Abstract This study analyzes the microphysical characteristics of lightning initiation environments over Guangzhou, China, based on vertical radar reflectivity cores. Results indicate that the vertical reflectivity cores for both intracloud (IC) and negative cloud-to-ground (NCG) lightning initiations are concentrated within similar ranges. Approximately 88% of NCG initiations and 86% of IC initiations are associated with reflectivity cores between 35 and 60 dBZ within the 1–7 km altitude layer.Most NCG flashes initiate within a vertical range of −4–5 km around the reflectivity core, whereas IC flashes typically initiate 2–12 km above the core. While the primary initiation height of NCG flashes varies noticeably with changes in core altitude, that of IC flashes remains relatively stable.As the reflectivity core descends from higher to lower altitudes, the initiation frequency of both IC and NCG flashes first increases then decreases, peaking when the core is located at 2–3 km. However, the core altitude corresponding to peak initiation within the center and its immediate vicinity (±1 km) differs: 4–5 km for IC flashes versus 2–3 km for NCG flashes. Additionally, the NCG/IC initiation ratio generally increases as the core descends.These findings suggest that the charge layer near the reflectivity core—likely corresponding to the lower positive charge region in a tripolar structure—significantly modulates NCG lightning occurrence. The observed correlations between flash activity and core height further imply that variations in the vertical reflectivity core are synchronized with the evolution of the intracloud charge structure.

Abstract Brown carbon (BrC), a light‐absorbing organic aerosol, exhibits higher absorption coefficients at short wavelengths. Partial BrC can be formed via secondary process. In this study, we isolated the secondary BrC (σabs,sec BrC) between urban surface and mountain stations (which receive surface pollutants during convective mixing) to investigate how atmospheric lifetime variations influence its absorption properties. Although the surface provided more favorable conditions for precursor concentrations and physicochemical reactions, the surface station observed lower σabs,sec BrC during the most developed planetary boundary layer period. This was driven by low temperatures and relative humidity (RH) during uplift, which extended the atmospheric lifetime of high‐viscosity secondary BrC, thereby enhancing σabs,sec BrC observed at the mountain station. Variations in near‐surface emission intensity dominated peak σabs,sec BrC values observed at the mountain station during 14:00–15:00. Moreover, decreasing RH promoted higher viscosity, which enhanced σabs,sec BrC.

Based on MODIS cloud products, GPM precipitation data, and ERA5 reanalysis, this study investigated the cloud characteristics during a cross-seasonal super-drought event from autumn 2009 to spring 2010 over the Yunnan-Guizhou Plateau (YGP). The Comprehensive Multiscalar Index (CMI) was employed to measure the drought intensity. This drought event can be divided into the development phase, the severe phase, and the mitigation phase based on the CMI and precipitation anomalies of the YGP. During the development phase, suppressed cloud vertical growth lowered cloud top height (CTH) from a range of 5-8 km to a range of 3-5 km. Meanwhile, a consistent decline in the ice water path (IWP) was observed. Furthermore, only 24.6% of clouds were mixed-phase, a condition that inhibits the Bergeron and riming processes, thereby reducing precipitation. In the severe phase, the cloud optical thickness (COT) dropped by 12.9%, and the average mixed-phase cloud water path fell to 294.5 g m-2, which further limited the precipitation. During the mitigation phase, the CTH rose to 6-9 km, and the proportion of mixed-phase clouds increased to 83.0%. Moreover, a synchronous increase in ice and liquid water paths reestablished favorable conditions for precipitation, thereby mitigating the drought.

The aggregate measure known as oxidative potential (OP) is used to assess the health risk associated with exposure to fine particulate matter (PM2.5). Evaluation of the contributions of PM2.5 sources to OP, especially typical industrial sources, is critical for human health. In this study, samples were collected from an industrial park, an urban site, and various pollution sources in a metal-smelting city (Baotou) across all four seasons in 2021, and the oxidative potential (OP) of PM2.5 was investigated using the dithiothreitol (DTT) assay. CMB model were used to determine the connections between PM2.5 and pollution sources.Moreover, a new method was proposed to quantify the contributions of various sources to the OP of ambient PM2.5. The DTTm of ambient PM2.5 during the sample period was 14.40 +/- 6.73 pmol min(-1) mu g(-1), with significant seasonal variations ranked as autumn > summer > winter > spring. Most detected constituents, such as secondary inorganic aerosol (SIA) species and some transition metals, exhibited positive correlations with DTTm (P < 0.05). According to the measurement of OP of different pollution sources, the sixteen sources ranked as follows: slag separation > electrolytic aluminum emissions > coal dust > vehicle exhaust > coking > fugitive dust from urban surfaces > tailings > steel slag > street dust > crushing plant emissions > soil > pulverized coal > dust from residual anode assembly > dust from roasted aluminum ash > sintered ash > sintering emissions. In general, the dominant sources of OP in ambient PM2.5 are slag separation and electrolytic aluminum emissions.

