海南岛地区大气输送和扩散特征的数值模拟

采用中尺度气象模式WRF及风场诊断模式CALMET,结合轨迹分析和拉格朗日随机游走模拟方法,分析了海南岛地区低层大气中尺度水平输送和扩散特性,并计算了各季平均大气扩散模态.结果表明,该区域大气污染物的扩散和输送主要受到大尺度背景环流、海陆风等局地环流及地形绕流等的影响.海陆风局地环流是沿海城市源排放的大气污染物向海南本岛输送和扩散的主要机制.北部城市海口的大气扩散对岛内影响最大,冬季平均影响范围可覆盖西北半部;春、秋季主要影响西北和北部区域;夏季对本岛的影响仅限于北部沿岸.南部城市三亚的大气扩散对岛内影响较小,秋季向西南海面的扩散对本岛几乎没有影响;冬、春季对三亚以西沿岸的影响有所增加;夏季扩散影响全面指向岛内,并因地形的作用而东、西向大角度扩展,影响海岛南部的大部分沿岸地区.西北部昌江的平均输送扩散方向与当地海岸线的走向基本一致,污染影响不易深入到岛内.其中,秋季扩散影响以偏西南方向为主,仅对昌江西南部分海岸有少量影响;冬、春季扩散形态类似但影响范围扩大到以东方市为代表的低山盆地地带;海岛西北部大部分沿海地带可受到昌江夏季扩散的影响,但平均扩散方向指向东北偏北的海面.

Numerical simulation of atmospheric transport and diffusion over Hainan Island

The trajectory analysis and random walk simulation, driven by the meteorological field from WRF and CALMET models, were used to reveal the effects of atmospheric meso-scale transport and diffusion over Hainan Island. Results show that atmospheric transport and diffusion are affected by synoptic winds, local sea-land breezes circulation and orographic effects. The sea breeze circulation is the main mechanism of transporting and spreading air pollutants from coastal source emissions inland. The pollutants from Haikou exert the greatest influence on the main island, with the average sphere of influence covering the northwest half the island in winter, the northwest and northern parts in spring and autumn, and limited to the northern coast in summer. By contrast, the diffusion from Sanya affects the island lightly. The diffusion to the southwest sea causes little effect on air quality over the island. But there is an increase in the influence on the west coast of Sanya in winter and spring. The atmospheric diffusion in summer exercises an overall influence on the southern coastal inland region, which shows a wide-angle expansion along the coast from west to east because of topography. The average transport and diffusion presents a consistent trend with the local coastline. Consequently, it is not easy and smooth for air pollutants to penetrate inland. The diffusion process tends to the southwest in autumn with little effect on southwest seashore of Changjiang. Diffusion behavior in winter and spring presents similar patterns and expands to hilly and basin zone near Dongfang. Most of coastal regions in northwest of the island is under the influence of summer pollutants spreading of Changjiang mainly towards north-northeast sea.