重度霾和强浓雾形成及相互转化的关键气象条件研究

Fog and haze can transform from/to each other under such a typical evolution pattern as “heavy haze – extremely dense fog – heavy haze”; however, not all heavy hazes can develop to dense fog, or extremely dense fog, and vice versa. Many studies have shown that the evolution process depends on meteorological conditions, but it is still not clear about which meteorological factors play as key roles during the transformation between fog and haze. To explore this issue, the present project includes a comprehensive analysis of heavy haze events and extremely dense fogs occurred in several representative cities in Anhui Province during the years after 2010, boundary layer sounding data in Shouxian National Climate Observatory (SNCO), and multi-model based numerical simulation. Through the analysis on history records, boundary sounding detections will be conducted at SNCO in fog/haze high-occurrence months to obtain high temporal-spatial resolution meteorological data in boundary layer on those fog/haze days. Based on these, the transformation mechanisms and the key meteorological factors between heavy haze and extremely dense fog will be explored by comparative analysis of the multi-scale weather background and some physical parameters between events of extremely dense fog and heavy haze, which include the combinations of impacting weather systems of different scales, divergence/convergence and warm/cold advection at different heights, vertical structures of temperature, humidity and wind in boundary layer at different stages during the fog/haze events. Typical cases will be investigated by the meso-scale meteorological model (WRF) and a one-dimensional fog model coupled with detailed micro-physics of aerosol (PAFOG). Based on the results of the above comparative analysis, targeted sensitive experiments will be designed to make further clear the key meteorological factors determining the transformation patterns between heavy haze and extremely dense fog. The results will be helpful for improving the forecasting of extremely dense fog and heavy haze.

雾和霾可以相互转化，其一般的演变模式为“重度霾-强浓雾-重度霾”，但并非所有的重度霾都能发展为强浓雾，也并非所有的强浓雾后必为重度霾。其中，气象条件是决定因素，但决定雾、霾转化的关键气象因子目前尚不十分清楚。本项目拟对安徽省代表性城市2010年以来重度霾和强浓雾事件进行系统分析，结合外场观测和数值模拟，探究重度霾和强浓雾形成的气象条件及相互转化的关键气象因子。通过对历史资料统计分析，挑选雾、霾高发月份在寿县国家气候观象台开展雾、霾边界层气象要素加密探空观测，对比分析强浓雾和单纯重度霾个例生消过程不同阶段不同尺度天气系统的配置、不同高度的辐散辐合、冷暖平流、边界层温、湿、风垂直分布，利用中尺度气象模式(WRF) 耦合考虑气溶胶粒子微物理过程的一维雾模式（PAFOG）对典型个例进行模拟研究。根据模拟结果，设计敏感性数值试验，探讨雾-霾转化机理及转化的关键气象因子，为强浓雾生消预报提供参考依据。

雾和霾可以相互转化，其一般的演变模式为“重度霾-强浓雾-重度霾”，但并非所有的重度霾都能发展为强浓雾, 也并非所有的强浓雾后必为重度霾。其中，气象条件是决定因素。.项目利用多源资料，结合外场观测、数值模拟，以安徽为例，通过对比研究了揭示重度霾向强浓雾转化的关键因子。主要研究成果包括：（1）基于雾、霾发生物理条件，建立了不同等级雾和重度霾的诊断方法；根据强浓雾发生的同步性，将安徽分为5个雾的统计特征不同的区域；通过对比分析，阐明重度霾能否演变为强浓雾的关键地面气象因子是风速、风向和降温幅度；利用1980-2019年的数据，研究确立了区域性强浓雾的判断标准，分析了区域性强浓雾的变化趋势及影响因子。（2）在寿县观象台组织开展2次冬季雾外场试验，基于试验资料研究了不同等级雾的微物理特征;对比研究了不同等级雾及重度霾过程中边界层结构特征的异同;提出重度霾转化到强浓雾取决于边界层上下是否存在风向转变及如何转变的猜想。（3）对淮河以北西部和东部(强浓雾高发地区）08时(强浓雾高发时段）超过15年的强浓雾和重度霾个例的环流分别进行客观分型；并对比强浓雾和重度霾不同环流形势下的地面及边界层气象条件的差异,阐明差异形成机制；验证上述猜想，并将“充足的水汽输入”补充进重度霾向强浓雾的地面关键因子。(4)利用中尺度气象模式WRF对寿县观测到的强浓雾个例进行了模拟试验,结果进一步验证了边界层上下风向转变对重度霾向强浓雾转化的关键作用。根据上述研究，构建了强浓雾形成的动力机制概念图，提出了一套强浓雾诊断预报指标。（5）基于综合分析和数值模拟，揭示中东部地区持续性大范围重度霾及PM2.5重污染过程生消机制。本项目的完成有助于我们更好地理解强浓雾形成机制，为强浓雾的预报提供新的思路和方法。