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 Energy & Environment. This report has been prepared by Ricardo Energy & Environment, on behalf of Birmingham Airport, to provide analysis and commentary on the 2021 dataset.

Data in the annual report have been processed according to the rigorous quality assurance and quality control procedures used by Ricardo Energy & Environment. 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.

2.1 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) ².

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.

2.3 Automatic Monitoring Techniques

The following techniques were used for the automatic monitoring of NO_x (i.e. NO and NO₂), PM₁₀, O₃, CO and SO₂:

• PM₁₀, PM_2.5 - 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 Energy & Environment. Data are downloaded hourly. The data are converted to concentration units at Ricardo Energy & Environment 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 Energy & Environment, are used to scale and ratify the data. This data scaling and ratification is carried out by Ricardo Energy & Environment. 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 20^oC, 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 1^st July 2020 the old TEOM unit was replaced with a FIDAS which measures both PM₁₀ and PM_2.5.

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 NO_x has been calculated as follows:
NO_x μg m^-3 = (NO ppb+NO₂ ppb)*1.91 and is termed “NO_x 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.

3.3 Comparison with Air Quality Objectives

None of the AQS objectives for CO, SO₂, NO_x, PM₁₀ or PM_2.5 were exceeded at Birmingham Airport 2 monitoring location in 2021. O₃ failed to meet the AQS objective. Details of UK air quality standards and objectives are provided in Table 1.

• The AQS objective for hourly mean NO₂ concentration is 200 μg m^-3 which may be exceeded up to 18 times per calendar year. During 2021 there were no hourly mean NO₂ measurements exceeding 200 μg m^-3. The lower threshold of the Defra “Moderate” air quality band is 201 μg m^-3 as an hourly mean. Therefore NO₂ levels at stayed within the Defra “Low” band for the whole year. The AQS objective was achieved for 2021.
  
• The annual mean AQS objective for NO₂ is 40 μg m^-3. This objective was also met at Birmingham Airport 2, where the calculated annual mean was 13.9 μg m^-3.
• The AQS objective for PM₁₀ is 50 μg m^-3 for the daily mean, not to be exceeded more than 35 times a year. Results show that one exceedance of this objective was registered, with a maximum daily mean of 56.9 μg m^-3. The site met the AQS objective for 24 hour mean PM₁₀.
• The annual mean AQS objective for PM₁₀ is 40 μg m^-3. The site measured an annual mean of 10.3 μg m^-3, this objective was therefore met.
• The annual mean for PM_2.5 data was 6.8 μg m^-3. Therefore, this monitoring site met the AQS objective of 25 μg m^-3 (in England).
• The AQS objective for maximum daily 8-hour running mean O₃ is 100 μg m^-3 (not to be exceeded more than 10 days a year). There were 143 occasions when any 8-hour running mean exceeded 100 μg m^-3, on 22 separate days. Birmingham Airport 2 therefore did not meet the AQS objective for ozone during 2021. The maximum hourly mean concentration of ozone was 162.2 μg m^-3: this was measured registered on 8^th September 2021.

Ozone 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 ozone concentrations in their areas. The Government has recognised the problems associated with achieving the air quality objective for ozone, and this is not included in the LAQM regime.

CO and SO₂ measured at Birmingham Airport 2 met all the AQS objectives for 2021, both with zero exceedances during the year.

3.7 Seasonal Variation

NO_x and CO at Birmingham Airport 2 showed typical seasonal patterns for urban areas though 2021, as can be observed in the above ‘month’ plots. The highest concentrations of these pollutants 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.

SO₂ shows a very different seasonal pattern compared to previous years. Given the sites close location to the runway the main source of SO₂ is likely to be aircraft emissions. Peak emmissions are about 50% of that of 2020 and the SO₂ seasonal variation in 2021 has a closer match to the strictness of covid restrictions, tighter controls over the winter months resulting in fewer flights and lower SO₂, and an easing over the summer.

PM₁₀ and PM_2.5 seasonal patterns are much less pronounced and are to an extent masked by pollution events.

O₃ concentrations registered at Birmingham Airport 2 continue to follow a typical seasonal variation for this pollutant, with higher concentrations being registered during late 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 ozone 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).

3.8 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 ozone) 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, NO_x 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 2021.

3.9 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. NO, NO₂ and CO early morning and late afternoon rush hour peaks are in general much more pronounced on weekdays as opposed to during the weekends.

PM and SO₂ concentrations don’t appear to vary much during the week.

Weekends registered the lowest concentrations of NO_x (NO/NO₂) and CO. SO₂ concentrations were lowest on Saturdays, PM₁₀ and PM_2.5 lowest on Fridays and O₃ lowest on Thursdays.