洲际传输对我国对流层臭氧影响的数值模拟

采用MOZART-4模式并引入在线源追踪方法量化分析北美和欧洲对我国对流层臭氧（O₃）的贡献，整体来说模拟值能较好地与观测值对应.结果表明，北美和欧洲对流层对我国近地层O₃贡献较低，夏季体积分数分别为0.3×10^-9和0.6×10^-9；冬季略高，均为0.9×10^-9.北美对我国自由对流层O₃贡献较高，不同季节体积分数峰值均超过3.8×10^-9，而欧洲对我国自由对流层的贡献在夏季最高可达7.3×10^-9.呈现以上特征的原因是虽然冬季弱光照条件不利于O₃生成，但东亚的下沉气流能增加北美和欧洲对我国近地层O₃的贡献；夏季北美和欧洲对流层内O₃的生成量大幅增加，但地中海沿岸的下沉气流能减少北美和欧洲大陆西岸对中国O₃的贡献而对欧洲整体影响较弱.此外中国地表的上升气流也会减少北美和欧洲对中国近地层O₃的贡献.HYSPLIT模拟的输送路径表明冬季由于下沉气流的影响，北美近地层气团难以传输至我国，而自由对流层有13条轨迹到达我国；此时欧洲在东亚下沉气流作用下不同高度均有较多轨迹到达我国.夏季受地中海下沉气流影响北美没有到达中国的轨迹，欧洲到达我国的轨迹同样为一年中最少.

Numerical simulation of the impact of intercontinental transmission on tropospheric ozone in China

The contribution of tropospheric ozone (O₃) transported from North America to China was analyzed quantitatively using MOZART-4 model and the online tagging method. The analysis indicated that the modelled results were consistent with the observations. In summer, the concentrations of near-surface O₃ in China that transported from North America and Europe were 0.3×10^-9 and 0.6×10^-9, respectively, and were both 0.9×10^-9 in winter. Concentrations of free-troposphere O₃ in China transported from North America exceeded 3.8×10^-9 in four seasons, while that from Europe was up to 7.3×10^-9 in summer. The reason was that the wintertime downdraft in East Asia could enhance the sinking of O₃ to the surface layer in China, regardless of the unfavorable illumination condition. In summer, the production of O₃ in troposphere increased dramatically in Europe and North America, but due to the downdraft along the Mediterranean coast, the transportation of O₃ from North America and the west coast of Europe was declined, while the impact of the downdraft was weak in Europe. In addition, because of the updraft in summer, the near-surface O₃ that came from North America and Europe was reduced. The trajectories simulation using HYSPLIT model indicated that the near-surface air mass in North America could hardly transport to China due to the wintertime downdraft. While for the free-troposphere, 13 trajectories were found from North America to China. The trajectories transported from Europe to China were found at multiple altitudes due to the downdraft in winter. While in summer, because of the downdraft along the Mediterranean coast, no trajectory could transport from North America to China, and the number of trajectories transported from Europe to China reached its annual low.