Air Quality at Birmingham International Airport
Annual Report for 2023
| Authors | Sion Carpenter |
| Compilation date | 08/05/2024 |
| Customer | Birmingham Airport Ltd |
| Approved by | Jo Solan |
| Copyright | Ricardo |
| EULA | Ricardo Report EULA |
| Contract reference | ED79001 | Report reference | Issue 1 |
Executive summary
This report provides details of air quality monitoring conducted at Birmingham Airport during 2023. The work, carried out by Ricardo on behalf of Birmingham Airport Ltd, is a continuation of monitoring undertaken at Birmingham Airport since 1995. The aims of the programme are to monitor air pollution around the airport, to assess compliance with relevant national air quality objectives, and to investigate changes in air pollutant concentrations over time.
Automatic continuous monitoring was carried out at one location, referred to as Birmingham Airport 2. The site monitored oxides of nitrogen (nitric oxide and nitrogen dioxide), ozone, carbon monoxide, sulphur dioxide, PM10 and PM2.5.
A data capture target of 85% is recommended in the Defra Technical Guidance LAQM.TG(22)(“Local Air Quality Management - Technical Guidance LAQM.TG (22)” 2022) was achieved for all pollutants in 2023.
The UK Air Quality Strategy (AQS) hourly mean objective for NO2 is 200 μg m-3, with no more than 18 exceedances allowed each year. The monitoring site has registered no exceedances of this value during the year, and therefore met this objective for 2023.
The annual mean AQS objective for NO2 is 40 μg m-3. This objective was also met in 2023; an annual mean of 14.9 μg m-3 was measured. This value is lower than the one measured in 2022 (15.4 μg m-3).
PM10 may exceed the 24-hour mean limit of 50 μg m-3 no more than 35 times per year to meet the AQS objective. During 2023, there were no exceedances of the limit value registered at the site. This AQS objective was therefore met in 2023. The annual mean AQS for PM10 is 40 μg m-3. This objective was met at Birmingham Airport 2 with an annual mean of 10.2 μg m-3.
The UK AQS objective for O3 is 100 μg m-3, as a maximum daily 8-hour mean, not to be exceeded more than 10 days a year. The O3 levels measured at Birmingham Airport monitoring station show that this objective was exceeded on 15 days during 2023. The AQS objective for O3 was therefore not met in 2023. O3 is a transboundary pollutant which is difficult to control by local measures: it is therefore not currently included in the Local Air Quality Management regime.
The AQS objectives for CO and SO2 were met at Birmingham Airport 2 monitoring station in 2023.
1 Introduction
1.1 Background
Birmingham Airport Ltd (referred to here as “Birmingham Airport”) has undertaken continuous ambient air quality monitoring at a monitoring station on the airport premises since April 1995. This forms part of the Airport’s commitment to monitor air quality through the requirements of the Section 106 Planning Agreement between Solihull Metropolitan Borough Council (SMBC) and Birmingham Airport. The monitoring is intended to provide information on current air quality in the area and the levels of pollution to which the neighbouring community is exposed. The data from the air monitoring station are managed and collated by Ricardo. This report has been prepared by Ricardo, on behalf of Birmingham Airport, to provide analysis and commentary on the 2023 dataset.
Data in the annual report have been processed according to the rigorous quality assurance and quality control procedures used by Ricardo. These ensure the data are reliable, accurate and traceable to UK national measurement standards.
1.2 Aims and objectives
The aim of this monitoring programme is to monitor concentrations of several important air pollutants at the airport. The results of the monitoring are used to assess whether applicable national air quality objectives have been met, and how pollutant concentrations in the area have changed over time. Additionally, meteorological data were used to investigate the importance of various sources of pollution.
It is important to note that the pollutants measured in this study could have originated from a wide variety of sources, both local and long range. Not all of these sources will be directly connected with the airport.
Monitoring data collected at Birmingham Airport are compared in this report with:
- Relevant UK air quality limit values and objectives.
- Relevant periods of regional/national elevated pollutant concentrations.
- Corresponding results from a selection of national air pollution monitoring sites.
2 Details of the Monitoring Programme
2.1 Pollutants Monitored
The monitoring programme concentrates on the pollutants which may be of concern around airports. These are listed below. The emission statistics presented here all come from the National Atmospheric Emission Inventory (NAEI) (Air Quality Expert Group, 2004).
