回流指数在空气质量变化研究中的应用

将回流指数引入珠三角污染气象条件的研究中,尝试使用回流指数判别形成区域大气污染的机理.运用中尺度数值模式WRF得到珠三角精细化的回流指数时空分布,同时与边界层外场观测试验结果进行比对从而验证模式对边界层内风场的模拟效果.最后,分别对干湿季冷高压影响下的污染过程进行分析,湿季选取2013年4月13—16日的珠三角重污染过程,干季选取同年12月8—10日的污染过程.结果表明:在本研究的两次过程中,使用回流指数Rcritical=0.6作为阈值能较好地区分局地污染物回流堆积与上风向污染物输送两种因素在冷高压型污染过程中何者占主导,当区域中回流指数普遍低于0.6则是污染物局地回流堆积作用更明显,若普遍高于0.6则是受上风向污染物的输送影响更明显;在局地回流堆积为主要形成机理的污染过程中,地面污染物浓度与边界层整体回流系数呈反方向变化关系,地面污染物浓度峰值对应边界层回流系数谷值;在污染物输送为主要形成因素的污染过程中,边界层中低层回流系数达到峰值时代表该区域此时受上风向风场输送作用最显著,地面污染物浓度同时达到峰值.

Application of recirculation index in air quality research

The Recirculation Index(RI) was used in distinguishing different formation mechanisms of regional air pollution processes over Pearl River Delta(PRD) region. To calculate the RI values over the whole PRD, a numerical study using WRF was proceeded. Wind profiles, achieved from a field campaign, were used to evaluate the modeling wind field results in the boundary layers. Analyses for two typical periods were made:one was during April 13^th to 16^th 2013 in the rainy season and the other was during December 8^th to 10^th in the dry season. It was found that a critical value(0.6) of RI could efficiently determine the dominant factors for the specific polluted areas-when RI values were lower(higher) than 0.6, the air pollution were mainly caused by the accumulation of local pollutants(by transport of upwind pollutants). For local accumulation pollution episode, there was a strong negative correlation between pollutant concentration and RI in the boundary layers. For transport pollution episode, peak values of RI in the boundary layers represented regions affected by the upwind pollutants, and the pollutant concentration reached the maximum.