Chemical composition of nanoparticles from α-pinene nucleation and the influence of isoprene and relative humidity at low temperature
Authors: Caudillo Lucía , Rörup Birte , Heinritzi Martin , Marie Guillaume , Simon Mario , Wagner Andrea C. , Müller Tatjana , Granzin Manuel , Amorim Antonio , Ataei Farnoush , Baalbaki Rima , Bertozzi Barbara , Brasseur Zoé , Chiu Randall , Chu Biwu , Dada Lubna , Duplissy Jonathan , Finkenzeller Henning , Gonzalez Carracedo Loïc , He Xu-Cheng , Hofbauer Victoria , Kong Weimeng , Lamkaddam Houssni , Lee Chuan P. , Lopez Brandon , Mahfouz Naser G. A. , Makhmutov Vladimir , Manninen Hanna E. , Marten Ruby , Massabò Dario , Mauldin Roy L. , Mentler Bernhard , Molteni Ugo , Onnela Antti , Pfeifer Joschka , Philippov Maxim , Piedehierro Ana A. , Schervish Meredith , Scholz Wiebke , Schulze Benjamin , Shen Jiali , Stolzenburg Dominik , Stozhkov Yuri , Surdu Mihnea , Tauber Christian , Tham Yee Jun , Tian Ping , Tomé António , Vogt Steffen , Wang Mingyi , Wang Dongyu S. , Weber Stefan K. , Welti André , Yonghong Wang , Yusheng Wu , Zauner-Wieczorek Marcel , Baltensperger Urs , El Haddad Imad , Flagan Richard C. , Hansel Armin , Höhler Kristina , Kirkby Jasper , Kulmala Markku , Lehtipalo Katrianne , Möhler Ottmar , Saathoff Harald , Volkamer Rainer , Winkler Paul M. , Donahue Neil M. , Kürten Andreas , Curtius Joachim 
Published: November 2021

Abstract. Biogenic organic precursors play an important role in
atmospheric new particle formation (NPF). One of the major precursor species
is α-pinene, which upon oxidation can form a suite of products
covering a wide range of volatilities. Highly oxygenated organic molecules
(HOMs) comprise a fraction of the oxidation products formed. While it is
known that HOMs contribute to secondary organic aerosol (SOA) formation,
including NPF, they have not been well studied in newly formed particles due
to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures
(−50 and −30 ∘C) and relative
humidities (20 % and 60 %) relevant in the upper free troposphere. The
measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD)
chamber. The particle chemical composition was analyzed by a thermal
desorption differential mobility analyzer (TD-DMA) coupled to a nitrate
chemical ionization–atmospheric pressure interface–time-of-flight
(CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our
measurements revealed the presence of C8−10 monomers and C18−20
dimers as the major compounds in the particles (diameter up to
∼ 100 nm). Particularly, for the system with isoprene added,
C5 (C5H10O5−7) and C15 compounds
(C15H24O5−10) were detected. This observation is consistent
with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate,
our measurements indicate that they can still contribute to the particle
growth at free tropospheric conditions. For the experiments reported here,
most likely isoprene oxidation products enhance the growth of particles
larger than 15 nm. Additionally, we report on the nucleation rates measured
at 1.7 nm (J1.7 nm) and compared with previous studies, we found lower
J1.7 nm values, very likely due to the higher α-pinene and
ozone mixing ratios used in the present study.