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Title: Relative humidity effect on the formation of highly oxidized molecules and new particles during monoterpene oxidation
Abstract. It has been widely observed around the world that the frequency and intensityof new particle formation (NPF) events are reduced during periods of highrelative humidity (RH). The current study focuses on how RH affects theformation of highly oxidized molecules (HOMs), which are key components ofNPF and initial growth caused by oxidized organics. The ozonolysis ofα-pinene, limonene, and Δ3-carene, with and without OHscavengers, were carried out under low NOx conditions undera range of RH (from ∼3 % to ∼92 %) in atemperature-controlled flow tube to generate secondary organic aerosol (SOA).A Scanning Mobility Particle Sizer (SMPS) was used to measure the sizedistribution of generated particles, and a novel transverse ionizationchemical ionization inlet with a high-resolution time-of-fight massspectrometer detected HOMs. A major finding from this work is that neitherthe detected HOMs nor their abundance changed significantly with RH, whichindicates that the detected HOMs must be formed from water-independentpathways. In fact, the distinguished OH- and O3-derived peroxyradicals (RO2), HOM monomers, and HOM dimers could mostly beexplained by the autoxidation of RO2 followed by bimolecularreactions with other RO2 or hydroperoxy radicals (HO2),rather than from a water-influenced pathway like through the formation of astabilized Criegee intermediate (sCI). However, as RH increased from ∼3 % to ∼92 %, the total SOA number concentrations decreased bya factor of 2–3 while SOA mass concentrations remained relatively constant. These observations show that, whilehigh RH appears to inhibit NPF as evident by the decreasing numberconcentration, this reduction is not caused by a decrease inRO2-derived HOM formation. Possible explanations for these phenomenawere discussed.  more » « less
Award ID(s):
1762098
PAR ID:
10091125
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Atmospheric Chemistry and Physics
Volume:
19
Issue:
3
ISSN:
1680-7324
Page Range / eLocation ID:
1555 to 1570
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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