Must read – A warning from 15,000 world scientists


25 years ago, in 1992, 1700 independent scientists already told us in their “World Scientists – Warning to Humanity – 1st Notice”. And yet, it seems that was not sufficient. This month, a second notice was submitted, this time by about 15,000 worldwide scientists. And the message is still quite clear: “the world is going toward catastrophic biodiversity loss and untold amounts of human misery” and we have little time to act before avoiding this.

This may sound like an unrealistic, even irrational alarmist message. But it is worth reminding that, since its beginning, science work (and scientists) is beforehand based on observations, facts, interpretations with evaluation of uncertainties, implementing models that are then continuously and thoroughly evaluated  by confronting with observations.

This article is relatively short and very simple to read. No need to be an expert, every citizen can easily understand all the messages. I think this is the duty to each of us to take some minutes for reviewing it, and then thinking about our actions. Especially, the causes are nowadays well identified: rapid population growth, deforestation, agricultural production, and rising greenhouse gases from burning fossil fuels that has triggered and driven our climate change.

For this last one, in spite of continuous denial and unjustified claims (especially in the USA), the odds from IPCC and COP23 are pretty clear: CO2 – Carbon dioxide and CH4 – Methane amount in the atmosphere are historically unique, and the emissions keep increasing. Some of these increases are also even observable from space.

Atmospheric levels of CH4 – Methane from 2003 to 2005 and 2008 to 2010, showing  increased concentrations in the latter dataset (in red). The newly released ‘Climate Research Data Package No. 3’ covers more than one decade (2003–14) of atmospheric data products used to get information on the sources and sinks of carbon dioxide and methane. The data products are available through the website: (Source ESA:


A positive sign: stratospheric O3 – Ozone hole over Antarctic is recovering. If our actions have allowed to create and then solved this problem, then we can still do something, at every level, about the greenhouse gases.

Several journals and websites forwarded this article. But I have the feeling yet it could reach more and more people and lead to further discussions and actions in our societies. Hope this is not too late…


More information?

  • Ripple et al., 2017: Full articles World Scientists’ Warning to Humanity, 1st and 2nd notices here. You can also endorse the 2017 article here
  • European Space Agency (ESA): CO2 – Carbon dioxide and CH4 – Methane on the rise here
  • CO2 – Carbon dioxide WebPage here
  • CH4 – Methane WebPage Here


No borders for particles! – Red Sun, Saharan dust and smoke over whole Europe

What happened on Monday 16th October 2017? From diverse countries (France, United Kingdom, the Netherlands, Finland), people reported to have observed a “red Sun”. This is a direct result of natural events, although issued from different sources and locations, which combined together over the whole Europe.

During a couple of days, between 16th and 18th October 2017, northern Portugal and Spain were victims of violent wildfires ravaging parts of their territory. These fires released large amounts of fine black particles, also named aerosols, that can absorb the Sun light.

Aerosol optical depth (AOD) (550 nm) simulated by CAMS forecasts of aerosol optical depth (AOD) show enhanced AOD extending from the Iberian peninsula CAMS) on 2017.10.16 (Source:

The Copernicus Atmosphere Monitoring Service (CAMS) forecasts of aerosol optical depth (AOD) show high values extending from the Iberian peninsula to the British Isles.

In addition to these fires, a tropical storm, named Ophelia, appeared 1300 km south-west of the Azores islands and some 2000 km off the African coast. Originally classified as a tropical storm, it was upgraded to a hurricane. The storm moved north-easterly, towards Spain and Britain, collecting sand from the Sahara desert. The related dust particles were then mixed with the black carbon from Portugal fires. Their scattering properties with the solar light led to this red Sun observed by many Europeans, instead of its natural yellow colour in clear sky or white/milky in presence of thin cloud.

The Ophelia storm as observed by the Sentinel-3 A satellite. Left: image on 11.102017, when Hurricane Ophelia was about 1300 km south-west of the Azores islands and some 2000 km off the African coast. Right: Brightness temperature of the clouds at the top of the storm, some 12–15 km above the ocean, range from about –50°C near the eye of the storm to about 15°C at the edges on17.10.2017. Copyright ESA (Source:

The dust particles can be observed through the visible colour composite image from the MODIS instrument, on-board Aqua, on 16.10.2017: some yellow colours are mixed with some thin clouds.