2.1.1 Nitrogen Oxides (NOx)
Combustion processes emit a mixture of oxides of nitrogen - NO and NO2 - collectively termed NOx.
NO is described as a primary pollutant (meaning it is directly emitted from source). NO is not known to have any harmful effects on human health at ambient concentrations. However, it undergoes oxidation in the atmosphere to form the secondary pollutant NO2.
NO2 has a primary (directly emitted) component and a secondary component, formed by oxidation of NO. NO2 is a respiratory irritant and is toxic at high concentrations. It is also involved in the formation of photochemical smog and acid rain and may cause damage to crops and vegetation.
Based on 2022 calendar year emissions data from the 2024 submission of National Atmospheric Emissions Inventory (NAEI) data to the EU, in the UK, civil aircraft taking off and landing (up to a height of 1000m) are estimated to contribute 1.6% to the total reported UK emissions of NOx (NAEI, UK (beis.gov.uk), 2024).
The Air Quality Expert Group (Air Quality Expert Group, 2004) (AQEG) has stated that: “Around a third of all NOx emissions from the aircraft (including ground-level emissions from auxiliary power units, engine testing etc., as well as take-off and landing) occur below 100 m in height. The remaining two-thirds occur between 100 m and 1000 m and contribute little to ground-level concentrations. Receptor modelling studies show the impact of airport activities on ground-level NO2 concentrations. Studies have shown that although emissions associated with road traffic are smaller than those associated with aircraft, their impact on population exposure at locations around the airport are larger.” Previous rounds of review and assessment within the LAQM process have not highlighted any cases where airports appear to have caused exceedances of air quality objectives for particulate matter measured as PM10. Therefore, in the context of Local Air Quality Management (LAQM), the key pollutant of concern from airports is NO2. Local authorities whose areas contain airports with over 10 million passengers per annum must take these into account in their annual review and assessment of air quality.
2.1.2 PM10 and PM2.5 Particulate Matter
Airborne particulate matter varies widely in its physical and chemical composition, source and particle size. Particulate matter is categorised by particle size: it is most commonly monitored as PM10 (i.e. particles whose effective size is <10 μm) and PM2.5 (i.e. particles with effective size <2.5 μm). Fine particles are of most concern, as they are small enough to penetrate deep into the lungs, where they can have the greatest impact upon health.
The main sources of airborne particulate matter in the UK are combustion (industrial, commercial and residential fuel use). This is followed by road vehicle emissions. Based on 2021 calendar year emissions data from the 2023 submission of National Atmospheric Emissions Inventory (NAEI) data to the EU, civil aircraft taking off and landing (up to a height of 1000 m) was estimated to contribute 0.1% to the total reported UK emissions of PM10 and PM2.5 (NAEI, UK (beis.gov.uk), 2024).
Previous rounds of review and assessment within the LAQM process have not highlighted any cases where airports appear to have caused exceedances of air quality objectives for particulate matter measured as PM10.
2.1.3 Ozone (O3)
Ozone is not emitted directly into the atmosphere in significant quantities, but is a secondary pollutant produced by reaction between nitrogen dioxide (NO2) and hydrocarbons, in the presence of sunlight. Whereas nitrogen dioxide (NO2) contributes to ozone formation, nitrogen oxide (NO) destroys ozone and therefore acts as a local sink. For this reason, ozone levels are not as high in urban areas (where NO is emitted from vehicles) as in rural areas. Ozone levels are usually highest in rural areas, particularly in hot, still, sunny weather conditions giving rise to “summer smog.”
2.1.4 Carbon Monoxide (CO)
Carbon monoxide is a gas that results as a product of the incomplete combustion of fuels. In the presence of an adequate O2 supply, CO gets oxidized, and turns into CO2. The highest levels of CO occur generally in areas with intense traffic, being released by the exhaust pipe of internal combustion engines. Other CO emission sources may include some industrial processes, biomass burning for heating or natural sources like forest fires. CO causes can cause harmful health effects, as it reduces the oxygen delivery to the body’s organs and tissues.
2.1.5 Sulphur Dioxide (SO2)
Sulphur dioxide is a colourless gas mainly originated by activities related to burning of fossil fuels (diesel burning of heavy vehicles), and burning of coal and oil in power plants. In nature, SO2 can also be released to the atmosphere from a volcanic eruption. The sulphur reacts with oxygen to form SO2, which in contact with the moisture in the air can create sulphuric acid, a component of acid rain.