Abstract This study investigates the characteristics of negative cloud‐to‐ground (CG) lightning flashes across varying peak current (PCs) ranges by combining 3D location data from 2,597 negative CG flashes with radar observations. The flashes were classified into five PC bins: −25 kA < PC < 0 kA, −50 kA < PC < −25 kA, −75 kA < PC ≤ −50 kA, −100 kA < PC ≤ −75 kA, and PC ≤ −100 kA. Key parameters analyzed include initiation altitude, reflectivity at initiation points, vertical reflectivity cores, lightning extension spaces, horizontal distances between initiation and grounding points (HD), and time differences between the first‐detected radiation source and the first return stroke (TD). Results reveal that while initiation environments were broadly similar across PC ranges, large‐PC flashes tended to initiate at lower altitudes (1–3 km). These flashes form first return strokes faster (the median TD for current bins below −75 kA is less than 44 ms, whereas for bins above −75 kA the median TD is greater than 57 ms) after shorter horizontal propagation (The median HD for current bins below −75 kA is around 1.0 km, while for bins above −75 kA the median HD exceeds 1.2 km), with smaller pre‐return‐stroke extension areas. Despite this, large‐PC flashes usually develop more extensive total channel areas. These findings underscore the distinct environmental conditions that facilitate the initiation and propagation of large‐PC negative CG flashes during thunderstorms.

The vertical distribution of aerosol hygroscopicity is crucial for investigating the interaction between aerosols and cloud microphysics, as it is closely linked to the aerosol activation capacity at different altitudes. In this study, the aircraft-observed vertical distributions of aerosol hygroscopicity (kappa) are parameterized and incorporated into the WRF fast-SBM (fast-Spectral Bin Microphysics) scheme (kappa-SBM). Using 2D idealized sensitivity experiments under high and low relative humidity conditions, it was found that during the small droplet stage, the droplet size distribution differs significantly between these two conditions. However, in the large droplet stage, the spectral characteristics become similar. Comparison between 3D real-case simulations and comprehensive observations indicate that the new scheme can more accurately simulate the droplet spectrum near cloud base, reducing the overestimation of small droplets while improving the representation of larger droplets. Relative to the original SBM, the cloud droplet size distribution simulated using kappa-SBM shows a lower peak concentration (similar to 600 vs. similar to 1000 cm(-3)) and larger droplets, with the maximum mean diameter increasing from similar to 40 to similar to 60 mu m. Correspondingly, budget analysis indicates that the collision-coalescence and activation processes derived from the kappa-SBM contribute more to cloud water content (4.3%-5.1% and 6.3%-8.9%, respectively) but less to droplet number concentration, revealing a shift toward fewer yet larger cloud droplets. These results suggest the new scheme can improve the simulation of droplet activation, spectral evolution, and subsequent microphysical growth, highlighting that vertical variation in aerosol hygroscopicity should be adequately considered in cloud microphysics simulations.

This study analyzes 53 storms that occurred in the summer of 2015, using data from the Guangdong-Hong Kong-Macao Lightning Location System (GLLS) and an S-band Doppler radar observation. Among these storms, 34 produced large-peak-current cloud-to-ground (LCG) lightning, 10 produced only small-peak-current CG (SCG) lightning, and 9 produced no detectable CG lightning. The results show that the combination of 40 dBZ echo top height (Top40) and 40 dBZ echo area at 5 km altitude (Area40_5) effectively distinguishes LCG-dominant storms from non-LCG storms. The analysis reveals that updraft intensity fundamentally controls LCG production. Storms exhibiting maximum Top40 >= 12 km show evidently higher peak LCG frequencies and greater total LCG counts compared to storms with weaker updrafts. Notably, even storms with maximum Top40 < 12 km can achieve substantial LCG production when these moderately intense updrafts exhibit prolonged duration. A robust correlation emerges between the maximum Top40 values recorded during the 30-min period preceding LCG initiation and subsequent LCG counts in the initial active phase. Throughout storm lifetimes, Top40 variations mirror LCG frequency trends, with Top40 and Area40_5 values during LCG-active periods consistently exceeding those during SCG-only periods. Primary LCG activity predominantly occurs during Area40_5's growth phase prior to peak development, followed by rapid weakening or diminishment after the peak. These findings confirm that LCGs result from active updrafts, which may provide both favorable conditions for vigorous electrification and formation of high-density charge structures. Consequently, frequent LCG activity serves as an indicator of active updraft periods in storms. It should be noted that the thunderstorm cases analyzed in this study were all from a single summer season. Although the fundamental trends and relationships identified are expected to be robust, some specific quantitative values may vary interannually. Furthermore, the analysis primarily focused on localized, small-scale thunderstorms, which represent the most common type during the local summer. Consequently, the conclusions drawn here may not be fully applicable to larger-scale convective systems and should be interpreted with caution in such contexts.

