Aerosols and ozone have significant influences on air qualities, human health, and climate changes. To further understand the characteristics and interactions among different urban air pollutants in the west Yangtze River Delta (YRD) region, continuous measurements of low-layer atmospheric particles and trace gases have been performed at an urban site in Nanjing from September 2016 to February 2017 in this study. In the urban area of the west YRD, the mean PM₁₀ and O₃ concentrations are 86.3 µg m⁻³ and 37.7 ppb, respectively, with significant seasonal and diurnal variations. Particles, which are dominated by fine aerosols, are relatively scattering. And most of their optical properties have similar variations to the aerosol concentrations. Results also show that the west YRD could still suffer severe air pollution, although the seasonal mean aerosol concentrations have decreased in recent years. Even in cold seasons, O₃ could exceed the National Ambient Air Quality Standards for about 40 days during the sampling period. Most of polluted episodes are caused by local and subregional emissions. A case study for a typical O₃ and PM_2.5 episode in December 2016 demonstrates that the episode was generally associated with regional transport and a stable weather system. Air pollutants were mostly transported from the western areas with high emissions, as well as with an anticyclone and high-pressure system in this region. Correlation analysis reveals that the interactions between O₃ and PM are complex, with a combination of inhibition and promotion under different conditions. The inhibition effect might result from the reduction of photolysis frequency near the surface due to aerosols in addition to their positive correlations with precursors, while the promotion effect is from the formation of secondary aerosols under high concentrations of oxidants and solar radiation. However, the interaction between O₃ and BC shows an inhibiting effect due to its chemical stability. This also indicated a VOC-sensitive regime for photochemical production of O₃ in this region. This study further improves insight into the characteristics and interactions of main pollutants and may contribute to the improvement of the simulation and prediction of aerosols and gases in the urban area of the YRD.

Atmospheric black carbon (BC) in the Tibetan Plateau (TP) can largely impact regional and global climate. Still, studies on the inter-annual variation in atmospheric BC over the TP and associated variation in BC sources and controlling factors are rather limited. In this study, we characterize the variations in atmospheric BC over the TP surface layer through analysis of 20-year (1995–2014) simulations from a global chemical transport model, GEOS-Chem. The results show that surface BC concentrations over the TP vary largely in space and by season, reflecting complicated interplays of BC sources from different origins. Of all areas in the TP, surface BC concentrations are highest over the eastern and southern TP, where surface BC is susceptible to BC transport from East Asia and South Asia, respectively. Applying a backward-trajectory method that combines BC concentrations from GEOS-Chem and trajectories from the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, we assess the contributions of worldwide source regions to surface BC in the TP. We estimate that on the 20-year average, 77 % of surface BC in the TP comes from South Asia (43 %) and East Asia (35 %). Regarding seasonal variation in non-local influences, South Asia and East Asia are dominant source regions in winter and summer, respectively, in terms of the amount of BC imported. However, in terms of affected areas in the TP, South Asia is the dominant contributor throughout the year. Inter-annually, surface BC over the TP is largely modulated by atmospheric transport of BC from non-local regions year-round and by biomass burning in South Asia, mostly in spring. We find that the extremely strong biomass burning in South Asia in the spring of 1999 greatly enhanced surface BC concentrations in the TP (31 % relative to the climatology). We find that the strength of the Asian monsoon correlates significantly with the inter-annual variation in the amount of BC transported to the TP from non-local regions. In summer, a stronger East Asian summer monsoon and a stronger South Asian summer monsoon tend to, respectively, lead to more BC transport from central China and north-eastern South Asia to the TP. In winter, BC transport from central China is enhanced in years with a strong East Asian winter monsoon or a strong Siberian High. A stronger Siberian High can also bring more BC from northern South Asia to the TP. This study underscores the impacts of atmospheric transport and biomass burning on the inter-annual variation in surface BC over the TP. It reveals a close connection between the Asian monsoon and atmospheric transport of BC from non-local regions to the TP.

The optical and physical properties as well as the direct radiative forcings (DRFs) of fractionated aerosols in the urban area of the western Yangtze River Delta (YRD) are investigated with measurements from a Cimel sun photometer combined with a radiation transfer model. Ground-based observations of aerosols have much higher temporal resolutions than satellite retrievals. An initial analysis reveals the characteristics of the optical properties of different types of fractionated aerosols in the western YRD. The total aerosols, mostly composed of scattering components (93.8 %), have mean optical depths of 0.65 at 550 nm and refractive index of 1.44 + 0.0084i at 440 nm. The fine aerosols are approximately four times more abundant and have very different compositions from coarse aerosols. The absorbing components account for only ∼ 4.6 % of fine aerosols and 15.5 % of coarse aerosols and have smaller sizes than the scattering aerosols within the same mode. Therefore, fine particles have stronger scattering than coarse ones, simultaneously reflecting the different size distributions between the absorbing and scattering aerosols. The relationships among the optical properties quantify the aerosol mixing and imply that approximately 15 and 27.5 % of the total occurrences result in dust- and black-carbon-dominating mixing aerosols, respectively, in the western YRD. Unlike the optical properties, the size distributions of aerosols in the western YRD are similar to those found at other sites over eastern China on a climatological scale, peaking at radii of 0.148 and 2.94 µm. However, further analysis reveals that the coarse-dominated particles can also lead to severe haze pollution over the YRD. Observation-based estimations indicate that both fine and coarse aerosols in the western YRD exert negative DRFs, and this is especially true for fine aerosols (−11.17 W m⁻² at the top of atmosphere, TOA). A higher absorption fraction leads directly to the negative DRF being further offset for coarse aerosols (−0.33 W m⁻²) at the TOA. Similarly, the coarse-mode DRF contributes to only 13.3 % of the total scattering aerosols but > 33.7 % to the total absorbing aerosols. A sensitivity analysis states that aerosol DRFs are not highly sensitive to their profiles in clear-sky conditions. Most of the aerosol properties and DRFs have substantial seasonality in the western YRD. The results further reveal the contributions of each component of the different size particles to the total aerosol optical depths (AODs) and DRFs. Additionally, these results can be used to improve aerosol modelling performance and the modelling of aerosol effects in the eastern regions of China.

