Sarah Safieddine

First simultaneous space measurements of atmospheric pollutants in the boundary layer from IASI: a case study in the North China Plain

In this paper we investigate a severe pollution episode that occurred in Beijing, Tianjin, and the Hebei province in January 2013. The episode was caused by the combination of anthropogenic emissions and a high-pressure system that trapped pollutants in the boundary layer. Using IASI (Infrared Atmospheric Sounding Interferometer) satellite measurements, high concentrations of key trace gases such as carbon monoxide (CO), sulfur dioxide (SO2), and ammonia (NH3) along with ammonium sulfate aerosol ((NH4)2SO4) are found. We show that IASI is able to detect boundary layer pollution in case of large negative thermal contrast combined with high levels of pollution. Our findings demonstrate that anthropogenic key pollutants, such as CO and SO2, can be monitored by IASI in the North China Plain during wintertime in support of air quality evaluation and management.

A Global Assessment of Dissolved Organic Carbon in Precipitation

Precipitation is the largest physical removal pathway of atmospheric reactive organic carbon in the form of dissolved organic carbon (DOC). We present the first global DOC distribution simulated with a global model. A total of 85 and 188 TgCyr-1 are deposited to the ocean and the land respectively, with DOC ranging between 0.1 and 10 mgCL-1 in this GEOS-Chem simulation. We compare the 2010 simulated DOC to a 30-year synthesis of measurements. Despite limited measurements and imperfect temporal matching, the model is able to reproduce much of the spatial variability of DOC (r= 0.63), with a low bias of 35%. We present the global average carbon oxidation state ( OSc¯) as a simple metric for describing the chemical composition. In the atmosphere, −1.8≤OSc¯≤−0.6 and the increase in solubility upon oxidation leads to a global increase in OSc¯ in precipitation with −0.6≤OSc¯DOC≤0.

Observation of Air Pollution over China Using the IASI Thermal Infrared Space Sensor

In this chapter we describe what is achievable in terms of pollutant tracking from space using observations provided by thermal infrared remote sensors. After a general introduction on infrared remote sensing, we exploit the data provided by the Infrared Atmospheric Sounding Interferometer (IASI) missions onboard the Metop series of satellite to illustrate pollution detection at various spatial and temporal scales. Then, we focus on air pollution over China and discuss three case studies involving different pollutants. The first example discusses the geophysical conditions for detection of ammonia (NH3) and sulfur dioxide (SO2), both precursors of particulate matter (PM). The second case illustrates the seasonal variation of ozone (O3), in particular during the monsoon period. The third case shows the local accumulation of enhanced levels of carbon monoxide (CO) when pollution episodes occur.

IASI/METOP sounder contribution for atmospheric composition monitoring

During the last decades, remote sensing sounders have demonstrated their capability for monitoring atmospheric composition and pollution. With now 5 years of continuous observations of IASI instrument, flying on board of MetOp-A platform, we are able to analyze long term variations of atmospheric molecules. This article involves new tendencies for CO and CO2 molecules based on IASI LIC radiances. Comparisons with total columns are also provided.Water vapor is a key gas for the climate system. Its radiative properties make it the strongest atmospheric greenhouse gas. But above all, humidity largely controls dynamic processes which regulate the global circulation of the atmosphere and therefore the climate. Tropospheric water is also associated with two major climate feedbacks, namely cloud and water vapour feedbacks. However, there is still an insufficient quantitative understanding of the global hydrological cycle to ensure reliable climate predictions. Measurements of the isotopologues ratios of water vapour ( D) in the atmosphere give information on exchange processes, which are helpful for constraining the atmospheric water budget and for identifying and quantifying the associated processes of the hydrological cycle. In this perspective the demonstrated capabilities of the Infrared Atmospheric Sounding Interferometer (IASI on MetOp) to measure water vapour isotopologues at any place twice a day, with relatively high spatial resolution and in a unique long term perspective (total period of 15 years) are of great interest for climate research. Due to the high spatial and temporal variability of water (latitudinal and vertical), retrieving isotopologues ratios at the required accuracy is a challenging task. In order to get meaningful results the retrieval needs to be well constrained. Using the optimal estimation method, this constraint is here applied using an a priori probability density function containing correlation information between HDO and H2O.We present in this work retrievals of D from IASI radiance measurements.We show that these are mainly sensitive to D in the troposphere between 3 and 6 km. We discuss our choice of a priori information as well as other retrieval parameters. Spatial and temporal distributions of D in selected regions are used to evaluate and to exploit our retrievals. In particular we present times series at both a subsidence site (Izana) and a convective site (Darwin) and monthly variations of D latitudinal gradient. Comparisons of our results with isotopologue-enabled Global Circulation Model (LMDz) will also be presented.