Ozone (O₃) concentrations in the Pearl River Delta (PRD) during summer are typically low and often overlooked. However, integrated observational data indicate a consistent increase in summer O₃ levels over recent decades (+0.96 ppb yr⁻¹), contradicting China's efforts to reduce anthropogenic emissions. Our dynamically calculated natural emissions show that biogenic volatile organic compound (BVOC) emissions in the region significantly increased between 2001 and 2020, primarily due to climate change and alterations in vegetation cover, with climate-driven BVOC emissions accounting for approximately 80 % of the increase. Furthermore, parallel simulations using the Weather Research and Forecasting–Community Multiscale Air Quality (WRF–CMAQ) model indicate that climate-driven BVOC emissions, by enhancing atmospheric oxidative capacity and accelerating O₃ formation, have weakened or even offset the benefits of anthropogenic emission reductions, contributing 6.2 ppb to O₃ formation and leading to an unexpected rise in O₃ levels. This study enhances our understanding of the mechanisms behind natural emissions in urban O₃ formation under climate change and provides insights for future O₃ pollution control strategies.

Observations of the vertical wind profile in Chongqing, a typical mountainous city in China, are important, but they are sparse and have low resolution. To obtain more wind profile data, this study matched the Aeolus track with ground-based wind observation sites in Chongqing in 2021. Based on the obtained results, verification and quality control studies were conducted on the wind observations of a wind profile radar (WPR) with radiosonde (RS) data, and a comparison of the Aeolus Mie-cloudy and Rayleigh-clear wind products (Aeolus winds measured in cloudy and aerosol-rich atmospheric conditions from Mie-channel-collected data and winds measured in clear-air conditions from Rayleigh-collected data) with WPR data was then performed. The conclusions can be summarized as follows: (1) a clear correlation between the wind observations of WPR and RS was found, with a correlation coefficient (R) of 0.71. Their root mean square deviation increased with height but decreased at heights between 3 and 4 km. (2) After quality control using Gaussian filtering (GF) and empirical orthogonal function construction (EOFc; G=87.23 %) of the WPR data, the R between the WPR and RS reached 0.83 and 0.95, respectively. The vertical distribution showed that GF could better retain the characteristics of WPR wind observations but with limited improvement in decreasing deviations, whereas EOFc performed better in decreasing deviations but considerably modified the original characteristics of the wind field, especially regarding intensive vertical wind shear in strong convective weather processes. (3) In terms of the differences between the Aeolus and WPR data, 56.0 % and 67.8 % deviations were observed within ±5 m s⁻¹ for Rayleigh-clear and Mie-cloudy winds (Aeolus winds measured in cloudy and aerosol-rich atmospheric conditions from Mie-channel-collected data and winds measured in clear-air conditions from Rayleigh-collected data) vs WPR winds, respectively. Vertically, large mean differences of both Rayleigh-clean and Mie-cloudy winds versus WPR winds appeared below 1.5 km, which is attributed to the prevailing quiet and small winds within the boundary layer in Chongqing; in this case the movement of molecules and aerosols is mostly affected by irregular turbulence. Additionally, large mean differences at a height range between 4 and 8 km for Mie-cloudy versus WPR winds may be related to the high content of cloud liquid water in the middle troposphere of Chongqing. (4) The differences in both Rayleigh-clear and Mie-cloudy versus WPR winds had changed. Deviations of 58.9 % and 59.6 % were concentrated within ±5 m s⁻¹ for Rayleigh-clear versus WPR winds with GF and EOFc quality control, respectively. In contrast, 69.1 % and 70.2 % of deviations appeared within ±5 m s⁻¹ for Rayleigh-clear versus WPR and EOFc WPR winds, respectively. These results shed light on the comprehensive applications of multi-source wind profile data in mountainous cities or areas with sparse ground-based wind observations.

