Spatiotemporal variations and source on black carbon over Chongqing, China: Long-term changes and observational experiments.

Black carbon (BC), as a critical light-absorbing constituent within aerosols, exerts profound effects on atmospheric radiation balance, climate, air quality and human health, etc. And it is also a long-standing focus in rapidly developing megacities. So, this study primarily focuses on investigating the variation characteristics and underlying causes of BC in Chongqing (31,914,300 population), which is one of the municipalities directly under the central government of China, serving as a pivotal economic hub in southwest China. Utilizing MERRA-2 reanalysis data, we examined the long-term changes of atmospheric BC over Chongqing 20 years (from 2002 to 2021). Moreover, BC mass concentration observations were conducted using an Aethalometer (AE-33) from March 15 to June 14, 2021 in Liangping District, Chongqing. The statistical analysis over the last 20 years reveals an annual mean BC concentration in Chongqing of 3.42 ± 0.20 µg/m3, exhibiting growth from 2002 to 2008, followed by a decline from 2008 to 2021. Monthly concentration displays a "U-shaped" trend, with the lowest values occurring in summer and the highest in winter. Due to topographical and meteorological influences, local emissions primarily contribute to BC pollution, characterized by a spatial distribution pattern of high in the west and low in the east. Ground observation indicates a distinct dual-peaked pattern in the diurnal variation of BC, with peak concentrations aligning with periods of high traffic emissions. The variation in BC is significantly influenced by meteorological conditions (wind, temperature, atmospheric boundary layer) and local pollution sources (predominantly traffic). Furthermore, extreme events analysis suggests that local emissions and regional transport (with higher contributions from Chongqing and the Sichuan Basin) predominantly contributed to BC pollution. This study effectively makes up for the deficiency in analyzing the distribution and sources of BC pollution in Chongqing, providing valuable scientific insights for the atmospheric environment of megacities.

Advances in coastal ocean boundary layer detection technology and equipment in China.

Accurate and comprehensive knowledge of the atmospheric environment and its evolution within the coastal ocean boundary layer are necessary for understanding the sources, chemical mechanisms, and transport processes of air pollution in land, sea, and atmosphere. We present an overview of coastal ocean boundary layer detection technology and equipment in China and summarize the progress and main achievements in recent years. China has developed a series of coastal ocean boundary layer detection technologies, including Light Detection and Ranging (LIDAR), turbulent exchange analyzer, air-sea flux analyzer, stereoscopic remote sensing of air pollutants, and oceanic aerosol detection equipment to address the technical bottleneck caused by harsh environmental conditions in coastal ocean regions. Advances in these technologies and equipment have provided scientific assistance for addressing air pollution issues and understanding land-sea-atmosphere interactions over coastal ocean regions in China. In the future, routine atmospheric observations should cover the coastal ocean boundary layer of China.

Estimation of turbulence parameters in the atmospheric boundary layer of the Bohai Sea, China, by coherent Doppler lidar and mesoscale model.

Obtaining turbulence parameters in the marine atmospheric boundary layer (MABL) is limited by the observation environment and cost. Therefore, estimating based on the weather forecast model or combining the model output with limited observations is a more flexible choice. We conducted cruise observation experiments in the Bohai Sea, China, from May 17 to June 4, 2021. On the basis of the wind profile observed by the coherent Doppler lidar and the temperature, as well as pressure profiles output by the Weather Research and Forecasting (WRF) model, we implemented the Tatarskii turbulence model to estimate the refractive index structure constant C n2 in the atmospheric boundary layer of the Bohai Sea under clear sky. The temporal and spatial variations of turbulence in the Bohai Sea atmospheric boundary layer are studied by combining the vertical velocity variance σ w2, skewness Ske and kurtosis Kur. The performance of simulated C n2 and meteorological parameters in the WRF in the atmospheric boundary layer at the Bohai Sea is evaluated through the experimental measurements of UAV-borne (unmanned aerial vehicle) radiosonde and lidar. Finally, we give the model of the C n2 variation with height in the atmospheric boundary layer at the Bohai Sea. The results show that WRF can better simulate C n2 in most cases. The bias between the measured and simulated C n2 is within one order of magnitude, and the root mean square error ( RMSE ) is within two orders of magnitude. Due to the potential uncertainty of the WRF, the RMSE between the measured and simulated wind speed is 4 ms-1 to 6 ms-1, which is almost two times of the result in previous studies on the underlying land surface. The overall changes of C n2 and σ w2 are similar when the turbulence is well mixed and developed, which shows the consistency in both of optical and dynamics turbulence. But this consistency is not absolute. The temperature difference between the sea surface and the atmosphere leads to the widespread existence of an inversion layer from the sea surface to hundreds of meters in the Bohai Sea. The suppression of the inversion layer weakens the near sea surface turbulence. There is an enhancement of turbulence intensity below the inversion layer and a decrease from the upper inversion layer to top of the boundary layer among the entire boundary layer, also, the position of the inflection point is determined by the height of top of the inversion layer. The main results of this study are the reference significance for further understanding the development and change characteristics of turbulence in the MABL.