MODIS-Aqua visible image on 16.10.2017 (left) and 17.10.2017 (right) acquired in early afternoon: dust particles in yellow over France, united Kingdom and the Netherlands (Source:

It remains, overall, challenging for satellite measurements acquired in the visible spectrum to easily distinguish dust particles from transparent clouds or cirrus.

Aerosol Absorbing Index (AAI) from GOME-2 sensor on-board MetOp-B platform on 16-17-18.10.2017. Copyright KNMI, EUMETSAT and the Atmospheric Composition (AC) Satellite Applicattion facilities (SAF) (Source:

GOME-2 and OMI satellite sensors also reveal through the AAI index, with high values in red, the presence of black absorbing particles (i.e. smoke from biomass fires in Portugal) in large quantity. These particles were released in the North of Portugal before being transported to the North (UK) and then East (the Netherlands, Finland and Russia).

Aerosol Absorbing Index (AAI) from OMI sensor on-board the Aura platform on 16-17.10.2017. Copyright KNMI, FMI and NASA. (Source:

Although the aerosol particles were the visible part of the pollutant transport, IASI sensor revealed the additional presence of CO – Carbon monoxide, a toxic gas issued from incomplete biomass combustion by the fires. CO is a gas pollutant that cannot be visible in the eyes. It can only be measured in the shortwave or thermal infrared spectrum such as the IASI measurement.

Total CO – Carbon monoxide column observed by the IASI sensor on-board MetOp platforms. Copyright LATMOS-ULB & AC SAF (Source:

This impressive pollutant transport is quite unique due the combination of heterogeneous sources at different locations. But, similar episodes of particle and gas pollution were observed last Summer in Canada as well, as described in our last post Canada wildfires from space and ground – Seeing beyond the flames: a series of observations.

All these worldwide satellite pictures very well illustrate that, although emissions can be national, mix of pollutants and their transport are not contained within the limits of borders. This shows how much pollution and their scientific and societal challenges are an international concern!

More information?

  • CAMS, Saharan dust and smoke over France and UK here
  • GOME-2 AAI index by KNMI, EUMETSAT AC SAF & TEMIS here
  • OMI AAI maps on the TEMIS website here
  • The Ophelia storm as seen by the ESA Sentinel-3 mission here
  • OMI sensor here & IASI sensor here
  • Canada wildfires from space and ground – Seeing beyond the flames: a series of observations WebPage here

Don’t miss #GRS_TROPOMI event, a series of post on “why are we excited this week about #TROPOMI #Sentinel5P launch?!”


Why are we (I and my colleagues) that excited this week? Why is TROPOMI so much important for the new coming era in air quality & climate satellite era?

Throughout the week, we will post more information on our GRS TU Delft website and also be using the #GRS_TROPOMI on social media (Twitter and Instagram) as we explain more about the mission, its goals, and how it all works in relation to the goals and work being done in our department. The week will culminate with the Sentinel-5P launch event taking place at the Space Expo in Noordwijk.


More information?


20th OMI Science Meeting at NASA Goddard Space Institute

During 3 days, from 12 to 14 September 2017, I had the pleasure to attend, with my KNMI colleagues from the R&D satellite department, the 20th OMI Science Team Meeting hosted by NASA Goddard Space Institute in Greenbelt MD (close to Washington DC) in the USA.

Group picture at NASA, Goddard Space Institute, Greenbelt MD, Virginia, USA, 2017.09.13 in front the morning and A-Train satellite constellation, with all our OMI colleagues.

Despite its quite advance age for a satellite mission (13 years old!), OMI is still delivering remarkable measurements about our atmospheric composition and air quality. So many talks and discussions on the aerosol global record over cloud-free scenes and above clouds, decade global volcanic SO2 – Sulfur dioxide missions, the use of OMI data by air quality model simulations to inform air quality policy, the case studies on emissions monitoring and to support authorities and clean-tech industry, the new generation of the Quality Assurance For Essential Climate Variables (QA4ECV), the evolution in the ozone trends and related mechanisms, and of course the future with the forthcoming TROPOMI (Sentinel-5 Precursor) mission, TEMPO (NASA Geostationary) and TROPOLITE.

