Parametric studies of contrail ice particle formation in jet regime using microphysical parcel modeling

Abstract

Abstract. Condensation trails (contrails) formed from water vapor emissions behind aircraft engines are the most uncertain components of the aviation impacts on climate change. To gain improved knowledge of contrail and contrail-induced cirrus cloud formation, understanding of contrail ice particle formation immediately after aircraft engines is needed. Despite many efforts spent in modeling the microphysics of ice crystal formation in jet regime (with a plume age <5 s), systematic understanding of parametric effects of variables affecting contrail ice particle formation is still limited. In this work, we apply a microphysical parcel modeling approach to study contrail ice particle formation in nearfield aircraft plumes up to 1000 m downstream of an aircraft engine in the soot-rich regime (soot number emission index >1×10 15 (kg-fuel) −1 ) at cruise. The effects of dilution history, ion-mediated nucleation, ambient relative humidity, fuel sulfur contents, and initial soot emissions were investigated. Our simulation results suggest that ice particles are mainly formed by water condensation on emitted soot particles. The growth of ice coated soot particles is driven by water vapor emissions in the first 1000 m and by ambient relative humidity afterwards. The presence of chemi-ions does not significantly contribute to the formation of ice particles in the soot-rich regime, and the effect of fuel sulfur contents is small over the range typical of standard jet fuels. The initial properties of soot emissions play the most critical role, and our calculations suggest that higher number concentration and smaller size of contrail particle nuclei may be able to effectively suppress the formation of contrail ice particles. Further modeling and experimental studies are needed to verify if our findings can provide a possible approach for contrail mitigation.

Laboratory and modeling studies on the effects of water and soot emissions and ambient conditions on the properties of contrail ice particles in the jet regime

“…Our OPC results suggest that smaller ice particles were formed when higher concentration of soot particles was introduced, implying that competition for water vapor condensation among soot particles existed. This is also consistent with findings from our previous modeling study (Wong and Miake-Lye, 2010).…”

“…Coagulation of different liquid particles is described using Brownian coagulation kernels (Fuchs, 1989). Activation of hydrophobic soot surface and condensational growth of water vapor on soot are treated the same way as in Kärcher (1998) and our previous studies (Wong et al, 2008;Wong and Miake-Lye, 2010;Wong et al, 2011). Finally, the heterogeneous freezing rate of liquid water coatings on soot is described by the expression reported by Fornea et al (2009).…”

“…Increased fuel sulfur was also found to cause sooner onset of contrail formation and a 25-50 % increase in number particulates. Recent modeling studies (Kärcher and Yu, 2009;Wong and Miake-Lye, 2010) suggested that soot emissions could affect optical depth of initial contrails and ice particle size and number density. These parameters, though not critical for the threshold temperature of contrail formation, may play an important role in determining ice particle properties used in large-scale models to predict contrail radiative forcing and their climate impacts, especially for scenarios reflecting future fleet emissions burning alternative fuels.…”

“…The Particle Aerosol Laboratory (PAL) at the NASA Glenn Research Center (Tacina and Heath, 2010) was employed to simulate a broad range of conditions that bracket those found in the exhaust from aircraft engines at cruise altitudes. The Aerodyne microphysical parcel model for contrail ice particle formation (Wong and Miake-Lye, 2010) was used to guide experimental design and analyze experimental results. Experimental setup and procedures, modeling methodologies, and the results obtained from our studies are presented.…”

Dimension of aircraft exhaust plumes at cruise conditions: effect of wake vortices

“…This work bridges the gap between analytical jet expansion laws describing the plume mixing within the first seconds behind the aircraft and the later dispersion in the free atmosphere after aircraft-induced effects have vanished. For box model studies of the jet phase, often treating the contrail formation, analytical jet expansion laws are used (Kärcher and Yu, 2009;Wong and Miake-Lye, 2010). Especially for chemistry applications, box models treat the plume evolution also beyond the end of the jet phase (Miake-Lye et al, 1993;Danilin et al, 1994;Kärcher, 1995;Kärcher et al, 1996).…”