Columnar modelling of nucleation burst evolution in the convective boundary layer – first results from a feasibilitystudy Part IV: A compilation of previous observations for valuation of simulation results from a columnar modelling study

[摘要] In the preceding Papers I, II and IIIa revised columnar high-order modellingapproach to model gas-aerosol-turbulence interactions in the convectiveboundary layer (CBL) was proposed, andsimulation results of two synthetic nucleation scenarios (binary vs. ternary)on new particle formation (NPF) in the anthropogenically influencedCBL were presented and discussed. The purpose of the present finishingPaper IV is twofold: Firstly, an attempt is made to compileprevious observational findings on NPF bursts in the CBL,obtained from a number of field experiments. Secondly, the scenariosimulations discussed in Paper IIIwill be evaluated with respect to therole of CBL turbulence in NPF burst evolution. It wasdemonstrated, that completely different nucleation mechanismscan lead to the occurrence of NPF bursts in the surface layer,but the corresponding evolution patterns strongly differwith respect to the origin, amplitude and phase of the NPF burstas well as with respectto the time-height evolution of turbulent vertical fluxes anddouble correlation terms of physicochemical andaerosoldynamical variables. The large differencesbetween the binary and ternarycase scenario indicate, that ammonia (NH₃) can not be consideredas a time-independent tuning parameter in nucleationmodelling. Its contribution to the evolution of the NPF burst pattern is muchmore complicated and reflects the influence ofCBL turbulence as well as the strong non-linearityof the ternary nucleation rate. The impact of water (H₂O) vapouron the nucleation rate is quite varyingdepending on the considered nucleation mechanism. According to theclassical theory of binary nucleation involving H₂O andsulphuric acid (H₂SO₄), H₂O vapour favours NPF,according to the classical theory of ternary nuncleationinvolving H₂O, H₂SO₄ and NH₃and according to organic nucleation via chemical reactions involvingstabilised Criegee intermediates (SCIs), H₂O vapour disfavours nucleation,and according to the parameterisation ofthe collision-controlled binary nucleation rate proposed by Weber et al. (1996), H₂O vapour does not explicitly affectthe particle formation. Since the H₂SO₄ concentrationis overpredicted in thesimulations presented in Paper III, the nucleation rates are too highcompared to previous estimations. Therefore, the results arenot directly comparable to measurements. Especially NPF events,where organics are suspected toplay a key role, such as those observedat the boreal forest station in Hyytiälä(Southern Finland) orat Hohenpeissenberg (mountain site in Southern Germany),can not be explained by employingsimple sulphur/ammonia chemistry. However, some valuable hintsregarding the role of CBL turbulencein NPF can be obtained. In the literaturea number of observations on the linkbetween turbulence and NPF can be found,whose burst patterns support a strong contribution ofCBL turbulence to the NPF burst evolution simulated here. Observations,that do not correspond to the scenariosare discussed with respect to possible reasons for thedifferences between model and observation. The model simulationssupport some state-of-the-art hypotheseson the contribution of CBL turbulence to NPF. Considering theapplication of box models, the present study shows,that CBL turbulence,not explicitly considered in such models,can strongly affect the spatio-temporal NPF burst evolution. The columnarhigh-order model presented here is ahelpful tool to elucidate gas-aerosol-turbulence interactions,especially the genesis of NPF bursts in the CBL. An advanceddescription of the cluster formation and condensation growthis required as well asa comprehensive verification/validation study using observedhigh-order moments. Further scenario simulationsremain to be performed.

[学科分类] 大气科学