Air Quality Monitoring

This page contains data collected before we became aware of an issue with hydrogen sulphide (H₂S) monitoring data. As a result, the H₂S data obtained before September 2023 is likely to have a greater degree of uncertainty than previously understood. It is only the monitoring data for H₂S that is affected.

Data collected by the H₂S analyser in all MMFs (Mobile Monitoring Facilities) are now being recorded using the adjusted calibration method, which has been checked with the manufacturer. We are confident in the H₂S data recorded in MMFs since September.

Latest Air Monitoring Data

The table below contains a summary of the raw data collected from our mobile monitoring facilities in the period 22 - 28 April inclusive. It is important to note that this data is based on indicative and incomplete raw data. It does not provide the magnitude of H₂S detected, but a percentage of time above the WHO odour annoyance guideline level. The data has not been subjected to quality assurance checking or calibrations and should therefore be treated with caution as it will change once these processes have been undertaken. Rectified data which has been subject to quality assurance and calibration is published monthly on the right hand side of this page.

Earlier in the year we were working to establish a new location as the site at Silverdale Pumping Station was no longer available to us. The new site was going to be called MMF4 but this has not worked out and we have now been able to go back into Silverdale Pumping Station. As the monitoring at the Silverdale Pumping Station is a continuation of the previous dataset, we will continue to call this MMF2 Silverdale Pumping Station.

The image below shows the number of odour reports the Environment Agency received during the week of 22 - 28 April 2024.

Mobile Monitoring Facilities (MMFs)

In March 2021 we deployed two MMFs to Silverdale in response to reports of ongoing air pollution and odour nuisance in the vicinity of Walleys Quarry Landfill Site (WQLS). MMF2 was deployed on Silverdale Road and MMF9 was deployed at Galingale View, both at the locations of pumping stations run by Severn Trent Water Limited. In April 2021, two additional MMFs were deployed in Silverdale. MMF1 was deployed near the Silverdale Cemetery and MMF6 was deployed at the Newcastle Community Fire Station.

A range of factors have to be considered when choosing monitoring locations. We chose the monitoring sites here, in particular, because they were within residential areas where complaints had been received and had access to the necessary power supply. We also had regard to prevailing wind direction, the local topography, and the requirement for suitable hard standing. The MMFs monitor ambient air around WQLS generally, which may include emissions from other local sources.

The pollutants being monitored are hydrogen sulphide (H₂S), methane (CH₄), oxides of nitrogen (NO_x), sulphur dioxide (SO₂), different particulate matter size fractions (Total Suspended Particulate (TSP), PM₁₀ and PM_2.5) and the BTEX group of organic compounds. As it is not possible to measure odour pollution in the way the human nose detects it, we use methane and hydrogen sulphide as a surrogate or alternative for measuring odour pollution. Methane and hydrogen sulphide are major components of landfill gas.

Where possible, we consider these pollutants against the UK Air Quality Strategy (AQS) objectives, or where this is not possible, against other commonly used guidelines such as the World Health Organisation (WHO) air quality guidelines or the health-based guidance values used by the UK Health Security Agency (UKHSA).

We also monitor meteorological conditions, namely wind direction, wind speed, temperature and pressure, at the MMFs.

Figure 1: Location of the Mobile Monitoring FacilitiesTable 1: Summary of monitoring locations in relation to Walleys Quarry

Picture 1: The air quality mobile monitoring facility (MMF9) situated at Galingale View Pumping StationThe network of MMFs that we currently have in place has proved very effective. The data capture rates have been very high and enable us to build a very detailed picture of the local ambient air quality.

Picture 2: Annotated diagram of MMF exterior

We have put together a video which explains what an MMF does and what is inside an MMF, which you can view here.

Monitoring and data

We use the data gathered to help assess the type, time and nature of landfill gas emissions from WQLS, and the effectiveness of the measures we have required the operator to implement. This in turn helps inform any further regulatory action.

We share this monitoring data with our partners, UKHSA, Staffordshire County Council and Newcastle-under-Lyme Borough Council. UKHSA uses the data provided in producing its monthly health risk assessments, which you can find on the right hand side of the page.

Monitoring reports

Our national Ambient Air Monitoring Team operates the MMFs. It produces monthly Air Quality Reports, monthly Rectified Air Quality Data, and longer term (interim) Air Quality Reports.

The team conducts all its monitoring and data handling using approved standards and methodologies. Rectified Data, which appears in our weekly updates and monthly Air Quality Reports, is data that has been subject to basic quality assurance checking. It may be revised once calibrations are applied to the full data when monitoring is concluded. This is a standard approach taken when conducting highly sensitive ambient air monitoring.

Hydrogen Sulphide levels

Hydrogen Sulphide concentrations continue to be greatly reduced compared with the period when monitoring began, in both the source emission and ambient air measurements. Air quality monitoring data provides additional confidence that our ongoing regulation is ensuring the source emission of hydrogen sulphide from the landfill site continues to remain low.

It is important to note that there will always be short-term fluctuations in the concentrations of hydrogen sulphide leaving the site, especially given the low concentrations we are monitoring. The causes can include factors such as the impact of improvement works being carried out on site and changes in the weather.

Concentrations of landfill gas emissions generally increase overnight, during periods of colder weather, and in still wind conditions with clear skies. Certain weather conditions and the local topography can cause odour to be more noticeable at this landfill site. This is due to something called katabatic flow. You can find our short animation to help explain why here: How weather affects landfill sites.

By contrast, in warmer weather the gases are naturally more diluted due to higher temperatures and rising air. This means improvements from measures implemented at WQLS could be less noticeable during warmer periods.