1Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany
2Institute for Atmospheric and Earth System Research (INAR)/Physics, Faculty of Science, University of Helsinki, 00014 Helsinki, Finland
3Department of Chemistry & CIRES, University of Colorado Boulder, Boulder, CO, 80309-0215, USA
4Max Planck Institute for Chemistry, Mainz, 55128, Germany
5CENTRA and FCUL, University of Lisbon, 1749-016 Lisbon, Portugal
6Leibniz Institute for Tropospheric Research, Leipzig, 04318, Germany
7Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
8Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
9Helsinki Institute of Physics, University of Helsinki, 00014 Helsinki, Finland
10Faculty of Physics, University of Vienna, 1090 Vienna, Austria
11Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
12Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
13California Air Resources Board, Sacramento, CA 95814, USA
14Lebedev Physical Institute, Russian Academy of Sciences, 119991, Moscow, Russia
15CERN, 1211 Geneva, Switzerland
16Dipartimento di Fisica, Università di Genova and INFN, 16146 Genova, Italy
17Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, CO 80309, USA
18Institute for Ion and Applied Physics, University of Innsbruck, 6020 Innsbruck, Austria
19Ionicon Analytik GmbH, 6020 Innsbruck, Austria
20Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research, 8903 Birmensdorf, Switzerland
21Department of Chemistry, University of California, Irvine, Irvine, CA 92697, USA
22Finnish Meteorological Institute, 00560 Helsinki, Finland
23Beijing Weather Modification Office, China
24IDL, Universidade da Beira Interior, R. Marquês de Ávila e Bolama, Covilhã, 6201-001, Portugal
25Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, P.R. China
26Moscow Institute of Physics and Technology (National Research University), 117303, Moscow, Russia
1Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany
2Institute for Atmospheric and Earth System Research (INAR)/Physics, Faculty of Science, University of Helsinki, 00014 Helsinki, Finland
3Department of Chemistry & CIRES, University of Colorado Boulder, Boulder, CO, 80309-0215, USA
4Max Planck Institute for Chemistry, Mainz, 55128, Germany
5CENTRA and FCUL, University of Lisbon, 1749-016 Lisbon, Portugal
6Leibniz Institute for Tropospheric Research, Leipzig, 04318, Germany
7Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
8Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
9Helsinki Institute of Physics, University of Helsinki, 00014 Helsinki, Finland
10Faculty of Physics, University of Vienna, 1090 Vienna, Austria
11Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
12Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
13California Air Resources Board, Sacramento, CA 95814, USA
14Lebedev Physical Institute, Russian Academy of Sciences, 119991, Moscow, Russia
15CERN, 1211 Geneva, Switzerland
16Dipartimento di Fisica, Università di Genova and INFN, 16146 Genova, Italy
17Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, CO 80309, USA
18Institute for Ion and Applied Physics, University of Innsbruck, 6020 Innsbruck, Austria
19Ionicon Analytik GmbH, 6020 Innsbruck, Austria
20Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research, 8903 Birmensdorf, Switzerland
21Department of Chemistry, University of California, Irvine, Irvine, CA 92697, USA
22Finnish Meteorological Institute, 00560 Helsinki, Finland
23Beijing Weather Modification Office, China
24IDL, Universidade da Beira Interior, R. Marquês de Ávila e Bolama, Covilhã, 6201-001, Portugal
25Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, P.R. China
26Moscow Institute of Physics and Technology (National Research University), 117303, Moscow, Russia
Received: 16 Jun 2021 – Accepted for review: 07 Jul 2021 – Discussion started: 07 Jul 2021
Abstract. New Particle Formation (NPF) from biogenic organic precursors is an important atmospheric process. One of the major species is α-pinene, which upon oxidation, can form a suite of products covering a wide range of volatilities. A fraction of the oxidation products is termed Highly Oxygenated Organic Molecules (HOM). These play a crucial role for nucleation and the formation of Secondary Organic Aerosol (SOA). However, measuring the composition of newly formed particles is challenging due to their very small mass. Here, we present results on the gas and particle phase chemical composition for a system where α-pinene was oxidized by ozone, and for a mixed system of α-pinene and isoprene, respectively. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber at temperatures between −50 °C and −30 °C and at low and high relative humidity (20 % and 60 to 100 % RH). These conditions were chosen to simulate pure biogenic new particle formation in the upper free troposphere. The particle chemical composition was analyzed by the Thermal Desorption-Differential Mobility Analyzer (TD-DMA) coupled to a nitrate chemical ionization time-of-flight mass spectrometer. This instrument can be used for particle and gas phase measurements using 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) are 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 might enhance growth at particle sizes larger than 15 nm. Besides the chemical information regarding the HOM formation for the α-pinene (plus isoprene) system, we report on the nucleation rates measured at 1.7 nm and found that the lower J1.7nm values compared with previous studies are very likely due to the higher α-pinene and ozone mixing ratios used in the present study
