Renmin Yuan

The large aperture scintillometer (LAS) measures sensible and latent heat flux at scales of 200 m to 10 km. Existing theory predicts a -13/3 power-law decay for the high-frequency spectrum of received light intensity fluctuations, yet observations consistently show a -8/3 exponent. This discrepancy hinders accurate retrieval of the refractive index structure parameter (C_n^2). This study investigates its origin through experiments and theoretical analysis. Comparative observations with two LAS instruments were conducted, varying the LED emitting aperture of one while keeping the other unchanged. Results reveal a negative correlation between LED aperture and the relative ratio of log-intensity variances, indicating that the transmitter aperture differs from the collimating lens diameter assumed in traditional theory. An equivalent transmitter aperture is thus introduced and determined from the variance ratio curve. Additionally, wind speed fluctuations significantly affect the spectrum: larger standard deviations produce slower high-frequency decay. Incorporating the equivalent aperture and measured wind statistics into the theoretical model yields a spectral exponent near -8/3, matching observations. The revised theoretical spectrum agrees well with measurements, and the calculated C_n^2 shows improved consistency with observed values.

Near-surface aerosol fluxes over open water are critical for understanding air–sea interactions and atmospheric radiative budgets, yet direct micrometeorological observations remain very limited. To address this gap, this study presents the first application of a large-aperture scintillometer (LAS) for retrieving aerosol mass fluxes over open-water environments, including an inland lake and a coastal bay. LAS-derived fluxes were compared with conventional eddy-covariance (EC) measurements and independent dry-deposition calculations. Under conditions without severe optical attenuation, the LAS-derived fluxes exhibited temporal variations broadly consistent with EC measurements, with normalized root-mean-square errors (NRMSEs) to 15.0%–16.8%. The coastal campaigns revealed the operational boundary of this optical approach: dense fog and persistent high humidity severely attenuated the LAS signal and caused extended data gaps. Comparisons with dry-deposition calculations further showed that the path-averaged LAS measurements may better capture site-scale variability at the coastal site. Overall, these results demonstrate the potential of LAS as a valuable complements to traditional point measurements for characterizing aerosol exchange over open water.

Near-surface aerosol fluxes over open water are critical for understanding air–sea interactions and atmospheric radiative budgets, yet direct micrometeorological observations remain very limited. To address this gap, this study presents the first application of a large-aperture scintillometer (LAS) for retrieving aerosol mass fluxes over open-water environments, including an inland lake and a coastal bay. LAS-derived fluxes were compared with conventional eddy-covariance (EC) measurements and independent dry-deposition calculations. Under conditions without severe optical attenuation, the LAS-derived fluxes exhibited temporal variations broadly consistent with EC measurements, with normalized root-mean-square errors (NRMSEs) to 15.0%–16.8%. The coastal campaigns revealed the operational boundary of this optical approach: dense fog and persistent high humidity severely attenuated the LAS signal and caused extended data gaps. Comparisons with dry-deposition calculations further showed that the path-averaged LAS measurements may better capture site-scale variability at the coastal site. Overall, these results demonstrate the potential of LAS as a valuable complements to traditional point measurements for characterizing aerosol exchange over open water.

Monitoring seismic velocity variations in Earth’s critical zone (CZ) provides crucial information on Earth’s environmental changes. However, monitoring of urban near-surface environments at high temporal resolution is still challenging. Combining distributed acoustic sensing (DAS) and seismic interferometry, we acquired hourly high-precision seismic velocity variations in downtown Hefei city, China, with amplitude up to 10 ^-3 . Velocity variations exhibit long-term and diurnal signals with amplitudes of ～10 ^-4 . Sub-daily signals are also presented with amplitudes one order smaller. The long-term and diurnal variations of seismic velocity are well explained by thermoelastic effect modeling, and transient signals (~ 0.05%) are well fitted by hydraulic force modeling from groundwater data and precipitation data. We also conclude that the semi-diurnal velocity variations are caused by the interaction of barometric pressure and the water table. This work demonstrates the capability of DAS to conduct hourly monitoring of Earth’s CZ in urban areas and cast insight into land-atmosphere coupling from a seismological perspective.

Near-surface aerosol fluxes over open water are critical for understanding air–sea interactions and atmospheric radiative budgets, yet direct micrometeorological observations remain very limited. To address this gap, this study presents the first application of a large-aperture scintillometer (LAS) for retrieving aerosol mass fluxes over open-water environments, including an inland lake and a coastal bay. LAS-derived fluxes were compared with conventional eddy-covariance (EC) measurements and independent dry-deposition calculations. Under conditions without severe optical attenuation, the LAS-derived fluxes exhibited temporal variations broadly consistent with EC measurements, with normalized root-mean-square errors (NRMSEs) to 15.0%–16.8%. The coastal campaigns revealed the operational boundary of this optical approach: dense fog and persistent high humidity severely attenuated the LAS signal and caused extended data gaps. Comparisons with dry-deposition calculations further showed that the path-averaged LAS measurements may better capture site-scale variability at the coastal site. Overall, these results demonstrate the potential of LAS as a valuable complements to traditional point measurements for characterizing aerosol exchange over open water.

