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A new, more physically based wet removal scheme for aerosols has beenimplemented in the Lagrangian particle dispersion model FLEXPART. It usesthree-dimensional cloud water fields from the European Centre forMedium-Range Weather Forecasts (ECMWF) to determine cloud extent anddistinguishes between in-cloud and below-cloud scavenging. The new in-cloudnucleation scavenging depends on cloud water phase (liquid, ice ormixed-phase), based on the aerosol's prescribed efficiency to serve as icecrystal nuclei and liquid water nuclei, respectively. The impactionscavenging scheme now parameterizes below-cloud removal as a function ofaerosol particle size and precipitation type (snow or rain) and intensity. Sensitivity tests with the new scavenging scheme and comparisons withobservational data were conducted for three distinct types of primaryaerosols, which pose different challenges for modeling wet scavenging due totheir differences in solubility, volatility and size distribution:(1) 137Cs released during the Fukushima nuclear accident attached mainlyto highly soluble sulphate aerosol particles, (2) black carbon (BC) aerosolparticles, and (3) mineral dust. Calculated e-folding lifetimes ofaccumulation mode aerosols for these three aerosol types were 11.7, 16.0, and31.6 days respectively, when well mixed in the atmosphere. These are longerlifetimes than those obtained by the previous removal schem, and, for mineraldust in particular, primarily result from very slow in-cloud removal, whichglobally is the primary removal mechanism for these accumulation modeparticles. Calculated e-folding lifetimes in FLEXPART also have a strong sizedependence, with the longest lifetimes found for the accumulation-modeaerosols. For example, for dust particles emitted at the surface thelifetimes were 13.8 days for particles with 1 µm diameter and afew hours for 10 µm particles. A strong size dependence inbelow-cloud scavenging, combined with increased dry removal, is the primaryreason for the shorter lifetimes of the larger particles. The most frequentremoval is in-cloud scavenging (85 % of all scavenging events) but itoccurs primarily in the free troposphere, while below-cloud removal is morefrequent below 1000 m (52 % of all events) and can be importantfor the initial fate of species emitted at the surface, such as thoseexamined here. For assumed realistic in-cloud removal efficiencies, both BC and sulphatehave a slight overestimation of observed atmospheric concentrations (a factorof 1.6 and 1.2 respectively). However, this overestimation is largest closeto the sources and thus appears more related to overestimated emissionsrather than underestimated removal. The new aerosol wet removal scheme ofFLEXPART incorporates more realistic information about clouds and aerosolproperties and it compares better with both observed lifetimes andconcentration than the old scheme

A new aerosol wet removal scheme for the Lagrangian particle model FLEXPART v10