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珠江三角洲霾天气的近地层输送条件研究
Transport Condition of Surface Layer Under Haze Weather over the Pearl River Delta
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摘要: 近年来, 珠江三角洲地区气溶胶污染日趋严重, 霾天气造成能见度恶化和空气质量下降。近地层输送条件即地面流场与大气污染物稀释扩散密切相关。利用2004—2005年广东省466个地面自动气象站资料、广州观象台常规气象资料、珠江三角洲大气成分站网器测能见度资料、珠江三角洲城市环境监测站网的PM10浓度资料等, 使用矢量和分析方法, 分析珠江三角洲近地层风及其对严重霾天气过程和清洁对照过程的影响。结果表明: 2004年霾天气高发季节, 东亚纬向环流比2005年同期显著, 纬向环流不显著的年份, 气流南北交换显著, 冷空气跨越南岭、到达珠江三角洲的机会比较大, 伴随冷空气的大风等天气有利于污染物扩散; 纬向环流显著的年份, 冷空气跨越南岭、到达珠江三角洲的机会比较小, 污染物易于堆积。珠江三角洲霾天气具有区域性特征, 旱季出现最多, 雨季出现最少。严重霾天气过程出现在每年12月至次年4月, 清洁对照过程出现在台风直接影响或冷空气活动频繁的季节。与2004年相比, 2005年的静风频率较低, 且旱季风速较大, 不利于霾天气的形成。矢量和分析表明:区域霾天气过程与区域内静小风过程, 即出现气流停滞区有密切联系, 清洁对照过程与强平流输送有关。Abstract: In recent years, the aerosol pollution over the Pearl River Delta (PRD) region is getting worse, resulting in haze weather with visibility decreasing and air quality deterioration. The surface layer transport condition such as airflow is closely related to the dilution and diffusion of atmospheric pollutants. By using statistic method under a set standard based on dataset from 466 Guangdong provincial surface automatic weather stations, Guangzhou operational weather stations, visibility data of PRD's atmospheric component observational network, and PM10 data of PRD's urban environmental observational network, typical haze weather and cleaning weather processes are analyzed in 2004 and 2005. The surface wind and its effect on heavy haze and cleaning weather processes are analyzed using Vector Sum Technique. The zonal circulation over Eastern Asia in favorite haze season in 2004 is stronger than that in 2005. The year with weak zonal circulation has marked exchange between the north and the south, allowing much cold air to cross Nanling Mountain to reach PRD, the accompanying strong wind is favor for the diffusion of the pollutants. In the year with strong zonal circulation cold air has little chance to cross Nanling Mountain to reach PRD so that the pollutants accumulate much easily. The haze weather over PRD has the regional features with the most likely occurrences in dry season and the least in rainy season. The haze processes often happen from October to next April, while cleaning processes often occur in the seasons when typhoon or cold air is prone to occurrence. Compared to 2004, the frequency of still wind is lower and the wind speed in dry season is larger in 2005, those factors are not favor for the form of haze weather. Analysis using Vector Sum Technique shows that regional haze process is closely related to the regional still wind process by which formation of airflow stagnation area is led to, while cleaning process is related to strong advection transport.
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图 3 2004年和2005年广州平均风速变化
Fig. 3 Variation of mean wind speed in Guangzhou during 2004—2005
图 4 2004年珠江三角洲平均流场 (单位: m·s-1)
Fig. 4 Mean stream field of the Pearl River Delta in 2004 (unit: m·s-1)
图 6 广州严重霾日的逐月变化
(能见度<5 km, 相对湿度<90%)
Fig. 6 Monthly variation of serious hazy days in Guangzhou
(visibility <5 km, relative humidity <90%)
图 7 2004年1月1—13日 (a) 和2005年11月12—24日 (b) 珠江三角洲日平均风速与广州VAPI的点聚图
Fig. 7 Scatter diagram for diurnal mean wind speed in the Pearl River Delta and VAPI in Guangzhou during Jan 1—13, 2004 (a) and Nov 12—24, 2005 (b)
图 8 风的120 h矢量和 (a) 2004年1月5—9日, (b) 2005年11月16—20日 (单位: m·s-1)
Fig. 8 Sum of wind vectors for 120 hours during Jan 5—9, 2004 (a) and Nov 16—20, 2005 (b)(unit : m·s-1)
表 1 2004年、2005年珠江三角洲6城市霾日数 (单位: d)
Table 1 Number of hazy days for six cities in the Pearl River Delta in 2004 and 2005 (unit:d)
表 2 典型霾天气过程的选取
Table 2 Selection of weather processes for typical hazy weather
表 3 清洁对照天气过程的选取
Table 3 Selection of weather processes for clean control
表 4 典型霾天气过程的选取 (VAPI=73.9)
Table 4 Same as in Table 2, but for VAPI=73.9
表 5 清洁对照天气过程的选取 (VAPI=73.9)
Table 5 Same as in Table 3, but for VAPI=73.9
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