2.2 Air Quality Limit Values and Objectives
This report compares the results of the monitoring survey with air quality limit values and objectives applicable in the UK. These are summarised below.
2.2.1 World Health Organisation
The World Health Organisation (WHO) issued non-mandatory, advisory, guidelines for a variety of pollutants in 2005 using currently available scientific evidence on the effects of air pollution on human health. New, updated, guidelines were introduced in September 2021(WHO, 2021) which significantly reduced the Annual mean limit of NO2 from 40 μg m-3 to 10 μg m-3 and the 24-hr mean being reduced to 25 μg m-3.
In light of the growing evidence of harm that PM10 and PM2.5 can cause the Annual mean limits were reduced from 20 μg m-3 to 15 μg m-3 and 10 μg m-3 to 5 μg m-3 respectively.
2.2.2 The UK Air Quality Strategy
The Environment Act 1995 required the UK to transpose the original EU Directive on Ambient Air Quality and Cleaner Air for Europe (2008/50/EC and its update EU/1480) (“Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on Ambient Air Quality and Cleaner Air for Europe” 2008) into UK law. It also placed a requirement on the Secretary of State for the Environment to produce a national Air Quality Strategy (AQS) containing standards, objectives and measures for improving ambient air quality. The original AQS was published in 1997, and contained air quality objectives based on the recommendations of the Expert Panel on Air Quality Standards (EPAQS) regarding the levels of air pollutants at which there would be little risk to human health.
The AQS has since undergone a number of revisions, and as of the Environment Act 2021 must be reviewed at least every 5 years. These revisions have reflected improvements in the understanding of air pollutants and their health effects. They also incorporated new European limit values, both for pollutants already covered by the Strategy and for newly introduced pollutants such as polycyclic aromatic hydrocarbons and PM2.5 particulate matter. The latest version of the strategy was published by Defra in 2007 (“The Air Quality Strategy for England, Scotland, Wales and Northern Ireland (Volume 1)” 2007). With the UK’s exit from the EU the UK’s AQS is no longer tied to that of the EU, however the current objectives are at least as stringent as the EC limit values.
The current UK air quality objectives for the pollutants monitored at Birmingham Airport are presented below.
2.2.3 Monitoring Sites and Methods
The monitoring site is located on the airfield near airport buildings to the east of the runway and north-west of the Main Terminal (OS grid ref. 417395, 284240), having previously been located to the west of the apron area, approximately 300 m due west of the Main Terminal. The site relocation occurred in January 2006. The current location of the monitoring site is shown below. A map showing the old and new locations is included in Appendix 1.
2.3 Automatic Monitoring Techniques
The following techniques were used for the automatic monitoring of NOx (i.e. NO and NO2), PM10, O3, CO and SO2:
- PM10, PM2.5 - Fine Dust Analysis System (FIDAS)
- NO, NO2 - Chemiluminescence;
- O3 - UV absorption analyser;
- CO - Non dispersive infrared absorption (NDIR);
- SO2 - Ultraviolet Fluorescence (UVF).
Further information on these techniques is provided in Appendix 2 of this report. These analysers provide a continuous output, proportional to the pollutant concentration. This output is recorded and stored every 10 seconds, and averaged to 15-minute mean values by internal data loggers. The analysers are connected to a modem and interrogated through a GPRS internet device to download the data to Ricardo. Data are downloaded hourly. The data are converted to concentration units at Ricardo then averaged to hourly mean concentrations.
Fortnightly calibrations are performed by Local Site Operators (LSOs) based at Birmingham Airport, to monitor the performance of the analysers. Data from these fortnightly checks, and from six-monthly independent QA/QC audits carried out by Ricardo, are used to scale and ratify the data. This data scaling and ratification is carried out by Ricardo. The analysers are also serviced on a six-monthly basis to ensure their continued operation.
All ambient concentration measurements in the report are quoted in micrograms per cubic metre (μg m-3) or in the case of carbon monoxide milligrams per cubic metre (mg m-3) at reference conditions of 20oC, 1013 mbar.
Improvement to our data management systems meant that between 2016 and 2017 there was an increase in the data precision that we are able to report. For pollutants with very low concentrations (such as CO and SO2) this means a much reduced level of noise on the hourly data which in turn manifests itself in an apparent step change in averages. This step change should therefore simply be considered as improved accuracy, not any significant change in ambient concentrations.
