Atmospheric turbulence represents a quintessential multiscale, intermittent dynamical system in which energy transfer occurs through complex cascade processes. In atmospheric surface layers (ASLs), these processes are complicated by ground roughness, giving rise to pronounced intermittency and coherent turbulence structures. This study investigates ASL turbulence, characterizes the multifractal features, and examines the coherent structures in intermittency. Wind tunnel experiments unveil how idealized, identical roughness elements affect aerodynamic resistance and transport. Moreover, field measurements are collected by an eddy covariance system over 2 months in a suburban area to complement the experimental results. Multifractal detrended fluctuation analysis and empirical mode decomposition are concertedly adopted to contrast multifractal properties of all sizes. The results reveal consistent multifractal behavior in both streamwise and vertical velocity fluctuations across laboratory and field datasets that consolidate a cascade mechanism regardless of physical dimensions. Aerodynamic resistance plays a critical role, enhancing multifractality due to intensified turbulent mixing and complex energy cascade. Multiscale analysis results demonstrate that the multifractal index exhibits a specific growth pattern: it initially increases, reaches a peak, then stabilizes thereafter with increasing scale. Both laboratory and field results indicate that ASL turbulence exhibits the most notable multifractal behavior at intermediate scales. Asymmetry analysis reveals a consistent transition from positive to negative across a range of surface roughness, indicating growing uniformity in smaller-scale processes. These results clarify how ground configuration influences turbulence intermittency and energy transfer in the urban atmospheric boundary layer, thereby improving the understanding of turbulent transport and multiscale airflow dynamics.

Ammonia(NH₃) is the most abundant alkaline gas in the atmosphere. It is the root cause of the formation of most secondary particulates in PM2.5 and the accelerator of the haze pollution formation in the atmosphere. Therefore the monitoring of the NH₃ concentration is very important to the environmental protection. In this paper, the principle of NH₃ concentration detection based on Lambert-Beer law has been introduced. A dual-channel modulated ultraviolet photoelectric signal detection circuit for NH₃ concentration has been designed and its performance index has been studied. And then a precision detection circuit is designed, which is composed of a trans-impedance amplifier and a lock-in amplifier, with which the output of the UV photoelectric detector can be amplified to a suitable voltage range, and the DC noise of the pre-stage amplifier is effectively removed by the lock-in amplifier. The designed circuit has been tested for the NH3 concentration quantitative measuring in the laboratory, with the exchange calibration method being used to ensure the consistency of the two channels. It can be drawn from the test results that the designed circuit is of high SNR, measuring accuracy and a large dynamic range. The NH₃ concentration detection limit of vehicle emissions can reach 2ppm, while the detection precision is ±19ppm.

Elucidating the dynamics in the roughness sublayer (RSL) of a city is crucial for assessing street-level turbulence, ventilation, and heat removal over heterogeneous urban morphology. Although building-height variability has been examined in urban-canopy studies, its role in regulating RSL turbulence and ventilation under controlled uniform- and non-uniform-height configurations still needs further quantification. In this paper, we conduct a wind tunnel investigation using LEGO® bricks to fabricate building arrays of both uniform (h, 2h, 3h, 4h) and non-uniform (3h + 2h, 4h + 2h) heights. Here, h is the height of a LEGO brick. Hot-wire anemometry is employed to measure mean wind speed, turbulence statistics, boundary-layer parameters, turbulent length scale, and ventilation efficiency. Results show that height heterogeneity amplifies turbulence and vertical momentum flux, thereby enhancing the mixing within RSLs. The RSLs over non-uniform-height configurations are higher than their uniform-height counterparts, underscoring the critical role of building height variability. Across all the configurations tested, RSL turbulent length scales deviate significantly from classical predictions, reflecting local building-induced disturbance and distinct turbulence generation mechanisms. A tight correlation between the square root of the drag coefficient Cd 1/2 and ventilation efficiency is found that offers a reliable estimate for RSL ventilation in urban environments. These findings demonstrate the important role of building heterogeneity in RSL dynamics and reveal deviations from classical scaling in response to heterogeneous urban surfaces. This improved understanding advances the parameterization of RSL dynamics as well as sheds light on the transport mechanism, effectuating ventilation strategies in complex, heterogeneous built environments.