汽车尾气颗粒物的STXM和NEXAFS研究

Research on automobile exhaust particles by STXM and NEXAFS

为了研究汽车尾气颗粒物的结构和氮的种态,使用扫描透射X射线显微成像(STXM)技术研究了桑塔纳3000和高尔汽车尾气颗粒物.STXM表明单颗粒物的粒径为500nm,颗粒物质量分布不均匀,有中间空洞.比较汽车尾气颗粒物和(NH4)2SO4和NaNO3中N的1sX射线近边吸收精细结构谱(NEXAFS),铵盐在406eV有显著的σ*吸收峰,有肩部结构;汽车尾气颗粒物和NaNO3中N的近边吸收谱在412eV和418.5eV有明显的σ吸收峰;(NH4)2SO4中N的近边吸收谱在413.5eV和421.8eV更宽的σ吸收峰.硝酸盐是汽车尾气颗粒物中的N化学种态的主要存在形式.在395—418eV能量范围内对桑塔纳3000汽车尾气颗粒物进行堆栈扫描,经过主成分分析和聚类分析,发现其表层主要为硝酸盐,内部有少量铵盐.

In order to understand the structures of automobile exhaust particles and the components of nitrogen inside them, automobile exhaust particles from Santana 3000 and Golcars are investigated with scanning transmission X-ray microscopy （STXM） and the near edge X-ray absorption fine structure （NEXAFS） spectra. The results of STXM show that single particulate has a size of 500 nm and a nonuniform mass distribution with an empty hole inside it. Compared with the NEXAFS spectra,（ NH4 ）2SO4 and NaNO3 spectra show many different σ＊ resonances at 406 eV,the spectrum of ammonium has a shoulder structure. NaNO3 and automobile exhaust particles show significant σ resonances at 412 eV and 418. 5 eV. However,（NH4）2SO4 shows wider σ resonances 413. 5 eV and 421. 8 eV. Nitrates are main chemical species of nitrogen in automobile exhaust particles. In an energy range from 395 eV to 418 eV,Santana 3000 automobile exhaust particles are stack scanned. The principal component analysis and cluster analysis indicate that there exist nitrates in surface layer and minor ammonium inside it.