The vertical distribution of light-absorbing carbonaceous aerosols significantly affects atmospheric radiative forcing properties. A novel method combining HYSPLIT trajectory ensemble and concentration-weighted trajectory (CWT) analysis (Ens-HYSPLIT-CWT) was employed in this study to distinguish local emission events from all air mass sources. The aerosol profile distribution under pollution control measures in Beijing was investigated using continuous and simultaneous measurements at both surface and mountain stations. By applying the wavelength dependence of the absorption Ångström exponent (WDA) method, more accurate brown carbon (BrC) absorption coefficients at 370 and 470 nm were derived, better aligning with the observed wavelengths of the AE33 instrument. We found a larger vertical decrease for BrC compared to black carbon (BC) particles, resulting in an enhanced fraction of BC absorption relative to BrC measured at the mountain station. Furthermore, we investigated the columnar aerosol optical properties at 550 nm by combining BC and BrC absorption, and aerosol scattering properties derived from Mie theory. Peak values of aerosol optical depth (AOD) and absorption aerosol optical depth (AAOD) both occurred at noon during locally emitted pollution events. AOD increased by 1.91 times, and AAOD increased by 1.93. Additionally, due to the higher transport efficiency of BC particles compared to non-BC particles during locally emitted pollution events, the single scattering albedo (SSA) exhibited a valley at noon.

Understanding the changes in particle physical and chemical characteristics is critical for investigating the formation mechanisms of particles. This study conducted an observation campaign at the National Background Station on the Qinghai-Tibetan Plateau. We employed a Scanning Mobility Particle Sizer (SMPS) for measuring particle number concentration (PNC), sized from 3.85 to 478.30 nm. The observation was conducted from September 17th to October 14th, 2013, aiming to analyze particle size distributions of new particle formation (NPF) events and non-NPF in an environment free from complex human-induced disturbances, allowing for a more isolated study on the processes of particle formation and growth. We found that the NPF events occurred frequently (about 80 % days of the observation period) in this high-altitude region. Further source analysis identified four factors: nucleation sources, nucleation aging sources, combustion emissions sources, and secondary formation sources. Distinct differences existed in the diurnal variations of these factors between NPF and non-NPF periods. In summary, with the absence of significant human interference, we identified the major drivers of the four sources: 1) nucleation source was primarily driven by gaseous sulfuric acid at low wind speeds; 2) the levels of O3 mainly impacted nucleation aging sources; 3) combustion emissions sources originated from nearby anthropogenic activities, and 4) the boundary layer dynamics greatly influenced secondary aerosols. Results highlighted the significant roles of different atmospheric factors, including aerosol chemical composition and condensation sink efficiency, in influencing NPF.

Warm rain prevails in clean marine clouds and is one of the most abundant types of precipitation in the world. However, warm rain is rarely observed in urban polluted atmospheric environments due to high number concentrations of aerosols generally suppress the occurrence of warm rain. Three aircraft observation of clouds were used during summer in Beijing area. Here, we documented warm rain processes similar to shallow marine clouds in the urban (Beijing) atmospheric environment after cleansing air pollution by extensive precipitation observed on 11 September 2019. Our results showed that, compared with aircraft observations of similar cumulus clouds under polluted conditions, large-scale precipitation can efficiently scavenge air pollution in Beijing and lead to marine-like clouds with warm rain. The average aerosol concentration (Na) near the cloud base in these clean cases was only 225 cm-3 with cloud droplet number concentration (Nd) of 36 cm-3, (maximum of 142 cm-3) which led to enhanced coalescence. The warm rain was initiated at 600 m above the cloud base. Our results highlight the significance of pollution scavenging by precipitation in warm rain production in urban environment.

