珠江三角洲区域大气输送和扩散的季节特征
The Seasonal Characteristics of Regional Atmospheric Transport and Dispersion over the Pearl River Delta
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摘要: 根据1985—2004年NCEP/NCAR再分析资料,采用HYSPLIT扩散模式和虚拟源方法,模拟分析了珠江三角洲大气污染物的空间和时间分布状况,初步讨论了珠江三角洲大气输送和扩散的季节特征,及其长期变化趋势。结果表明:珠江三角洲大气的输送和扩散有明显的季节变化特征,春、夏季大气污染物汇聚区位于珠江三角洲的西北侧,秋、冬季位于偏西侧;春、夏季的汇聚区明显强于秋、冬季。春、夏季大气分别向珠江三角洲西北和偏北方向的山区输送和扩散,而秋、冬季则沿着较为平坦的粤西海岸,向西南偏西方向输送和扩散。秋、冬季大气污染物的滞留时间明显比春、夏季短。1985—2004年大气输送和扩散能力存在年际差异,其中以2004年的输送和扩散能力最弱、1996年最强。Abstract: After being emitted from the sources, air pollutants experience a series of atmospheric physical and chemical processes before reaching the receptor, in which the core process is the atmospheric transport, diffusion process and the clearance changes accompanied with them. Understanding the climatic background of atmospheric transport and diffusion of the Pearl River Delta would be helpful to determine the area affected by air pollutants, the regularity of air pollutants input, output and detention over this area, providing scientific basis for air pollution prediction, control and management. Based on the meteorological field of wind, temperature, humidity, geopotential height and precipitation from the NCEP/NCAR reanalysis for the period of 1985—2004, the HYSPLIT dispersion model and setting virtual air pollution sources approach are adopted to simulate the distribution of air pollutant, dispersive path and detention time over the Pearl River Delta, with full consideration of wet and dry removal processes. The seasonal characteristics and long term trends of atmospheric transport and diffusion process over this region are examined, and the main results are shown as follows. The significant differences of the distribution, diffusive paths and detention time of virtual air pollutants among four seasons suggest that there are remarkable seasonal variations of atmospheric transport and diffusion processes over the Pearl River Delta. In spring and summer, the air pollutant convergence zone is located at northwest side of the Pearl River Delta, while in autumn and winter it lies on the northwest side of the Pearl River Delta. Among four seasons, the convergence zone in summer is the strongest, followed by spring, autumn and winter. In spring and summer, the air pollutants are transported and dispersed to the mountainous area of the northwest and north side of the Pearl River Delta, respectively, while in autumn and winter, those are transported and dispersed along the relatively flat coast of western Guangdong to the west southwest. In autumn and winter, the atmospheric transport and diffusion rates are significantly higher than those in spring and summer. Pollutants stay over the Pearl River Delta for longer than 24 hours for 66.7% and 75.3% of all the air pollution events in spring and summer, respectively, while in autumn and winter, there are only 22.1% and 30.4%. The terrain effect is one of the possible factors that responsible for the weaker atmospheric transport and diffusion in spring and summer. For the period of 1985—2004, atmospheric transport and diffusion ability are weakest in 2004 and strongest in 1996 with significant annual differences, which may be caused by the variation of atmospheric systems.
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图 2 NCEP/NCAR再分析资料的2.5°×2.5°水平风场与经过线性内插后的0.5°×0.5°水平风场
(a) NCEP/NCAR夏季水平风场,(b) NCEP/NCAR冬季水平风场,(c) 经内插处理后的夏季水平风场,(d) 经内插处理后的冬季水平风场
Fig. 2 The original 2.5°X2.5° horizontal wind field of NCEP/NCARreanalysis and the linear-interpolated 0.5°×0.5° horizontal wind field
(a) the original wind field for summer, (b) the original wind field forwinter, (c) the liner-interpolated wind field for summer, (d) the linear-interpolated wind field for winter
表 1 4个季节大气污染物滞留时间的统计结果
Table 1 The statistics of、air pollutant detention-time for four seasons
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