2015—2021年南京市大气污染特征及污染个例研究

探究细颗粒物(PM_2.5)和臭氧(O₃)污染的时间变化特征，阐明PM_2.5和O₃复合污染过程中不同阶段环境空气污染物及气溶胶粒径分布的详细演变过程，对南京及长三角地区的大气污染防治具有重要指导意义.本文使用2015—2021年南京市环境空气污染物小时浓度数据，分析了该地区多年大气污染演变过程，并选取2015年10月12—17日时间段作为复合污染典型个例，对其生消过程和内在机理进行了详细分析.结果表明：(1)2015—2021年南京市各种大气污染物的变化特征具有明显差异. PM_2.5、PM₁₀和SO₂浓度的年下降率分别为8.9%、6.2%和15.4%,O₃浓度变化较小. CO浓度在2016年达峰后以每年7.6%的速率下降.NO₂浓度在2015—2019年呈增加趋势.(2)2015—2021年污染特征发生较大变化，由PM_2.5为主导变为由O₃为主导的大...

Analysis of Air Pollution Characteristics and Associated Compound Air Pollution Case in Nanjing from 2015 to 2021

The Yangtze River Delta (YRD) urban agglomeration is the most economically developed and urbanized area in China, and it is an important intersection between the ‘Belt and Road Initiative’ and the Yangtze River Economic Belt. Nanjing is a megacity in the YRD region and an important central city in the eastern region. The rapid development of urbanization has an obvious regional radiation effect. The industry, traffic and population of Nanjing and surrounding areas have shown rapid growing pollution problems. Studies on the spatial-temporal characteristics of air pollution have been extensively carried out, but research remains scarce in long-term systematic tracking investigation on the relationship between air pollutants and meteorological variables, especially in China′s urban sites (e.g. Nanjing) and recent comprehensive environmental pollution control. Here, we used hourly concentrations of six air pollutants and meteorological data in Nanjing between 2015 and 2021 and revealed the characteristics of PM_2.5 and ozone (O₃) pollution and their interactions with meteorological conditions. In addition, the pollution types of megacities were mostly compound air pollution. Based on aerosol size distribution data (10 nm-10 μm), we selected a typical compound air pollution episode (October 12th to 17th, 2015) in Nanjing to further clarify the local pollution characteristics. The results showed that the characteristics of six ambient air pollutants differed from one another. The concentrations of PM_2.5, PM_10, and SO₂ decreased significantly, with an average annual decline rate of 8.9%, 6.2% and 15.4%, respectively. In contrast, NO₂ showed an upward trend from 2015 to 2019. CO peaked in 2016 and then declined at a rate of 7.6% per year. The concentration of O₃ showed a small variation during 2015-2021. Overall, the type of air pollution in Nanjing underwent complex changes, shifting from PM_2.5 dominance to O₃ dominance. The frequency and intensity of PM_2.5 dominated pollution decreased notably, while the frequency and intensity of O₃ dominated pollution did not change significantly. At different air pollution evolution stages, the number concentration spectra of aerosols were bimodal while the peak particle size and concentration were different. The peak aerosol concentrations were the lowest in the PM_2.5 pollution stage, with peak values of 30 nm and 100 nm, respectively. The aerosol size distribution peaks in nucleation mode shifted to smaller size pattern in the NO₂ pollution stage, and the value was 22-26 nm. In PM_2.5 and O₃ combined pollution stage, the first peak of aerosol distribution in nucleation mode shifted to a larger size pattern around 30 nm, which differed from that in accumulation mode, and the second peak concentration increased and peak width became wider, especially for the size > 100 nm. In the O₃ dominated pollution stage, the peak aerosol size remained unchanged, but the peak concentration increased significantly, especially the nucleation mode aerosol, which was 3-5 times higher than the counterpart before the pollution. In all different pollution stages, ambient air pollutants and aerosol number concentrations in different modes showed obvious diurnal variations. The coordinated prevention and control of PM_2.5 and O₃ pollution in Nanjing City needs to focus on the characteristics of local pollutants and the impact of emission sources, especially the variation and emission sources of precursors affecting O₃ pollution.