Caudillo and co-authors present and discuss the gas and particle phase composition of pure biogenic nucleation events measured with a nitrate chemical ionization atmospheric pressure interface time of flight mass spectrometer (coupled with a thermal desorption-differential mobility analyzer for the particle phase) in the CLOUD chamber at a range of conditions representing free tropospheric conditions. Specifically, alpha-pinene and a mix of alpha-pinene and isoprene were oxidized at -30 deg C and - 50 deg C, and at 20 % or 60 - 100 % relative humidity. The authors find C8-10 monomers and C18-20 dimers as major compounds, and C5 and C15 compounds contributing to particle growth when isoprene is present in the system. I very much appreciate the systematic analysis. The manuscript is well-written and the experimental results are thoroughly discussed. In my opinion, this is an original and valuable contribution to the field. Therefore, it should be published in ACP after minor revisions.
Specific comments: In the abstract, the last sentence ("Besides the chemical information...", lines 64-66) was confusing to me. After reading section 3.4.1, I suggest to be more specific in the abstract, e.g. "Compared with previous studies, we found lower nucleation rates measured at 1.7 nm, very likely due to higher alpha-pinene and ozone mixing ratios used in the present study."
In section 2.1, there is no information about GCR conditions during the experiments, please add.
In section 2.2, please add some more information about the heating procedure of the filament. Is the temperature slowly ramped up, or do you apply high temperature directly to instantaneously vaporize the sample? This is also relevant for the discussion of potential thermal decomposition of molecules in section 3.2.2.
Regarding the non-size selective mode of operation of the TD-DMA, it would be helpful to get an idea about the contribution of freshly nucleated particles vs. grown particles to the sampled mass. From the measured particle size distributions and the PSM and CPC total number concentrations, could you calculate a rough estimate of the volume/mass fraction of particles < 15 nm in the samples collected in the periods shown in Figure 1 as shaded areas? Please add this information to Table 1.
In Figure 3f, to me it is not obvious that specifically C4-5 and C13-16 compounds are enhanced as stated in lines 237/238. Please clarify.
In section 3.3, looking at Figures 5 and S4 I agree with the statement that mainly LVOC and ELVOC compounds were detected in the particle phase, however, the ULVOC compounds appear to be a minor fraction.
Section 3.4.2: Regarding the discussion of isoprene suppression of new particle formation, please consider adding a reference to Lee et al. (2016), doi:10.1002/2016JD024844.
In Figures 6 and 8, please explain the meaning of "1α run-to-run uncertainty".
Technical comments: lines 225, 301, 322 : Make sure that there is no line break between sign and number in "- 30" and "- 50". line 226: "While the gas..." is not a full sentence. Section 3.2, first paragraph: When presenting and discussing Figure 2, add a reference to supplementary material Figures S1 and S2 for other systems. line 248: "While GR..." is not a full sentence. line 285: Change "autooxidation" to "autoxidation" to be consistent throughout the manuscript. lines 204, 312, 336, 375: Here, "new particle formation rate" is used, while J_1.7nm is introduced as "nucleation rate" in the manuscript. For consistency, I recommend using "nucleation rate" throughout the manuscript. In Figures 6 and 8: "GRC" should read "GCR" in the figure legend. Also, in the last sentence of the figure caption, remove "and" before "is not shown".
We performed experiments in the CLOUD chamber at CERN at low temperatures to simulate new particle formation in the upper free troposphere (at −30 °C and −50 °C). We measured particle and gas phase and found that most of the compounds that are present in the gas phase are detected as well in the particle phase. The major compounds in the particles are C8-10 and C18-20. Specifically, we showed that C5 and C15 compounds are detected in a mixed system with isoprene and α-pinene at −30 °C, 20 % RH.
We performed experiments in the CLOUD chamber at CERN at low temperatures to simulate new...
