京津廊城市气团光化学污染潜势分析

Analysis of photochemical pollution potential of air masses from various cities in Beijing-Tianjin-Langfang border

选取京津廊三市交界处,于2019年和2021年的7月开展PAN(过氧乙酰硝酸酯)在线监测、空间来源解析与反应产率研究,以评估北京、天津、廊坊不同城市气团的光化学污染潜势及近年变化趋势.观测结果表明,三市交界处2021年夏季PAN浓度均值(0.89±0.21)×10^(-9),较2019年同期(2.45±0.71)×10^(-9)下降63.8%.PAN在夏季大气寿命很短,其在该观测点浓度主要受周边城市气团光化学反应控制,其产率呈现明显双峰特征,峰值水平在2019年和2021年的7月分别为3.08×10^(-9)/h、1.75×10^(-9)/h,2021年较2019年下降43.18%,与PAN的年际变化趋势吻合.该观测点PAN的潜在源贡献函数(PSCF)高值区在2个观测月均出现在东南方向50km范围内,显示了天津市气团输送对该观测点PAN浓度的显著贡献.当该观测点受天津城市气团绝对影响时,PAN生成潜势和前体物NO_(2)均呈最高水平,约为受北京城市气团影响时的2.03倍和2.01倍,为受廊坊城市气团影响时的1.53和1.21倍.可见,天津城市气团具有最高的光化学污染潜势,其与北京气团的差异主要源自NO_(x),而与廊坊气团的差异则来自NO_(x)和VOCs两类前体物.

PAN online measurement,spatial source apportionment and reaction yield study were carried out in July of 2019 and 2021 in the border of Beijing,Tianjin and Hebei,to evaluate the photochemical pollution potential of air masses originating from surrounding cities.The observations showed that the mean of PAN in the studied days of 2021 was(0.89±0.21)×10^(-9),about 63.8%lower than that in the studied days of 2019[(2.45±0.71)×10^(-9)].Due to the very short lifetime of PAN in summer,PAN in the border was mainly decided by the photochemical reactions of air masses from surrounding cities that carried the abundant precursors NO_(x) and VOCs.The yield rate of PAN presented the dual-peak pattern with the peak value of 3.08×10^(-9)/h and 1.75×10^(-9)/h respectively in July of 2019 and 2021,which was consistent with the interannual variation of PAN concentration.The higher values of potential source contribution function(PSCF)of PAN appeared within 50 km southeast of the PAN observation site in both studied months,indicating the bigger contribution of air mass transport from Tianjin to PAN in the border.The PAN formation potential and precursor NO_(2) were both the highest when the observation site was absolutely controlled by Tianjin air masses,which was about 2.03 and 2.01 as higher as those under Beijing air masses,and about 1.53 and 1.21 as higher as those under Langfang air masses.These indicated that the photochemical pollution potential of Tianjin air masses was the highest,which prominence compared to Beijing air masses mainly resulted from NO_(x) and which compared to Langfang air masses resulted from both NO_(x) and VOCs precursors.