Evaluation of aircraft emissions at London Heathrow Airport

Highlights

• Departing aircraft emit more Nucleation particles then landing aircraft.

• Larger aircraft emit more UFP than smaller aircraft.

• Particle size distribution of UFP is very dependent on aircraft activity at the airport.

• High concentrations of UV-active Black carbon can be seen from tyres during landing.

• PM10 and PM2.5 concentrations at the airport mostly originate from other sources.

Abstract

A study to monitor Ultrafine Particles (UFP) at Heathrow Airport was undertaken in the autumn of 2017. The campaign followed on from a similar study in 2016, which put UFP at the airport into context with nearby measurements. The objective of the 2017 study was to undertake UFP monitoring at higher time resolution (60 second scans) and in a narrower particle size range (6–100 nm). High resolution data from the NOx, PM and Black Carbon analysers on site was also collected during the survey. Measurements were made at the runway station, LHR2 to attempt to characterise individual aircraft using the runway. Nucleation mode particles are again seen to predominantly originate from the airport, with highest concentrations associated with departing aircraft. While there is some correlation of nucleation particles with NOx and BC, these pollutants, together with PM mass and Aitken mode particles, also show strong associations with winds from off-airport directions. There is some evidence that BC emissions from landing aircraft are enriched in UV-active BC (UVPM), most likely as a result of tyre abrasion upon landing. Comparison of UFP measurements with the 2016 survey was not possible because of the differences in configuration of the SMPS for the two surveys. This observation demonstrates the importance of documenting SMPS configuration, to determine if comparison between published data is possible. Analysis of the 1 minute measurement data with associated aircraft departure information was used to group the data by aircraft type. Larger aircraft departing from the runway recorded higher measurements of nucleation particles and NOx compared to smaller aircraft, while emissions of BC, UVPM and NO₂ appear to be dependent upon the age of the engine design, rather than the size of the aircraft.

Introduction

Heathrow Airport is the busiest two-runway airport in the world. In 2017, the airport handled over 78.0 million passengers and approximately 471,000 aircraft movements (https://www.heathrow.com/content/dam/heathrow/web/common/documents/company/investor/reports-and-presentations/financial-results/2017/2017-FY-Heathrow-SP-results-release.pdf). The airport is located in a complex environment: bounded by the M25 and M4 motorways on two sides, and by the outskirts of London on a third side.

The history of AQ measurements at Heathrow Airport, together with review of UFP at airports and the results of our UFP study at Heathrow Airport in 2016 are extensively discussed in Stacey (2019) and Stacey et al. (2020).

An increasing amount of research has been undertaken close to airports, to better understand the nature of ultrafine particles (UFP) emitted from aircraft. The literature review by Stacey (2019) collected the most relevant literature at the time into a single document. Prior research undertaken and referenced in this review, together with a research study of UFP measurements undertaken at Heathrow Airport in 2016 by Stacey et al. (2020), informs the direction of research and analysis throughout this paper. More recently studies by, for example Henry et al. (2019), Lopes et al. (2019), Bousiotis et al. (2019) and Rivas et al. (2020) have supported the work of others that UFP from airports and aircraft can be observed many kilometres downwind of an airport. Fushimi et al. (2019) found that a significant proportion of UFP measured at Narita Airport consisted of unburned jet lubrication oil.

Similarly, the impact of UFP on health has been increasingly studied in recent years. Bendtsten et al. (2019) reported that the UFP sampled at two airports in Denmark is comparable in toxicity to UFP from diesel exhaust. Habre et al. (2019) found observable health impacts in sensitive receptors downwind of Los Angeles International Airport (LAX), while Wing et al. (2020) also identified a link between exposure to aircraft-related UFP and pre-term birth in the region of LAX.

For the first time, a panel of experts (Cassee et al., White paper, 2019) has put forward a proposal to regulate exposure to concentrations of UFP. In terms of mitigation, both Cassee et al. (2019) and De Jesus et al. (2019) found that reducing emissions of PM_2.5 was not likely to have any significant effect on measured concentrations of UFP.

The Stacey et al. (2020) study showed that UFP concentrations at Heathrow in 2016 were clearly influenced by aircraft activity and wind direction. The smallest particles were associated with winds from the airfield, and the particle size distribution of the airport-derived airmass was clearly different to typical urban roadside, urban background and rural distributions. The study focussed on ensuring comparability with the reference monitoring stations, which report measurements every three minutes. At this time resolution, it is not possible to use the data to identify individual aircraft, which depart or arrive on average every 90 s at Heathrow.

A follow-up campaign was therefore devised to measure UFP, and where possible the other pollutants at the monitoring station, at a faster time resolution to evaluate individual aircraft emissions and the relationships between aircraft, UFP and other pollutants. This paper builds on the 2016 report and presents the results of the 2017 study.