This study evaluated the possibility to improve OMItroposphericNO2 retrieval over China by creating and exploiting an aerosol vertical profile climatology database from 9 years of CALIOP observations. Among other elements, it shows the potential benefits to use satellite observations in a synergistic way (OMI–MODIS-CALIOP) and how to constrain better aerosol models in view of correcting aerosol scattering and absorption effects in UV-vis satellite measurements.
This notably leads to an update of the POMINO dataset from Lin et al. (2014, 2015).
Almost 3 months ago, on 2018.09.10, I had the privilege to defend my research thesis at Delft University of Technology. A big moment after 4 years of intensive collaboration with my colleagues of the Geoscience & Remote Sensing Department and KNMI and in the presence of several friends and relatives. An very strict protocol to follow according to the Dutch rules and tradition.
My thesis book is now available online as an Ebook here! Feel free to have a look if you are interested by aerosol layer height retrieval, UV-Vis satellite measurements such as OMI, troposphericNO2, air quality and climate observations. My main papers are concatenated there.
Analyses of the trends is possible but overall a challenging and sensitive task. Over 20 years, very different sensor techniques, instrument specificities & degradations, variable pixel sizes, cloud detection possibilities etc… A lot of works to harmonise these data!
Atmosphericaerosol are particles suspended in the air. Their sources are very mixed. Aerosol can be man-made or natural: e.g. smoke, desert dust, sea spray, nitrates and sulfates. The aerosol effects on the sunlight modify the shortwave radiation field in the atmosphere. This directly impacts the climate and the satellite observations devoted to ocean surface, land surface, vegetation, and atmospheric gases. Furthermore, heavy load of aerosols affects our air quality.
In spite of many progresses during the last 10-20 years, aerosol observations from space-borne instruments remain incredibly complex. One of the main reasons is their heterogeneity: aerosols are everywhere, but with very variable quantities spatially (horizontally and vertically!), and temporally. And, as highlighted by this NASA picture, aerosol types are also very heterogeneous! Retrieving all these parameters from single satellite measurements, without ambiguity with respect to surface characteristics and clouds, is the difficult task of the scientists working with atmospheric satellite measurements. Many works to continue to do…
NASA WebPage “Just another Day on Aerosol Earth” here
This paper is based on the last developments we published during 2016, 2017, and 2018. During these years, not only the OMI cloud algorithm was improved (Veefkind et al., 2016), but also an OMIaerosol layer height (and optical thickness) neural network algorithm was developed (Chimot et al., 2017, 2018). This time, we directly evaluate the impacts of these developments to correct of aerosol absorption and scattering effects in the visible spectral range in view of retrieving troposphericNO2, an important trace gas affecting air quality in urban and industrialised areas.
This paper is based on the work of 2017, in which a neural network algorithm was developed for retrieving aerosol layer height (ALH) from the OMI O2-O2 visible measurements. This time, we directly compare our retrievals with CALIOPaerosol observations and evaluate the spatial patterns on several remarkable case studies including urban pollution, biomass burning events and a Saharan dust outbreak!
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.
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 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.
It remains, overall, challenging for satellite measurements acquired in the visible spectrum to easily distinguish dust particles from transparent clouds or cirrus.
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).
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.
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!
CAMS, Saharan dust and smoke over France and UK here
GOME-2 AAI index by KNMI, EUMETSAT AC SAF & TEMIS here