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 2019 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 been 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) ¹.

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 - Tapered Element Oscillating Microbalance (TEOM);
• 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.

2.4 VCM Correction of PM₁₀ Data

The TEOM particulate monitor uses a 50^oC heated sample inlet to prevent condensation on the filter. Although necessary, this elevated temperature can result in the loss of volatile and semi-volatile components of PM₁₀, such as ammonium nitrate.

It is not possible to address this problem by applying a simple correction factor. However, King’s College London (KCL) have developed a Volatile Correction Model ⁷, which allows TEOM PM₁₀ data to be corrected for the volatile components lost as a result of the TEOM’s heated inlet. The model is available at http://www.volatile-correction-model.info/Default.aspx. It uses data from nearby TEOM-FDMS particulate analysers, which measure the volatile and non-volatile components of the PM₁₀. The volatile component (which typically does not vary much over a large region), can be added to the TEOM measurement. KCL state that the resulting corrected measurements have been demonstrated as equivalent to the gravimetric reference equivalent. In this report, the VCM has been used to correct PM₁₀ data where applicable. Where this has been done, it is clearly indicated.

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 PM₁₀ measured using the TEOM instrument has been converted to gravimetric equivalent using the King’s College London Volatile Correction Model⁸ where appropriate.

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 O₃, CO, SO₂, NO_x or PM₁₀ were exceeded at Birmingham Airport 2 monitoring location in 2019. 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 2019 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 2019.
  
• 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 18.6 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 51.4 μg m^-3 after VCM correction. 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 13.8 μg m^-3 after VCM correction; this objective was therefore met.
• 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 62 occasions when any 8-hour running mean exceeded 100 μg m^-3, on 9 separate days. Birmingham Airport 2 therefore met the AQS objective for ozone during 2019 and was within the permitted maximum of 10 days. The maximum hourly mean concentration of ozone was 167.7 μg m^-3: this was measured registered on 25^th July 2019.

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 2019, both with zero exceedances during the year.

3.7 Seasonal Variation

NO_x, CO and PM₁₀ at Birmingham Airport 2 showed typical seasonal patterns for urban areas though 2019, 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. Anomalously low NO₂ data was recorded in the month of March at the same time O₃ was higher than expected sugesting that this is metrological. The same pattern is seen at local AURN monitoring stations.

SO₂ seasonal patterns are much less pronounced and are masked by pollution events and the change in data collection system (which changed the accuracy of recorded data) and so does not display typical seasonal variation. SO₂ seasonal variation should follow a typical winter trend, as the major source of this pollutant is the combustion of coal and oil; this increases during winter, mainly because of domestic and industrial heating requirements and reduced pollutant dispersion. The SO₂ measurements are all very low during 2019.

O₃ concentrations registered at Birmingham Airport 2 continue to follow a typical seasonal variation for this pollutant, with higher concentrations being registered in April, May, and June. 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, SO₂ 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.

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 (VOC’s), 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 PM₁₀ 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 PM₁₀ at this site showed an evening rush-hour peak during 2019.

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. PM₁₀ concentrations don’t appear to vary much during the week. Saturday registers the lowest concentrations of CO, PM₁₀, SO₂, and NO_x (NO/NO₂). Sunday gave the highest readings of O₃.

The SO₂ weekly pattern appears to show little to no variation through out the week.