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Furthermore, particles impact the environment at regional scale through the contamination of soil and water after deposition, and at global scale on climate change by triggering cloud formation.
Current legislation and methods_ EU ambient air regulation (Directive 96/62/EC) was established in 1996 in order to reduce undesired health effects.
by Erika Herms,
EASA Environmental Protection Officer
Since the late 1970s, there is a growing concern regarding aircraft engine emissions and their effects
on local air quality and global climate change. When the First Edition of the International Civil Aviation Organization (ICAO) Annex 16 Volume II was adopted in 1981, it was focused on the control of common air pollutants emissions which have an effect on local air quality: carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) and smoke. Many changes have been introduced in the Annex 16 volume II since that time. The most significant changes were the introduction of more stringent limits for NOx emissions while the other limits remained unchanged.
Smoke was originally controlled mostly for visibility reasons as the appearance of black smoke at the exhaust of aircraft engines was considered undesirable.
Nowadays, due to progress in technology, aircraft engines are considered to be smoke-free. However, in reality, the particles which are emitted are so small that they are not visible.
In the ambient air, particulate matter (PM) consists of a mixture of solid and liquid particles that are suspended in the air. They vary in size, composition
and origin. PM is either directly emitted into the air or formed from gaseous precursors. The direct
emissions of particles from aircraft engines are non-volatile particles containing carbon. They are the result of an incomplete combustion processes. The main volatile PM precursors/substances emitted
by aircraft engines are sulphur oxides (SOx), nitrogen
oxides (NOx) and unburned hydrocarbons (HC). Combustion-related particles are small in size, as opposed to coarse particles stemming from natural sources (salt, sand, dust). While aviation contributes significantly, the majority of global PM pollution can be attributed to road vehicles, power/heating plants and various industrial processes.
Small particles – dangerous, but as yet unmeasured_
When it comes to their effect on health, the size of particles is an important issue. The smaller the particle, the deeper it enters into the lungs. Fine particles are strongly associated with heart and lung diseases which, in extreme cases, can
Aircraft engine particle emissions: a new certification parameter
10. 2009
07
Europeaean Aviation Safety Agency
EASANEWS
As particles larger than 10μm (1x10-6m) in diameter do not cause major problems because they are filtered
by the nose and throat, the first regulation on PM in ambient air was based on the measurement of the mass of particles smaller than 10μm (PM10). Following the Cleaner Air for Europe (CAFE) initiative,
the latest Directive (2008/50/EC) on ambient air quality also introduces a PM2.5 mass limit value (diameter smaller than 2.5μm) which better represents
the impact on human health. It should be noted that compliance with this Directive is expected
to be a problem at some European airports.
In order to reduce the concentrations of PM in ambient air it is necessary to mitigate the emissions
at all sources. Since the early 1990s, the European
car legislation has prescribed limitations in particle mass emissions. The latest car emissions legislation, Euro5 and Euro6, introduce more stringent
PM mass standards and non-volatile particle number limits. As for aircraft engine emissions, ICAO Annex 16 Volume II prescribes certification limits for smoke emissions using a visibility parameter
known as a “Smoke Number (SN)”. This procedure
measures the obscuration (opacity) of a spot on a filter and is only linked to visibility properties. The gaseous precursors which form secondary particles
in the plume are also regulated as ICAO has established standards for nitrogen oxides (NOx) and unburned hydrocarbon (HC). The emissions of sulphur oxides (SOx) are indirectly regulated via the fuel specifications which place a limit on sulphur content. Within the UK Def. Stan. and US ASTM specifications, this content is currently limited
to 0.3% in mass for commercial aviation fuel.
Working towards a new regulation_ As mentioned
above, the smoke requirement was mainly created to address the issue of visibility of exhaust emissions. Particle emissions from aircraft engines are now very small, and so SN is no longer an appropriate
indicator although it is still used for the certification of aircraft engines. In order to evaluate the trend in engine technology advances as regards particle emissions and their subsequent impact on local air quality and climate change, we have to focus on the measurement of particulate matter
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EASA-Newsletter-issue-3(5)