Absorbing aerosols have significant influences on tropospheric photochemistry and regional climate change. Here, the direct radiative effects of absorbing aerosols at the major AERONET sites in East Asia and corresponding impacts on near-surface photochemical processes were quantified by employing a radiation transfer model. The average annual aerosol optical depth (AOD) of sites in China, Korea, and Japan was 1.15, 1.02 and 0.94, respectively, and the corresponding proportion of absorbing aerosol optical depth (AAOD) was 8.61%, 6.69%, and 6.49%, respectively. The influence of absorbing aerosol on ultraviolet (UV) radiation mainly focused on UV-A band (315–400 nm). Under the influence of such radiative effect, the annual mean near-surface J[NO₂] (J[O¹D]) of sites in China, Korea, and Japan decreased by 16.95% (22.42%), 9.61% (13.55%), and 9.63% (13.79%), respectively. In Beijing–Tianjin–Hebei (BTH) and Yangtze River Delta (YRD) region, the annual average AOD was 1.48 and 1.29, and the AAOD was 0.14 and 0.13, respectively. The UV radiative forcing caused by aerosols dominated by black carbon (BC-dominated aerosols) on the surface was −3.19 and −2.98 W m⁻², respectively, accounting for about 40% of the total aerosol radiative forcing, indicating that the reduction efficiency of BC-dominated aerosols on solar radiation was higher than that of other types of aerosols. The annual mean J[NO₂] (J[O¹D]) decreased by 14.90% (20.53%) and 13.71% (18.20%) due to the BC-dominated aerosols. The daily maximum photolysis rate usually occurred near noon due to the diurnal variation of solar zenith angle and, thus, the daily average photolysis rate decreased by 2–3% higher than that average during 10:00–14:00.

The complex summer weather in East Asia poses significant challenges of precipitation forecasting. Despite the promising capabilities of deep learning models in conventional forecasting tasks, their black‐box nature limits physical interpretability. In this study, we developed PS2F‐Net, a physics‐constrained hierarchical spatio‐temporal feature fusion network. The model integrates multi‐scale physical features through a multi‐head attention mixing block and embeds the vertically integrated water vapor flux term as a physical constraint in the loss function. This physics‐informed design enhances precipitation classification and maintains forecast stability over extended lead times. Compared with the ECMWF IFS, PS2F‐Net substantially improves precipitation forecast accuracy and can predict heavy rainfall events up to 2 weeks in advance, including both typical monsoonal and typhoon‐induced extremes. Feature attribution analyses highlight the importance of nonlinear relationships in improving forecast skill. These results provide new insights and methodological support for physics‐guided deep learning in East Asian precipitation prediction.

The aerosol optical and physical properties as well as its direct radiative forcing (DRF) in urban area of Nanjing (urNJ) are investigated, based on the measurements of Cimel sun-photometer combined with a radiation transfer model. We find that the annual mean 550 nm aerosol optical depth (AOD) of the total aerosols is about 0.65, dominated by scattering aerosols (about 94 %), resulting in a mean single scattering albedo (SSA) of 0.93 at 550 nm and refractive index of 1.44 + 0.0084i at 440 nm during the sampling period. The scattering aerosol has larger size than the absorbing aerosol, with Ångström exponents (AE) of 1.19 at 440/870 nm, 0.13 smaller than the latter one. The coarse mode fraction for the scattering aerosol (18.03 %) is much smaller than the absorbing aerosol's (43.91 %). Thus, the fine mode aerosols presents more scattering (SSA = 0.95) while the coarse aerosol is more absorption (SSA = 0.82). Analysis implies that there are about 15 % and 27.5 % occurrences of dust and black carbon dominated mixing aerosols, respectively, during the sampling period. All the optical properties follow a simple unimodal pattern. Aerosols in urNJ have a two-mode lognormal pattern in volume size distribution, peaking at the radius of 0.148 and 2.94 µm, and the AOD positively depends on them. Although the fine mode aerosol has a much smaller sizes than the coarse one, they have the same level of the volume concentrations (about 0.12 µm³/cm³) due to much higher fraction of the fine aerosol. Estimations present that the mean aerosol DRFs at the top of atmosphere (TOA) are −10.69, −16.45, +5.76 W/m², respectively, for the total, scattering and absorbing aerosols in clear sky. At the surface, the DRFs are 1.1–2.5 times stronger than those at TOA, and the fine aerosol DRFs in these three type of aerosols account for 83.7 %, 91.7 % and 67.2 %, respectively, to their totals. Normally, aerosol DRFs is not very sensitive (no more than 5 %) to its profiles in clear sky condition (extreme cases excepted), although both aerosol scattering and absorption could become weaker to some extent if more aerosols were in lower layers. Both the aerosol properties and DRFs have substantial seasonality.