1954-2004年珠江三角洲大气能见度变化趋势

Visibility Variations in the Pearl River Delta of China During the Period of 1954—2004

利用珠江三角洲5个城市气象观测站(广州、深圳、台山、惠州、高要)的长期能见度观测资料,采用累积百分率、Ridit分析法和烟幕/霾日频率3种统计分析方法,分析了1954—2004年珠江三角洲能见度变化趋势,初步探讨了珠江三角洲大气环境的变化特征及其可能原因。结果表明:近50年来,珠江三角洲城市能见度呈显著下降趋势。能见度的下降起始于20世纪70年代初,并在经济高速发展的80—90年代初进一步恶化,90年代中期之后虽然能见度变化趋于平缓,但能见度下降的趋势仍未从根本上改变。珠江三角洲能见度与当地的人口增加和经济发展程度有密切的关系,同时污染物的区域输送对西部下风向城市能见度也有很大影响。珠江三角洲能见度未得到有效改善的主要原因,很可能是由于细粒子污染,尤其是二次粒子前体物如SO2和NOX等的排放未得到有效控制。

Atmospheric visibility is one of the good indicators of atmospheric fine particle pollution. To well understand the evolvement course of atmospheric environment of the Pearl River Delta （PRD）, the temporal variation of visibility is examined by using three statistical methods, namely, cumulative percentiles, Ridit analysis and frequency of smoke/haze days, based on the historical visibility data of five geographically dispersed cities （Shenzhen, Gaoyao, Guangzhou, Taishan and Huiyang） from 1954 to 2004. The characteristics of visibility variation and its possible cause are investigated preliminarily. The temporal variation shows that there is a remarkable decline in visibility for all cities of PRD in the 51 years studied. At the end of 1950s visibility in some cities, e.g. , Guangzhou and Gaoyao, evolves from low to high. The increasing consumption of coal and decreasing usage of trees seems to be responsible for this trend. In 1960s,visibility is generally high and experienced very good air quality in PRD. The visibility degradation for PRD is at early 1970s, which is prior to that of some other areas in China. Between the early 1980s and early 1990s, a stage of high-speed economic growth, the visibility gets worse. After the middle of 1990s the decline trends of visibility eventually become moderate. In the course of visibility variation of PRD, it should be pointed out that the visibility trend for PRD in the 51 years studied actually descends all the same even though the visibility declining rate slows down after the middle of 1990s. From 1960s to the period of 2001-2004, the declines of the average visibility are about 62.1%, 55.7 %, 50.4 %, 50.3 % and 47.2 %, in Shenzhen, Gaoyao, Guangzhou, Taishan and Huiyang, respectively, and the average extinction coefficient of atmosphere for the period of 2001-2004 is about 2.6, 2.3, 2.0, 2.0 and 1.9 times of that of 1960s. In recent years, Shenzhen has the lowest visibility in PRD, followed in turn by Gaoyao, Guangzhou, Taishan and Huiyang. The trend of visibility in PRD is mostly in accordance with local economic development and population growth in this period. It is also found that Gaoyao, a city located at the western part of PRD, has a lower visibility in comparison with the eastern city of PRD. It shows that the regional transport of atmospheric pollutants has a significant effect on the visibility over the down wind area. Furthermore, the relationship of visibility trends with atmospheric pollutant emissions in recent years is also discussed. It is found that visibility in PRD has not been improved substantively while the direct emission of particles has markedly decreased in the past few years since a series of prevention and control projects of atmospheric pollutants are implemented. The likely cause is that gas-phase aerosol precursor species, especially SO2 and NOx, have not been under control.