Study of Chinese atmospheric pollution by modelling and remote sensing observations

As a result of its significant economic development, Chinese society has transformed itself and today faces a global environmental crisis. In everyday life, China's big cities are covered with a thick smog of gas and particles, which is responsible for more than 1.6 million premature deaths, making China the most affected country by air pollution, along with its neighbor, India. In China, there are many sources of air pollution linked to human activities [traffic, industry, agriculture, energy production, construction], but also various natural sources of pollutants, in particular emissions of mineral dust from the deserts of Asia, in western China. The People's Republic of China has begun to regulate activities that may affect air quality. The effectiveness of such actions is conditioned by the detailed knowledge of the anthropogenic contribution to this pollution and the complex relationship between primary and secondary pollutants. In this thesis, we have investigated, on the one hand, the impact of primary pollutant reduction policies on ammonia concentrations and more generally inorganic aerosols, and on the other hand, the contribution of desert aerosol to the particulate matter load in Chinese urban agglomerations. To do so, we combined data sources and tools such as satellite observations and numerical modelling. We use the CHIMERE regional chemistry transport model to study and characterize air pollution in China. First, we carried out a detailed evaluation of the simulations performed with a configuration of the CHIMERE model set up for China. For this, we relied on satellite observations, remote sensing, and in-situ measurements of particulate concentrations and gaseous [inorganic] precursors. The results obtained show that the model works satisfactorily according to criteria given in the literature. Regarding the impact of emission reduction policies - especially for sulfur and nitrogen oxides, long term measurements with the OMI instrument aboard the AURA satellite show a sharp decrease in the atmospheric sulfur dioxide and nitrogen dioxide columns. From these observations, it was possible to derive corrected emissions [compared to the available 2010 inventory] for the years 2013 and 2015 for NOX and SO₂. The derived emission trends were then used to study the impacts on atmospheric composition, particularly on the formation of inorganic particles and associated gases such as ammonia, whose concentrations appeared to strongly increase in recent years. Simulations showed that the sharp decrease in SO₂ and NO₂ emissions between 2011 and 2015 led to a overall 14% decrease in nitrate, sulphate and ammonium aerosol concentrations, as well as an increase of nearly 50% of ammonia column levels, a value corroborated by the IASI observations that indicate an increase in ammonia columns of +65?% under the same conditions. In a second step, the objective was to evaluate the contribution of desert aerosol to the particulate matter load in several Chinese cities. Dust emission modeling by Asian desert regions was first evaluated using remote sensing observations. Then, we verified the model's ability to represent PM_2.5 and PM₁₀ concentrations in Chinese megacities by comparing measurements of ground based observation networks. The study focuses mainly on three of the most populated PRC cities with different geographic locations, Beijing, Chengdu and Shanghai. It appears that mineral dust impacts these 3 cities for 6.6 %[Beijing], 9.5 %[Chengdu] and 9.3 %[Shanghai] PM₁₀ on an annual average. The frequencies of dust participation in particulate pollution [i.e. when dust contributes more than 25% to the daily averages of >25% of the mass of PM₁₀] have been determined for all spring days, as well as for the 25% of the most polluted spring days. It appears that, over this season, dust contributes more significantly to pollution events: in Beijing it accounts for 22% of polluted days compared to 18% for all spring days, in Chengdu for 52% of polluted days compared to 31% for all spring days, and in Shanghai for 43% of polluted days compared to 19% for all spring days. On the contrary, for all seasons combined and especially for peaks of particulate pollution in winter, the anthropogenic origin of pollution is highlighted. (author)