In recent years, ozone (O₃) pollution has become a prominent air quality concern in the Sichuan Basin (SCB). Based on surface O₃ measurements from 22 cities between 2015 and 2024, this study investigates the evolution of extreme O₃ pollution events and their underlying causes. While the average O₃ concentration, the number of affected cities, and the total O₃ pollution hours have all increased during the past decade, extreme O₃ concentrations have shown a significant decline since 2020. These trends suggest that O₃ pollution in the SCB has become more spatially extensive and less intense. Decomposition analysis attributed ~75% of the post-2020 decline in extreme O₃ concentrations to precursor emission reductions, with meteorological variability explaining the remaining ~25%. Satellite observations of formaldehyde (HCHO) and nitrogen dioxide (NO₂) column densities indicate a regional shift in O₃ formation regimes across the SCB, with many areas transitioning from VOC (volatile organic compound)-limited to transitional or NO_x (nitrogen oxide)-limited conditions. This shift likely contributed to the broader spatial extent and longer duration of O₃ pollution in recent years. Model sensitivity simulations and Integrated Reaction Rate (IRR) analysis demonstrate that reductions in precursor emissions, particularly NO_x, directly weakened daytime photochemical O₃ production and disrupted NO_x-driven radical propagation under transition and NO_x-limited conditions, collectively driving the observed decline in extreme O₃ concentrations.

O₃ concentrations in the Pearl River Delta (PRD) during summer are typically low and often overlooked. However, integrated observational data reveal a consistent increase in summer O₃ levels over recent decades (+0.96 ppb/year), contradicting China's efforts to reduce anthropogenic emissions. Our dynamically calculated natural emissions show that biogenic volatile organic compound (BVOC) emissions in the region significantly increased between 2001 and 2020, primarily due to climate change and alterations in vegetation cover, with climate-driven BVOC emissions accounting for approximately 80 % of the increase. Furthermore, parallel simulations using the WRF-CMAQ model indicate that climate-driven BVOC emissions, by enhancing atmospheric oxidative capacity and accelerating O₃ formation, have weakened or even offset the benefits of anthropogenic emission reductions, contributing 6.2 ppb to O₃ formation and leading to an unexpected rise in O₃ levels. This study enhances our understanding of the mechanisms behind natural emissions in urban O₃ formation under climate change and provides insights for future O₃ pollution control strategies.

O₃ concentrations in the Pearl River Delta (PRD) during summer are typically low and often overlooked. However, integrated observational data reveal a consistent increase in summer O₃ levels over recent decades (+0.96 ppb/year), contradicting China's efforts to reduce anthropogenic emissions. Our dynamically calculated natural emissions show that biogenic volatile organic compound (BVOC) emissions in the region significantly increased between 2001 and 2020, primarily due to climate change and alterations in vegetation cover, with climate-driven BVOC emissions accounting for approximately 80 % of the increase. Furthermore, parallel simulations using the WRF-CMAQ model indicate that climate-driven BVOC emissions, by enhancing atmospheric oxidative capacity and accelerating O₃ formation, have weakened or even offset the benefits of anthropogenic emission reductions, contributing 6.2 ppb to O₃ formation and leading to an unexpected rise in O₃ levels. This study enhances our understanding of the mechanisms behind natural emissions in urban O₃ formation under climate change and provides insights for future O₃ pollution control strategies.

O₃ concentrations in the Pearl River Delta (PRD) during summer are typically low and often overlooked. However, integrated observational data reveal a consistent increase in summer O₃ levels over recent decades (+0.96 ppb/year), contradicting China's efforts to reduce anthropogenic emissions. Our dynamically calculated natural emissions show that biogenic volatile organic compound (BVOC) emissions in the region significantly increased between 2001 and 2020, primarily due to climate change and alterations in vegetation cover, with climate-driven BVOC emissions accounting for approximately 80 % of the increase. Furthermore, parallel simulations using the WRF-CMAQ model indicate that climate-driven BVOC emissions, by enhancing atmospheric oxidative capacity and accelerating O₃ formation, have weakened or even offset the benefits of anthropogenic emission reductions, contributing 6.2 ppb to O₃ formation and leading to an unexpected rise in O₃ levels. This study enhances our understanding of the mechanisms behind natural emissions in urban O₃ formation under climate change and provides insights for future O₃ pollution control strategies.