Black Death - Blue Skies - White Clouds : Water Vapour Uptake of Particles Produced from Traffic Exhaust and their Effect on Climate

• Main Author: Wittbom, Cerina
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Fysiska institutionen, Lunds universitet 2017
• Subjects: Engineering and Technology; Environmental Engineering; CCN ACTIVATION; Soot; water vapour; climate; SOA; Traffic emission; Fysicumarkivet A:2017:Wittbom; Arctic
• Online Access: https://lup.lub.lu.se/record/9749903c-3644-4083-81fb-4f9db46bea70; https://portal.research.lu.se/files/24523605/Cerina_Wittbom_webb.pdf

Aerosol particles are everywhere in the air around us, regardless of whether you are in a busy city or in the serene Arctic. Airborne particles can be produced naturally or anthropogenically, and their properties changes during the time they spend in the atmosphere. Their sizes range from about 1 nm to 100 μm, and affect us in two ways; firstly, our health by deposition in the respiratory tract, and secondly via pertubation of the climate.The Earth’s climate is affected by the radiation balance, which is in turn affected by the presence of particles and the formation of cloud droplets. Cloud droplets form on pre-existing particles by condensation of watervapour. These particles, which act as seeds for the condensation of water, are called cloud condensation nuclei (CCN).The ability of particles to take up water vapour depends on their chemical and physical properties, and is described by particle hygroscopicity. The theoretical framework used in this work to calculate particle hygroscopicity was first introduced by Köhler in 1936, and has since then been developed to account for nonideal conditions. Particle hygroscopicity of fresh and aged traffic exhaust was investigated in laboratory measurements. The complete transformation of soot particles, from fresh emissions of hydrophobic, aspherical soot agglomerates to compacted soot particles coated with secondary organic aerosol (SOA), which are able to act as CCN, was captured for the first time. The SOA produced from traffic emissions showed differences in water vapour uptake, when measured in the subsaturated compared to supersaturated regimes. Theoretical analysis using modified Köhler theory, indicated that these measured differences could be explained by limitation of the solubility of the SOA that was condensed on the seed particles.Ambient measurements of particle hygroscopicity associated with traffic emissions were performed in urban and rural environments. The urban aerosol showed a clear diurnal variation as well as a dependence on air mass origin. The ...