arXiv subjects

Florence K. A. Gregson

Publications and source records attributed to Florence K. A. Gregson.

2 recordsLinked to original sources

arXiv2022

How effective are face coverings in reducing transmission of COVID-19?

In the COVID-19 pandemic, billions are wearing face masks, in both health care settings and in public. Which type of mask we should wear in what situation, is therefore important. There are three basic types: cotton, surgical, and respirators (e.g. FFP2, N95 and similar). All are essentially air filters worn on the face. Air filtration is relatively well understood, however, we have almost no direct evidence on the relative role played by aerosol particles of differing sizes in disease transmission. But if the virus concentration is assumed independent of aerosol particle size, then most virus will be in particles > 1 $μ$m. We develop a model that predicts surgical masks are effective at reducing the risk of airborne transmission because the filtering material most surgical masks use is highly effective at filtering particles with diameters > 1 $μ$m. However, surgical masks are significantly less effective than masks of FFP2, N95 and similar standards, mostly due to the poor fit of surgical masks. Earlier work found that ~30% of the air bypasses a surgical mask and is not filtered. This highlights the fact that standards for surgical masks do not specify how well the mask should fit, and so are not adequate for protection against COVID-19.

cond-mat.soft↗

arXiv2019

Nucleation kinetics in drying sodium nitrate aerosols

A quantitative understanding of the evaporative drying kinetics and nucleation rates of aqueous based aerosol droplets is important for a wide range of applications, from atmospheric aerosols to industrial processes such as spray drying. Here, we introduce a numerical model for interpreting measurements of the evaporation rate and phase change of drying free droplets made using a single particle approach. We explore the evaporation of aqueous sodium chloride and sodium nitrate solution droplets. Although the chloride salt is observed to reproducibly crystallise at all drying rates, the nitrate salt solution can lose virtually all of its water content without crystallising. The latter phenomenon has implications for our understanding of the competition between the drying rate and nucleation kinetics in these two systems. The nucleation model is used in combination with the measurements of crystallisation events to infer nucleation rates at varying equilibrium state points, showing that classical nucleation theory provides a good description of the crystallisation of the chloride salt but not the nitrate salt solution droplets. The reasons for this difference are considered.

cond-mat.soft↗