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Recent evolution of NOx and VOCs emissions in urbanized regions of the the Northern Hemisphere : impact on tropospheric ozone


According to the World Health Organization, 4.2 million deaths are attributable to exposure to air pollution around the world, making air quality improvement a major environmental issue. Significant efforts have been made in industrialized countries, such as Europe, since the 1990s to reduce emissions of major pollutants. More recently, developing countries, such as China, are also implementing mitigation strategies to reduce their pollutant emissions with the first effects starting to be visible.

The assessment of emission reduction policies is generally based on official emission inventories, derived from the declaration of activities, statistical data, etc, but often highly uncertain (e.g. 50 to 200% of uncertainties on the emissions due to transportation). Being able to accurately monitor the evolution of emissions and the trend of pollutants in urbanized regions is therefore an important issue for evaluating environmental policies and understanding the processes that drive these evolutions. In addition, a recent International Assessment Report on Tropospheric Ozone ( shows the complexity of establishing ozone trends for the recent period, as well as to identify the driven processes of this evolution, the proportion of the anthropogenic contribution (precursor emissions, nitrogen oxide, NOx, and volatile organic compounds, VOCs) being still difficult to quantify compared to the natural contributions.

In the framework of the PhD, we propose to study the evolution of NOx and VOCs emissions since 2005 in Europe and China, two regions with different trajectories in terms of emissions, and to quantify the impact of the emission changes on ozone production. The work will be based on the PYVAR-CHIMERE inverse modeling system, which will assimilate the NO2 and HCHO satellite observations of the OMI instrument over the 2005-2018 period. One of the challenges will be to separate the biogenic and anthropogenic contributions for the VOC emissions, the most unknown ones. Co-emissions between VOCs and NOx could be used to better constrain anthropogenic emissions of VOCs.  We will also explore the potential of the TROPOMI instrument, whose first data is available since July 2018, and its high spatial resolution (7x3.5 km2) to derive high-resolution optimized emissions and evaluate the capabilities to separate anthropogenic and biogenic emissions. Comparative studies between Europe and China will be conducted to identify the specificities of the respective regional plumes of pollution.

Desired profile

The candidate should have a Master degree with knowledge of remote sensing and/or physics and chemistry of the atmosphere and/or of applied mathematics. Knowledge of a programming language and the Linux / Unix environment would be highly appreciated.

Structure description
Host laboratory : LISA, Créteil
PhD/research supervisor : DUFOUR Gaëlle
Email of PhD/research supervisor :
Offer CNES supervisor : DENIEL Carole

To apply, we invite you to contact the PhD/research supervisor and fill, with him/her, the co-financing part of the online application form (Reply to the offer) by April 1st, 2019.


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