Winter has come in Europe – UV dose estimated from space

No doubt winter has come in Europe! The Earth inclination has changed.

As observed last Winter with GOME-2 UltraViolet (UV) measurements, a big change in the effective UV irradiance reaching the Earth surface is also seen over the day between last July and nowadays.

Here below is an example with the estimated reduced Vitamine D production in our skin as a direct consequence. These pictures are from the ESA / KNMI Tropospheric Emission Monitoring Internet Service (TEMIS). Satellite UV dose is computed from the assimilated global O3 – ozone field at local solar noon, and with surface downwelling solar (SDS) radiation & cloud information measured by the Meteosat Second Generation (MSG) satellites led by the EUMETSAT agency.


More information

  • WebBlog on Vitamin D estimated from GOME-2 UV measurements here
  • Clear-sky UV index forecast from the Tropospheric Emission Monitoring Internet Service (TEMIS) here, Credit ESA / KNMI

A new desert dust aerosol climatology from 9-year CALIOP observations over Asia – Very happy to co-author new ACP paper of Proestakis et al. (2018), from National Observatory of Athens (NOA)!

Spatial distribution of the seasonal mean CALIPSO AOD, D_AOD, optical depth difference between AOD and D_AOD (non-dust AOD), and the percentage of D_AOD with respect to the total AOD for the domain between 65–155 E and 5–55 N and for the period January 2007–December 2015 (Proestakis et al., 2018)

A recent work achieved by my colleagues of the National Observatory of Athens (NOA): 9 years of observations acquired by the CALIOP space-borne instrument were combined with EARLINET ground-based measurements to provide a climatology of desert dust particles over South and East Asia.

Having such a knowledge is important for many research studies focused on atmospheric transport and climate effect of dust.

You can see more details on my webpage here, and the paper of Proestakis et al. (2018) published in the Atmospheric Chemistry and Physics (ACP) journal 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?

Volcanic ‘plumerang’ or boomerang-like return of a volcanic plume with potential health-risk in Iceland

a) Location map of the Holuhraun eruption site (lava flow extent in red) and the two populated areas: Reykjavik, city capital area, and Reykjahlio. b) Holuhraun eruption during the January 2015 field campaign – activity exclusively effusive lava flow width ~ 50 m (Source: Ilyinska et al., 2017)

All volcanoes are on satellite watch due to their continuous gas emissions, in particular SO2 – Sulphur dioxide, and their impacts after eruptions on air quality and landslide risks. A new study, from University of Leeds (Ilyinska et al., 2017), has found a previously undetected potential health risk from the high concentration of small particles – aerosols – found in a boomerang-like return of a volcanic plume.

This study focused on the evolution of the plume chemistry from the 2014-2015 Icelandic Holuhraun lava field eruption and found a second type of plume that impacts air quality. This second plume had circled back to Icelandic cities and towns long after the health warning about the initial plume had been lifted.

The 2014–2015 Holuhraun eruption in Iceland, emitted ∼11 Tg of SO2 into the troposphere over 6 months, and caused one of the most intense and widespread volcanogenic air pollution events in centuries, exceeding hourly air quality standards (350 μg/m3) for SO2 on 88 occasions in Reykjahlíð town (100 km distance), and 34 occasions in Reykjavík capital area (250 km distance). Average daily concentration of volcanogenic sulphate particles exceeded 5μg/m3 on 30 days in Reykjavík capital area.

2 types of plume impacted the downwind populated areas:

  • The first type was characterised by high concentrations of both SO2 gas and fine particles,
  • The second type had a low SO2 gas concentration.

Ilyinska et al. (2017) suggest that this second type was a mature plume where sulphur had undergone significant gas-to-aerosol conversion in the atmosphere. This second plume had circled back to Icelandic cities and towns long after the health warning about the initial plume had been lifted. The return of this second mature plume, named as a ‘plumerang’, meant that the sulphur dioxide (SO2) levels were reduced and within the European Commission air quality standards and, therefore, there were no health advisory messages in place.