The Fenwei Plain (FWP) has experienced the most serious winter PM2.5 pollution in China since 2000. This study investigates causes behind interannual variability of wintertime PM2.5 concentration in the FWP during 2000-2021 and projects future trends through integrated observations, reanalysis data and simulations. The results show that the Eurasian-like (EUL) pattern is responsible for the interannual variability of PM2.5 concentration in the FWP, accounting for up to 55 % of the dominant pollution mode in the region. The EUL pattern modulates PM2.5 anomalies by causing higher relative humidity, more stable atmospheric stratification and anomalous southeasterly wind. Additionally, based on an EUL index, this study further projects that large-scale atmospheric circulation may exacerbate PM2.5 pollution in the FWP during 2035-2060. Specifically, the EUL pattern exhibits greater extremity and a higher frequency under high emission scenarios (i.e., 39.9 % in SSP585) compared to low emission scenarios (i.e., 19.9 % in SSP245), suggesting increased frequency of the EUL pattern and the associated PM2.5 pollution events in the FWP after 2035 in high emission scenarios. These insights provide scientific support for prevention and control of PM2.5 pollution in the FWP in winter.

The vertical distribution of reactive trace gases can greatly help understand the complex atmospheric evolution under the joint impacts of surface emission, chemical removal, and regional transport. Focusing on the core area of the North China Plain, aircraft-based observations were conducted in September 2017 and July 2019 to reveal the vertical distributions of volatile organic compounds (VOCs) measured by high-time resolution mass spectrometry. Generally decreasing trends of VOC concentrations with altitudes were captured, indicating strong surface source emissions and chemical removal within the planetary boundary layer (PBL). Ethanol exhibited the highest concentration within the PBL with an average of 46.7 ppbv and the largest ratio (16.5) between the average below and above the PBL heights. The vertical-averaged VOCs above Baoding were greater than those in Beijing by factors ranging from 1.2 to 3.5, suggesting richer precursors for secondary pollutant formation in Baoding. Increases of several VOC species, including styrene and acetonitrile, at high altitudes (>2500 m) were captured in Beijing. Correlation analysis further revealed the significant influences of industrial and biomass burning emissions. Our results highlight the critical role of both local emissions and regional transport in shaping the VOC vertical distributions, which may affect atmospheric organic chemistry across various atmospheric layers in the region.

The Beijing-Tianjin-Hebei urban agglomeration is one of the regions in China with the most severe air pollution. Using aircraft observations collected over Xingtai in May 2016 and multi-source data, such as aerosol chemical composition and lidar data, we analyzed aerosol composition and optical properties, vertical pollution characteristics of gases within the boundary layer, and their interactions with meteorological parameters. This study focuses on investigating the transport and evolution mechanisms of pollutants during transitions from polluted research flight No.7(RF7) to clean research flight No.8 (RF8) periods in summertime Xingtai. Results show that during RF7, the near-surface submicron aerosol (PM1) mass concentration was generally low (37.5 µg m−3), with the contribution of inorganic salts far exceeding that of organic matter. Aircraft observations indicated weak cold-air activities above 1000 m during RF8, while the southeasterly wind still prevailed below 1000 m, with a slight increase in wind speed. From RF7 to RF8, the overall vertical atmosphere gradually transitioned from polluted to clean conditions. During RF8, an inversion layer appeared in the temperature profile between 1100 and 1300 m, with 21.3

The relative dispersion of cloud and fog droplets has significant impacts on aerosol indirect effects, radiative transfer, and microphysical processes. However, previous studies have been mostly concerned with clouds, with limited studies on fog, particularly those that examine the combined influences of all key physical processes and their roles during fog evolution. As such, this study aims to conduct a comprehensive investigation by examining the relationships between relative dispersion and other microphysical variables, as well as the underlying microphysical and dynamic processes, based on field fog campaigns in polluted and clean conditions. In polluted fog, droplet concentrations are higher, leading to smaller droplets and increased dispersion. The correlation between dispersion and droplet volume-mean radius is positive in the polluted fog, but shifts to negative in clean fog. We attribute the difference to various microphysical processes like aerosol activation, condensation, collision-coalescence, and entrainment-mixing. In polluted fog, high aerosol concentrations, low supersaturations, and strong turbulence (entrainment-mixing) provide suitable conditions for the simultaneous occurrence of droplet condensation and aerosol activation, resulting in a positive correlation between dispersion and volume-mean radius, especially during the fog formation stage. In contrast, during the mature stage in clean fog, condensation is dominant with weak aerosol activation leading to a negative correlation between relative dispersion and volume-mean radius. The collision-coalescence process is more active in the mature stage, increasing radii and leading to the negative correlation between dispersion and volume-mean radius. This result sheds new light on understanding the relative dispersion and mechanisms in fog under different aerosol backgrounds.

