Satellite Observation And WRF-Dust/Chem Based Air Quality Simulation

Over the past decades,air pollution has been becoming an increasingly problem in China due to the rapid urbanization and industrialization. And the publics show a stronger desire to improve the air quality. Our knowledge of the air quality has been enriched due to the developments of advanced satellite observation, of numerical simulation and of ground-level in situ observation. In this thesis, we combined the three techniques to explore the China’s air quality, conducting case studies of the urban dust in Guanzhong Basin and the crop field burning(CFB) in the North China Plain(NCP). This thesis provides scientific references to improve the air quality in China.In the urban dust case, we firstly proposed a satellite-data based method to quantify the urban dust source distribution of urban constructions, barrens and croplands. Multiply satellite data of VHR, Lansat-8 OLI and MODIS was analyzed with the methods of visual interpretation, maximum likelihood classification, extrapolation and spatial overlaying. Each procedure was verified based on the error spread rule, and the final results performed well with high accuracy exceeding 88%. Secondly, we developed a regional dust dynamical model WRF-Dust. For the first time, detailed construction dust emissions have been introduced in a regional dust model in large cities of China, and the urban dust simulations were significantly improved. The dust concentration increased from 28 μg m-3 to 59 μg m-3, closing to the observation of 66 μg m-3. Meanwhile, the correlation coefficient is also improved from 0.17 to 0.57. The results found that the urban dust was mainly contributed from construction sources(42%), followed by barren(32%) and cropland(26%) sources.The satellite observation and numerical model based method are feasible and valuable due to their reasonable costs and widespread coverage. It provides a new perspective to estimate regional construction dust pollution, which is of great practical significance for China, where large number of construction activities resulted from rapid urbanization.In the CFB case, we firstly extracted a detailed CFB emission inventory. The provincial CFB emissions were estimated using statistical data. Thereafter, it was allocated based on CFB activities, which were generated from MODIS fire products(MCD14ML) and land cover products(MCD12Q1). Secondly, we reproduced the air pollution episode with WRF-Chem, which is a state-of the-art dynamical model. The simulations and observations agreed well: with correlation coefficients higher than 0.80 for PM2.5 concentration and larger than 0.65 for wind direction, wind speed and PBLH. Thirdly, the model was used to investigate the impacts of CFB to PM2.5 concentration and its evolution. The CFB caused a maximum of 35% PM2.5 increase in southern NCP(SNCP) and 32% PM2.5 increase in northern NCP(NNCP). The CFB contribution in SNCP was mainly resulted from local CFB emissions. Whereas CFB contribution in NNCP was mainly resulted from the long-range transport of pollution plume emitted from CFB in SNCP. Additionally, we evaluated the impacts of mountains on the haze incident. The mountains played important roles in enhancing the PM2.5 pollution in NNCP through the effects of blocking and guiding, especially along the foothill sites of mountains. The Taihang Mountains caused 56.0 μg m-3 and 36.1 μg m-3 of PM2.5 increase in the foothill and non-foothill sampling sites. The Yanshan Mountains caused 25.1 μg m-3 and 1.3 μg m-3 μg m-3 of PM2.5 increase in the foothill and non-foothill sampling sites. The Taihang Mountains had greater impacts on PM2.5 concentration than the Yanshan Mountains.This CFB case suggests that the detailed CFB emission inventory extracted from MODIS observations can be successfully applied to WRF-Chem model. The CFB prohibition in and around Beijing is not enough to avoid CFB pollution due to the probability of its pollution plume transmission from SNCP, where CFB occurred far away from Beijing. The mountains play significant role in enhancing the air pollution in NNCP, the PM2.5 emissions and precursors in the SNCP should be significantly limited in order to reduce the occurrences of heavy haze events in NNCP region, including the Beijing City.