Abstract:

Due to the increasingly prominent O₃ pollution problem in Chinese cities in recent years, near-surface O₃ has become one of the main air pollutants in Shenyang.. Based on the hourly data of near-surface ozone (O₃) and its precursors (VOCs and NO₂) in Shenyang, combined with the meteorological observation data of the same period, the seasonal variation characteristics of O₃ in Shenyang in 2019 were studied. The effects of VOCs, NO₂ and meteorological conditions on formation of O₃ were analyzed. The ozone generation potential (OFP) of VOCs were estimated using the maximum incremental reactivity (MIR), and the source apportionment of VOCs was studied based on the positive matrix factorization (PMF) method. The results show that the average O₃ mass concentration in 2019 of Shenyang was the highest in summer, followed by spring and autumn, and the lowest in winter. The O₃ mass concentrations in all four seasons showed the characteristics of uni-peak mode with the peak occurring at around 2 pm and the trough at around 7 am. The O₃ mass concentrations showed a positive correlation relationship with temperature and wind speed (P=0.001 and P=0.005, respectively), and a negative correlation with humidity (P=0.005). The O₃ mass concentration increased significantly when temperature reached above 30.0 ℃. The O₃ mass concentration was less than 75.0 μg∙m⁻³ when the wind speed was lower than 3.0 m∙s⁻¹, while the O₃ mass concentration increased rapidly to 100 μg∙m⁻³ when the wind speed exceeded 4.0 m∙s⁻¹. The O₃ mass concentration was higher when H_r<20%, and declined from 75.0 μg∙m⁻³ to 58.7 μg∙m⁻³ when H_r>80%. The O₃ mass concentration was also negatively correlated with VOCs and NO₂ (P=0.005). When the average mass concentration of O₃ reaches the maximum value, the mass concentration range of NO₂ was 20.0-30.0 μg∙m⁻³. In 2019, the annual OFP of various VOCs showed in order of alkene>aromatic hydrocarbons>alkanes>alkynes, and alkenes were the largest contributors in four seasons, indicating that alkenes have an important contribution to O₃ generation in Shenyang. In summer, the sources of VOCs mainly included petrochemicals, solvent usage, liquefied petroleum gas pollution, combustion, and motor vehicle emission sources. As China's traditional heavy industry base, strengthening supervision on petrochemical industry, solvent use and fuel volatilization are effective ways to reduce the atmospheric O₃ concentration level in Shenyang. This research can provide an important reference for O₃ pollution control in Shenyang.

Key words: Shenyang, ozone, VOCs, pollution characteristics, meteorological conditions, ozone generation potential, source apportionment

摘要：

近年来中国城市O₃污染问题日益突出，近地面O₃已成为沈阳市的主要空气污染物之一。基于沈阳市2019年近地面臭氧（O₃）及其前体物（VOCs和NO₂）的逐时数据，结合同期气象观测资料，研究了2019年沈阳大气O₃的季节变化特征，分析了VOCs和NO₂以及气象条件对O₃生成的影响；利用最大增量反应活性法（MIR）估算了沈阳大气VOCs的臭氧生成潜势（OFP），并运用正交矩阵因子分解法（PMF）进行了沈阳夏季VOCs的来源解析。结果表明：2019年沈阳市O₃平均质量浓度夏季最高，其次是春季和秋季，冬季最低；四季O₃日变化特征均表现为单峰型，质量浓度峰值出现在14:00左右，谷值出现在07:00左右。沈阳市O₃质量浓度与温度、风速均呈现正相关关系（P=0.001，P=0.005），与相对湿度呈负相关关系（P=0.005）；当温度达到30.0 ℃以上，O₃质量浓度明显升高；风速低于3.0 m∙s⁻¹时O₃质量浓度小于75.0 μg∙m⁻³，而风速超过4.0 m∙s⁻¹时O₃质量浓度迅速升高至100 μg∙m⁻³；湿度小于20%时O₃质量浓度较高，当湿度大于80%时O₃质量浓度显著降低，由75.0 μg∙m⁻³降低至58.7 μg∙m⁻³。O₃平均质量浓度与前体物VOCs和NO₂质量浓度呈负相关关系（P=0.005），O₃平均质量浓度最大值对应的NO₂质量浓度区间为20.0-30.0 μg∙m⁻³。2019年沈阳市大气VOCs的臭氧生成潜势依次表现为烯烃>芳香烃>烷烃>炔烃，烯烃在4个季节均为最大贡献者，表明烯烃对沈阳市O₃生成具有重要贡献。夏季沈阳市VOCs主要来源于石油化工源、溶剂使用源、液化石油气污染源、燃烧源和机动车排放源。沈阳作为我国传统重工业基地，加强对石油化工、溶剂使用和燃料挥发等方面的监管是降低沈阳市大气O₃质量浓度水平的有效途径。该研究可以为沈阳市O₃污染治理提供重要参考。

关键词: 沈阳, 臭氧, VOCs, 污染特征, 气象条件, 臭氧生成潜势, 来源解析