Multicomponent aerosol dynamics model UHMA: model development and validation

[摘要] A size-segregated aerosol dynamics model UHMA (University of Helsinki Multicomponent Aerosolmodel) was developed for studies of multicomponent tropospheric aerosol particles.The model includes major aerosol microphysical processes in the atmosphere witha focus on new particle formation and growth;thus it incorporates particle coagulation and multicomponent condensation,applying a revised treatment of condensation flux onto free molecular regime particlesand the activation of nanosized clusters by organic vapours (Nano-Köhler theory), as well asrecent parameterizations for binary H₂SO₄-H₂Oand ternary H₂SO₄-NH₃-H₂O homogeneous nucleation and dry deposition.The representation of particle size distribution can be chosen from three sectionalmethods:the hybrid method, the moving center method, and the retracking method in whichmoving sections are retracked to a fixed grid after a certain time interval.All these methods can treat particle emissions and atmospheric transport consistently, and are thereforesuitable for use in large scale atmospheric models.In a test simulation against an accurate high resolutionsolution, all the methods showed reasonable treatment of new particle formationwith 20 size sectionsalthough the hybrid and the retracking methods suffered from artificial wideningof the distribution.The moving center approach, on the other hand, showed extra dents in theparticle size distribution and failed to predict the onset of detectableparticle formation.In a separate test simulation of an observed nucleation event,the model captured the key qualitative behaviour of the system well.Furthermore, its predictionof the organic volume fraction in newly formed particles,suggesting values as high as 0.5 for 3–4 nm particles and approximately 0.8for 10 nm particles, agrees with recent indirect composition measurements.

[学科分类] 大气科学