1 Introduction

Heathrow Airport Limited have commissioned Ricardo to undertake a monitoring programme to investigate the concentrations of ultrafine particles (UFP) at Heathrow Airport.

WHO defines UFPs as particles greater than 10 nm in size. UFP are usually so small that they contribute very little to these mass measurements, so they are typically reported as the number of particles in a volume of air.

There are currently no national limits in place for UFPs, however, the World Health Organization (WHO) published a “good practice statement”¹ for UFPs, with thresholds associated with HIGH and LOW concentrations.

• HIGH concentrations: 24-hour mean > 10,000 particles/cm³ (24-hour mean) or 1-hour mean > 20,000 particles/cm³

• LOW concentrations: 24-hour mean < 1,000 particles/cm³ (24-hour mean)

This report presents preliminary data and analysis for the period 22^nd April 2023 to 31^st December 2023.

2 Monitoring Methodology

A Condensation Particle Counter (CPC) was installed at the LHR2 monitoring station in April 2023. LHR2 is an on-airport airside location station, situated inside the northern perimeter fence on an area of the old apron between the northern runway and the northern perimeter road, 14.5 m from the kerb and 179 m from the runway centre. The prevailing wind direction is from the south west and hence this site, situated to the north east of the airport, was selected to monitor air pollutants arising from the airport area. Although there are no EU limit values and UK AQS objectives for UFP it is worth noting, for the main relevant ambient air quality pollutants these limit values and objectives only apply to locations where public exposure may occur. As LHR2 is located within the airport perimeter, where members of the public do not have access, these limits do not apply.

The CPC measures ultrafine particle number concentrations down to 10 nm, meeting the requirements of the WHO “good practice statement”. Currently, there is no specification for particle size distribution, particle speciation, principle of operation or measurement uncertainty within the WHO guidance.

A datalogging system records values from the CPC every second. From these spot values, aggregated 1 minute values are calculated and logged, hourly and 24-hourly mean averages were subsequently then calculated. It should be noted that 1 second data above 100,000 particles/cm³ are higher than the range of the instrument, therefore these readings have a much higher associated uncertainty.

It is worth noting, and as you will see within this report, a high proportion of the recorded measurements are above the instruments accurate working range. In terms of the overall monitoring survey, the analyser is able to assess whether the WHO guidelines are breached at the LHR2 location, however measuring an accurate background concentration appears not to be possible with the current sampling infrastructure. There are potential enhancements that can be made to the instrumentation (by way of installing a dilution system) to enable a background concentration to be defined more accurately. This should be considered for the continuation of the survey, depending on HAL’s overall objectives.

3 Preliminary Results