Regional visibility and health are associated with chemical and physical properties of ambient aerosols. Taking advantage of the real-time aerosol instrumentations at the HKUST Supersite and elsewhere, this thesis aims to examine the aerosol properties based on a combination of field and laboratory studies. Simultaneous growth factor (GF) and composition measurements were made with a hygroscopic tandem differential mobility analyzer (HTDMA) and a high-resolution aerosol mass spectrometer (AMS), respectively, at the HKUST Supersite in 2011 to evaluate if typical GF measurements at fixed relative humidity (RH) of 85% or 90% can adequately describe aerosol hygroscopicity at lower RHs. The average increase in the hygroscopic parameter, κ, was 45% from 90% RH to 40% RH, but the diffe...[ Read more ]

Regional visibility and health are associated with chemical and physical properties of ambient aerosols. Taking advantage of the real-time aerosol instrumentations at the HKUST Supersite and elsewhere, this thesis aims to examine the aerosol properties based on a combination of field and laboratory studies. Simultaneous growth factor (GF) and composition measurements were made with a hygroscopic tandem differential mobility analyzer (HTDMA) and a high-resolution aerosol mass spectrometer (AMS), respectively, at the HKUST Supersite in 2011 to evaluate if typical GF measurements at fixed relative humidity (RH) of 85% or 90% can adequately describe aerosol hygroscopicity at lower RHs. The average increase in the hygroscopic parameter, κ, was 45% from 90% RH to 40% RH, but the difference yielded insignificant changes in the GF-RH curves. GF predictions using the empirical correlation of K with AMS mass fractions were within 10% in additional measurements at 10-93% RH.

Aerosol volatility and its correlation with carbonaceous matters was characterized based on simultaneous measurements of a volatility TDMA (VTDMA) and an organic carbon/ elemental carbon (OC/EC) analyzer in Guangzhou in 2014. Medium and high volatility particles at 300°C in the VTDMA contributed to 57-71% of number concentrations for 40-300 nm particles. Closure analysis and comparison of diurnal variations in the non-volatile materials at 300°C, EC and non-volatile OC at 475°C or above suggest that non-volatile OC, in addition to EC, was one of the non-volatile components measured by the VTDMA, especially in the afternoon.

Laboratory study on the aqueous phase photo-oxidation was conducted for two phenolic carbonyls, namely syringaldehyde and acetosyringone, emitted from biomass burning to study the formation of secondary organic aerosols (SOA) in a photochemical reactor simulating cloudy and foggy conditions. The observed degradation rates of both precursors without external photosensitizers are comparable to those of the phenols in the presence of photosensitizers, suggesting that direct photo-oxidation of phenolic carbonyls could be an important contribution to SOA formation in clouds.