Dispersion model of hourly-mean SO2 (left) and sulphate aerosol (SO42−, right) surface mass concentrations (μg/m3) in September 2014. Panels (a) and (b) show a mature low Sgas/SAerosolplume reaching the Reykjavik capital area on 14 and 20 September 2014 (right), whereas SO2 mass concentrations are very low in the same location on those days (left). Panel (c) shows a ‘near-miss’ situation with a highly sulphate-rich mature plume narrowly passing the densely populated south-east coast of Iceland on 8 September 2014.

However, both types of plume were rich in fine aerosol, sulphate (on average ∼90% of the aerosol mass) and various trace species, including heavy metals. The fine size of the volcanic aerosol mass (~75–80%), combined with chemical components, have potential adverse implications for environmental and health impacts (e.g. exacerbating asthma attacks). The concentrations of these trace metals did not reduce as the plume matured and included heavy metals found in human-made air pollution that are linked to negative health effects. But, only the dispersion of volcanic SO2 gas was forecast in public warnings and operationally monitored during the eruption.

On at least 18 days during the 6-month long eruption the plumerang was in the capital city of Reykjavík, while the official forecast showed ‘no plume’.” (said lead author, Dr Ilyinskaya from the Institute of Geophysics and Tectonics at Leeds). “We spoke to people living in Reykjavik who described a burning sensation in the throat and eyes when the SO2 levels would have been well within air quality standards but the particle-rich plumerang would have been over the city.”

For the future, Ilyinska et al. (2017) strongly recommends that in future gas-rich eruptions both the young and mature plumes should be considered when forecasting air pollution and the dispersion and transport pattern of the plume.

The gas-to-particle conversion is quite typical for some so-called trace gases that are also precursor of aerosol particles, such as NO2 – Nitrogen dioxide, and SO2.


More information on:

  • WebPage on aerosol particles here
  • Previous WebPost on “Volcanoes on Sentinel-2 and OMI satellites watch – First global emission maps!” here
  • Ilyinska et al. (2017): Evgenia Ilyinskaya, Anja Schmidt, Tamsin A. Mather, Francis D. Pope, Claire Witham, Peter Baxter, Thorsteinn Jóhannsson, Melissa Pfeffer, Sara Barsotti, Ajit Singh, Paul Sanderson, Baldur Bergsson, Brendan McCormick Kilbride, Amy Donovan, Nial Peters, Clive Oppenheimer, Marie Edmonds. Understanding the environmental impacts of large fissure eruptions: Aerosol and gas emissions from the 2014–2015 Holuhraun eruption (Iceland). Earth and Planetary Science Letters, 2017; DOI: 10.1016/j.epsl.2017.05.025 here
  • “Volcanic ‘plumerang’ could impact human health” on geology page here


New book: climate atlas and challenges due to warming climate


A new book that I strongly recommend to my French fellows (or anyone speaking French)!

Written by Dr. Francois-Marie Breon, and Gilles Luneau, it greatly explains the climate system, its past story and what we know (with high certainty) about its warming future and the consequences. Nicely illustrated, it also summarizes the planned and potential worldwide initiatives to face the on-going changes.

Non-experts and experts may appreciate this book!

Global ammonia hot-spots revealed by AIRS!

Aqua Ammonia
Trends of AIRS NH3 from 2002 to 2013 (Source: Warmer et al., 2017)

For the first time, a University of Maryland-led team (Warmer et al.) revealed, in Geophysical Research Letters, a global atmospheric NH3 — Ammonia from 2002 to 2016 over four of the world’s more productive agricultural regions: United States, Europes, China and India. All these countries show increased NH3 concentrations!

NH3 concentrations are estimated from the NASA’s Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua satellite. Like NO2 – Nitrogen dioxide, NH3 is part of the nitrogen cycle and a precursor of ammonium and nitrate aerosols. Excess reactive nitrogen reduces biodiversity and causes harmful algal blooms and anoxic conditions. Dry deposition of gaseous ammonia may have substantially greater adverse impacts on ecosystem health than deposition of ammonium in aerosols or precipitation. The main sources of atmospheric NH3 are farming and animal husbandry involving reactive nitrogen ultimately derived from fertilizer use. The rate of these emissions is also sensitive to climate change.

