Chemistry of the Atmosphere: Field Experiment over the Pacific

Mission status: scheduled

Persons in Charge


  •  Jos Lelieveld (MPI-M)
  •  Joachim Curtius (Univ. Frankfurt)

Scientific Co-Leadership


Mission coordinator​


Contact point at DLR-FX for this mission:


HALO Deployment Base

Time Period

October 2023 – March 2024

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Project description

The CAFE‐Pacific mission, coordinated by the Max Planck Institute for Chemistry and the Goethe Univ. Frankfurt, will be the third in a triad of measurement campaigns with the High Altitude – Long Range (HALO) aircraft to investigate photochemical and aerosol processes in the tropical troposphere. HALO has been uniquely equipped with a custom designed payload by three departments of the MPIC and partner institutes. It consists of highly sensitive mass spectrometric and optical instrumentation, to comprehensively characterize atmospheric oxidation mechanisms, as well as their control of particle production and growth throughout the troposphere; from reactive radicals to large volatile organic compounds and their reaction products, and from small clusters to stable aerosol particles.

Scientific rationale

The tropical region is of particular relevance on Earth because it represents a large fraction of the troposphere where oxidation processes are most efficient, and directly connects to the stratosphere through the upward motion generated by the formation of deep convective clouds. For example, about 80 – 90% of atmospheric methane oxidation takes place in the tropics, even though the largest fraction is emitted at higher latitudes. The tropical troposphere is referred to as the “wash room” of the atmosphere. Moreover, tropical atmospheric chemistry and aerosol processes have been much less studied compared to the extra‐tropics.


The main objective of the CAFE missions is to investigate tropical tropospheric oxidant  photochemistry in combination with aerosol particle formation and growth under clean, pristine conditions over land, and contrast the results with those in marine and polluted conditions. The measurements constrain computer models that represent chemical processes, environmental feedback mechanisms up to the Earth system, in order to generalize the results to regional and global scales. The data support studies of the atmospheric oxidation capacity and the abundance of fine particulate matter in relation to clouds, climate and planetary health. The studies of unpolluted, pristine conditions provide a reference for human‐induced perturbations in the Anthropocene, as well as constraints on atmospheric conditions in the Earth’s history.

The CAFE triad

  • •The first of the three tropical campaigns, CAFE‐Africa, was conducted during the summer of 2018 to measure the monsoon outflow of continental emissions over the Atlantic Ocean. It characterized the combination of dust emissions with those from African biomass burning and urban‐industrial activity in West Africa. Preliminary results show that part of the African pollution travels across the Atlantic Ocean to South America, and how the Saharan dust plumes are chemically processed during transport.  
  • The second is CAFE‐Brazil, to be conducted towards the end of the wet season over the Amazon in 2020, when anthropogenic influences (e.g. biomass burning) are minimal while deep convection still occurs regularly. The aircraft measurements are coordinated with those from the Amazon Tall Tower Observatory (ATTO) to study the forest influence, e.g. the emissions of biogenic volatile organic compounds, on the troposphere from low to high altitudes, related to vertical transport by deep convective clouds.
  • The third will be CAFE‐Pacific in the area of Indonesia and the Pacific warm pool, where deep convection is most intense on Earth. The region is sometimes referred to as the “heat engine” of the globe. While it is expected that continental (forest) emissions dominate tropospheric chemistry in CAFE‐Brazil, during CAFE‐Pacific clean marine conditions will be predominant. The combination of Amazon‐ and Pacific‐pristine conditions will provide fundamental insights into natural tropospheric chemistry and aerosol processes in terrestrial and marine environments in the tropics. Since tropical forest and urban‐industrial influences are also present in Indonesia, the comparison with measurements from the earlier CAFE missions will be very valuable in view of global processes and anthropogenic impacts.

Logistics, instrumentation, work program
The CAFE‐Pacific aircraft measurements will likely be performed from Cairns in North Australia from where both Indonesia and the Pacific warm pool (e.g. Micronesia and the Solomon Islands) can be easily reached. Cairns offers excellent infrastructure for aircraft operation, and has been used for meteorological studies of deep convection in the past. The convectively most intense period is December – February, which will be aimed for in the period 2022 – 2023. The number of HALO flight hours needed on location is about 100, and by including transfer and test flights, a total of 160 flight hours are planned.

The payload is planned to be the same as the CAFE‐Brazil payload. This payload offers a unique instrumental combination that allows to study simultaneously a comprehensive set of radical and trace gas species to study the oxidative chemistry, aerosol formation and initial growth, as well as aerosol composition and CCN properties at an unprecedented level of completeness and precision. The instrumentation includes in situ measurements of numerous gas phase species, aerosol and photochemical properties (OH, HO 2 , H 2 O 2 , RO 2 , O 3 , NO, NO 2 , PAN/PAA, ClNO 2 , HCl, H 2 O, SO 2 , H 2 SO 4 , HOMs, clusters, NMVOC, OVOC, HCHO, CO, CH 4 ; aerosol composition (non‐refractory), aerosol number, aerosol size distribution, CCN, BC, actinic flux).

Preparing and conducting the CAFE‐Pacific mission, analyzing the data and integral interpretation combined with state‐of‐the‐art modelling will comprise a three‐year program.


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Scientific instruments and payload configuration

  • List of scientific instruments for the mission:

DescriptionPrincipal investigator​Institution
HALO-CIMSDescriptionJohn CrowleyMPI-C Mainz
HALO-MGCDescriptionJonathan WilliamsMPI-C Mainz
TRIHOPDescriptionHorst FischerMPI-C Mainz
PTR-MS TOFDescriptionJonathan WilliamsMPI-C Mainz
HORUSDescriptionHartwig HarderMPI-C Mainz
AMETYSTDescriptionJohannes Schneider, MPI-C Mainz
HALO_C-ToF-AMSDescriptionJohannes SchneiderMPI-C Mainz
ALABAMADescriptionJohannes SchneiderMPI-C Mainz

Cabin and exterior configuration of HALO for the mission

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HALO flights for this mission

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More information

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