On the 1st July 2020 the old TEOM unit was replaced with a FIDAS which measures both PM10 and PM2.5.
3 Results and Discussion
3.1 Units
Measured concentrations are reported in microgrammes per cubic metre (μg m-3).
PM10 is conventionally reported in units of μg m-3, microgrammes per cubic metre.
In this report, the mass concentration of NOx has been calculated as follows:
NOx μg m-3 = (NO ppb+NO2 ppb)*1.91 and is termed “NOx reported as NO2.”
This conforms to the requirements of the EC Directive on Ambient Air Quality and Cleaner Air for Europe and is also the convention generally adopted in air quality modelling.
3.2 Summary Statistics
Overall data capture statistics for Birmingham Airport 2 are given in Tables 2-6. These represent the percentage of valid data for the whole reporting period. A data capture target of 85% is recommended in the Defra Technical Guidance LAQM.TG(22) (“Local Air Quality Management - Technical Guidance LAQM.TG (22)” 2022). All pollutants achieved a data capture of at least 85%. This data capture target does not include losses due to regular calibration or maintenance of the instrument. Any data capture rate above 75% is deemed representative of the full annual period. We will continue to review, assess and advise Birmingham Airport if this situation changes.
Also displayed are pie charts showing the percentage and number of readings in each of the Air Quality Index bands for each pollutant with the exception of SO2 and CO, both of which stayed in Band 1 the entire period. For more information on these bands please use the following link (https://uk-air.defra.gov.uk/air-pollution/daqi?view=more-info).
There were no significant data gaps for any pollutant in 2023.
NO2
SO2
CO
O3
PM10
PM2.5
3.3 Comparison with Air Quality Objectives
None of the AQS objectives for CO, SO2, NOx, PM10 or PM2.5 were exceeded at Birmingham Airport 2 monitoring location in 2023. O3 failed to meet the AQS objective. Details of UK air quality standards and objectives are provided in Table 1.
The annual mean AQS objective for NO2 is 40 μg m-3. Birmingham Airport 2 didn’t exceeded the annual mean, AQS objective of 40 μg m-3 for NO2 in 2023, with an annual mean of 14.9 μg m-3.
Birmingham Airport 2 didn’t exceeded the AQS objective of 200 μg m-3 for hourly mean NO2 more than the 18 permitted times per year during 2023.
The short term AQS objective for PM10 is a maximum of 50 μg m-3 for 24 hour mean periods, not to be exceeded more than 35 times a year. Birmingham Airport 2 did not exceeded this limit and so was well within the yearly maximum permitted number of exceedances of 35, thus meeting the AQS objective for 24 hour mean PM10. The annual mean AQS objective for PM10 is 40 μg m-3, this was met at Birmingham Airport with an annual mean of 10.2 μg m-3.
While no AQS objective exists for PM2.5, there is an annual mean objective of 25 μg m-3, although this is a non-mandatory compliance target. This was met with an annual mean of 6.5 μg m-3. This is less than half of the average concentration target limit.
The O3 AQS objective for daily maximum on an 8 hour running mean is of 100 μg m-3 (not to be exceeded more than 10 days a year). Birmingham Airport exceeded the AQS objective O3 106 times over 15 days during 2023. These exceedances were common at monitoring sites across background and rural sites in the midlands. O3 is a secondary pollutant; it is formed by chemical reactions in the air, involving precursor pollutants, rather than emitted directly from source. It is therefore trans-boundary in nature. As a result, Local Authorities have little control over O3 concentrations in their areas. The Government has recognised the problems associated with achieving the air quality objective for O3, and this is not included in the LAQM regime.
CO and SO2 measured at Birmingham Airport met all the AQS objectives for 2023, both with zero exceedances during the year.
3.4 Time Series Plot
Daily average and hourly time series plots of all pollutant data for the full year, as measured by the automatic monitoring site, are shown below. The plots are interactive and can be manipulated to show specific time periods or concentration bands.
It must be noted that an improvement to our data management systems meant that between 2016 and 2017 there was an increase in the data precision that we are able to report. For pollutants with very low concentrations (such as CO and SO2) this means a much reduced level of noise on the hourly data which in turn manifests itself in an apparent step change in averages. This step change should therefore simply be considered as improved accuracy, not any significant change in ambient concentrations.
