AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
The Sensitivity of a Q-ACSM in Measuring Chamber Generated SOA with Different Oxidation States
Yan Ma, XIAOXIAO LI, Hui Chen, Xin Ma, Youling Jiang, Rujin Yin, Jiming Hao, Jun Zheng, Jingkun Jiang, Tsinghua University
Abstract Number: 45 Working Group: Instrumentation and Methods
Abstract The accuracy in quantifying secondary organic aerosols (SOA) using an aerosol chemical speciation monitor with a quadrupole mass spectrometer (Q-ACSM) was studied. Pure SOA were generated under simulated photochemical oxidation conditions in a 4.5 m3 Teflon chamber from three different volatile organic compound (VOC) precursors at atmospheric relevant concentrations (dozens of ppbv): α-pinene, isoprene and toluene, representing both biogenic and anthropogenic VOCs. Different SOA oxidation states were achieved by changing the reaction ratio of the VOC precursor to the oxidants (O3 or OH). SMPS and APM were used to measure the number-size distribution and the mass of the generated SOA, which were then used to deduce the SOA mass concentration. The sensitivity of the Q-ACSM to a specific SOA was found to be anti-correlated with the O/C ratio regardless of the VOC precursors. This may be due to the decreasing of relative ionization efficiency (RIE) or the decreased collection efficiency (CE) of the Q-ACSM for more oxidized SOA. To pinpoint the actual cause, (NH4)2SO4 seed particles were injected into the chamber before SOAs were produced from VOC precursor. After coating with SOA, the sulfate signal increased significantly, indicating increased CE of coated (NH4)2SO4 particles. However, it appears that CE of SOA coated (NH4)2SO4 particles did not change substantially with changing O/C ratio, which then can be taken into account as a correction factor of the CE of the chamber generated SOAs for the Q-ACSM.