monitoring instruments and ancillary equipment

  • detailed instrument calibration and servicing records – these must be kept as they will invariably be referred to during the data quality assurance process

  • site logs – it is important to record all visits and activities undertaken at a site, with reference (where necessary) to the appropriate calibration and servicing records for more detailed information

  • documentation of instrument types, date of installation and serial numbers for all equipment at a monitoring site – this allows for easy tracking of instrument replacements and translocations, as well as for asset management purposes

  • site metadata – consisting of a compilation of information relating to a particular site (refer to section 8.8 for a list of recommended parameters).

It is recommended as good practice that two copies of all paper records be kept, particularly for instrument maintenance and site logs (one copy on site and one appropriately filed at the main office). Electronic records should be filed in an appropriate database that is regularly backed up.

Examples of instrument check-sheets and maintenance record templates are provided in Appendices E and F.

While it may seem that excessive documentation is required, once the systems are established, maintaining them is a relatively straightforward matter of regular audits and refinements as necessary. Systems should be as simple and transparent as possible. Installing and operating an air quality monitoring station or network is an expensive and labour-intensive process, so it is essential to have a quality data output. Note that much of the documentation work may already be done by adopting and incorporating the procedures and recommendations contained in the standard methods and the detailed operation and maintenance manuals that accompany standard method-compliant instruments.

Organisations may wish to structure their air quality monitoring documentation and procedures by incorporating them into a quality management system such as the ISO 9000 series, which would formalise the tracking and auditing framework. A quality management system is primarily concerned with what an organisation does to achieve:

  • data end-users’ (such as scientists and policy analysts within an organisation, central government, research providers and consultants) quality requirements

  • applicable regulatory requirements (NES for air quality and applicable standard methods), while aiming to enhance customer satisfaction (confidence in monitoring results)

  • continual improvement of its performance (high data quality, low data loss, efficient operating systems) in pursuit of these objectives.

Regional councils (or their contractors) have to conform to regulatory requirements (NES for air quality and applicable standard methods), and so appropriate procedures and documentation to achieve high-quality monitoring data and data capture targets are recommended. The adoption of a quality management system is a logical step.

Recommendation 19: Calibration and maintenance documentation

As a vital part of data quality assurance it is recommended that detailed procedure manuals and schedules for instrument maintenance and calibration be established.

7.5 Training

Training of technicians carrying out calibration and maintenance work on air quality monitoring instruments is vital, as most instruments are a sophisticated combination of pneumatics, electronics, mechanical components and software. Training should be an integral part of establishing and operating an air quality monitoring site.

Several types of training should be provided (considered as core competencies) to technical staff, including:

  • an introduction to fundamental air pollution processes and air pollution monitoring techniques (eg, Clean Air Society of Australia and New Zealand courses)

  • specific training on instrumentation operation and maintenance (usually through systems providers)

  • electronics and electrical systems

  • quality systems management and quality assurance in analytical techniques.

Appropriately trained staff could apply for International Accreditation New Zealand (IANZ) or National Association of Testing Authorities (NATA) accreditation for a monitoring method that meshes well with a quality management system. IANZ or NATA accreditation recognises and facilitates competency in specific types of testing, measurement, inspection or calibration.

Another effective method of training and systems improvement is to participate in reciprocal auditing activities between monitoring agencies. The level of formality of the arrangement is up to the agencies involved, but is likely to work well at any level. The general approach is for technicians from one monitoring agency to visit and audit the procedures and methods (such as calibration and maintenance activities) used at another agency, in relation to both the auditee’s own systems and documented procedures as well as against accepted industry practices and standard methods. Both auditee and auditor learn through this exercise, with the ultimate aim of continual improvement in monitoring systems and data quality.

Recommendation 20: Training

Air quality monitoring technical staff should be provided with basic training on core air quality monitoring competencies.

Another effective method of training and systems improvement is to participate in reciprocal auditing activities between monitoring agencies.

7.6 Recommended equipment calibration methods for NES for air quality contaminant monitoring

The following sections provide an overview and guidance on the calibration and maintenance of instruments for specific contaminants covered by the NES for air quality (standard methods only). It is not intended to be an exhaustive list or a ‘how to’ manual, but has been compiled to inform organisations intending to set up monitoring systems of some of the operational requirements and equipment necessary so that they may be included in the budgeting process. The frequency of inspection and maintenance often depends on the environmental conditions at a monitoring site location. For example, sample inlets and lines are likely to require more frequent cleaning or replacement for sites next to busy roads due to higher road-dust and exhaust emission concentrations. Further detail and guidance are provided in the standards and instrument manufacturers’ operation and service manuals.

7.6.1 Chemiluminescent NOx analyser AS 3580.5.1-1993

Calibration

  • The analyser is checked or calibrated against the known NO (in N2) concentration diluted with zero air (see AS3580.2.2) using a mass flow calibrator at least six-monthly or after an extended power outage, maintenance and servicing.

  • The recommended standard NO calibration gas concentration is 20–100 ppm (for a 0–500 ppb ambient range).

Refer to the manufacturer’s instructions and relevant standard for specific guidance.

Note that there can be considerable lead-time (four to five months) between ordering NO calibration gas and subsequent delivery.

Maintenance

  • Check the molybdenum converter efficiency three-monthly by gas-phase titration of NO with O3 (or more often in high NO2 atmospheres) and change as necessary.