Lake-land thermal contrasts significantly modulate regional air quality, yet the coupling mechanisms by which inland lakes regulate the diurnal evolution of PM_2.5 and its components remain poorly understood. This study conducts high-resolution (1 km) WRF-Chem simulations over Lake Chaohu and the adjacent megacity of Hefei, China, during spring to elucidate these interactions. Results reveal a distinct diurnal reversal effect. During daytime, the lake presence facilitates PM_2.5 increases of predominantly 0–10 µg m⁻³ both over the lake and in surrounding urban areas by suppressed planetary boundary layer height, weakened vertical mixing, and reduced dry deposition velocities, which collectively transform the lake into “storage zone” that prolongs PM_2.5 lifetimes. This accumulation is dominated by secondary PM_2.5, as the cooler and more humid lake air thermodynamically favors the ammonium nitrate formation. Furthermore, convergence zones where lake breezes meet background winds create localized stagnation traps that intensify shoreline pollution. At night, while the lake surface maintains higher PM_2.5 concentrations than surrounding land, its impact on the city reverses, exerting a purification effect with urban PM_2.5 decreasing by predominantly 0–10 µg m⁻³ as land-breeze circulation enhances vertical mixing and facilitates primary pollutant dispersion. Sensitivity experiments reveal that failing to distinguish lake surfaces in emission inventories can significantly amplify daytime pollution. These findings emphasize that lakes act as complex dual regulators of urban air quality, with identified mechanisms likely applicable to other urban-lake systems globally. This study highlights the necessity of high-resolution meteorological modeling and precise surface characterization for improved air quality forecasting in lake-adjacent megacities regions.

Near-surface aerosol fluxes over open water are critical for understanding air–sea interactions and atmospheric radiative budgets, yet direct micrometeorological observations remain very limited. To address this gap, this study presents the first application of a large-aperture scintillometer (LAS) for retrieving aerosol mass fluxes over open-water environments, including an inland lake and a coastal bay. LAS-derived fluxes were compared with conventional eddy-covariance (EC) measurements and independent dry-deposition calculations. Under conditions without severe optical attenuation, the LAS-derived fluxes exhibited temporal variations broadly consistent with EC measurements, with normalized root-mean-square errors (NRMSEs) to 15.0%–16.8%. The coastal campaigns revealed the operational boundary of this optical approach: dense fog and persistent high humidity severely attenuated the LAS signal and caused extended data gaps. Comparisons with dry-deposition calculations further showed that the path-averaged LAS measurements may better capture site-scale variability at the coastal site. Overall, these results demonstrate the potential of LAS as a valuable complements to traditional point measurements for characterizing aerosol exchange over open water.

Lake-land thermal contrasts significantly modulate regional air quality, yet the coupling mechanisms which inland lakes regulate the diurnal evolution of PM_2.5 and its components remain poorly understood. This study conducts high-resolution (1 km) WRF-Chem simulations over Lake Chaohu and the adjacent megacity of Hefei, China, to elucidate these interactions. Results reveal a distinct diurnal reversal effect. During daytime, the lake presence facilitates a PM_2.5 increase exceeding 10 ug/m³ both over the lake and in surrounding urban areas by suppressed planetary boundary layer height, weakened vertical mixing, and reduced dry deposition velocities, which collectively transform the lake into a "storage zone" that prolongs PM_2.5 lifetimes. This accumulation is dominated by secondary PM_2.5, as the cooler and more humid lake air thermodynamically favors the ammonium nitrate formation. Furthermore, convergence zones where lake breezes meet background winds create localized stagnation traps that intensify shoreline pollution. At night, while the lake surface maintains higher PM_2.5 concentrations than surrounding land, its impact on the city reverses, exerting a purification effect with urban PM_2.5 decreasing by over 10 μg/m³ as land-breeze circulation enhances vertical mixing and facilitates primary pollutant dispersion. Sensitivity experiments reveal that failing to distinguish lake surfaces in emission inventories can significantly amplify daytime pollution. These findings emphasize that lakes act as complex dual regulators of urban air quality, with the identified mechanisms likely applicable to other urban-lake systems globally. This study highlights the necessity of high-resolution meteorological modeling and precise surface characterization for improved air quality forecasting in lake-adjacent megacities regions.

Lake-land thermal contrasts significantly modulate regional air quality, yet the coupling mechanisms which inland lakes regulate the diurnal evolution of PM_2.5 and its components remain poorly understood. This study conducts high-resolution (1 km) WRF-Chem simulations over Lake Chaohu and the adjacent megacity of Hefei, China, to elucidate these interactions. Results reveal a distinct diurnal reversal effect. During daytime, the lake presence facilitates a PM_2.5 increase exceeding 10 ug/m³ both over the lake and in surrounding urban areas by suppressed planetary boundary layer height, weakened vertical mixing, and reduced dry deposition velocities, which collectively transform the lake into a "storage zone" that prolongs PM_2.5 lifetimes. This accumulation is dominated by secondary PM_2.5, as the cooler and more humid lake air thermodynamically favors the ammonium nitrate formation. Furthermore, convergence zones where lake breezes meet background winds create localized stagnation traps that intensify shoreline pollution. At night, while the lake surface maintains higher PM_2.5 concentrations than surrounding land, its impact on the city reverses, exerting a purification effect with urban PM_2.5 decreasing by over 10 μg/m³ as land-breeze circulation enhances vertical mixing and facilitates primary pollutant dispersion. Sensitivity experiments reveal that failing to distinguish lake surfaces in emission inventories can significantly amplify daytime pollution. These findings emphasize that lakes act as complex dual regulators of urban air quality, with the identified mechanisms likely applicable to other urban-lake systems globally. This study highlights the necessity of high-resolution meteorological modeling and precise surface characterization for improved air quality forecasting in lake-adjacent megacities regions.