Skip to main content

Air quality monitoring frequently asked questions

A selection of frequently asked questions about air quality are provided below - if you have any additional questions that are not covered below please get in touch

SEPA's monitoring is robustly reviewed by the Mossmorran and Braefoot Bay Community and Safety Liaison Committee Expert Advisory Group on air quality (previously the Mossmorran and Braefoot Bay  Independent Air Quality Monitoring Review Group), which includes independent technical expertise from the Institute of Occupational Medicine (who audited our data and data handling processes). Further information can be found on Fife Councils website.

The air quality in Scotland website contains a lot of useful information on air quality and provides access to the wider Scottish air quality network. It also provides further information on the air pollutants which are being measured by this network, including any relevant air quality standards and objectives.

Changes to monitoring

In 2019 we confirmed that our air quality monitoring around the Mossmorran Complex would continue throughout the period of investment and the installation of new flare tips and ground flares. At the same time, we committed to working with partner agencies with air quality responsibilities to assess future requirements.

In September 2021, we held four community engagement sessions in partnership with Fife Council and the Health and Safety Executive to listen to the needs of the community. We used the feedback to inform our review of the monitoring we undertake and how we share the results of that monitoring with the local community.

To date, our monitoring has shown no breaches of the air quality objectives, but it was clear in hearing from the community that there continues to be a concern about air quality in the area. The community asked for:

  • Permanent monitoring of air quality in the communities around Mossmorran.
  • Simple, easy to understand and timely data, with the ability to get more detail if required.

We have reviewed how we will monitor air quality and, taking the feedback from communities into account, we have made changes to how we monitor and how we make information available in a way that will hopefully provide greater reassurance to local communities. We have implemented a new monitoring plan that:

  • changed the monitoring locations;
  • increased the number of monitoring points;
  • increased the range of air pollutants that we measure.

The new monitoring enables us to offer improved ways of presenting data on the levels of the pollutants measured, including near to real time data provision.


Reference analysers are complex instruments which require housing in a temperature-controlled environment and need frequent maintenance and quality control checks to allow high quality data to be provided. They undergo a rigorous assessment and are accredited for air quality monitoring purposes. Data obtained from reference analysers are deemed "provisional" until a full quality control assessment can be undertaken. This is usually done annually. Whilst data can be provided in near to real time, this data will be provisional.

More information on data verification and ratification can be found on the air quality in Scotland website.

The AQMesh analysers do not require such housing, are small - and therefore much easier to deploy - and do not have the same level of maintenance and quality control requirements. They can readily host several sensors in a single unit. This allows much greater geographical coverage as well as allowing a wider range of pollutants to be assessed. The data can be provided in near to real time.

The data from the AQMesh analysers are not able to match the quality of the data from the reference analysers, however, with careful quality control and calibration they are a powerful tool when used in combination.

The reference analysers located at Auchtertool are certified and run to a high standard which allows for official comparison with air quality standards. The AQMesh analysers are indicative, and the results can only be treated as such, allowing for short term trend analysis. We have located one AQMesh analyser in the same location as the reference analysers so that the results from the two set ups can be compared.

The geographic coverage of the AQMesh analysers allows comparison in communities all around the Mossmorran complex, giving a greater understanding of the overall air quality in the area.


Reference analysers sited at Auchtertool:

Chemiluminescence NO/NO2/NOX

  • Analyser Manufacturer’s specifications: T200 
  • MCERTS Continuous Ambient Air Monitoring System certification - MC05006812 

BAM1020 PM2.5 Analyser: 

  • Manufacturer’s specifications: BAM 1020 
  • MCERTS Continuous Ambient Air Monitoring System & MCERTS for UK Particulate Matter: MC13023704 

BAM1020 PM10 Analyser: 

  • Manufacturer’s specifications: BAM 1020  
  • MCERTS Continuous Ambient Air Monitoring System & MCERTS for UK Particulate Matter: MC14025403 


Short term elevated levels of some pollutants, especially PM10 and PM2.5, can be expected due to local activities such as traffic; agricultural activities (ploughing, harvesting, etc); domestic sources such as solid fuel burners or bonfires and transboundary air pollution episodes.

It is important to note that due to the nature of the AQMesh analysers there may be occasions when high concentrations are displayed for pollutants which are due to circumstances other than pollution. This can happen due to electrical interference, weather conditions or sensor failures.

All the near real time data is provisional and should be treated with caution caution as it may change once verified. This is done at least annually.

At very low air pollution concentrations, where the air is very clean, the measurements may on occasion fall below zero. This can occur for a number of reasons, including instrument drift.

