Capillary Sampling Interface For Nanoparticles

Aerosol particles are the essential components of air pollutants and new particle formation is the important source of secondary fine particles in the air.The particles generated from new particle formation locate at nucleation mode and usually their sizes are less than 20 nm.Although the mass concentration of these fine nanoparticles is very low,their number density is large and in the atmosphere they can continue to grow up,absorb and scatter the sunlight and further lead to haze.The information of the chemical components of these nanoparticles is significant for understanding the nucleation and growth mechanism of new particles and revealing the formation routes of atmospheric compound pollutants.Aerosol mass spectrometer is an effective instrument for detecting the chemical composition of aerosol particles in the atmosphere.Aerodynamic lenses,nozzle and capillary as common inlets have been used in aerosol mass spectrometry to transfer particles.However,limited by their small size,it is of a great challenge for aerosol nanoparticles to be sampled into vacuum with high efficiency,and thus hinder the chemical components of the nanoparticles to be probed.In order to partially solve the above problems,in this dissertation,we propose and design a capillary sampling interface to deliver nanoparticles at nucleation mode from atmospheric pressure to vacuum region.The capillary sampling interface can be combined in the aerosol mass spectrometer to detect the chemical composition of nanoparticles,especially the particles in nucleation mode generated from new particle formation.The dissertation can be divided into three parts:1.The transmission characteristics of nanoparticles in capillary at atmospheric pressure.A home-made X-ray ion-induced nucleation reactor was designed and used to generate nanoparticles with high concentration and a commercial nanometer scanning mobility particle sizer(Nano-SMPS)was employed to measure the penetration efficiency of nanoparticles at nucleation mode in capillary.The aerosol transport and deposition model are also adopted to analyze the relationship between the penetration efficiency and the dimensions of the capillary and the flow rate in capillary.It is shown that the penetration efficiency changes with the inner diameter,length and flow rate of the capillary.The present experiments reveal that the penetration efficiency of nanoparticles in capillary increases obviously with the particle size.Decreasing of the inner diameter of capillary or increasing the length of capillary would decrease the penetration efficiency of particles.Increasing the flow rate in the capillary will increase the penetration efficiency of particles.2.The construction of a capillary sampling interface and its characterization.We use the flow field simulation software to simulate the gas flow field in capillary sampling interface.Then the trajectory of nanoparticles in the flow field was calculated and used to design the mechanical structure and the vacuum system of the capillary sampling interface.In addition,combined with the ion induced nucleation reactor as particle source and a current detection device,the overall transmission efficiency of nanoparticles in the capillary sampling interface was measured and analyzed.Our results show that the transmission efficiency of nanoparticles in the capillary sampling interface increases with the flow rate.A large flow rate can reduce the diffusion loss of nanoparticles in the interface.When the flow rate was increased to a value of 1500 ml/min,the transmission efficiency can be approached to 0.3%.3.The preliminary application of the capillary sampling interface in laser ionization single particle aerosol mass spectrometer.The capillary sampling interface was installed in the aerosol mass spectrometer to deliver nanoparticles.The chemical composition of the nanoparticles from a commerical aerosol generator and the ion induced nucleation reactor were analyzed with a 266 nm laser ablation and multiphoton ionization.The results of the aerosol mass spectrometer were also discussed,and the feasibility of the capillary sampling interface in the future application was evaluated.