Analysis and mitigation of the carrier phase delay effect of the digital phase generated carrier algorithm.

We present an improved digital phase generated carrier algorithm based on the synchronous carrier restoration (SCR) method to mitigate the carrier phase delay effect. The most distinguishing feature of this method is that it directly picks up the carrier signal information (frequency and phase) from the interference signal and synchronically accomplishes the processing of carrier signal restoration. In comparison to the traditional method, which adopts the initial carrier signal, total-harmonic-distortion with SCR is only 0.091%, lower than the traditional SCR of 18.38%, and the signal-to-noise ratio increases by 29 dB. Further, we derived the analytic expression of the distortion component and verified it by experiments. This technique may be potentially applied to a long-distance large-scale distributed fiber-optic interferometric sensor array.

[Measurement and retrieval of indicators for fast VOCs atmospheric photochemistry with differential optical absorption spectroscopy].

Featuring excellent response characteristics and detection sensitivity and with much lower operational cost, differential optical absorption spectroscopy (DOAS) can be a powerful tool to trace concentration variation of trace indicators -O3, Ox (O3 + NO2) and HCHO for fast VOCs atmospheric photochemistry. But it's difficult to measure those gases accurately because of trace concentration. Here using a self-made DOAS system, the accurate measurement of those indicators was achieved through improving the ratio of signal to noise ratio and correcting the background scattering light; the retrieving method of those indicators was developed through eliminating the temperature effect of absorption cross section, accurately removing the intrinsic structure and lamp structure of spectrum. The preference of different spectral windows that could be used for the concentration retrieval of those indicators was analyzed and compared including interfering factors, results retrieved and the accuracy.

[Research on cluster-assistant multiple ionization of acetonitrile by intense nanosecond laser].

To further investigate the relation between cluster and multi-charged ions, the photo-ionization of acetonitrile molecular beam carried by helium was studied by time-of-flight mass spectrometry using 25 ns, 532 nm and 1 064 nm Nd-YAG laser with an intensity of 10(10) W x cm(-2). When the effused beam of CH3CN at a pressure of about 11 kPa was irradiated by a 532 nm laser, only a few mono-charged ions appeared in the mass spectrum and were clearly resolved, While the pulsed molecular beam seeded in 0.15 MPa He, multi-charged species appeared between H+ and C+, and parent ions containing one or more acetonitrile molecules were also discovered. The intrinsical difference between effused beam and pulsed one was that for the latter it was easier to generate molecule clusters. Adjusting delay time between laser and pulsed valve to shine the laser on different potions of pulsed beam, the change tendency of integral intensity of different multi-charged ions was found to remain similar to that of acetonitrile cluster, and the highest intensity of different ion species appeared at the same 0.75 ms delay time. When the wavelength of laser was changed from 532 nm to 1064 nm, the type of ions and their proportion from effused beam were alike except intensity, but the result of pulsed beam altered obviously. Multi-charged ions showed peak splitting, which characters CE (Coulomb explode). As a powerful tool to understand some chemical physics processes involved, correlation analysis of the time of flight mass spectrum was used. The spectrum of 532 nm was selected owing to its multi-charged ions distinguished easily. The correlations among N(n+) (n = 2-5) and C(n+) (n = 2-4) were all above 0.25, with some even above 0.7, indicating that these ions are highly correlated and probably come from the CE events simultaneously. An electron re-scattering and re-colliding ionization model was proposed to explain the appearances of those multiple charged ions under such low laser intensity. From the theory, the longer wavelength facilitates the energy absorption rate during inverse bremsstrahlung, which leads to the resulting wavelength dependence of the multi-charged atomic ions.