The optical characteristics of vertically distributed aerosols over Saudi Arabia were investigated using the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data from 2007 to 2019. The study region was divided into three parts (Region I: Tabuk, Makkah, Al Madinah, Asir, Al Bahah, Jizan, Riyadh, Mecca, Medina, the eastern region, Kassim, Hale, Asir, Baha, Tabuk, the northern border region, Jizan, Najilan, and Jufu. Region II: Ar, Al, Ha, Al, and Najran. Region III Al Hudud ash Shamaliyah and Ash Sharqiyah) to understand regional aerosol characteristics by performing interannual and seasonal analysis for nine aerosol types during the day and nighttime. We found that the aerosol optical depth (AOD) estimates were the highest over eastern Saudi Arabia (region III) and were seemingly driven by the presence of an expansive desert in the region. As anticipated, the AOD observations were substantially higher in spring and summer than in autumn and winter owing to the frequent occurrence of dust events during the former. Daytime observations exhibited higher AOD values than those at nighttime, which might be related to higher daytime anthropogenic activities. The estimates of the base height of the lowest aerosol layer (HB₁) and the top altitude of the highest aerosol layer (TAH) were altered depending on the topography (the higher the altitude, the higher the annual mean value of HB₁ and TAH). The aerosol layers (N) were relatively abundant over region III, seemingly due to the relatively stronger atmospheric convection over this region. The volume depolarization ratio of the lowest aerosol layer (VDR₁) was considerable during the night due to deposition at nighttime, and VDR₁ was relatively substantial in spring and summer. The color ratio of the lowest aerosol layer (CR₁) estimates over regions II and III was higher at night. We report a weak positive correlation between the thickness of the lowest aerosol layer (HTH₁) and the AOD of the lowest aerosol layer (AOD₁) in the three regions, a strong positive correlation between TAH and N, and a negative correlation between the AOD proportion of the lowest aerosol layer (PAOD₁) and N in Saudi Arabia. In this paper, the optical and physical properties of aerosols in Saudi Arabia have been studied for 13 years. Our results could provide references for researchers and the government, and relevant departments with data support on the aerosol layer to help control air pollution in Saudi Arabia.

The spatio-temporal characteristics of particulate matter with a particle size less than or equal to 2.5 μm (PM2.5), particulate matter with a particle size less than or equal to 10 μm (PM10), meteorological parameters from September 2018 to September 2019, and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) aerosol optical depth (AOD) from 2007 to 2019 were investigated over the Central Line Project of China’s South-North Water Diversion (CSNWD) in Henan Province. To better understand the characteristics of the atmospheric environment over the CSNWD, air quality monitoring stations were installed in Nanyang (in the upper reaches), Zhengzhou (in the middle reaches), and Anyang (in the lower reaches). In this study, daily, monthly, and seasonal statistical analyses of PM2.5 and PM10 concentrations were performed and their relationship with meteorological parameters was investigated. The results show extremely poor air quality conditions over the Zhengzhou Station compared with the Nanyang and Anyang Stations. The annual average PM2.5 concentration did not meet China’s ambient air secondary standard (35 μg/m3 annual mean) over all the stations, while the annual average PM10 concentration satisfied China’s ambient air secondary standard (100 μg/m3 annual mean) over the Anyang and Nanyang Stations, except for the Zhengzhou Station. The highest PM2.5 and PM10 concentrations were observed during winter compared with the other seasons. The results show that PM2.5 and PM10 concentrations were negatively correlated with wind speed and temperature at the Nanyang and Zhengzhou Stations, but positively correlated with relative humidity. However, no significant negative or positive correlation was observed at Anyang Station. There is a strong linear positive correlation between PM2.5 and PM10 (R = 0.99), which indicates that the particulate matter at the three stations was mainly caused by local emissions. Additionally, the AOD values at the three stations were the highest in summer, which may be related to the residues of crops burned in Henan Province in summer.

Photosynthetic activity across the Qinghai–Tibet Plateau is strongly shaped by seasonal and elevational environmental gradients, yet their roles in recent SIF changes remain insufficiently resolved. We integrated monthly GOSIF, ERA5-Land and GLEAM4.2a data from 2001 to 2024 and combined trend analysis, bidirectional geographical convergent cross mapping (GCCM), spatially blocked XGBoost and TreeSHAP. Annual SIF increased significantly at 0.00270 W m⁻² μm⁻¹ sr⁻¹ decade⁻¹, with significant increases across 64.3% of the valid area. Summer showed the strongest mean increase, whereas autumn exhibited the broadest seasonal increase. Growing-season and summer trends were greatest at 3500–4500 m, while elevations above 4500 m showed the broadest annual increase, revealing clear separation between the trend magnitude and spatial prevalence. GCCM identified shortwave radiation as the environmental variable with the strongest climatological spatial cross-mapping relationship with SIF. Summer radiation converged in both directions and exceeded spatially constrained null expectations, while root-zone soil moisture showed the most consistent positive endpoint difference between the two cross-mapping directions. XGBoost identified period-specific conditional spatial associations, with root-zone soil moisture ranking first in the annual and autumn models and shortwave radiation ranking first in the growing-season and summer models. However, the SHAP contribution of radiation declined as radiation increased, indicating that this spatial relationship should not be interpreted as evidence that increasing radiation enhanced SIF through time. Spatial block bootstrap analysis identified reproducible response transitions for annual and autumn soil moisture at 0.325 (0.304, 0.334) and 0.335 (0.323, 0.344) m³ m⁻³ and for growing-season and summer radiation at 22.60 (21.78, 23.29) and 22.82 (21.91, 23.27) MJ m⁻² d⁻¹, respectively. These results distinguish recent temporal increases in Plateau SIF from the seasonally varying environmental organization of its climatological spatial pattern.