The visible step change in SO2 data seen in July 2020 was accepted by the Quality Assurance and Quality Control meeting. It was attributed to the manifold pump being fixed.
The TEOM instrument for PM10 was replaced and a new FIDAS instrument providing PM10 and PM2.5 data was installed on the 1st July 2020.
Following a site intervention on the 11th January 2022 the CO data became significantly noisier, this was then rectified by a futher site intervention on the 25th of April 2023. This can be seen as a step change in the data, after discussion during our expert quality circle it was decided that because concentrations were still below the instrument limit value, the instrument had passed its QAQC audits, and no issues were identified at its services, that the data be considered valid.
NO2 Daily
NO2 Hourly
SO2 Daily
SO2 Hourly
CO Daily
CO Hourly
O3 Daily
O3 Hourly
PM10 Daily
PM2.5 Daily
3.5 Smooth Trend Plot
Below are smoothed time series plots of with points representing monthly concentration and bold lines representing trend modelled by Generalised Additive Model (GAM).
NO2
SO2
CO
O3
PM10
PM2.5
3.6 Time Variation Plot
NO2
SO2
CO
O3
PM10
PM2.5
3.6.1 Seasonal Variation
NO2 at Birmingham Airport 2 showed typical seasonal patterns for urban areas though 2023, as can be observed in the above ‘month’ plots. The highest concentrations of this pollutant occurred during the winter months. This pattern was also observed in previous years and is typical of urban monitoring sites. The highest levels of primary pollutants tend to occur in the winter months, when emissions may be higher, and periods of cold, still weather reduce pollutant dispersion.
PM10 and PM2.5 showed little seasonal variation in 2023 suggesting that these pollutants are strongly influenced by individual pollution episodes.
SO2 shows a very different seasonal pattern. Given the sites close location to the runway the main source of SO2 is likely to be aircraft emissions, with higher emissions during the busier summer months.
CO doesn’t exhibit any significant seasonal variation, which is to be expected given how low the readings for this pollutant are.
O3 concentrations registered at Birmingham Airport 2 continue to follow a typical seasonal variation for this pollutant, with higher concentrations being registered during spring to late summer. At low/mid latitudes, high O3 concentrations are generally observed during late spring and/or summer months, where anti cyclonic conditions (characterized by warm and dry weather systems) help increase photochemical reactions in the atmosphere, responsible for the increasing of ground level O3 production. In addition, the convective fluxes created during hot summer days can also be responsible for an increase of O3 (stratospheric intrusion). The hot air generated at ground level due to high temperatures is lighter and tends to ascend, being replaced by colder stratospheric air masses coming from above, dragging stratospheric O3 down into the troposphere (the lowest part of the atmosphere).
3.6.2 Diurnal Variations
The diurnal variation analyses viewed in the ‘hour’ plots showed typical urban area daily patterns for NO2 and CO. Pronounced peaks can be seen for these pollutants during the mornings, corresponding to rush hour traffic at around 07:00-09:00. Concentrations tend to decrease during the middle of the day, with a much broader evening road traffic rush-hour peak in building up from early afternoon. NO generally show a much smaller peak than NO2 in the afternoons. This is likely to be because concentrations of oxidising agents in the atmosphere (particularly O3) tend to increase in the afternoon, leading to enhanced oxidation of NO to NO2.
SO2 followed the same pattern as previous years with concentrations building during the day and falling overnight.
The concentration of O3 at Birmingham Airport 2 follows a typical diurnal pattern. O3 concentrations always increase during daylight hours due to the photochemical reactions of NO2 and photo oxidation of Volatile Organic Compounds (VOCs), CO, hydrocarbons, (O3 precursors). In the afternoon/ night O3 gets consumed by a fast reaction with NO (titration of O3 by NO). The absence of sunlight prevents the photolysis of the O3 precursors.
The diurnal patterns for PM are determined by two main factors. The first is emissions of primary particulate matter, from sources such as vehicles. The second factor is the reaction that occurs between sulphur dioxide, NOx and other chemical species, forming secondary sulphate and nitrate particles. The PM at this site showed both a morning and an evening rush-hour peak during 2023.
