Black carbon (BC) aerosols, which arise from incomplete combustion processes, possess the capacity to absorb solar radiation, thereby contributing significantly to the issue of climate warming. However, accurately estimating their radiative effect is challenging, influenced by emissions, sizing, morphology, and mixing state. BC particles undergo aging processes that can alter their physical characteristics and mixing state, consequently affecting their optical properties. In this study, we assessed the mixing state of BC across diverse atmospheric environments. Results demonstrate that mixing state heterogeneity is a ubiquitous phenomenon. In background atmospheres, BC exhibited less homogeneous states compared to those in urban and suburban areas, where heterogeneity was driven by primary emissions. Our study provides direct observational evidence that the heterogeneity of particle-particle mixing can reduce the light absorption enhancement of BC in all atmospheres, with a deviation of up to approximately 24% under background conditions.

The new particle formation (NPF) process is a significant source of atmospheric secondary particles, which has remarkable impacts on the regional air quality and global radiative forcing. Most NPF studies conduct their measurements at a single site, which can hardly provide information about the regionality of NPF events at large scales (>100 km). During the 2022 Winter Olympic and Paralympic Games, simultaneous measurements of particle number size distributions and NPF-associated precursors were conducted at a mountainous site close to the Winter Olympic Village in Chongli (CL), Zhangjiakou, and an urban site in Beijing (BJ) located 150 km southeast of the CL site. High NPF frequencies were observed at the CL (50%) and BJ (52%) sites; however, the fraction of concurrent NPF events was smaller than the results in other regions. In addition, the wind distributions exhibited distinct air mass origins at the two sites during the concurrent NPF events. Compared with the BJ site, the NPF growth rates were higher at the CL site due to higher levels of volatile organic compounds (VOCs) and radiation. Surprisingly, the formation rates at the CL site were lower than at the BJ site, even with a higher sulfuric acid concentration and lower CS, which may be attributed to lower dimethylamine concentrations in the mountainous area. This study reveals that, although NPF events are commonly thought to occur on regional scales, their intensity and mechanisms may have significant spatial inhomogeneity. Further studies are required to reduce the uncertainty when expanding the mechanisms based on the urban conditions to regional or global scales in the models.

细颗粒物（PM2.5）和臭氧（O3）是我国当前最关注的两种大气污染物，影响空气质量并危害人体健康。本文以2013~2020年北京大气污染物浓度水平和气象数据为基础，揭示PM2.5与O3污染的逐年变化特征及典型污染过程的“发生-发展-消除”规律。研究表明，PM2.5污染过程的发生频次、持续时间、峰值浓度均逐年下降；相比之下，O3污染过程的年际变化趋势不明显，在历年的5~7月中大约1/3时间处于O3污染过程之中；且在2018年，O3超标天数首次超过PM2.5超标天数，暗示O3可能正在取代PM2.5成为北京空气质量超标的主要污染物。通过剖析3次PM2.5污染过程、3次O3污染过程、3次PM2.5与O3双污染过程，发现PM2.5爆发时和O3爆发前对应着高氮氧化物（NOx）浓度。PM2.5超标天多发生在冬季及其前后，且一个污染过程持续时间较长，PM2.5浓度变化呈现横跨多天的山峰型或阶梯型；而O3超标天多发生在夏季及其前后，O3浓度呈现明显的日变化规律，即日间高夜间低；当O3污染持续时间较长时，可能发展成O3与PM2.5双超标，此时两种污染物的浓度会在时间序列上呈现一定的峰谷交替现象，且与温湿度的昼夜变化规律较为吻合。本文结果可为相关部门明晰与协同控制PM2.5和O3提供一定的理论依据，在现阶段大气污染防治已取得长足进展的基础之上，进一步提升空气质量。

In urban and remote atmospheres, new particle formation (NPF) events often occur after dust storms, which can have further impacts on regional and global climate. Additionally, the levels of gaseous precursors and condensation sink (CS) resulting from anthropogenic emissions can also influence the occurrence and intensity of NPF events. Over the past decade, China has implemented various air quality improvement actions, leading to significant changes in air pollutant emissions. However, there have been limited studies on the long-term evolution of NPF events caused by the synergy of dust storms and anthropogenic emissions.This study aims to analyze the characteristics of dust-related NPF events in Beijing from 2009 to 2017 and compare them with non-dust NPF events. The results show that the formation rates of dust-related NPF events decreased due to the reduction of SO2 emissions. However, the growth rates remained stable, possibly due to the increasing oxidation capacity in Beijing. These findings contribute to a deeper understanding of the climate effects of natural dust under the influence of anthropogenic emission control measures.