Influence Factors of Hit-Rate and Instrument Status of SPAMS

Online analysis of particle source based on single particle aerosol mass spectrometry (SPAMS) was widely used in Beijing, Guangzhou, Shijiazhuang and many other cities in China, because its operation, maintenance and data processing was relatively simple. The differences of different regions and pollution processes can be obtained by building sites all around and analyzing data through networking. And because the monitoring results of SPAMS with different time and place need to be compared, and SPAMS is a semi-quantitative detecting method for particulate, so it is especially important to ensure the reliability of the SPAMS’s data. Atmospheric monitoring was conducted in air quality integrated observation laboratory of Beijing Municipal Environmental Monitoring Center by SPAMS during January to December of 2013. The results showed that the hit-rate of SPAMS was related to amount of particles, relative humidity of atmosphere, particle components and particle size. When the instrument was in normal state, the hit-rate was high when the amount of particle was small and the atmospheric relative humidity was low. The hit-rate was positively related to the amount of particles which contained K⁺, HSO₄^-, OCEC, NO₃^- as well as particles with the size of 0.2-0.3 μm, 0.3-0.4 μm, 0.4-0.5 μm, and was inversely related to the amount of particles with the size of 0.1-0.2 μm, 0.5-0.6 μm, 0.6-0.7 μm. The relationship between the hit-rate and amount of NH₄⁺, SiO₃^- particles was related to the pollution characteristics and so on. The hit-rate was low and the relationship between the hit-rate and the impact factors changed when the instrument was in poor condition. This study provided a possible method for judging the status of the instrument, finding the instrument’s failures in advance, and then improving the data quality by analyzing the hit-rate and the relationship between the hit-rate and the impact factors. Through the method, the fault parts of which the state parameters could not be displayed in the instrument control software could be found. These fault parts mainly refered to diameter measurement and ionization part, such as the deviation of laser light path, the change of spot size, the loss of the mirror and so on. Usually these components were tested only when the data were obviously abnormal while the state of other parts were normal.