AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Insights into PM2.5 Chemical Composition and Sources in Beijing Using an Extractive Electrospray Ionisation Long-Time-Of-Flight Mass Spectrometer (EESI-LTOF)
YANDONG TONG, Veronika Pospisilova, Lu Qi, Giulia Stefenelli, Varun Kumar, Urs Baltensperger, Junji Cao, Rujin Huang, Andre S.H. Prévôt, Jay G. Slowik, Paul Scherrer Institute
Abstract Number: 655 Working Group: Source Apportionment
Abstract Serious haze events in Beijing are mostly characterised by fine particulate matter (PM2.5) and extreme pollution events are dominated by secondary aerosol (Huang et al., 2014). The recent development of a novel extractive electrospray ionisation long-time-of-flight mass spectrometer (EESI-LTOF, Lopez-Hilfiker et al., 2019) enables rapid, online OA measurements at atmospherically relevant concentrations with soft ionisation, providing near-molecular chemical information while avoiding thermal decomposition or ionisation-induced fragmentation, which potentially enable the identification and quantification of secondary organic aerosols.
As the first trial of field-deployable EESI-LTOF implementation in heavy mass loading condition, an intensive online campaign in Beijing was conducted from the beginning of October to mid-December using an EESI-LTOF, together with an Aerodyne long-time-of-flight aerosol mass spectrometer (L-TOF-AMS) equipped with a PM2.5 aerodynamic lens and other supporting measurements. OA sources/processes were investigated by positive matrix factorisation (PMF) implemented by the multilinear engine (ME-2) using the Source Finder (SoFi) interface (Canonaco et al., 2013).
This ten-week campaign covers two distinctive periods: autumn non-heating season and winter heating season. PMF analysis of AMS resolves four primary sources (cooking-related OA, coal combustions OA, biomass burning OA and hydrocarbon-like OA) and four secondary factors (two less oxygenated OAs and two more oxygenated OAs). Among the eight factors, SOA accounts for a significant and sometimes dominant fraction of OA, highlighting the importance of determining the physicochemical and/or meteorological processes governing SOA accumulation. Interestingly, one less oxygenated OA and one more oxygenated OA contribute more mass in the non-heating season haze events than heating season haze, whereas the other less oxygenated OA shows the opposite pattern. The limited chemical information provided by the AMS makes a mechanistic interpretation challenging, and we exploit EESI-TOF tracer ions and PMF analysis to constrain the sources and physicochemical processes governing SOA accumulation during extreme haze.