疫情管控期西安PM2.5和O3污染特征及成因分析

基于西安疫情管控期空气监测数据，分析PM_2.5和O₃的时空序列特征，从PM_2.5源解析、O₃前体物VOCs溯源、气象要素和区域传输方向探讨污染成因.结果表明：(1)管控期PM_2.5和O₃分别同比上升20.39%和23.72%，其他参数均下降；与管控前后时期相比，管控期PM_2.5和PM₁₀日均值协同变化趋势减弱，O₃和NO₂此消彼长趋势增强；相比去年同期，PM_2.5小时值升高11～19μg·m^-3,O₃小时值夜间18:00～23:00升幅增大，为10～19μg·m^-3.(2)污染物浓度变化呈现一定的空间聚集协同性；受地形及植被阻滞吸附影响，PM_2.5污染集中在北部，由于城郊NO₂滴定效果弱于城区，表现为南部郊区O₃污染较...

Analysis of the Characteristics and Causes of PM2.5 and O3 Pollution in Xi''an During the Epidemic Lockdown Period

Based on the air monitoring data during the epidemic lockdown period in Xi''an, the spatiotemporal characteristics of PM_2.5 and O₃ were analyzed, and the pollution sources of PM_2.5, VOCs as O₃ precursors, meteorological factors, and regional transport directions were discussed to explore the causes of pollution. The results showed that： ① during the lockdown period, PM_2.5 and O₃ increased by 20.39% and 23.72%, respectively, compared to that in the same period the previous year, whereas other parameters decreased. Compared with that in the period before and after lockdown, the co-variation trend of PM_2.5 and PM₁₀ daily averages weakened during the lockdown period, whereas the trend of O₃ and NO₂ showed an opposite change. Compared with that in the same period the previous year, the hourly PM_2.5 values increased by 11-19 μg·m^-3, and the hourly O₃ values increased during the night from 18：00 to 23：00 by 10-19 μg·m^-3. ② The change in pollutant concentrations showed a certain spatial clustering effect； due to the influence of topography and vegetation adsorption, PM_2.5 pollution was concentrated in the northern part, whereas O₃ pollution was more severe in the southern suburban area due to the weaker effect of NO₂ titration in the suburbs compared to that in the urban area. ③ During the lockdown period, the contribution of mobile sources to PM_2.5 decreased, whereas the contribution of fossil fuel combustion sources and industrial processes increased. The volume fraction of oxygen-containing VOCs increased due to the large-scale spraying of highly oxidizing disinfectants for epidemic prevention and control, accounting for 86.02% of the total VOCs, and acetaldehyde, propionaldehyde, and butenal were identified as priority control species among the VOCs as O₃ precursors. The impact of meteorological factors on pollutant concentrations was not a simple linear relationship； in the RH < P75 range, the mean PM_2.5 concentration increased with the increase in RH, whereas in the T > P25 range, the mean O₃ concentration increased with the increase in temperature. Cluster analysis showed that the local contribution rate was higher during the lockdown period, accounting for 32.80%, the significant increase in O₃ during the lockdown period promoted the secondary formation of PM_2.5, and regional heavy pollution transport enhanced the situation of non-decrease and rebound of PM_2.5.