3.6.3 Weekly Variations
The analyses of each pollutants weekly variation showed that the same type of diurnal patterns occur for all the days of the week. NO2 early morning and late afternoon rush hour peaks are in general much more pronounced on weekdays as opposed to during the weekends.
Concentrations of the other pollutants don’t appear to vary much during the week.
3.7 Calendar Plot
The below calendar plots show how pollutant levels change on a day by day basis and make it easy to identify both short and long term pollution events, along with periods of low pollution. The numerical date is coloured by the wind speed for that day. The actual value can also be seen by hovering the mouse on the cell.
It can be seen that the highest NO2 value was recorded on the 24th January, SO2 on the 8th September, CO on the 18th April, O3 on the 11th June, PM10 the 8th September and PM2.5 on the 14th February.
NO2
SO2
CO
O3
PM10
PM2.5
3.8 Periods of Elevated Pollutant Concentration
This section reviews the most significant periods of high air pollution concentrations for the whole year. It is important to stress that, despite there being some periods when pollutant concentrations exceeded the applicable air quality objectives, these were attributable to specific external sources. The DEFRA Air Quality Index (DAQI) calculates air quality index bands that go from 1 (Low) to 10 (Very High). Plotted below are interactive maps that show DAQI levels at AURN stations during periods of elevated pollution episodes, some of which were also recorded at Birmingham Airport during 2023.
3.8.1 5th to 9th February
Elevated NO2 pollution was recorded at numerous stations across central and southern England between the 5th and 9th February, though in the West Midlands (including Birmingham Airport) these remained in the “low” catagory. The elevated NO2 was primarily caused by settled atmospheric conditions allowing the build up of local emissions in addition to trapping transported of pollution from continental Europe.
3.8.2 7th to 20th June
Moderate to high levels of O3 were recorded across the entire UK between the 7th and 20th of June. Hot, sunny days enabled ground level O3formation from both local and imported precursors.
3.8.3 3rd to 10th September
Moderate to high levels of PM10, PM2.5 and O3 were recorded across the UK between the 3rd and 10th of September. Hot, sunny days enabled ground level O3 formation from local precursors and those imported by light winds from continental Europe.
3.9 Polar plot map
In order to investigate the possible sources of air pollution being monitored around Birmingham Airport, real meteorological data measured at the Airport was used to add a directional component to the air pollutant concentrations.
The above plot shows that westerly winds prevailed and the mean wind speed was 4.1 m s-1. The maximum measured wind speed was 16.2 m s-1.
The below plots show hourly mean concentrations of NO2, SO2, CO, O3, PM10, PM2.5 at Birmingham Airport 2 against wind speed and wind direction. These plots should be interpreted as follows:
- The wind speed is indicated by the distance from the centre of the plot; the grey circles indicate wind speeds in 5 m s-1 intervals.
- The pollutant concentration is indicated by the colour (as indicated by the scale).
These plots therefore show how pollutant concentrations varied with wind direction and wind speed.
The plots do not show distance of pollutant emission sources from the monitoring site. However, in the case of primary pollutants such as NO, the concentrations at very low wind speeds are dominated by emission sources close by, while at higher wind speeds, effects are seen from sources further away.
NO2, which has both a primary and secondary component, shows significant sources at high wind speeds (> 15 m s-1) to the northwest to northeast quadrant, the direction of the Birmingham residential areas. A smaller sources can be seen to the southeast where the terminal and drop off area is situated. Elevated concentrations were also registered at low wind speeds, which indicates that a proportion of the NO2 measured has its origin from local emission sources, mainly by the fast reaction of NO with O3 in the presence of UV light.
The pollution rose for PM10 shows a major contribution round from the northwest to the southeast where built up urban areas, as well as the drop off, car park and external commercial areas are. Further sources can be seen at moderate wind speeds from the southwest most likely the runway. PM2.5 shows an almost identical distribution.
The plot of CO shows that the highest concentrations are from the north with moderate to high wind speeds. Lower, but still elevated, concentrations can be been in the south and when there are low wind speeds. This is in line with what is observed for NO2 and PM10 suggesting that the pollutants come from the same emission source.