Abstract. The influence of anthropogenic aerosols on cloud formation and precipitation, through their effects on cloud microphysics and thermodynamics, is crucial for understanding the environmental impacts of human activities. This study uses the WRF-Chem model to simulate a mixed-phase cloud precipitation event during the early Meiyu season over the Yangtze River Delta, China, focusing on how anthropogenic aerosols influence cloud and precipitation processes via microphysical and thermodynamic mechanisms. Model experiments indicate that anthropogenic emissions, ranging from very low to normal levels, lead to a 2 % increase in ice crystal mixing ratio and a 50 % increase in latent heat release (peak at 8 km with a rate of 1.2 K h-1), thereby strengthening convection and enhancing precipitation by 6 %. In contrast, high emissions elevate cloud condensation nuclei (CCN) and cloud droplet number concentration, but decrease ice crystal production by 14 % and reduce the mean radius of cloud droplets by 37 %. These changes weaken the falling speed and collision efficiency of cloud droplets, leading to enhanced evaporative cooling and reduced vertical velocity, ultimately resulting in a 28 % decrease in precipitation. Process analysis reveals that cloud droplets below 5 km are transported downstream and subsequently uplifted to 12 km, where they contribute to the formation of additional ice crystals, releasing latent heat that strengthens convection and increases precipitation in the downstream region. This work provides insights into the impacts of anthropogenic aerosol emissions on precipitation, offering valuable reference data for future research on aerosol-cloud-precipitation interactions.

Particulate organic nitrates (pON) significantly contribute to the mass of organic aerosol and influence the nitrogen oxides cycle in the atmosphere, but their evolution and lifetime remain uncertain. This study performed simultaneous measurements on the anthropogenically affected surface site and the mountain site on top of the polluted planetary boundary layer (PBL). After aging in the PBL, organic nitrate was converted from primary sources (decreased from 8.7% to 4.3%) to secondary sources (increased from 6.3% to 36.1%), spanning from the surface to the mountain. The evaporation of more volatile inorganic nitrate and the production of secondary organic nitrate during aging in the PBL contributed to the enhanced pON fraction over the top of PBL. The contribution of light absorption by brown carbon increased by 57% at the top of PBL compared to the surface, consistent with the higher fraction of nitrogenous organic aerosols over the mountain. The results provide field evidence that the nitrogenous organic aerosols (OA) may be preserved by adding into secondary OA and significantly contribute to the enhanced importance of brown carbon after aging during vertical transport in the PBL.

The microphysical properties associated with ice production importantly determine precipitation rates. In this study, the microphysical properties of stratiform clouds with embedded convection during an extratropical cyclone over northern China were characterized in situ. Stages of clouds, including young cells rich in liquid water and developing and mature stages with high number concentrations of ice particles (NIce), were investigated. NIce could reach 300 L-1 in the mature stage, approximately 2 orders of magnitude higher than the primary NIce. The secondary ice production (SIP) rate was 0.005-1.8 L-1 s-1, which was derived from the measured NIce. The SIP rate could be produced using a simplified collision-coalescence model by considering the collection of large droplets by graupel. The collection efficiency between the graupel and the droplet was found to increase when the size of the droplet approached that of the graupel, which may improve the agreement between the measurements and the model. Importantly, the overall NIce was found to be highly related to the distance to the cloud top (DCT). The level with a larger DCT had more rimed graupel falling from the upper levels, which promoted coalescence processes between the graupel and the droplets, producing a greater fraction of smaller ice. This seeder-feeder process extended the avalanche SIP process at lower temperatures to -14 degrees C, beyond the temperature region of the Hallett-Mossop process. The results illustrate the microphysical properties of clouds with convective cells at different stages, which will improve the understanding of the key processes in controlling the cloud glaciation and precipitation processes.

