【作者】 段玉森；

【导师】 束炯；

【作者基本信息】 华东师范大学 ， 气象学， 2005， 硕士

【摘要】 通常的能见度是指水平能见度,即视力正常的人在当时天气条件下,能够从天空背景中看到和辨认出目标物（黑色、大小适度）的最大水平距离;夜间则是指能看到和确定出的一定强度灯光的最大水平距离。 众所周知,能见度是一种复杂的大气现象,与空气质量和气象条件密切相关。研究发现能见度与吸湿性的颗粒状污染物和相对湿度密切相关,特别是硫酸盐颗粒潮解起着重要作用;就天气背景而言,能见度往往是大、中、小尺度天气系统和包括大气化学反应的空气污染过程共同作用的结果;考虑特定的沿海城市背景,还需着重考虑不同天气条件下,城市热岛环流和海陆风对不同粒径的气溶胶输送及光化学烟雾形成的影响。 为了搞清沿海城市能见度变化的物理化学机制,本论文通过对1998～2002年5年能见度和气象资料、污染资料的分析,对能见度本身的变化特征及其影响因子特别是由气—粒转化大气化学过程产生的二次粒子做了深入探讨,在此基础上开发了基于系统辨识理论的上海市水平大气能见度预报模式。具体工作及结果如下: 1、本市能见度的变化与气象条件和污染排放有着较大的关系。在一天中,以早晨为最差,午后为最好,其日变化十分明显,这种变化特征与气象条件尤其是对流混合层高度的变化密切相关。在月变化方面,一年中的7月～10月为最好季节。 2、影响能见度的空气污染因子,不仅包括一次源,还应包括经由气-粒转化化学反应而产生的硫酸盐、硝酸盐等二次污染粒子。引入气—粒转化化学反应模式,更加贴近能见度变化过程的大气物理和化学机制。 3、通过探讨由气相H₂SO₄,HNO₃,NH₃和H₂O形成二次气溶胶的理论,建立了气-粒转化模型,模式考虑了两个方面的化学反应机制,即:SO₂转化为SO₄^2-;NO_x（包括NO+NO₂）物质转化为NO₃^-的化学反应机制。利用此模式的个例计算结果表明,SO₂和NO_x的转换率以及硝酸的形成率均随温度升高而增大,得到了与北京（2.3%/h）和广州（2.9%/h）夏季观测值比较一致的结果。 4、利用因子分析方法,将影响能见度的诸多因子归纳总结为6类公因子,即:（1）公因子F1,代表常规气象因子;（2）公因子F2,代表污染因子;（3）公因子F3,代表气粒转化速率因子;（4）公因子F4,代表绝对湿度因子;（5）公因子F5,代表云量因子:（6）公因子F6,代表风向、风速和稳定度因子,以反映污染物质的扩散和运移能力,简化了模型结构。 5、基于系统辨识理论的水平能见度预报模式考虑了气象以及污染因子对能见度的影响,考虑了能见度预报方程中预报历史对当次预报结果的影响,根据三更多还原

【Abstract】 Visibility is usually defined to mean the furthest distance one can see and identify an object in the atmosphere.As is known to all, as a complex atmospheric phenomenon, visibility is related to air quality and meteorological condition. Several recent research show that visibility is tied up to particle and relative humidity, especially play an important role in sulfate particle’s deliquescence. As weather system is concerned, visibility results from the interaction between variable scale weather system and air pollution process including atmospheric chemistry actions. For special coastal cities, Aerosol transportation and photochemical smog formation shall be considered from the influence of urban heat island current and sea-land wind under different weather conditions.Based on 5-year’s visibility data, meteorological data and pollutant data from 1998 to 2002, the paper presents a study for the visibility’s characteristic and its impact, especially to second particle derived from gas-to-particle transformation. Then the author developed a horizontal visibility forecast mode with system identification. Detailed contents and results are as followed:1. There is a great relationship between visibility variety and weather condition or pollutant emissions in Shanghai. The diurnal variation of visibility in Shanghai was apparent. There was low visibility in the morning and high visibility in the afternoon. This phenomenon was correlated to meteorological conditions, especially mixed-layer height. There appears high visibility during Jul. to Oct. in one year as for monthly variation.2. Air pollution factors include sulfate or nitrate second particles derived from gas-to-particle transformation as well as original particles. It will be better/ appropriate to atmospheric physics and chemistry mechanism for visibility variety if gas-to-particle chemistry actions are taken into account.3. Based on gas-phase to second-particle theory, we developed a gas-to-particle transformation mechanism including two chemical actions: SO₂ to SO₄= and NO_X to NO₃.The results show that the transformation rate of SO₂ and NO_X or the formation rate of nitric acid is increasing with temperature. We got simulated rates 2.3%/h in Beijing and 2.9%/h in Guangzhou in summer which are consistent to monitoring values/observations.4. The factors which impact visibility are induced into 6 species by factor analysis:F1-general meteorological factor; F2-pollutant factor; F3-gas to particle transformation rate; F4-absolute humidity; F5-cloudage/cloud cover; F6-wind direction, wind speed/velocity and atmospheric stability.5. The horizontal visibility forecast mode based on/with system recognition theory took into account the influence of meteorological factor and pollutant factor to visibility as well as the influence of forecast history to current forecast outcome in visibility forecast functions. According to three-year’s forecast results, the forecast precision reaches 68.0%, while the primary forecast precision is 81.0%. The mode has a simple structure and high forecast precision, which shall be used in visibility forecast operation.This research is significant not only to help us make it clear the physical and chemical mechanism of coastal city’s visibility variety but also to improve urban atmospheric environment and build-up favorable urban visualize during EXPO 2010 Shanghai.更多还原