Development Of Miniature Plate DMA For Ultrafine-Particle Size Measurement

Recently,the number of mobile pollution sources represented by motor vehicles and ships has increased dramatically.The latest Beijing and Jinan PM2,5 source analysis reports show that mobile sources have become the primary source of PM2.5 pollution in the local atmosphere.Particles in the exhaust gas will not only damage the ecological environment,but also endanger human health.The existing laws and regulations have stipulated the quality limit and number limit of particles above 23nm in the exhaust,and there is no relevant regulation on particle size spectrum.The mobile source particle size monitoring equipment relies on imports in China,and the existing commercial instruments are large in size,high in price,and low in efficiency.The importance of increasing the development of portable mobile source particle size monitoring instruments has become increasingly prominent.Differential mobility analyzers(DMAs)have been the primary tool for characterizing fine and ultrafine aerosol particles in the atmosphere for a number of years.Compared with traditional cylindrical DMAs,plate DMAs are more suitable for outdoor,portable applications with smaller size,lighter weight and simpler manufacturing process.Aiming at the above requirements,this paper focuses on study of the miniature plate DMA for ultrafine-particle size measurement.Based on the working principle and empirical knowledge of plate DMA,the simulations of velocity-field and particle-trajectory were finished to select the size of particle-classification zone and other key parameters.The structural design and control system design was completed.According to the experimental results and simulation results,three versions of plat DMA with different sizes(the particle size ranges are 50～250nm,50～400nm,and 20～500nm,respectively)were optimized and designed.The experimental results show that the theoretical values of applied voltages are in good agreement with the experimental values.Based on the comparison of the three DMAs,the impact of the size of classification zone,sheath gas and sample gas on the performance of DMA was analyzed,and the simulation results were used to analyze the impact of process-parameter to prepare for the next optimization.The small ultrafine particle size spectrometer was integrated by the third DMA,a charger module and a micro charge detection module,and a preliminary comparison test was performed with a commercial particle size spectrometer.The preliminary field application of the small ultrafine particle size spectrometer was completed at Nankai University,and a comparison test was conducted with a commercial mobile source particle size spectrometer.The results show that the self-developed particle size spectrometer can achieve monitoring for 20～500nm particles and the spectrometer has good consistency with the commercial instrument.