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Seasonal and diurnal characteristics of the vertical profiles of aerosol properties are essential for detecting the regional transport and the climatic radiative effects of aerosol particles. We have studied the seasonal and diurnal characteristics of the vertical distribution of aerosols in urban Beijing from 2017 to 2021 based on long-term Raman–Mie LiDAR observations. The influence of the vertical distribution of aerosols, the meteorological conditions within the boundary layer, the optical–radiometric properties of aerosols, and their interconnections, were investigated during a heavy haze pollution event in Beijing from 8 to 15 February 2020 using both meteorological and sun photometer data. The aerosol extinction coefficient was highest in summer (0.4 km−1), followed by winter (0.35 km−1), and roughly equal in spring and autumn (0.3 km−1). The aerosol extinction coefficient showed clear daily variations and was different in different seasons as a result of the variation in the height of the boundary layer. During the haze pollution event, the particulate matter mainly consisted of scattered spherical fine particles and the accumulation time of pollutants measured via the AOD440nm and PM2.5 mass concentration was different as a result of the hygroscopic growth of the aerosol particles. This growth increased scattering and led to an increase in the aerosol optical depth. The vertical transport of particulate matter also contributed to the increase in the aerosol optical depth. [ABSTRACT FROM AUTHOR]

Aerosols can affect vertical thermal structure during heavily polluted episodes (HPEs). Here, we selected four typical HPEs in 2018, which were further subdivided into dust and haze events. The vertical distribution of aerosols extinction coefficient (EC) and variations in columnar optical properties were investigated based on sun-photometer and Lidar observation at an urban site in Beijing. The vertical characteristics in shortwave radiative heating rate (HR) of aerosols were studied using NASA/Goddard radiative transfer model along with observational data. In the haze episode, EC layer is less than 1.5 km and shows strong scattering, with single-scattering albedo (SSA440nm) of ~0.97. The heating effects are observed at the middle and upper atmosphere, and slight heating effects are found at the lower layer. The mean HR within 1.5 km can be up to 16.3 K day−1 with EC of 1.27 km−1, whereas the HR within 0.5 km is only 1.3 K day−1. In the dust episode, dust aerosols present the absorption with SSA440nm of ~0.88, which would heat the lower atmosphere to promote vertical turbulence, and the height of EC layer can be up to 2.0–3.5 km. In addition, the strong heating effects of dust layer produced cooling effects near the surface. Therefore, the accurate measurement of aerosols optical properties in HPEs is of great significance for modeling aerosols direct radiative effects. [ABSTRACT FROM AUTHOR]

Aerosol microphysical and optical properties as well as aerosol direct radiative effect (ADRE) were measured at a few ground sites to investigate aerosol optical‐radiative characteristics in northeastern China. Bimodal size distributions showed a dominance of fine mode particles at Shenyang, a megacity, and more impacts from larger particles at Fushun and Dalian, industrial and coastal sites, respectively. High aerosol optical depths at 440 nm in July (0.67–1.25) were ascribed to hygroscopic effects or cloud processing. Single scattering albedos at 440 nm show strong to moderate absorption at the urban and industrial sites (0.84–0.86) and weaker absorption at the coastal and rural sites (0.92–0.94). The single scattering albedo wavelength dependence implied influences of dust at the urban, industrial, and coastal regions (shorter wavelengths) and biomass emissions at the rural site (longer wavelengths). Absorptive aerosol optical depths at the urban and industrial sites were ~2.5 and 3.7 times higher than at the coastal and rural sites. Large negative ADREs at the bottom of the atmosphere at the urban and industrial sites implied strong surface cooling and the larger ADREs at the top of the atmosphere at the coastal site indicated more cooling of the Earth‐atmosphere system. The main aerosol types at the urban and industrial sites were mixed absorbing particles, while weakly‐absorbing fine mode particles dominated the coastal and rural sites. This study provides new information on the aerosol distributions and potential regional climate effects of aerosols in northeastern China. Key Points: High AODs in July were ascribed to hygroscopic effects in Northeast ChinaThe SSA440 nm show strong to slight absorption over the study regionThere is stronger surface cooling effect at the urban and industrial sites [ABSTRACT FROM AUTHOR]

