Chemical composition and radiative properties of nascent particulate matter emitted by an aircraft turbofan burning conventional and alternative fuels

Aircraft engines are a unique source of carbonaceous aerosols in the upper troposphere. There, these particles can more efficiently interact with solar radiation than at ground. Due to the lack of measurement data, the radiative forcing from aircraft exhaust aerosol remains uncertain. To better estimate the global radiative effects of aircraft exhaust aerosol, its optical properties need to be comprehensively characterized. In this work we present the link between the chemical composition and the optical properties of the particulate matter (PM) measured at the engine exit plane of a CFM56-7B turbofan. The measurements covered a wide range of power settings (thrust), ranging from ground idle to take-off, using four different fuel blends of conventional Jet A-1 and hydro-processed ester and fatty acids (HEFA) biofuel. At the two measurement wavelengths (532 and 870 nm) and for all tested fuels, the absorption and scattering coefficients increased with thrust, as did the PM mass. The analysis of elemental carbon (EC) and organic carbon (OC) revealed a significant mass fraction of OC (up to 90 %) at low thrust levels, while EC mass dominated at medium and high thrust. The use of HEFA blends induced a significant decrease in the PM mass and the optical coefficients at all thrust levels. The HEFA effect was highest at low thrust levels, where the EC mass was reduced by up to 50 %–60 %. The variability in the chemical composition of the particles was the main reason for the strong thrust dependency of the single scattering albedo (SSA), which followed the same trend as the fraction of OC to total carbon (TC). Mass absorption coefficients (MACs) were determined from the correlations between aerosol light absorption and EC mass concentration. The obtained MAC values (MAC532=7.5±0.3 m2 g−1 and MAC870=5.2±0.9 m2 g−1) are in excellent agreement with previous literature values of absorption cross section for freshly generated soot. While the MAC values were found to be independent of the thrust level and fuel type, the mass scattering coefficients (MSCs) significantly varied with thrust. For cruise conditions we obtained MSC532=4.5±0.4 m2 g−1 and MSC870=0.54±0.04 m2 g−1, which fall within the higher end of MSCs measured for fresh biomass smoke. However, the latter comparison is limited by the strong dependency of MSC on the particles' size, morphology and chemical composition. The use of the HEFA fuel blends significantly decreased PM emissions, but no changes were observed in terms of EC∕OC composition and radiative properties

Nonvolatile particulate matter emissions of a business jet measured at ground level and estimated for cruising altitudes

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Environmental Science & Technology, copyright © American Chemical Society after peer review and technical editing by the publisher.Business aviation is a relatively small but steadily growing and little investigated emission source. Regarding emissions, aircraft turbine engines rated at and below 26.7 kN thrust are certified only for visible smoke and are excluded from the nonvolatile particulate matter (nvPM) standard. Here, we report nvPM emission characteristics of a widely used small turbofan engine determined in a ground test of a Dassault Falcon 900EX business jet. These are the first reported nvPM emissions of a small in-production turbofan engine determined with a standardized measurement system used for emissions certification of large turbofan engines. The ground-level measurements together with a detailed engine performance model were used to predict emissions at cruising altitudes. The measured nvPM emission characteristics strongly depended on engine thrust. The geometric mean diameter increased from 17 nm at idle to 45 nm at take-off. The nvPM emission indices peaked at low thrust levels (7 and 40% take-off thrust in terms of nvPM number and mass, respectively). A comparison with a commercial airliner shows that a business jet may produce higher nvPM emissions from flight missions as well as from landing and take-off operations. This study will aid the development of emission inventories for small aircraft turbine engines and future emission standards

Non-volatile particle emissions from aircraft turbine engines at ground-idle induce oxidative stress in bronchial cells

Aircraft emissions contribute to local and global air pollution. Health effects of particulate matter (PM) from aircraft engines are largely unknown, since controlled cell exposures at relevant conditions are challenging. We examined the toxicity of non-volatile PM (nvPM) emissions from a CFM56-7B26 turbofan, the world's most used aircraft turbine using an unprecedented exposure setup. We combined direct turbine-exhaust sampling under realistic engine operating conditions and the Nano-Aerosol Chamber for In vitro Toxicity to deposit particles onto air-liquid-interface cultures of human bronchial epithelial cells (BEAS-2B) at physiological conditions. We evaluated acute cellular responses after 1-h exposures to diluted exhaust from conventional or alternative fuel combustion. We show that single, short-term exposures to nvPM impair bronchial epithelial cells, and PM from conventional fuel at ground-idle conditions is the most hazardous. Electron microscopy of soot reveals varying reactivity matching the observed cellular responses. Stronger responses at lower mass concentrations suggest that additional metrics are necessary to evaluate health risks of this increasingly important emission source

Characterizing and predicting nvPM size distributions for aviation emission inventories and environmental impact