Abstract. The microphysical properties associated with the ice production importantly determine the precipitation rate of clouds. In this study, the microphysical properties including the size distribution and particle morphology of water and ice for stratocumulus during an extratropical cyclone over the northern China were in-situ characterized. Stages of cloud were investigated including young cells rich of liquid water, developing and mature stages with high number concentration of ice particles (Nice). The Nice could reach 300 L-1 at the mature stage, about two orders of magnitudes higher than the primary ice number concentration calculated from ice nucleation. This high Nice occurred at about −5 to −12 °C, spanning the temperature region of Hallett-Mossop process and possible other mechanisms for the secondary ice production (SIP). The Nice was positively associated with the number concentrations of large graupel with diameter (d) > 250 μm and large supercooled droplet (d > 50 μm). The SIP rate was 0.005-1.8 L-1s-1 derived from the measured Nice with known ice growth rate between two sizes. The SIP rate could be produced by a simplified collision-coalescence model within an uncertainty factor of 5, by considering the collection of large droplets by graupel. The collection efficiency between was found to increase when the size of droplet was closer to graupel which may improve the agreement between measurement and model. Importantly, the overall Nice was found to be highly related to the distance to cloud-top (DCT). The level with larger DCT had more abundant rimmed graupels falling from the above level, which promoted the coalescence processes between graupels and droplets, producing a higher fraction of smaller ice through SIP. This seeder-feeder process extended the avalanche SIP at lower temperature up to −14 °C beyond the temperature region of Hallett-Mossop process. The results illustrated the microphysical properties of clouds with convective cells under different stages, which will improve the understanding of the key processes in controlling the cloud glaciation and precipitation process.

The microphysical attributes of black carbon (BC) can determine its absorption and hygroscopic properties. However, long-term information is difficult to obtain from the field. In this study, the BC properties including mass concentration, the coating volume ratio (VR) relative to the refractory BC (rBC), the rBC diameter and the fraction of cloud condensation nuclei (CCN), are derived from a number of field experiments using a random forest model. This model effectively derives the long-term BC microphysical properties in the Beijing region from 2013 to 2020 using continuous measurements of particulate matter, gas, BC mass concentration and meteorological parameters. The results reveal notably higher BC coatings (mean VR = 7.2) and a greater fraction of CCN-like BC (51%) in the winter compared to other seasons. Following the implementation of national air pollution control measures in 2017, BC mass exhibited a substantial reduction of 60% (29%) in the winter (summer), and VR decreased by 45% (24%). Apart from the influence of meteorological variations, these can be attributed to the declined primary emissions and the gas precursors which are associated with secondary formation of BC coatings. The reduction of both BC mass loading and coatings leads to its solar absorption decreasing by 50%, and the fraction of CCN-like BC (likely in clouds) decreasing by 23%. Environmental regulation will therefore continue to reduce both direct and indirect radiative impacts of BC in this region.

In this study, an aerosol chemical speciation monitor (ACSM) and various collocated instruments are used to observe and analyze the chemical compositions, sources and extinction characteristics of submicron aerosol (PM1; aerodynamic diameter < 1 µm) in Beijing from July to September 2012. The results show that the average mass concentration of the PM1 for the entire observation period is 53.8 µg m−3, accounting for 70–85% on average of the PM2.5, and the average mass concentration of the non-refractory submicron aerosol (NR-PM1) declines monthly from July to September as the fraction of organic aerosol (OA) in it increases. During clean days, OA forms the largest mass fraction of the PM1, and the fraction of inorganics shows a significant increasing trend as pollutants accumulate. The effects of meteorology on PM pollution and aerosol processing are also explored. In particular, the SOR increases significantly during periods of elevated relative humidity (RH), suggesting that SO2 is more efficiently converted to SO42− during pollution episodes via aqueous-phase oxidation than gas-phase oxidation. In addition, the effect of wind speed is significantly weaker on primary species (PPM) than secondary species (SPM). Furthermore, the mass concentration of the SPM (or organics) is more sensitive than that of the PPM (or inorganics) to changes in wind speed. The proportion of oxygenated OA (OOA) is significantly higher than that of hydrocarbon-like OA (HOA) in the OA, and as the proportion of OA in the PM1 increases, the mass fraction of OOA in the OA gradually decreases. Moreover, the aerosol acidity in Beijing is essentially neutral during the observation period. The total extinction coefficient of the particulate matter (PM) correlates well with the mass concentration of the PM1 (r2 = 0.72), and the extinction efficiency of the secondary particulate matter (SPM) (r2 = 0.92) is significantly higher than that of the primary particulate matter (PPM) (r2 = 0.58). Meanwhile, the correlation is weaker between the OA and the extinction coefficient (r2 = 0.56) than between the inorganic aerosol and the extinction coefficient (r2 = 0.86).