This work investigated the size distribution of the droplet nuclei and coughed droplets by test subjects. The size distributions of droplet nuclei coughed by test subjects were determined with an aerodynamic particle sizer (APS) and scanning mobility particle sizer (SMPS) system (system 1). Coughed droplets were only sampled with the APS system (system 2). Two different schemes were employed in system 2. Furthermore, the size distribution of coughed droplets of different ages and gender was investigated to identify the effects of age and gender on droplet size distribution. Results indicated the total average size distribution of the droplet nuclei was 0.58-5.42 microm, and 82% of droplet nuclei centered in 0.74-2.12 microm. The entire average size distribution of the coughed droplets was 0.62-15.9 microm, and the average mode size was 8.35 microm. The size distribution of the coughed droplets was multimodal. The size distribution of coughed droplets showed three peaks at approximately 1 microm, 2 microm, and 8 microm. These analytical findings indicate that variation for average droplet size among the three age groups was insignificant (p > 0.1). Moreover, the variation in average droplet size between males and females was also insignificant (p > 0.1). Also, the variation in droplet concentration between males and females was significant (p > 0.1). Droplet nuclei concentrations from male subjects were considerably higher than that from females. Comparison of the droplet concentrations for subjects in different age groups demonstrated that subjects in the 30-50-year age group have the largest droplet concentrations.

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This study focused on the investigation of the effectiveness of negative air ionization (NAI), photocatalytic oxidation (PCO), and the combination of NAI and PCO on the removal of aerosolized Escherichia coli, Candida famata, and vir phage under different relative humidity. The experiments were conducted with a stainless steel reactor equipped with a negative air ion generator, a photocatalytic filter, and two ultraviolet lamps with 365 nm wavelength. The removal efficiency ( ), defined as one minus the ratio of the outlet concentration to the inlet concentration of the appropriate bioaerosol, was used to evaluate the effectiveness of the removal methods. The combination of NAI and PCO was the most efficient removal method for aerosolized E. coli ( =0.304±0.06.0.364±0.008), C. famata ( =0.433±0.08.0.598±0.047), and vir phage ( =0.689±0.02.0.903±0.06). In this removal method, the contributions of NAI were higher than those of PCO for the removal of E. coli and C. famata; for the removal of virus phage the contributions of NAI and PCO were comparable NAI was the least efficient removal method for bioaerosols, and the removal efficiencies are: = 0.175 ± 0.04.0.245 ± 0.03 for E. coli; = 0.216 ± 0.007.0.297 ± 0.044 for C. famata; and = 0.299 ± 0.12.0.384 ± 0.02 for vir phage. ᭧

This study investigated the deliquescence of sodium chloride aerosol with surfactants at a retention time of 4.24 sec. Two surfactants used in this study, glutaric acid and pyruvic acid, are found in atmospheric aerosol and have a high hydrophile-lipophile balance (HLB) value. The experimental system consisted of a relative humidity conditioner, a tandem differential mobility analyzer (TDMA) and a scanning mobility particle sizing (SMPS) system. Results obtained from the observation of TDMA presented the deliquescence point of sodium chloride aerosol at 75% RH. In addition, the growth size of sodium chloride aerosol was observed to be 79.47 nm and the growth ratio was 77.94%, when the initial size of aerosol was 101.82 nm. Surfactants were internally mixed with sodium chloride at six different weight fractions, i.e. 2.5, 5, 10, 20, 40, and 60% by weight of surfactants in dry aerosol. Both surfactants apparently decreased the deliquescence point of sodium chloride, in which the lowest deliquescence point appeared at about 71% RH when the weight fraction of surfactants is 60% by weight of surfactants in dry aerosol. Moreover, the smallest size of sodium chloride aerosol with surfactants was 142.7 nm at 60% by weight of pyruvic acid in dry aerosol. Our results further demonstrate that the deliquescence point and size of sodium chloride aerosol with surfactants are related to the weight fraction of surfactants.

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