Overview

Project Highlights:

  • Perform the first ever satellite retrievals of atmospheric isoprene
  • Develop and apply state-of-the-art satellite retrieval algorithms
  • Produce a long-term global isoprene dataset that will be used throughout the atmospheric modelling community

 

Overview:

It is well established that terrestrial vegetation emits a diverse range of reactive biogenic volatile organic compounds (BVOCs) into the atmosphere, which serve important roles in the biosphere, influencing global atmospheric chemistry and affecting climate. The most important BVOC is isoprene, whose annual emissions of ~500 Tg C / yr comprise nearly half the total global BVOC budget.

Isoprene is a precursor for tropospheric ozone, which is the third most important greenhouse gas and a surface air pollutant that affects the human respiratory system and agricultural crop yields. Tropospheric ozone is also the dominant source of the hydroxyl radical (OH), which initiates tropospheric oxidation chemistry, and is an important chemical sink of other greenhouse gases (e.g., methane). Isoprene is also a precursor for secondary organic aerosols (SOA) that affect air quality, cloud properties, and influence direct radiative forcing.

Accurate knowledge of isoprene emissions is therefore critical for understanding and predicting the atmospheric distributions of tropospheric ozone and SOA. Satellite observations of atmospheric isoprene would provide an unprecedented opportunity to conduct detailed studies of the biosphere-atmosphere exchange of terrestrial ecosystems, and through inversion of the retrieved measurements, would enable continuous top-down monitoring of global isoprene emissions over multiple years. Over large, remote, and often high isoprene emitting regions such as the tropics, satellites offer the only means of observing ecosystem dynamics.

This project offers an exciting opportunity to obtain the first spaceborne measurements of isoprene from the Infrared Atmospheric Sounding Interferometer (IASI) instruments through the development and application of an optimal estimation retrieval algorithm which utilises a new high resolution IR absorption cross-section dataset. The IASI isoprene retrievals will be critically assessed over different ecosystems, through direct and indirect comparisons with campaign field data and atmospheric model outputs, provided by world-leading groups and teams.

Figure 1: Plants in many different ecosystems, such as rainforests, emit isoprene in huge quantities thereby influencing global atmospheric chemistry.

Methodology

The student will use data from the series of IASI nadir-sounding spectrometers on EUMETSAT’s Metop-A (launched 2006), MetOp-B (launched 2012) and MetOp-C (scheduled for launch in November 2018) satellites, each offering twice daily global coverage through a swath width of 2200 km, with a 12 km sub-satellite pixel footprint, and delivering thousands of radiance observations per day. To retrieve isoprene from IASI radiances the student will adapt an existing retrieval code (ULIRS) with a proven credibility in determining trace gas measurements from IASI spectra. The aim is to retrieve weekly-to-monthly observations of column-integrated isoprene at horizontal resolutions of less than 5°×5° over multiple years (2007 to present). The IASI isoprene measurements will be critically evaluated against a wealth of in-situ observations, and compared with estimates from chemical transport models (CTMs) such as GEOS-Chem. The creation of this global dataset will provide invaluable data for improving both BVOC emission and CTMs.

Training and Skills

Throughout this project the student will receive extensive training to become adept in (1) remote sensing techniques, satellite retrieval algorithms, laboratory and atmospheric spectroscopy; (2) environmental science (e.g., atmospheric physics and chemistry) and environmental issues (e.g., climate change, air pollution); (3) data visualisation and data analysis techniques; (4) methods to compare satellite datasets with in situ and model data; (5) key programming languages (e.g., python, IDL) and the use of high performance computing (HPC) environments; (6) transferrable skills such as oral and poster presentations, publication writing, networking, grant applications, time management, data management, and team working.

 

Timeline

Year 1: Perform retrievals of isoprene from IASI radiance spectra.

Year 2: Finalise isoprene retrievals and begin a critical assessment over different ecosystems.

Year 3: Finalise the critical assessment by direct and indirect comparisons with campaign field data and atmospheric model outputs.

Partners and collaboration (including CASE)

This project offers the chance to interact and collaborate with world-leading scientists who regularly measure isoprene on field campaigns using in situ techniques. The student will also collaborate with modellers within the National Centre for Earth Observation (NCEO). The NCEO (www.nceo.ac.uk) is a distributed NERC centre providing the UK with national capability in EO science. The student will therefore be exposed to a wide range of research techniques in a multi-disciplinary research environment.

Further Details

Based in the Earth Observation Science (EOS) group at the University of Leicester, Dr Jeremy Harrison is an expert in atmospheric spectroscopy and the remote sensing of trace gases. Dr Michael Barkley is an expert in investigating mapping reactive carbon emissions from space using a combination of models and multiple satellite data sets. Dr David Moore is an expert in remote sensing of trace gases, particularly using IASI data.

Interested applicants are invited to contact Dr Jeremy Harrison (jh592@leicester.ac.uk). Note that all potential applicants are strongly advised to make contact before applying.

https://www2.le.ac.uk/departments/physics/people/jeremyharrison/jeremyharrison