How well does water activity determine homogeneous ice nucleation temperature in aqueous sulfuric acid and ammonium sulfate droplets?
نویسنده
چکیده
Frozen fraction measurements made using a droplet free-fall freezing tube apparatus are presented and used, with other recent laboratory measurements, to evaluate how well both the water activity idea and the translated meltingpoint curve idea of Koop et al. (2000) predict homogeneous freezing-point temperatures for aqueous ammonium sulfate and sulfuric acid solution droplets. The new freezing-point temperature data sets agree with the previous lowest temperature results for both solutes. The lowest measured freezing-point temperatures for aqueous ammonium sulfate solutions agree with a curve shaped like the translated melting-point curve. However, those for aqueous sulfuric acid solutions are significantly lower than predicted by the translated meltingpoint curve idea and a single water activity freezing-point temperature curve does not represent the lowest-temperture freezing-point temperature data for both solutes. A linear extrapolation of the new aqueous sulfuric acid solution freezing data to low-temperature predicts that high critical supersaturations in cloud-free regions of the upper troposphere will occur when homogeneous ice nucleation in aqueous sulfuric acid aerosol is the primary ice formation mechanism.
منابع مشابه
Laboratory measurements of the homogeneous freezing of aqueous sulfuric acid and ammonium sulfate droplets: How well does the translated melting-point curve model work?
Other recent laboratory measurements for aqueous ammonium sulfate and sulfuric acid solutions show considerable variability in freezing point temperatures – much more than is predicted by the widely-used translated melting-point curve (TMPC) idea of Koop et al. (2000). This paper reports on results from laboratory measurements of homogeneous ice nucleation in aqueous droplets containing two com...
متن کاملDo atmospheric aerosols form glasses?
A new process is presented by which water soluble organics might influence ice nucleation, ice growth, chemical reactions and water uptake of aerosols in the upper troposphere: the formation of glassy aerosol particles. Glasses are disordered amorphous (non-crystalline) solids that form when a liquid is cooled without crystallization until the viscosity increases exponentially and molecular dif...
متن کاملExperimental investigation of ice nucleation by different types of aerosols in the aerosol chamber AIDA: implications to microphysics of cirrus clouds
The aerosol chamber AIDA was used as a moderate expansion cloud chamber with cooling rates at the onset of ice nucleation between –1.3 and –3.0 K min−1 to investigate the nucleation and growth of ice crystals in sulphuric acid, ammonium sulphate, and mineral dust aerosols at temperatures between 196 and 224 K. Supercooled sulphuric acid droplets with mean diameters of about 0.2 to 0.3 μm nuclea...
متن کاملNear-Barrierless Ammonium Bisulfate Formation via a Loop-Structure Promoted Proton-Transfer Mechanism on the Surface of Water.
In the atmosphere, a well-known and conventional pathway toward the formation of ammonium sulfate is through the neutralization of sulfuric acid with ammonia (NH3) in water droplets. Here, we present direct ab initio molecular dynamics simulation evidence of the formation of ammonium bisulfate (NH4HSO4) from the hydrated NH3 and SO3 molecules in a water trimer as well as on the surface of a wat...
متن کاملTemperature-Dependent Heterogeneous Efflorescence of Mixed Ammonium Sulfate/Calcium Carbonate Particles
In this paper, we report observations on single internally mixed ammonium sulfate/calcium carbonate microparticles. Deliquescence and efflorescence relative humidities for this mixed system are reported. The slightly soluble CaCO3 has a negligible effect on the deliquescence relative humidity and the concentrationdependent water activities. Mixed particles at 298 K were observed to exist in two...
متن کامل