Aerosol Water Uptake: Its Controls, Impacts and Retrieval From Publicly Available Data

Abstract

Aerosol particles are ubiquitous in the atmosphere, impacting air quality, global climate and threatening public health. These aerosol-induced environmental impacts are tightly bounded by their water uptake. However, it is not yet well understood how complex chemical composition influences water uptake and the related impacts. In addition, direct observations (especially the long-term) of aerosol water uptake worldwide are still lacking due to expensive expenses. The aim of the presented thesis is to demonstrate the chemical controls of aerosol water uptake, its impacts on aerosol phase state and air pollution, and to retrieve hygroscopicity parameter from open-access data using a combination of laboratory chamber experiments, field observational data and theoretical calculations. Chamber experiments on the secondary organic aerosol (SOA) from mixed biogenic and anthropogenic precursors, showed that the water saturation ratio and organic mass fraction are the key factors of water uptake whereas the SOA composition plays a second-order role. For the reconciliation of sub- and super-saturated water uptake, the hygroscopicity parameter ksub/ksuper ratio increased with organic mass fraction. The factors which influence the aerosol water uptake, control the aerosol phase transition between the liquid and non-liquid. In addition, aerosol water uptake was found to play a key role in Beijing winter haze development via a positive feedback between aerosol liquid water and particulate nitrate formation, where the aerosol liquid water can contribute up to 24 % to visibility reduction. To resolve the shortage of hygroscopicity observations worldwide, a novel method was developed, based on k-Kohler and Mie theory, to retrieve aerosol hygroscopicity from open access PM2.5 mass concentration, ambient RH and visibility data. The method was applied in Delhi, India and reported the high aerosol hygroscopicity for the first time. To sum up, the presented thesis improved our understanding on water uptake of multi-component aerosol particles and the relevant impacts. More interestingly, the developed method is applicable in wider regions worldwide and make the aerosol hygroscopicity knowledge achievable. Furthermore, this method shed lights on the quantification of co-condensation of condensable vapours on aerosol hygroscoscopicity in future after its successful case in Delhi.

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	M. R. Alfarra (Supervisor) & Gordon Mcfiggans (Supervisor)