The bivariate plot for O3 shows a contrasting pattern to that of the other pollutants in that the lowest O3 concentrations are associated with calm conditions and with winds from the north. Being a secondary pollutant O3 is formed from chemical reactions in the ambient air. The plot demonstrates that higher concentrations of O3 are measured at the site when wind speeds are sufficient to bring in O3-rich air from other areas of the region. At very low wind speeds, when NO concentrations are highest, any O3 present reacts with the NO emitted by the sources in the immediate vicinity. This illustrates that the exceedances of the AQS objectives for O3 are not a direct result of Birmingham Airport’s activities but reflect regional O3 concentrations.
The pollution rose for SO2 show several concentration spots from multiple directions and wind speeds. The largest of these is to the south east, where the main airport terminal is located.
NO2
SO2
CO
O3
PM10
PM2.5
4 Comparison with Other Local Monitoring Sites
The below table compares the 2023 annual mean concentrations at Birmingham Airport and two local air quality monitoring sites in Birmingham as well as the previous years study at Birmingham Airport. The sites selected are all part of the UK’s national Automatic Urban and Rural Network (AURN) and are as follows:
Birmingham A4540 Roadside: An urban traffic site located on the east side of the A4540 in Bordesley.
Birmingham Ladywood: An urban background site, located to the rear of a Primary school on the western edges of the city centre.
All pollutants have units of μg m-3 except CO which is in mg m-3.
The annual mean concentration of PM10 measured at the Birmingham Airport site in 2023 was lower than those measured at the other Birmingham sites. As in previous years, the annual mean concentration of SO2 at Birmingham Airport was low. The annual mean concentrations of NO2 measured at Birmingham Airport were comparable with those measured at the urban background site of Ladywood (an urban background site located away from busy roads).
Concentrations of O3 are typically higher in rural areas, far away from sources of other pollutants such as NO (which removes O3 from the air by chemical reaction). The annual mean O3 concentration at Birmingham Airport is again comparable to those measured at the urban background site, O3 concentrations at the roadside sites are generally lower.
These statistics together indicate that the pollution levels registered at Birmingham Airport were consistent with those measured elsewhere in the city in and with the prior years monitoring.
5 Conclusions
The following conclusions have been drawn from the results of air quality monitoring at Birmingham Airport during 2023.
Oxides of nitrogen, particulate matter (as PM10), carbon monoxide (CO), sulphur dioxide (SO2) and ozone (O3) were monitored throughout 2023 at one monitoring site in Birmingham Airport (Birmingham Airport 2). The conclusions of the 2023 monitoring program are summarised below.
All pollutants achieved a data capture of at least 85%.
Birmingham Airport didn’t exceed the AQS objective of 200 μg m-3 for hourly mean NO2 more than the 18 permitted times per year during 2023.
Birmingham Airport didn’t exceed exceeded the annual mean, AQS objective of 40 μg m-3 for NO2 in 2023 with an annual mean of 14.9 μg m-3.
Birmingham Airport didn’t see exceedances of the AQS objective for 24 hour mean of 50 μg m-3, and so didn’t exceed more than 35 times a year, and had an annual mean below the objective of 40 μg m-3 for PM10, it being 10.2 μg m-3. The particulate matter was measured using a FIDAS instrument with no correction required for PM10. PM2.5 data has a correction factor applied, being divided by 1.06, as per the Certification - MCERTS for UK Particulate Matter specification.
O3 was measured at the site and it exceeded the AQS objective for O3 on 15 days in 2023 and so did not meet the AQS objective, However, this is not unexpected given the climatic conditions experienced in the region.
Seasonal variations in pollutant concentrations at Birmingham Airport show that NO2 exhibited higher concentrations during the winter months. O3 levels were highest during the spring and summer, as is typical. PM10, PM2.5, SO2 and CO showed little overall seasonal pattern and the concentrations are still low in the case of the latter two pollutants.
The diurnal patterns of concentrations of all pollutants were similar to those observed at other urban monitoring sites. Peak concentrations of NO2, particulate matter, and CO coincided with the morning and evening rush hour periods, and levels of O3 peaked in the afternoons. SO2 had no distinctive morning or afternoon peaks.
Meteorological data was used at Birmingham Airport, allowing the effect of wind direction and speed to be investigated. Bivariate plots of NO2 concentrations and wind data showed that concentrations of these pollutants at the monitoring site were typically high in calm conditions, indicating that the main sources of these pollutants were nearby, with a further large source being the residential area to the north. The pattern was slightly different for PM, with additional signals from the south east. CO concentrations appear to follow a similar profile to NO2, showing that its origin is both local and long range. SO2 emissions seem to originate from several sources from many directions.
