海南岛气溶胶时空变化及来源追溯

海南岛独特的区域和国家战略位置,使得了解和掌握该地区气溶胶时空格局特征及其大气污染物传输来源是海南大气环境质量监测和污染防治中重要的关注问题。选取MODIS 3 km分辨率气溶胶光学厚度（AOD）产品MOD04_3K,对海南岛2003—2017年AOD时空变化特征进行分析;以海口市为起始点,采用HYSPLIT模式对8次典型大气污染事件在10、500、1000 m 3个相对地面高度上进行48 h后向轨迹计算,以探究该区域大气污染物来源。结果表明：① 海南岛AOD在空间上呈较为明显的三级阶梯状分布,从西北方向向东南递减,2003—2017年在不同阶梯的空间变化趋势差异十分显著;② 2003—2017年海南岛AOD年均值为0.095,各年均值整体呈轻微升高趋势;季节均值差异表现为“春季>秋季>冬季>夏季”,此差异除受区域天气系统与地方风向特征的影响外,本区旅游业发展造成的大气污染物排放也不可忽视;③ 海南岛（海口市）2013—2017年典型大气污染事件发生期间大气污染气流在3个高度上（10、500、1000 m）的后向轨迹基本保持一致,均主要来自于海南岛东北方向。据此,位于该方向毗邻的珠江三角洲地区陆源大气污染物在东北盛行风的影响下被输送至海南岛,在区域天气系统（如大陆冷高压）和局部天气系统（如海风辐合）共同作用下,是促成该地区大气污染事件发生的重要因素。研究结果对深入理解海南岛近十多年来大气环境状况的变化规律、完善该区域大气污染联防联控机制具有重要的意义。

Spatiotemporal Dynamics and Tracing of Aerosol over Hainan Island

To serve as a basis for atmospheric environmental quality monitoring and pollution prevention & control in Hainan, which located in a specific geographical position with great strategic significance and national development potentiality, it is imperative to reveal the spatiotemporal dynamics patterns of aerosol over Hainan Island and clarify the sources of atmospheric pollutants. Hence, this study aims to investigate the spatiotemporal dynamics characteristics of the Aerosol Optical Depth (AOD) over Hainan Island by using the MODIS 3 km spatial resolution data (i.e., MOD04_3K product) from 2003 to 2017. Then, we calculated the 48-h backward trajectories at three above ground levels (10, 500, and 1000 m) of eight typical air pollution events in Haikou city, the capital and largest city of Hainan Province and the starting point to trace the sources of air pollutants in the region, by using the Hybrid Single Particle Lagrangian Integrated Trajectory(HYSPLIT) model. The results indicated that: (1) The average values of AODs during 2003-2017 over Hainan Island region exhibited a notable three-stage stepped-down spatial distribution from northwest to southeast, each of which displayed some distinctly spatial variations. (2) During the fifteen-year period, a slight increase tendency of the annual mean values of AODs was noted with their total mean value of 0.095 over Hainan Island, and the seasonal mean values of AODs were characterized with “spring > autumn > winter > summer”, the reasons for which could be derived from the common influences of regional weather systems and local winds, as well as the atmospheric pollutant emissions caused by tourism development. (3) In addition, during periods of typical atmospheric pollution events in Hainan Island (Haikou) from 2013 to 2017, the backward trajectories of air pollutants at three ground levels (10, 500, and 1000m) were primarily from the northeast direction of Hainan Island. Thus, the air pollutants originated from the mainland in the northeast direction such as the Pearl River Delta region were brought to Hainan Island along land tracks or coastal belts by the prevailing northeast winds; the plausible explanation of this could be that the atmospheric pollution events in Haikou occurred because of the joint effects of regional weather (e.g., continental cold high pressure) and local weather (e.g., sea-breeze convergence) systems. Perhaps, findings of this study could contribute to the understanding and assessing dynamic changes of the atmospheric environmental quality situation over decade in Hainan Island region and provide useful references for the establishment of joint prevention and control mechanism for air pollution.