The aerosol microphysical, optical and radiative properties of the whole column and upper planetary boundary layer (PBL) were investigated during 2013 to 2018 based on long-term sun-photometer observations at a surface site (~106 m a.s.l.) and a mountainous site (~1225 m a.s.l.) in Beijing. Raman-Mie lidar data combined with radiosonde data were used to explore the aerosol radiative effects to PBL during dust and haze episodes. The results showed size distribution exhibited mostly bimodal pattern for the whole column and the upper PBL throughout the year, except in July for the upper PBL, when a trimodal distribution occurred due to the coagulation and hygroscopic growth of fine particles. The seasonal mean values of aerosol optical depth at 440 nm for the upper PBL were 0.31 ± 0.34, 0.30 ± 0.37, 0.17 ± 0.30 and 0.14 ± 0.09 in spring, summer, autumn and winter, respectively. The single-scattering albedo at 440 nm of the upper PBL varied oppositely to that of the whole column, with the monthly mean value between 0.91 and 0.96, indicating weakly to slightly strong absorptive ability at visible spectrum. The monthly mean direct aerosol radiative forcing at the Earth's surface and the top of the atmosphere varied from −40 ± 7 to −105 ± 25 and from −18 ± 4 to −49 ± 17 W m−2, respectively, and the maximum atmospheric heating was found in summer (~66 ± 12 W m−2). From a radiative point of view, during dust episode, the presence of mineral dust heated the lower atmosphere, thus promoting vertical turbulence, causing more air pollutants being transported to the upper air by the increasing PBLH. In contrast, during haze episode, a large quantity of absorbing aerosols (such as black carbon) had a cooling effect on the surface and a heating effect on the upper atmosphere, which favored the stabilization of PBL and occurrence of inversion layer, contributing to the depression of the PBLH. Unlabelled Image • Aerosol optical properties for upper planetary boundary layer were showed in Beijing. • Aerosol radiative effects to planetary boundary layer were investigated. • Mineral dust heated middle to low atmosphere, thus promoted turbulence. • Absorptive aerosol facilitated the formation of inversion layer in haze episode. [ABSTRACT FROM AUTHOR]

The reduction of traffic flow in downtown areas during the Chinese National Day holiday and the fireworks during the Spring Festival provide a unique opportunity for investigating the impact of urban anthropogenic activities on aerosol optical properties during these important Chinese festivals in Beijing. The National Day in 2014 and 2015 and Spring Festival in 2015 and 2016 were selected as study periods. The aerosol optical depth (AOD) at 440 nm increased over the all holiday periods and the average AODs during the 2015 National Day, 2015 Spring Festival and 2016 Spring Festival were about 81%, 21% and 36% higher than the background levels, respectively. The average AOD in 2014 National Day holiday was lower than background level partly influenced by precipitation event. The absorption AOD (AAOD) at 440 nm showed consistent variations with the AOD and the average AAODs during the 2015 National Day, 2015 Spring Festival and 2016 Spring Festival holidays were about 75%, 19% and 23% higher than the background level, respectively. The mean values of single scattering albedo were greater than the background level during the Spring Festival holidays, whereas the values during the National Day holiday in 2015 were lower partly due to the reduction of vehicular emissions in downtown areas. Fine- and coarse-mode particle volumes during pollution periods in holidays were ~ 0.04–0.25 μm 3 and ~ 0.03–0.15 μm 3 larger than background level, respectively. The results of potential source contribution function and concentration-weighted trajectory analyses identified the areas south of Beijing as the main source regions of PM 2.5 and were responsible for the extremely high PM 2.5 concentrations in Beijing during the holiday periods. The findings of this study may aid understanding the effects of human activities on aerosol optical properties over Beijing area and contribute to improving regional air quality. [ABSTRACT FROM AUTHOR]

Since haze and other air pollution are frequently seen in the North China Plain (NCP), detail information on aerosol optical and radiative properties and its type classification is demanded for the study of regional environmental pollution. Here, a multiyear ground-based synchronous sun photometer observation at seven sites on North China Plain megalopolis from 2013 to 2018 was conducted. First, the annual and seasonal variation of these characteristics as well as the intercomparsion were analyzed. Then the potential relationships between these properties with meteorological factors and the aerosol type classification were discussed. The results show: Particle volume exhibited a decreasing trend from the urban downtown to suburban and the rural region. The annual average aerosol optical depth at 440 nm (AOD 440) varied from ∼0.43 to 0.86 over the NCP. Annual average single-scattering albedo at 440 nm (SSA 440) varied from ∼0.89 to 0.93, indicating a moderate to slight absorption capacity. Average absorption aerosol optical depth at 440 nm (AAOD 440) varied from ∼0.07 to 0.10. The absorption Ångström exponent (AAE) (∼0.89–1.40) indicated the multi-types of absorptive matters originated form nature and anthropogenic emission. The discussion of aerosol composition showed a smaller particle size of aerosol from biomass burning and/or fossil foil consumption with enhanced aerosol scattering and enlarged light extinction. Aerosol classification indicated a large percentage of mixed absorbing aerosol (∼20%–49%), which showed increasing trend between relative humidity (RH) with aerosol scattering and dust was an important environmental pollutant compared to southern China. • Long-term aerosol observation campaign was conducted in NCP megalopolis. • SSA indicated a moderate to slight absorption capacity of aerosol over seven sites. • Smaller aerosol size with enhanced aerosol scattering and extinction was found. • Dust was still an important environmental pollutant in northern China. [ABSTRACT FROM AUTHOR]