Concerns about civil aviation’s air quality and environmental impacts have led to recent regulations on nonvolatile particulate matter (nvPM) mass and number emissions. Although these regulations do not mandate measuring particle size distribution (PSD), understanding PSDs is vital for assessing the environmental impacts of aviation nvPM. This study introduces a comprehensive data set detailing PSD characteristics of 42 engines across 19 turbofan types, ranging from unregulated small business jets to regulated large commercial aircraft. Emission tests were independently performed by using the European and Swiss reference nvPM sampling and measurement systems with parallel PSD measurements. The geometric mean diameter (GMD) at the engine exit strongly correlated with the nvPM number-to-mass ratio (N/M) and thrust, varying from 7 to 52 nm. The engine-exit geometric standard deviation ranged from 1.7 to 2.5 (mean of 2.05). The study proposes empirical correlations to predict GMD from N/M data of emissions-certified engines. These predictions are expected to be effective for conventional rich-burn engines and might be extended to novel combustor technologies if additional data become available. The findings support the refinement of emission models and help in assessing the aviation non-CO2 climate and air quality impacts

Reduction of nonvolatile particulate matter emissions of a commercial turbofan engine at the ground level from the use of a sustainable aviation fuel blend

Non-volatile particulate matter (nvPM) emissions from aircraft turbine engines deteriorate air quality and contribute to climate change. These emissions can be reduced by using sustainable aviation fuels (SAFs). Here, we investigate the effects of a 32% SAF blend with fossil fuel on particle size distributions and nvPM emission indices of a widely used turbofan engine. The experiments were conducted in a test cell using a standardized sampling and measurement system. The geometric mean diameter (GMD) increased with thrust from ~8 nm at idle to ~40 nm at take-off, and the geometric standard deviation (GSD) was in the range of 1.74 to 2.01. The SAF blend reduced the GMD and GSD at each test point. The nvPM emission indices were reduced most markedly at idle by 70% in terms of nvPM mass and 60% for nvPM number. The relative reduction of nvPM emissions decreased with the increasing thrust. The SAF blend reduced the nvPM emissions from the standardized landing and take-off cycle by 20% in terms of nvPM mass and 25% in terms of nvPM number. This work will help develop standardized models of fuel composition effects on nvPM emissions and evaluate the impacts of SAF on air quality and climate

Chemical composition and radiative properties of nascent particulate matter emitted by an aircraft turbofan burning conventional and alternative fuels

Aircraft engines are a unique source of carbonaceous aerosols in the upper troposphere. There, these particles can more efficiently interact with solar radiation than at ground. Due to the lack of measurement data, the radiative forcing from aircraft exhaust aerosol remains uncertain. To better estimate the global radiative effects of aircraft exhaust aerosol, its optical properties need to be comprehensively characterized. In this work we present the link between the chemical composition and the optical properties of the particulate matter (PM) measured at the engine exit plane of a CFM56-7B turbofan. The measurements covered a wide range of power settings (thrust), ranging from ground idle to take-off, using four different fuel blends of conventional Jet A-1 and hydro-processed ester and fatty acids (HEFA) biofuel. At the two measurement wavelengths (532 and 870 nm) and for all tested fuels, the absorption and scattering coefficients increased with thrust, as did the PM mass. The analysis of elemental carbon (EC) and organic carbon (OC) revealed a significant mass fraction of OC (up to 90 %) at low thrust levels, while EC mass dominated at medium and high thrust. The use of HEFA blends induced a significant decrease in the PM mass and the optical coefficients at all thrust levels. The HEFA effect was highest at low thrust levels, where the EC mass was reduced by up to 50 %–60 %. The variability in the chemical composition of the particles was the main reason for the strong thrust dependency of the single scattering albedo (SSA), which followed the same trend as the fraction of OC to total carbon (TC). Mass absorption coefficients (MACs) were determined from the correlations between aerosol light absorption and EC mass concentration. The obtained MAC values (MAC532=7.5±0.3 m2 g−1 and MAC870=5.2±0.9 m2 g−1) are in excellent agreement with previous literature values of absorption cross section for freshly generated soot. While the MAC values were found to be independent of the thrust level and fuel type, the mass scattering coefficients (MSCs) significantly varied with thrust. For cruise conditions we obtained MSC532=4.5±0.4 m2 g−1 and MSC870=0.54±0.04 m2 g−1, which fall within the higher end of MSCs measured for fresh biomass smoke. However, the latter comparison is limited by the strong dependency of MSC on the particles' size, morphology and chemical composition. The use of the HEFA fuel blends significantly decreased PM emissions, but no changes were observed in terms of EC∕OC composition and radiative properties.ISSN:1680-7375ISSN:1680-736

Characterising particulate matter in the evolving exhaust plume of an aircraft engine in a test cell

