Viscosity and physical state of sucrose mixed with ammonium sulfate droplets

[摘要] Although knowledge of the physical state of aerosol particles is essential to understand atmospheric chemistry model and measurements, informationon the viscosity and physical state of aerosol particles consisting of organic and inorganic salts is still rare. Herein, we quantified viscositiesat 293  ±  1  K upon dehydration for the binary systems, sucrose– H 2 O and ammonium sulfate ( AS )– H 2 O , and theternary systems, sucrose– AS – H 2 O for organic-to-inorganic dry mass ratios (OIRs)  =   4:1 , 1:1 , and 1:4 using bead-mobility andpoke-and-flow techniques. Based on the viscosity value of the aerosol particles, we defined the physical states of the total aerosol particlesstudied in this work. For binary systems, the viscosity of sucrose– H 2 O particles gradually increased from ∼  4  ×  10 −1 to  >   ∼  1  ×  10 8   Pa s when the relative humidity (RH) decreased from ∼  81 % to ∼  24 %, ranging fromliquid to semisolid or solid state, which agrees with previous studies. The viscosity of AS – H 2 O particles remained in the liquidstate (  10 2   Pa s ) for RH  >   ∼  50 %, while for RH  ≤ ∼  50 %, the particles showed a viscosityof  >   ∼  1  ×  10 12   Pa s , corresponding to a solid state. In case of the ternary systems, the viscosity of organic-richparticles (OIR  =   4:1 ) gradually increased from ∼  1  ×  10 −1 to ∼  1  ×  10 8   Pa s for a RH decreasefrom ∼  81 % to ∼  18 %, similar to the binary sucrose– H 2 O particles. This indicates that thesucrose– AS – H 2 O particles range from liquid to semisolid or solid across the RH. In the ternary particles for OIR  =   1:1 , theviscosities ranged from less than ∼  1  ×  10 2 for RH  >  34 % to  >   ∼  1  ×  10 8   Pa s at ∼  27  % RH . The viscosities correspond to liquid for RH  >   ∼  34 %, semisolid for ∼  34 %   RH    ∼  27 %, and semisolid or solid for RH    ∼  27 %. Compared to the organic-rich particles, inthe inorganic-rich particles (OIR  =   1:4 ), drastic enhancement in viscosity was observed as RH decreased; the viscosity increased byapproximately 8 orders of magnitude during a decrease in RH from 43 % to 25 %, resulting in liquid to semisolid or solid in the RHrange. Overall, all particles studied in this work were observed to exist as a liquid, semisolid, or solid depending on the RH. Furthermore, wecompared the measured viscosities of ternary systems with OIRs of 4:1 , 1:1 , and 1:4 to the predicted viscosities using the AerosolInorganic–Organic Mixtures Functional groups Activity Coefficients Viscosity model (AIOMFAC-VISC) predictions with the Zdanovskii–Stokes–Robinson(ZSR) organic–inorganic mixing model, with excellent model–measurement agreement for all OIRs.

[学科分类] 医学（综合）