In the abstract, Warmer et al., (2017) says: “Significant increasing trends are seen over the U.S. (2.61% yr-1 ), the European Union (EU) (1.83% yr-1 ), and China (2.27% yr-1 ). Over the EU, the trend results from decreased scavenging by acid aerosols. Over the U.S., the increase results from a combination of decreased chemical loss and increased soil temperatures. Over China, decreased chemical loss, increasing temperatures, and increased fertilizer use all play a role. Over South Asia, increased NH3 emissions are masked by increased SO2 – Sulphur dioxide and NOx – Nitrogen oxides emissions, leading to increased aerosol loading and adverse health effects”.


More information:

  • Warner, J. X., R. R. Dickerson, Z. Wei, L. L. Strow, Y. Wang, and Q. Liang (2017), Increased atmospheric ammonia over the world’s major agricultural areas detected from space, Geophys. Res. Lett., 44, doi:10.1002/2016GL072305 here
  • The NASA AIRS sounder here 

Volcanoes on Sentinel-2 and OMI satellites watch – First global emission maps!

Colima volcano (Source:
Annual mean atmospheric SO2 columns from Indonesian volcanoes, estimated from the OMI satellite observations (Source:, credits: Jesse Allen / NASA’s Earth Observatory)

Atmospheric SO2 is not only emitted by humans (such this plume in Iraq) but also by volcanoes…

Volcanoes are on watch by satellite observations. This is of high importance as, about 22 volcanoes are active, and 1500 potentially active, around the world.

Optical sensors, such as Sentinel-2, are exploited to track their continuous eruptions (through thermal anomalies at the surface) and to assess the health of plant life and agriculture around the volcanoes. The knowledge of the extent of eruptive deposits is crucial for assessing a volcanic event and any follow-on landslide risk and the size of the affected area.

Furthermore, volcanoes do not only affect the land surfaces but also the atmosphere! They are responsible of continuous gas emissions such as water vapour laced with heavy metals, CO2 – Carbon dioxode, hydrogen sulfide and SO2 – Sulfure dioxide, among many other gases. Cumulative daily and big eruption emissions can be very significant.

The Dutch-Finnish OMI satellite missions provides with high values of atmospheric SO2 measurements. A research team from Michigan Technological University created the first, truly global inventory for volcanic SO2 emissions using OMI data. The publication in Scientific reports mentions that each year volcanoes collectively emit 20 to 25 million tons of SO2 into the atmosphere

The data set will help refine climate and atmospheric chemistry models and provide more insight into human and environmental health risks.

More information on:

How to fight against big (and complex) data set Neural network vs. conventional methods


The community of atmospheric satellite observations is facing more and more challenges due to the non-stop increasing number of observations. The OMI air quality space-borne has already delivered ~542 million spectra per year since 2004. And its successor TROPOMI (to be launched later this year) is expected to increase this number by a factor of 20.

The most conventional atmospheric retrieval methods try to compete between high accuracy for each single observation and fast processing time. But usually, there is always a cost somewhere.

Since our recent and novel aerosol layer height retrieval algorithm developed with success for the OMI satellite instrument (more details here), we are trying to address the issue of big and complex data set with machine learning approach in general, and neural network techniques more specifically.

I could address my specific and subjective thoughts about this subject during the Second Post-gradual Teaching Workshop of the Buys Ballot Research School, at KNMI, on 2017.03.24.

Slides available here.

I specifically thank Dr. Sybren Drijfhou for the invitation & the organisation, Dr. Tim Vlemmix, Dr. Pieternel Levelt, Dr. Pepijn Veefkind and all my GRS & KNMI colleagues for the diverse and inspiring discussions the last months. They motivated this talk. And finally, I gratefully acknowledge Dr. Maarten Sneep, Dr. Jacob van Peet (KNMI), Dr. Folkert Boersma (KNMI / WU) and Dr. Antonio di Noia (SRON) for their valuable inputs to my survey (cf. Survey Variational vs. statistical approaches to atmospheric parameter retrieval).


New page CH4 – Methane!


A new page hast been created in the “Atmosphere composition” section: CH4 – Methane.

What is CH4? How is CH4 produced? Why shall we observe atmosphere CH4? A typical CH4 satellite map? Some reference CH4 satellite missions / products?

If you are interested, you can find some answers here. Do not hesitate to comment or ask for more questions, via Twitter or the contact form!