Project A03:
Aerosol nucleation in the upper troposphere
Brief Summary
We propose that aerosol nucleation involving Highly Oxidized Organic Molecules (HOMs) from monoterpenes and taking place in the outflow region of deep convective clouds above tropical forests is a major source of particles for the tropical troposphere. Identification of the nucleation mechanisms and the key nucleating species is the central goal of this project. Above rain forest regions we expect that monoterpenes as well as isoprene survive convective transport and are then oxidized to form extremely low-volatile organics that undergo strong nucleation in the UT. Over oceans, probably other substances dominate the nucleation process in the outflow of deep convection, especially sulfuric acid (SA) and methanesulfonic acid (MSA) from the oxidation of dimethyl sulfide (DMS). These particles, newly formed in the tropical UT, are likely the dominant source of CCN in the entire tropical troposphere as well as the major source of the stratospheric background aerosol.
We plan to analyze the aircraft-based measurements of the low-volatility nucleating species measured by our CI-APi-TOF mass spectrometer during the missions CAFE-EU (2020), CAFE-BRAZIL (2021 or 2022, depending on Covid-19 situation) and CAFE-PACIFIC (2024) with the research aircraft HALO. The nucleation and early growth processes are studied at molecular level allowing the identification of the key nucleating species (role of HOMs, sulfuric acid, nitric acid, isoprene oxidation products, ammonia and their clusters for nucleation and early growth), assessment of the role of ions, low temperatures, low condensation sink, and high actinic flux as key elements for fostering the nucleation, as well as assessment of lightning-NOx for potentially reducing the formation of HOMs that are able to nucleate.
Besides the precursor concentrations, a second key variable for the UTLS nucleation measurements is the quantitative detection of nucleation mode particles at low ambient pressure. We plan to develop a dual-channel ultrafine condensation particle counter (uCPC) realizing two different cut-offs around 2.5 and 7 nm, to be operated onboard the Leajet for the planned UTLS experiment (see project B01). The instrument will be developed as a 19-inch rack component that will also be suitable for other research aircraft such as HALO.
The analysis will be complemented by model simulations for both the explanation of the observed mechanisms (via box modelling) using state-of-the-art aerosol nucleation and SOA schemes and the regional distributions of the aerosols (simulated with an identical aerosol scheme as in the box models) with the help of the regional chemistry climate modelling system MECO(n) and its nesting capabilities. This system is going to be applied in simulations for the CAFE campaigns. MECO(n) represents the convective uplifting either with the help of a convection parametrization and an associated tracer transport algorithm or by explicitly resolving the deep convection. For both variants an explicit scavenging / aqueous phase chemistry scheme is used, which is extended for the fate of dissolved species during freezing (i.e. retention). Hence, the complex chemical transformations in gas, aerosol and cloud phase are explicitly taken into account.
Members
Prof. Dr. Joachim Curtius
Principal Investigator
Goethe-Universität Frankfurt, Institut für Atmosphäre und Umwelt
curtius[at]iau.uni-frankfurt.de
Prof. Dr. Holger Tost
Principal Investigator
Johannes Gutenberg-Universität Mainz, Institut für Physik der Atmosphäre
tosth[at]uni-mainz.de
Sarah Richter
Doctoral Candidate
Goethe-Universität Frankfurt, Institut für Atmosphäre und Umwelt
richter[at]iau.uni-frankfurt.de
Kshitija Naktode
Doctoral Candidate
Johannes Gutenberg-Universität Mainz, Institut für Physik der Atmosphäre
knaktode[at]uni-mainz.de
Publications
Abdelkader, M., G. Stenchikov, A. Pozzer, H. Tost, and J. Lelieveld (2023): The effect of ash, water vapor, and heterogeneous chemistry on the evolution of a Pinatubo-size volcanic cloud. Atmospheric Chemistry and Physics 23 (1), 471–500. doi: https://doi.org/10.5194/acp-23-471-2023.
Zauner-Wieczorek, M., M. Heinritzi, M. Granzin, T. Keber, A. Kürten, K. Kaiser, J. Schneider, and J. Curtius (2022): Mass spectrometric measurements of ambient ions and estimation of gaseous sulfuric acid in the free troposphere and lowermost stratosphere during the CAFE-EU/BLUESKY campaign. Atmospheric Chemistry and Physics 22 (17), 11781–11794. doi: 10.5194/acp-22-11781-2022.