Toward closure between predicted and observed particle viscosity over a wide range of temperatures and relative humidity

Abstract

Abstract. Atmospheric aerosols can exist in amorphous semi-solid or glassy phase states whose viscosity varies with atmospheric temperature and relative humidity. The temperature and humidity dependence of viscosity has been hypothesized to be predictable from the combination of a water–organic binary mixing rule of the glass transition temperature, a glass-transition-temperature-scaled viscosity fragility parameterization, and a water uptake parameterization. This work presents a closure study between predicted and observed viscosity for sucrose and citric acid. Viscosity and glass transition temperature as a function of water content are compiled from literature data and used to constrain the fragility parameterization. New measurements characterizing viscosity of sub-100 nm particles using the dimer relaxation method are presented. These measurements extend the available data of temperature- and humidity-dependent viscosity to −28 ∘C. Predicted relationships agree well with observations at room temperature and with measured isopleths of constant viscosity at ∼107 Pa s at temperatures warmer than −28 ∘C. Discrepancies at colder temperatures are observed for sucrose particles. Simulations with the kinetic multi-layer model of gas–particle interactions suggest that the observed deviations at colder temperature for sucrose can be attributed to kinetic limitations associated with water uptake at the timescales of the dimer relaxation experiments. Using the available information, updated equilibrium phase-state diagrams (-80∘C<T<40∘C, temperature, and 0%<RH<100%, relative humidity) for sucrose and citric acid are constructed and associated equilibration timescales are identified.

Global Distribution of the Phase State and Mixing Times within Secondary Organic Aerosol Particles in the Troposphere Based on Room-Temperature Viscosity Measurements

“…Furthermore, for molar masses greater than 200 g mol –1 , D f is typically in the range of 5–20 and approaches a limit of ∼10 at molar masses greater than 400 g mol –1 . The value of D f was assumed to be independent of RH. ,− This assumption was consistent with previous studies which found that the values of D f in sucrose and citric acid were independent of water content, except when the water content was very low. ,, After T 0 (RH) was calculated, we calculated η­(RH, T ) using eq .…”

“…52,70−72 This assumption was consistent with previous studies which found that the values of D f in sucrose and citric acid were independent of water content, except when the water content was very low. 68,73,74 After T 0 (RH) was calculated, we calculated η(RH, T) using eq 4.…”

Open-hardware design and characterization of an electrostatic aerosol precipitator

“…For example, a 1 lm particle and a 0.5 L min À1 flow rate the calculated transmission is 0.0765, based on a critical mobility of 1.8 Â 10 9 m 2 V À1 s À1 and z DMA of 1.1 Â 10 9 m 2 V À1 s À1 . The primary use for the EP described here is to remove charged particles in the dual tandem DMA [16,19,22,39]. Traditionally, EPs have been used for estimating the neutral fraction after passage through a bipolar neutralizer.…”

“…The primary use for the EP described here is to remove charged particles in the dual tandem DMA [16] , [19] , [22] , [39] . Traditionally, EPs have been used for estimating the neutral fraction after passage through a bipolar neutralizer.…”

“…refs. [19] , [20] , [21] , [22] ). A simple DMA possesses an annulus gap between inner and outer cylinder columns where the applied electric potential drags the charged particles depending on their mobility with the sheath flow [23] .…”