Are emissions from aircraft harmful or not?

Article Summary:

Both the Department for Transport and Heathrow Airport state that aircraft do not cause emissions harmful to humans on the ground when the aircraft is above 100 metres, which is well within 2 kilometres from the boundary of the airport. Heathrow gave evidence on this to the Transport Committee of the House of Commons and the Department for Transport gave evidence on this to the Court in the Judicial Review application.

However, there is plenty of evidence that this is not the case and indeed the Department of the Environment Fisheries and Rural Affairs (DEFRA) specifically refer to research that states that both particulates and nitrogen oxides can travel downwind for a very substantial distance (up to 40 kilometres).

Nitrogen dioxide is a gas that can be very harmful and affect breathing. Particulates are dust particles and are also very harmful. NO2 and particulates together cause more than 28,000 deaths per year as seen below. Particulates can be divided into three categories:

  • PM10s: These are described by the rules as “particulate matter which passes through a size-selective inlet …… at 10 μm aerodynamic diameter” (μm stands for a micrometre which is one millionth of a metre so a PM10 filter is 10 millionths of a metre). These are termed relatively course particles
  • PM2.5s: These are “particulate matter which passes through a size-selective inlet ….at 2.5 μm aerodynamic diameter”. These are termed fine particles
  • “Ultrafine particles” are defined by DEFRA as “as those [particulate matter] with one dimension less than 100 nanometres”. A nanometre is one thousandth of a micrometre or one billionth of a metre. As they pass through the filter of a PM2.5, they are, by definition, PM2.5s under the EU Regulations.

The Air Quality Expert Group of DEFRA refer to three detailed empirical studies [there are a number of other investigative reports as well]:

Firstly “Hudda et al. [2014] measured concentrations of PN [Particulate Number] downwind of Los Angeles International Airport (LAX) using a mobile monitoring approach and detected at least a 2-fold increase in PN concentrations over baseline PN concentrations during most hours of the day, in an area of about 60 km2 that extended to 16 km downwind, and a 4- to 5-fold increase to 8–10 km downwind.”

Secondly “Keuken et al. (2015) made measurements at Adamse Bos, located 7 km from Schiphol, and in 2012 at Cabauw, a regional background site 40 km south of Schiphol. PNC increased during periods in which the wind direction was from Schiphol: at Cabauw by 20% and at Adamse Bos by a factor of three, from 14,100 (other wind directions) to 42,000 cm−3 between 06.00 and 23.00. The size distribution of Schiphol-related PNC was dominated by ultrafine particles, ranging from 10 to 20 nm”

Thirdly “Riley et al. (2016) measured downwind of two large airports in the USA: LAX (Los Angeles) and Hartsfield-Jackson International Airport (ATL – Atlanta, GA), using a mobile monitoring platform. Riley et al. (2016) found a 3–5-fold increase in UFP concentrations in transects under the landing approach path to both airports, relative to surrounding urban areas with similar ground traffic characteristics.”

In the conclusion to the DEFRA report, it is said:

“Research from mainland Europe and North America indicates that aviation emissions can have an appreciable impact upon particle number concentrations within tens of kilometres of major airports.”

The Hudda Report also found that “Over large areas downwind of LAX [Los Angeles Airport], concentrations of pollutants other than PN were also elevated. Figure 5(a)−(c) show nearly indistinguishable spatial patterns for PN [particulates], BC [black carbon], and NO2 concentration measured simultaneously at distances of 9.5−12 km from LAX. This suggests a common source for these pollutants, although the BC concentration increases were not large when compared to PN and NOx, about 0.5−1 μg/m3 at 8−10 km downwind.”

According to the Local London Air Quality Monitoring, NO2 in 2013, updated in 2016, exceeded a concentration of 43 μg/m3 and PM2.5s exceeded 15 μg/m3. NO2 should have been below 40 μg/m3. PM2.5s are required to be reduced over time.

The effect of exposure to particulate matter and NO2 should not be underestimated. The Royal College of Physicians in its report of February 2016 stated that:

“Air pollution, to which we are all exposed to a lesser or greater extent, has a significant public health burden. In 2010, the Department of Health’s Committee on the Medical Effects of Air Pollutants (COMEAP) reported that long-term exposure to outdoor air pollution caused the equivalent of approximately 29,000 deaths in 2008 in the UK. Current work by the committee suggests that the effect might be even greater.”


“1. PM (particulate matter) has significant effects on health

2.  the mortality effects of long-term exposure to PM should be quantified without threshold and without distinguishing between different types of particle

3.  these mortality impacts should be quantified using a response function in the order of a 6% change in impact per 10 μg/m3 PM2.5.”


“Table 1. COMEAP [Committee on the Medical Effects of Air Pollutants, advising the Government on all matters concerning the health effects of air pollutants study of 2010] results for effects of outdoor PM2.5 exposure on mortality for the UK

Measure of mortality Impact
Number of attributable deaths 28,861
Attributable deaths per 100,000 aged over 30 years 75
Burden on total survival (life-years lost) 340,000
Difference in life expectancy for the 2008 cohort (days)
Females 194
Males 182”


“When quantifying the total impact associated with exposure to both NO2 and PM2.5, it is therefore necessary to account for this overlap in the response functions. Defra estimates that the annual equivalent number of attributable deaths associated with the two pollutants combined is 44,750–52,500, with an associated annual social cost of £25.3 billion – £29.7 billion. However, a subsequent paper issued by COMEAP in December 2015 indicates that the level of overlap in estimates between pollutants may be greater than originally thought”

Research carried out by Queen Mary’s University has found PMs in the placentas of expectant mothers through getting into the blood stream – something that is acknowledged by DEFRA in the Ultra Fine Particles report. The Queen Mary’s University press release on its website states that:

Dr Liu added: “Our results provide the first evidence that inhaled pollution particles can move from the lungs into the circulation and then to the placenta. We do not know whether the particles we found could also move across into the foetus, but our evidence suggests that this is indeed possible. We also know that the particles do not need to get into the baby’s body to have an adverse effect, because if they have an effect on the placenta, this will have a direct impact on the foetus.”

Professor Mina Gaga, President of the European Respiratory Society who was not involved in the study, said:

“This new research suggests a possible mechanism of how babies are affected by pollution while being theoretically protected in the womb. This should raise awareness amongst clinicians and the public regarding the harmful effects of air pollution in pregnant women. We need stricter policies for cleaner air to reduce the impact of pollution on health worldwide because we are already seeing a new population of young adults with health issues.”

DEFRA in their Ultrafine Particles report state that:

“For example, a location such as Heathrow Airport, where aircraft tend to approach the airport from the east (flying over the London conurbation), there is potential for considerable exposure to UFP from aircraft”

Yet the Secretary of State and the Department for Transport and Heathrow stick resolutely to the 2 kilometre limit, and not carrying out their own empirical research. The DfT were re-tweeting that aircraft do not cause harmful emissions only two weeks ago. Citizens are entitled to know the consequences of these actions, which expose vulnerable people to serious harm and even death. Public Health England recorded that the fraction of mortality in London due to particulates rose from 6.4% to 6.5% from 2016 to 2017 and from 5.6% to 6.4% from 2015 to 2016.

Abstracts of the various reports can be found and full copies can be purchased at: