2013~2019年上海早晨接地逆温指标与PM2.5定量关系研究

利用2013~2019年上海宝山观象台08：00时高分辨率气象探空资料识别SBI并计算其3个指标（垂直温差、厚度、强度），发现在易污染月份（11月、12月、1月、2月）上海早晨SBI的发生频次为35.7%，垂直温差、厚度、强度分别为3.7℃、118m、3.6℃/100m.2013~2019年出现接地逆温的频次有所下降，但其3个指标均没有显著的年变化趋势.当出现接地逆温（SBI）时，2019年易污染月份早晨的PM_2.5浓度高达61.9µ；g/m³，较无逆温（NTI）时偏高了79%，表明SBI是促发早晨PM_2.5污染的重要气象条件之一.SBI的大气动力热力条件呈现水平风速降低（69%）、边界层通风能力下降（18%~44%）、垂直层结稳定（Ri>0.25）和低温（降低42%）、高湿（上升10%）的特点，非常有利于PM_2.5的局地累积和二次非均相生成，使得2013~2019年早晨的PM_2.5浓度较NTI时偏高了20%~107%.PM_2.5浓度与SBI的垂直温差、厚度都显著正相关，分别拟合为二次非线性关系（P<0.05），然而与强度的相关性不显著.当接地逆温的垂直温差大于4.6℃、或者厚度大于100m，PM_2.5浓度超过100µ；g/m³，可作为判别PM_2.5重污染天气的参考阈值.

Parameters of surface based inversion in the morning during 2013 to 2019 and its quantitative relationship with PM2.5 in Shanghai

SBI was one of the most important meteorological conditions favorable for the PM_2.5 pollution. In this article, the high-resolution radiosonde measurements launched at 08:00 (LST) at Shanghai Baoshan observatory during 2013 and 2019 were collected to explore the characteristics of SBI parameters (vertical temperature difference, depth and intensity) and their quantitative relationships with PM_2.5 mass concentrations. The mean frequency of SBI in the morning in pollution months was 35.7% observed in Shanghai. The mean vertical temperature difference, depth and intensity of SBI were calculated as 3.7℃、118m and 3.6℃/100m respectively, presenting insignificant annual variability during the study period. Under the condition of SBI, the meteorology exhibited lower dispersion capacity with weaker surface wind speed (69%), lower ventilation index (18%~44%) and stronger stable stratification (Ri>0.25) compared with that under the condition of NTI, which was conductive to the local PM_2.5 accumulation. In addition, the lower temperature and higher relative humidity near surface further accelerated the heterogeneous reaction of secondary inorganic aerosols. As a result, the morning PM_2.5 mass concentration was 20%~107% higher than that under the condition of NTI during 2013~2019. The PM_2.5 mass concentration was positively correlated with vertical temperature difference and depth of SBI respectively, while showing insignificant relationship with intensity. The PM_2.5 mass concentration increased with the enhanced vertical temperature difference and depth respectively, both of them were well fitted as the quadratic equations (P<0.05). It was found that the PM_2.5 level alleviated quickly and exceeded 100μg/m³ when vertical temperature difference was greater than 4.6℃ or the inversion depth over 100m.