The evolution of Particulate Matter (PM) emissions from a CFM56-7B aircraft engine in a controlled test cell was investigated in terms of their physical, chemical, and optical properties. Measurements were performed at the engine exit plane (P1), in front of the silencer (P2), and at the stack exit (P3) of the test cell at SR Technics, Zurich, Switzerland. Black carbon (BC) mass was measured using Micro Soot Sensor (MSS), Laser Induced Incandescence (LII), and Photoacoustic Extinctiometer (PAX). Elemental carbon (EC) and organic carbon (OC) analyses were performed using the Sunset Labs EC-OC analyser. Effective density was measured using a Centrifugal Particle Mass Analyzer (CPMA). Particle size distributions were measured with a Scanning Mobility Particle Sizer (SMPS). A nucleation mode was observed at low thrust for measurements at P2 and P3, which was not present at P1. The single scattering albedo (SSA) was determined at P1 and P2 with two PAX monitors (λ = 870 nm), and two Cavity Attenuated Phase Shift SSA monitors (CAPS PMSSA, λ = 660 and 532 nm), both operated at P2. A significant increase in the SSA was observed between P1 and P2 for thrust levels below 30%. The increase in SSA is most likely related to an increase in the light scattering due to condensed volatile material at P2

Assessment of Particle Pollution from Jetliners: from Smoke Visibility to Nanoparticle Counting

Aviation is a substantial and a fast growing emissions source. Besides greenhouse gases, aircraft engines emit black carbon (BC), a climate forcer and air pollutant. Aviation BC emissions have been regulated and estimated through exhaust smoke visibility (smoke number). Their impacts are poorly understood because emission inventories lack representative data. Here, we measured BC mass and number-based emissions of the most popular airliner’s engines according to a new emission standard. We used a calibrated engine performance model to determine the emissions on the ground, at cruise altitude, and over entire flight missions. Compared to previous estimates, we found up to a factor of 4 less BC mass emitted from the standardized landing and takeoff cycle and up to a factor of 40 less during taxiing. However, the taxi phase accounted for up to 30% of the total BC number emissions. Depending on the fuel composition and flight distance, the mass and number-based emission indices (/kg fuel burned) were 6.2–14.7 mg and 2.8 × 10¹⁴ – 8.7 × 10¹⁴, respectively. The BC mass emissions per passenger-km were similar to gasoline vehicles, but the number-based emissions were relatively higher, comparable to old diesel vehicles. This study provides representative data for models and will lead to more accurate assessments of environmental impacts of aviation

Corelease of Genotoxic Polycyclic Aromatic Hydrocarbons and Nanoparticles from a Commercial Aircraft Jet Engine – Dependence on Fuel and Thrust

Jet engines are important contributors to global CO2 emissions and release enormous numbers of ultrafine particles into different layers of the atmosphere. As a result, aviation emissions are affecting atmospheric chemistry and promote contrail and cloud formation with impacts on earth’s radiative balance and climate. Furthermore, the corelease of nanoparticles together with carcinogenic polycyclic aromatic hydrocarbons (PAHs) affects air quality at airports. We studied exhausts of a widely used turbofan engine (CFM56–7B26) operated at five static thrust levels (idle, 7, 30, 65, and 85%) with conventional Jet A-1 fuel and a biofuel blend composed of hydro-processed esters and fatty acids (HEFA). The particles released, the chemical composition of condensable material, and the genotoxic potential of these exhausts were studied. At ground operation, particle number emissions of 3.5 and 0.5 × 1014 particles/kg fuel were observed with highest genotoxic potentials of 41300 and 8800 ng toxicity equivalents (TEQ)/kg fuel at idle and 7% thrust, respectively. Blending jet fuel with HEFA lowered PAH and particle emissions by 7–34% and 65–67% at idle and 7% thrust, respectively, indicating that the use of paraffin-rich biofuels is an effective measure to reduce the exposure of airport personnel to nanoparticles coated with genotoxic PAHs (Trojan horse effect)

Responses of reconstituted human bronchial epithelia from normal and health-compromised donors to non-volatile particulate matter emissions from an aircraft turbofan engine.

Health effects of particulate matter (PM) from aircraft engines have not been adequately studied since controlled laboratory studies reflecting realistic conditions regarding aerosols, target tissue, particle exposure and deposited particle dose are logistically challenging. Due to the important contributions of aircraft engine emissions to air pollution, we employed a unique experimental setup to deposit exhaust particles directly from an aircraft engine onto re-differentiated human bronchial epithelia (HBE) at air-liquid interface under conditions similar to in vivo airways to mimic realistic human exposure. The toxicity of non-volatile PM (nvPM) from a CFM56-7B26 aircraft engine by sampling was evaluated under realistic engine conditions and exposing HBE derived from donors of normal and compromised health status to exhaust for one hour followed by biomarker analysis 24hours post exposure. Particle deposition varied depending on the engine thrust levels with 85% thrust producing the highest nvPM mass and number emissions with estimated surface deposition of 3.17 × 109 particles cm-2 or 337.1 ng cm-2. Transient increase in cytotoxicity was observed after exposure to nvPM in epithelia derived from a normal donor as well as a decrease in the secretion of interleukin 6 and monocyte chemotactic protein 1. Non-replicated multiple exposures of epithelia derived from a normal donor to nvPM primarily led to a pro-inflammatory response, while both cytotoxicity and oxidative stress induction remained unaffected. This raises concerns for the long-term implications of aircraft nvPM for human pulmonary health, especially in occupational settings