Mean concentrations of pollutants at the urban background Birmingham AURN site in 2023 were comparable with those measured at Birmingham Airport, and lower than those at the roadside site, with the exception of O3.
Appendix I
Map of BIA air monitoring sites.
Appendix II
The following continuous monitoring methods were used at the Birmingham Airport 2 air quality monitoring station:
- NO, NO2: chemiluminescence with ozone.
- PM10 and PM2.5: Optical measurement.
- O3: UV absorption analyser.
- CO: Non dispersive infrared absorption (NDIR)
- SO2: Ultraviolet Fluorescence (UVF)
These methods were selected in order to provide real-time data. The chemiluminescence and the UV absorption analysers are the European reference method for ambient NO2 and O3 monitoring.
The chemiluminescence with ozone analyser is based on the principle that nitric oxide (NO) and ozone react to produce excited NO2 molecules, which emit infrared photons (represented in the equation below by the photon’s energy, hv,) when going back to lower energy states:
NO + O3 -> NO2* + O2 -> NO2 + O2 + hv
A stream of purified air (dried with a NafionTM Dryer) passing through a silent discharge ozonator generates the ozone concentration needed for the chemiluminescent reaction. The specific luminescence signal intensity is therefore proportional to the NO concentration. A photomultiplier tube amplifies this signal. NO2 is detected as NO after reduction in a molybdenum (Mo) converter heated at about 325 degrees Celcius. The ambient air sample is drawn into the analyser, flows through a capillary, and then to a valve, which routes the sample either straight to the reaction chamber (NO detection), or through the converter and then to the reaction chamber (NOX detection). The calculated NO and NOX concentrations are stored and used to calculate NO2 concentrations (NO2 = NOx - NO), assuming that only NO2 is reduced in the Mo converter.
The UV absorption analyser determines ozone concentrations by measuring the absorption of O3 molecules at a wavelength of 254 nm (UV light) in the absorption cell, followed by the use of the Beer-Lambert law. The concentration of ozone is related to the magnitude of the absorption. The reference gas, generated by scrubbing ambient air, passes into one of the two absorption cells to establish a zero light intensity reading, I0. Then the sample passes through the other absorption cell to establish a sample light intensity reading, I. This cycle is reproduced with inverted cells. The average ratio R=I/I0 between 4 consecutive readings is directly related to the ozone concentration in the air sample through the Beer-Lambert law.
The Non-Dispersive Infra-Red (NDIR) detectors are the industry standard method of measuring the concentration of carbon monoxide (CO). Each constituent gas in a sample will absorb some infra-red at a particular frequency. By shining an infra-red beam through a sample cell (containing CO), and measuring the amount of infra-red absorbed by the sample at the necessary wavelength, a NDIR detector is able to measure the volumetric concentration of CO in the sample.
The Ultraviolet Fluorescence analyser determines SO2 by, at first, scrubbing the air flow to eliminate aromatic hydrocarbons. The air sample is then directed to a chamber where it is irradiated at 214 nm (UV), a wavelength where SO2 molecules absorb. The fluorescence signal emitted by the excited SO2 molecules going back to the ground state is filtered between 300 and 400 nm (specific of SO2) and amplified by a photomultiplier tube. A microprocessor receives the electrical zero and fluorescence reaction intensity signals and calculates SO2 based on a linear calibration curve.
The FIDAS unit employs a white light LED light scatter method that offers additional information on both particle size distribution from 0.18 to 30 microns (PM1, PM2.5, PM4, PM10 and Total Suspended Particles (TSP).
The analysers for NOx, O3, CO and SO2 are equipped with an automatic calibration system, which is triggered daily under the control of the data logger. Fully certificated calibration gas cylinders are also used at each site for manual calibration.
Each analyser provides a continuous output, proportional to the pollutant concentration. This output is recorded and stored every 10 seconds, and averaged to 15 minute average values by the on-site data logger. This logger is connected to a modem and interrogated twice daily, by telephone, to download the data to Ricardo. The data are then converted to concentration units and averaged to hourly mean concentrations.
6 References
| Name | Jo Solan |
| Address | Ricardo, Gemini Building, Harwell, Didcot, OX11 0QR, United Kingdom |
| Telephone | 07779038105 |
| Jo.Solan@ricardo.com |