There is a lower limit to which air pollutants can be measured reliably. Generally, a negative reading, if not indicative of a fault with the instrument, will mean that there are very low levels of air pollution.

Air quality objectives are presented as an air quality concentration (or standard) which can only be exceeded a certain number of times per year.

Air quality standards are calculated as an average of a series of measurements collected over a time period. This time period varies depending on the pollutant and the standard.

As we are presenting hourly-average real time data we are not displaying these in direct comparison to the air quality standards, which for most pollutants are averaged over longer than one hour periods.

As an example, for PM10 we are presenting hourly-averaged real time data, but there are two air quality standards - one based on averaging all the results collected over a 24-hour period and a second based on averaging all the results collected over a year.

Short term results may go above the numerical value of an air quality standard, but this should not cause concern. For example, elevated levels of particulate matter might occur if a diesel vehicle idles with its engine running close to one of our analysers. These standards are set as averages over longer periods to take account of short-term elevations in air pollutants.

Air quality objectives are the number of exceedances of an air quality standard permitted during a measurement year. As an example, for NO2 the 1 hour standard is not to be exceeded more than 18 times a year. See air quality Scotland for more details.

As we are presenting real time data we cannot compare against the air quality objectives which is judged against a count of the number of exceedances of the standard.

Nitrogen dioxide, PM10 and PM2.5 often show a diurnal pattern (that is a pattern over a 24-hour period). An example that can be observed in many locations is a peak in NO2 levels from vehicle exhausts during the main morning and evening commuting times. Ozone is dependent on sunlight levels and will therefore display a varying pattern based on levels of sunlight.

TO help you assess the health impacts of the air quality around you we have used a simplified form of the Daily Air Quality Index (DAQI) which has been applied to particulate and NO2 levels. This provides an immediate indicative assessment against agreed criteria to determine if these pollutants are at levels that may cause health impacts and provides health messages to at-risk people and the general population as a guide.

We will be producing annual summary reports to review longer term data. The monitors have recently been deployed, therefore there is currently no directly comparable historical data at these sites.

Longer term data and statistics for air quality monitoring sites operated by Defra, the Scottish Government and Local Authorities, which have been running for a longer period, are available at the air quality in Scotland website. The site also contains long-term trend graphs for NO2, PM10, PM2.5 and Ozone from selected monitoring sites

There are three main reasons why there might be missing data:

  • We are reliant on remote communications to our analysers and these can fail on occasions. This type of issue should be short term, and the analysers will continue to collect data that we can subsequently upload into the Mossmorran air quality network.
  • If an analyser breaks down we will have data gaps. We will seek to repair or replace the broken analyser as soon as we are able, but this might take several days depending on the issue. This will remain as a data gap once the unit is operational again.
  • If there is a power outage to any of our analysers they will stop working and we will have no data available.

Interpreting the data

To help you put into context what the data shared on this site might mean, we have provided a simplified form of the Daily Air Quality Index (DAQI)

The results from monitoring of pollutants emitted from process stacks, undertaken by the operators and independently on behalf of SEPA, are available upon request. These reports also contain a comparison of the measured results against any emission limit values set in the Pollution Prevention and Control permit for the relevant site.

The Scottish Pollutant Release Inventory (SPRI) is a Pollutant Release and Transfer Register (PRTR) and has the primary purpose of making publicly available officially reported annual releases of specified pollutants to air and water from SEPA-regulated industrial facilities. It also provides information on off-site transfers of waste and wastewater from these facilities.

The SPRI data is collected, quality assured and made public under the requirements of Freedom of Information and can be compared with PRTR information from other countries (the SPRI data also forms part of the wider UK-PRTR). SPRI dataset from 2002 to the present year (except 2003) are available and reported annually.

Monitoring during flaring

SEPA does not undertake any additional air quality monitoring during flaring events. Our air quality monitoring programme has been designed to provide data throughout the year and during all operational conditions at the plant. See "what we monitor and for what" section above for a comprehensive overview of the monitoring being undertaken by SEPA and monitoring results.

There is a ring of monitors around the site, to allow for differing wind directions. Any significant impacts on air quality at the monitoring locations should be detected. However, all monitoring evidence to date has shown no perceptible impact on air quality from flaring in the communities around the Mossmorran complex.

As discussed in the question "I'm seeing a higher concentration than normal reported from one of the air monitoring analysers - what might be causing this?", higher than normal levels of pollutants could be due to a range of reasons, not necessarily related to flaring events. If air quality is affected by any activity, including flaring, then it should be detectable in a downwind location.

Data from Auchencorth Moss is also provided alongside the SEPA monitoring data to show wider air pollution events, such as in the case of transboundary events across the region or Scotland as a whole.