  • Clean the reaction cell regularly (refer to the manufacturer’s instructions, as this can be checked before carrying out maintenance). More frequent maintenance will be required at locations with higher NOx concentrations (eg, roadside monitoring).

  • Check seals, pneumatic lines etc and replace as necessary (refer to the manufacturer’s instructions) due to the presence of corrosive O3 in the system.

  • Replace exhaust scrubber (for O3) regularly to protect the vacuum pump.

  • Change the inlet sample line and filter regularly, depending on ambient conditions.

  • Check the system for leaks regularly.

  • Check flows and pressures regularly.

Refer to the manufacturer’s instructions and relevant standard for specific guidance.

7.6.2 Direct reading CO infrared analyser AS 3580.7.1-1992

Calibration

  • Check the analyser or calibrate it against a known CO (in N2) concentration diluted with zero air (see AS3580.2.2) using a mass flow calibrator at least six-monthly, or after an extended power outage, maintenance and servicing.

  • The recommended standard CO calibration gas concentration is 0.2 per cent (for a 0–50 ppm ambient range).

  • CO standard gas bottle concentrations (eg, 10 ppm, 40 ppm) are readily available for span and intermediate checks instead of using a mass flow calibrator.

Refer to the manufacturer’s instructions and relevant standard for specific guidance.

Maintenance

  • Clean the sample cell mirrors regularly (refer to the manufacturer’s instructions).

  • Check the inlet sample lines and filter and change regularly, depending on local conditions.

  • Check the system for leaks regularly.

  • Check flows and pressures regularly.

Refer to the manufacturer’s instructions and relevant standard for specific guidance.

7.6.3 SO2 direct reading instrumental methods AS 3580.4.1-1990

Calibration

  • Check or calibrate the analyser against a known SO2 (in N2) concentration diluted with zero air (see AS3580.2.2) using a mass flow calibrator at least six-monthly or after power outage, maintenance and servicing.

  • The recommended standard SO2 calibration gas concentration is 20–50 ppm (for a 0–500 ppb ambient range).

Refer to the manufacturer’s instructions and relevant standard for specific guidance.

Note that there can be considerable lead-time (four to five months) between ordering SO2 calibration gas and subsequent delivery.

Maintenance

  • Clean the sample cell window regularly (refer to the manufacturer’s instructions).

  • Check the inlet sample lines and filter and change regularly, depending on ambient conditions.

  • Check the system for leaks regularly.

  • Check flows and pressures regularly.

Refer to the manufacturer’s instructions and relevant standard for specific guidance.

7.6.4 O3 direct reading instrumental method AS 3580.6.1-1990

Calibration

  • Due to its reactivity, O3 has to be generated in situ for calibration purposes. Most commercially available mass flow calibrators include the option of an O3 generator (also used for gas-phase titration of NOx instruments). Note that this is known as a secondary (transfer) reference standard and that it will require periodic calibration against a primary reference standard, as described in the O3 standard method.

  • Check or calibrate the analyser against known O3 concentrations generated with zero air using a mass flow calibrator at least six-monthly or after power outage, maintenance and servicing.

Refer to the manufacturer’s instructions and relevant standard for specific guidance.

Maintenance

  • Check the inlets, sample lines and filter for cleanliness and replace as necessary (refer to the manufacturer’s instructions), as O3 is reactive and will be removed from the sample stream before detection.

  • Clean the absorption tube/cell regularly.

  • Check the system for leaks regularly.

  • Check flows and pressures regularly.

Refer to the manufacturer’s instructions and relevant standard for specific guidance.

7.6.5 PM10 monitoring instruments

The following subsections provide guidance on calibration and maintenance for standard PM10 monitoring methods.

PM10 by gravimetry

With respect to standard methods, the following instrumentation calibration and maintenance frequencies should be met:

  • flow rate after any servicing, maintenance or moving of samplers

  • flow rate every two months for high-volume samplers

  • flow rate every six months for medium-volume samplers

  • size-selective inlets, seals and impactor plates inspected, cleaned and re-coated as necessary

  • laboratory analytical balance three-yearly (along with more frequent repeatability checks)

  • programmable time clock calibrated annually (or more often as necessary)

  • elapsed time meter (run-hours) calibrated annually (or more often as necessary)

  • temperature and pressure compensation sensors (if fitted) calibrated annually.

Refer to the manufacturer’s instructions and relevant standard for specific guidance.

PM10 by beta particle attenuation

With respect to standard methods, the following instrumentation calibration and maintenance frequencies should be met:

  • annual calibration by measuring the absorption of a blank filter tape and a calibration control membrane (calibration foil) with a known absorption coefficient

  • flow rate after any servicing, maintenance or moving of samplers

  • flow rate checked (and calibrated if necessary) every three months

  • beta attenuation calibrated annually

  • size-selective inlets and seals regularly inspected (monthly), and cleaned as necessary

  • temperature and pressure compensation sensors calibrated annually.

Refer to the manufacturer’s instructions and relevant standard for specific guidance.

PM10 by tapered element oscillating microbalance (TEOM)

With respect to standard methods, the following instrumentation calibration and maintenance frequencies should be met:

  • flow rates and mass transducer verification calibration after any servicing, maintenance or moving of samplers

  • flow rates checked (and calibrated if necessary) every six months

  • mass transducer verification calibration annually

  • size-selective inlets and seals regularly inspected (monthly), and cleaned as necessary

  • temperature and pressure compensation sensors calibrated annually.

Refer to the manufacturer’s instructions and relevant standard for specific guidance.