Current activities

What is it?

Since 2013, my current research (PhD) activity is focused on “Improved tropospheric NO2, aerosol and cloud retrievals from visible satellite measurements – Application to the the Dutch-Finnish Ozone Monitoring Instrument (OMI)“. This is done with Prof. dr. P.F. (Pieternel) Levelt, Dr. J.P. (Pepijn) Veefkind, and Dr. T. (Tim) Vlemmix from the ATMOS group of the Geoscience & Remote Sensing department of Delft (GRS, TU Delft – led by Prof. Dr. Herman Russchenberg), and the Royal Netherlands Meteorological Institute (KNMI) satellite department (led by Prof.dr. P.F. (Pieternel) Levelt).

The context

Nitrogen oxides (NOx = NO + NO2) play a key role in tropospheric chemistry. The Dutch-Finnish Ozone Monitoring Instrument (Levelt et al., 2006), launched in 2004 on NASA EOS-Aura satellite and led by KNMI, is a nadir-viewing imaging spectrometer that gives daily global coverage of key air quality components in the troposphere. The DOMINO(-2) project (Derivation of OMI tropospheric NO2) has allowed to develop a processing system that retrieves worldwide concentrations of NO2 in the troposphere (0-12 km altitude) using the Visible spectral measurements of the OMI satellite instrument.

Current representative OMI product DOMINO v2 does not explicitly account for the aerosol effects on the average light path, and therefore the impacts on the tropospheric NO2 retrieval. Like with OMI, these effects are not explicitly considered in the other UV-Vis satellite measurements (Valks et al., 2011). Since aerosols affect the top-of-atmosphere radiances in the Visible spectral band (Boersma et al., 2011; Leitao et al. , 2010), the net effect on the current OMI NO2 products is unclear.

Instead, a simple approach is implemented through the so-called OMI effective cloud parameters. These effective parameters are actually modified (or biased) in presence of aerosols. Therefore, implicitly, an aerosol correction is performed in the OMI tropospheric NO2 retrieval. But its overall accuracy is unclear at this stage.

Main objectives

The main objective is to answer the following questions: Do we need to take into account an explicit aerosol correction in the operational retrieval of tropospheric NO2 from the OMI Visible measurements? If yes, how to perform that?

To be able to answer these questions, the following issues have to be addressed:

  • What are the net aerosol effects on the Visible spectra radiance measured at the Top Of the Atmosphere?
  • How do the effective cloud parameters exactly response to the aerosol effects and correct them implicitly on the tropospheric NO2 retrievals?
  • How accurate is the current implicit aerosol correction?
  • Can we actually retrieve aerosol parameters from the OMI Visible spectra?
  • Can we exploit these aerosol parameters to mitigate their effects on the tropospheric NO2 retrievals?

Main achievements

The main achievements are the followings

  • Sensitivity analysis of the OMI tropospheric NO2 product (DOMINO v2, KNMI) & effective cloud (OMCLDO2, KNMI, NASA) datasets to the presence of aerosols

See paper of Chimot et al., (2016) published in the following AMT peer-review journal here, and summarized here.

  • Contribution to the updated OMCLDO2 cloud retrieval algorithm

See paper of Veefkind et al., (2016) here

  • Development of novel aerosol layer height and optical thickness (AOT) retrieval algorithms, based on a neural network approach, from the OMI 477 nm O2-O2 spectral band
  • Synergy of OMI and MODIS observations for an improved OMI aerosol layer height retrieval
  • Inter-comparison of collocated OMI aerosol layer height, CALIPSO aerosol profile and LIVAS vertical aerosol climatology database

See paper of Chimot et al., (2017) in the following peer-review AMT journal here, and summarized here.

  • Retrieval and evaluation of new OMI tropospheric NO2 vertical columns based on developed OMI aerosol and updated cloud retrieval algorithms


Additional tasks:

  • Publication of 3 peer-review papers, and 1 in preparation: 2 in the Atmospheric Measurement Techniques (AMT) journal, 1 in the Geophysical Research Letter (GRL) – AGU journal
  • Reviewer of 2 peer-review publications in ACP (Atmospheric Chemistry Physic) journal
  • Close collaboration with the KNMI satellite department (Dr. Folkert Boersma, Dr. Piet Stammes, Dr. Johan de Haan, Dr. Marteen Snep, Dr. Henk Heskes) and the National Observatory of Athens (NOA)
  • 7 oral & 3 poster presentations at international conferences


More information?

  • NO2 webpage here
  • Aerosol webpage here
  • NO2 product from OMI, and other missions, can be downloaded here
  • The DOMINO project (KNMI) here
  • The future of DOMINO, QA4ECV here
  • The OMI mission (PI: Prof.dr. P.F. (Pieternel) Levelt) :  here
  • The TROPOMI mission (successor of OMI) (PI: Dr. J.P. (Pepijn) Veefkind) here
  • The OMI effective clouds: paper here, and data here