AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
A Comprehensive Isomeric Identification of Particle-Phase Organic Nitrates by Gas Chromatography and Time-Of-Flight Mass Spectrometry Coupled with Electron Capture Ionization
XIAODI SHI, Xinghua Qiu, Peking University
Abstract Number: 871 Working Group: Instrumentation and Methods
Abstract Organic nitrates (ONs) are important composition of secondary organic aerosol (SOA) severing as the reservoir or sink of NOx. However, little information is available in urban area of developing counties characterized by high anthropogenic VOCs emission. Chemical composition of ONs in these area is crucial to uncover their formation mechanism. But current methods couldn’t meet the demand on individual or isomeric identification of ONs. In this study, a method based on gas chromatography/ electron capture negative ionization tandem time-of-flight mass spectrometry (GC/ECNI/ToF-MS) was established to comprehensively identify unknown ONs in PM2.5 sampled in Beijing. Under ECNI condition, ONs can cleavage into NO2-, [M-NO2]-. [M-NO2-H2]-. NO2- can be used as an indicator of ONs and another pair of ions can provide element composition. Deconvolution was performed and ONs were filtrated according to fragment rules after analyzing organic extracts of PM2.5 in full scan mode. 81 features were recognized as potential ONs. And 12 features were verified by the synthesized authentic standards. Potential ONs were composed of arylalkyl nitrate and hydroxy nitrate generated from styrene, alkenes and biogenic VOCs. Isomers of hydroxy nitrate formed from 1-alkenes were confirmed by synthesized authentic standard. Isomeric distribution was used to reveal the relative contribution of daytime and nighttime formation mechanism. High abundance of ONs with nitrate group located at α position suggesting that night formation mechanism was predominant. This method provides information on the individual species of ONs and can enhance our comprehension of the formation mechanism.