No abstract

This paper addresses the need for detailed chemical information on the fine particulate matter (PM) generated by commercial aviation engines. The exhaust plumes of seven turbofan engine models were sampled as part of the three test campaigns of the Aircraft Particle Emissions eXperiment (APEX). In these experiments, continuous measurements of black carbon (BC) and particle surface-bound polycyclic aromatic compounds (PAHs) were conducted. In addition, time-integrated sampling was performed for bulk elemental composition, water-soluble ions, organic and elemental carbon (OC and EC), and trace semivolatile organic compounds (SVOCs). The continuous BC and PAH monitoring showed a characteristic U-shaped curve of the emission index (EI or mass of pollutant/mass of fuel burned) vs fuel flow for the turbofan engines tested. The time-integrated EIs for both elemental composition and water-soluble ions were heavily dominated by sulfur and SO(4)(2-), respectively, with a ∼2.4% median conversion of fuel S(IV) to particle S(VI). The corrected OC and EC emission indices obtained in this study ranged from 37 to 83 mg/kg and 21 to 275 mg/kg, respectively, with the EC/OC ratio ranging from ∼0.3 to 7 depending on engine type and test conditions. Finally, the particle SVOC EIs varied by as much as 2 orders of magnitude with distinct variations in chemical composition observed for different engine types and operating conditions.

Roadside vegetation has been shown to impact downwind, near-road air quality, with some studies identifying reductions in air pollution concentrations and others indicating increases in pollutant levels when vegetation is present. These widely contradictory results have resulted in confusion regarding the capability of vegetative barriers to mitigate near-road air pollution, which numerous studies have associated with significant adverse human health effects. Roadside vegetation studies have investigated the impact of many different types and conditions of vegetation barriers and urban forests, including preserved, existing vegetation stands usually consisting of mixtures of trees and shrubs or plantings of individual trees. A study was conducted along a highway with differing vegetation characteristics to identify if and how the changing characteristics affected downwind air quality. The results indicated that roadside vegetation needed to be of sufficient height, thickness, and coverage to achieve downwind air pollutant reductions. A vegetation stand which was highly porous and contained large gaps within the stand structure had increased downwind pollutant concentrations. These field study results were consistent with other studies that the roadside vegetation could lead to reductions in average, downwind pollutant concentrations by as much as 50% when this vegetation was thick with no gaps or openings. However, the presence of highly porous vegetation with gaps resulted in similar or sometimes higher concentrations than measured in a clearing with no vegetation. The combination of air quality and meteorological measurements indicated that the vegetation affects downwind pollutant concentrations through attenuation of meteorological and vehicle-induced turbulence as air passes through the vegetation, enhanced mixing as portions of the traffic pollution plume are blocked and forced over the vegetation, and through particulate deposition onto leaf and branch surfaces. Computational fluid dynamic modeling highlighted that density of the vegetation barrier affects pollutant levels, with a leaf area density of 3.0 m 2 m −3 or higher needed to ensure downwind pollutant reductions for airborne particulate matter. These results show that roadside bushes and trees can be preserved or planted along highways and other localized pollution sources to mitigate air quality and human health impacts near the source if the planting adheres to important characteristics of height, thickness, and Highlights

No abstract

The fine particulate matter (PM) emissions from the use of two types of Fischer–Tropsch aviation fuels and their 50:50 blends with military JP-8 were quantified as part of the first Alternative Aviation Fuel Experiment (AAFEX). Measurements were made 30-m downstream of a CFM56-2C1 engine for PM mass and number, particle size distribution, black carbon (BC), and volatile PM (sulfate + organics) using selected online instrumentation. The PM number emission index (EIN) ranged from ∼2 × 1015 to 7 × 1016 particles/kg fuel burned depending on fuel flow, fuel composition, and sampling temperature with the magnitude of the emissions inversely correlated to fuel flow. The PM mass emissions (EIM) measured in the study varied from ∼5 to 680 mg/kg fuel, again depending on fuel flow, fuel type, and sampling temperature with a characteristic U-shaped curve of EIM with respect to fuel flow observed from the data. At low fuel flow (corresponding to low engine power), particle number and volume size distributions contained a single mode, whereas at higher engine power, a bimodal distribution was observed. The BC emissions varied from ∼3 to 415 mg/kg fuel depending on fuel type and were found to exponentially increase with engine power (fuel flow). The volatile PM varied with sample temperature, fuel type, and increasing fuel flow within the range of EIs from ∼0.4 to 11 mg/kg fuel with the highest values being at low fuel flow. Finally, the use of the two neat alternative fuels reduced the EIN by a median value of 70–73% and the EIM by ∼94% as compared to JP-8 across all power conditions tested.