I was honoured to present the status of our work on the retrieval of aerosol layer height from the OMI visible band using machine learning technique, and the results with single day CALIOP aerosol along-track observations.

Chimot J., Veefkind P., van Ouwerkerk G., Vlemmix T., Levelt P., Aerosol layer height retrieval from OMI and neural network- Possibility for a 13-year time series?, 20th OMI Science Team Meeting, NASA Goddard, Greenbelt MD, Virginia, USA, 2017.09.12 (Source:

Several nice social moments accompanied us during these 3 days:

  • The Nationals baseball game on Wednesday 13th September evening in Washington DC
  • The guided tour by NASA during lunch break, a great opportunity to see the control rooms of the Aura (OMI spacecraft!!), Aqua and Landsat missions!


I am very grateful to all the organizers for this inspiring meeting, and my current promotors (Dr. Pepijn Veefkind, Prof. Dr. Pieternel Levelt & Dr. Tim Vlemmix)!

In spite of being glad of having been part of this adventure, I cannot stop myself thinking this may have been my very last OMI conference, before finishing my current research project and starting new professional & personal adventures (still in satellite & atmospheric community of course!). But this last point will be specifically mentioned later in future weeks. Stay tuned!


More information?

Preparing TROPOMI to join OMI in space in Autumn 2017

Loading Sentinel-5P (Source:
S5P leaves UK
Moving Sentinel-5P on its way from Airbus Defence & Space in Stevenage, UK, to Standsted airport (Source:

Finally, that’s official! TROPOMI, on-board Sentinel-5 Precursor, the 1st European operational satellite mission devoted to air quality, ozone & climate monitoring, should be launched within the next weeks. And this looks very impressive!

What are the new signs? The Sentinel-5P campaign kicked off, the satellite left UK to Russia some days ago, and several media allow to follow it (through ESA blogs and Twitter accounts). All of these new elements have appeared just some days before our very soon 20th OMI Science Team Meeting focused on the last 13-year developments and data sets.

Let’s keep the fingers crossed that OMI can continue to fly and acquire new observations together with its successor TROPOMI. Autumn 2017 promises to be a very exciting season for our community!

More information?

  • TROPOMI WebPage here
  • OMI WebPage here
  • Sentinel-5P launch campaign kicks off on ESA blog here
  • Farewell to Sentinel-5P on ESA blog here
  • The 20th OMI Science Team Meeting WebPage announcement here


Neural Network, NO2 and aerosol height retrievals at the next 20th OMI Science Team Meeting at NASA, USA

© Rendering of Ozone Monitoring Instrument (OMI) on board of AURA in flight (Source:

The 20th OMI Science Team Meeting will be held at NASA Goddard in Greenbelt MD, USA from Tuesday September 12 through Thursday September 14, 2017. With nearly 14 years of data and the impending launch of TROPOMI on board-Sentinel-5 Precursor, there is much to discuss within the OMI (& TROPOMI) team and user community regarding the current state of OMI, trends and longer-terms records, comparisons with (satellite) data sets, and the validation of OMI data. This meeting will highlight recent OMI results as well as address research plans and program goals for the coming year.

On Tuesday afternoon, at 14:00 during the aerosol – cloud session, I will have the great opportunity to present the status of our activities. In particular, focus will be on the development, application and validation of the OMI aerosol layer height retrieval based on a neural network (i.e. machine learning) approach, and the correction of aerosol radiation effects in the OMI tropospheric NO2 observations.

Gotten curious? See you there then!


More information?

Measuring CO2, temperature and humidity in our office



Since beginning summer, tests and works have been undertaken at our office at the Geoscience & Remote Sensing (GRS) department of TU Delft to improve temperature conditions while working. In order to support these tests, some measurements have been acquired.

And it is still very interesting to observe not only the temporal variability of temperature, CO2 – Carbon dioxide concentrations and relative humidity but also the apparent nice correlations between them! Especially, CO2 in our office and temperature seem to follow similar diurnal variation. Of course, these variables, at a such local scale, are also strongly dependent on external parameters such as wind transport, the number of people present in the room, whether the windows are open etc…


More information?

  • CO2 – Carbon dioxide, an important greenhouse gas and its impacts on our changing climate here