(503f) Comparisons and Contrasts of Jet Engine Emissions with Other PM2.5 Combustion Sources

Jet engine aircraft exhaust contains combustion byproducts and particulate matter in the form of non-volatile particulate matter (nvPM), black carbon (BC) is used synonymously for nvPM throughout this paper. Aircraft cruise emissions are the only direct source of anthropogenic BC particles at altitudes above the tropopause.¹ Black carbon aerosols are strong solar radiation absorbers and have long atmospheric lifetimes.² Therefore, BC results in positive radiative forcing and is believed to be the second largest contributor to climate change.³ Additionally, upper troposphere and lower stratosphere BC particles contribute to climate forcing indirectly by acting as ice nucleation sites and cloud activators.^4-6 With regards to human health, a link between cardiopulmonary diseases and carbonaceous black particulate matter has recently been suggested.⁷ As concern for human health risks and environmental impacts caused by aviation BC emissions increases, emission reduction strategies will need to be implemented. An ambitious carbon, solid and gaseous, emission reduction goal of 50% reduction by 2050 as compared to 2000-2005 levels have already been defined by the International Air Transport Association and Advisory Council for Aviation Research and Innovation in Europe.⁸ Meeting these goals will require significant engineering advancements requiring a long implementation period. However, in the near term, alternative jet fuels with reduced aromatic content are an attractive solution for reducing BC emission.^9-12 Alternative aviation fuels containing synthetic blend components with near zero aromatic content (synthetic paraffinic kerosenes, SPKs) such as those synthesized via the Fischer-Tropsch (FT-SPK) process and hydrotreated esters and fatty acids (HEFA-SPK) overall contain highly reduced aromatic content compared to conventional fuel and thus significantly reduce aircraft engine BC emissions.^9-12

Currently there is not a direct regulation on BC emissions from jet engines. Rather, BC emissions during the landing and take-off (LTO) cycle are limited by the International Civil Aviation Organization (ICAO) through regulations on smoke number (SN).¹³ The smoke number regulation introduced in 1981 was put in place with the purpose of reducing plume visibility and no engines have failed this regulation since 1990.¹⁴ With increasing concern on both human health and environmental impacts caused by jet engine BC emissions the EPA is expected to place regulations on such emissions.¹⁵ The ICAO’s Committee on Aviation Environmental Protection is currently developing a regulatory standard for BC emissions.

To better understand regulatory needs and health impacts and related regulatory needs, further physical-chemical data on particulate emissions from jet engines is needed. To-date there is a large deficit of detailed characterization compared to emissions from other sources such as diesel engines, despite field campaigns in recent years. Accordingly, we have performed electron-based microscopy and spectroscopy upon samples collected from various jet engines in service. Fuel compositions have also been varied to test effects on EI_BC with further interest in changes to the nature of the emitted particulate. Analysis results from NASA campaigns, APEX, AAFEX I & II, and the recent ND-MAX conducted in Germany will be presented.

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