LAUSR

Particulate matter with diameters of 2.5 μm or smaller (PM2.5) and ozone (O3) are major pollutants in the urban atmosphere. PM2.5 can affect O3 by altering the photolysis rate and heterogeneous reactions. However, these two processes and their relative importance remain uncertain. In this paper, with Nanjing in China as the target city, we investigate the characteristics and mechanism of interactions between particles and O3 based on ground observations and numerical modeling. In 2008, the average concentrations of PM2.5 and O3 at Caochangmen station are 64.6±47.4 μg m−3 and 24.6±22.8 ppb, respectively, while at Pukou station they are 94.1 ± 63.4 μg m−3 and 16.9 ± 14.9 ppb. The correlation coefficient between PM2.5 and O3 is −0.46. In order to understand the reaction between PM2.5 and O3, we construct a box model, in which an aerosol optical property model, ultraviolet radiation model, gas phase chemistry model, and heterogeneous chemistry model, are coupled. The model is employed to investigate the relative contribution of the aforementioned two processes, which vary under different particle concentrations, scattering capability and VOCs/NOx ratios (VOCs: volatile organic compounds; NOx: nitric oxide and nitrogen dioxide). Generally, photolysis rate effect can cause a greater O3 reduction when the particle concentrations are higher, while heterogeneous reactions dominate O3 reduction with low-level particle concentrations. Moreover, in typical VOC-sensitive regions, O3 can even be increased by heterogeneous reactions. In Nanjing, both processes lead to O3 reduction, and photolysis rate effect is dominant. Our study underscores the importance of photolysis rate effect and heterogeneous reactions for O3, and such interaction processes should be fully considered in future atmospheric chemistry modeling.摘要PM2.5是指大气中空气动力学直径小于2.5 µm的细颗粒物. 细颗粒物(PM2.5)和臭氧(O3)是城市大气中的重要污染物. PM2.5可以通过影响光解反应过程和非均相化学反应过程来影响O3的浓度. 本文基于地面观测和数值模拟, 以中国南京为例研究了PM2.5与O3相互作用的特征和机理. 研究发现, 南京草场门站PM2.5和O3的平均浓度分别为64.6 ± 47.4 μg m-3和24.6 ± 22.8 ppb, 浦口站PM2.5和O3的平均浓度分别为94.1 ± 63.4 μg m-3和16.9 ± 14.9 ppb. PM2.5和O3之间的相关系数为-0.46. 为了深入理解PM2.5与O3之间的相互作用, 构建了一个包含气溶胶光学性质模块, 紫外辐射传输模块, 气相化学模块和非均相化学模型块的零维箱型模式, 用于研究在不同的PM2.5浓度, 大气散射能力和VOC/NOx(VOC: 挥发性有机化合物; NOx: 一氧化氮和二氧化氮)情况下, 光解反应和非均相化学反应过程的相对贡献及变化. 通常情况下, 当PM2.5浓度较低时, 颗粒物主要通过其表面发生的非均相反应导致O3减少; 当PM2.5浓度较高时, 颗粒物主要通过影响光解反应导致O3减少. 此外, 在典型的VOC敏感区域中, 非均相化学反应还可能导致O3浓度的增加. 在南京地区, PM2.5通过上述两个过程导致O3减少, 其中光解反应的影响占主导. 本研究强调了光解反应和非均相反应影响O3的重要性, 在未来的大气化学模型中应充分考虑PM2.5与O3之间的相互作用.