Search

This paper presents a simulation approach to solve the steady-state corona model of a rod-type static discharger with a sharp tip. Based on the requirement of charge density distribution on the corona boundary, a novel iteration calculation method is proposed to automatically solve the corona zone range of the electrode boundary that cannot be predetermined for a sharp electrode. Moreover, a recursive calculation strategy that uses the corona convergence solution of some high-voltage parameters as the initial solution is employed to improve the computational stability and efficiency in scanning simulations with different voltage and wind speed parameters. Through the simulation and verification of a typical rod-type static discharger, we observed that the convergence is fast for the boundary range iteration, and the recursive calculation strategy is also effective. In addition, the volt–ampere characteristics and inception voltage obtained using the simulation were in good agreement with the measurement. Through simulation of a static discharger applied in a typical longitudinal wind field environment, we observed that the proposed approach is still effective at wind speeds up to hundreds of m/s. [ABSTRACT FROM AUTHOR]

The B-dot sensor is a type of Rogowski coil widely used in the measurement of current. However, the accuracy of the B-dot for measuring aircraft high-frequency lightning current is greatly affected by factors such as numerical integration drift, high-frequency oscillation, and calibration. In this study, a new design and optimization for improving the B-dot measuring accuracy was carried out. To correct the drift of the numerical integral of the measurement signal in differential mode, the measuring current was reconstructed based on the nonlinear least squares method. The sensor was then optimized by isolating the sampling resistance and matching the impedance with a voltage follower. A low-cost coaxial loop calibration system was also designed to calibrate the high frequency and strong magnetic fields more accurately. Finally, the optimized B-dot sensor accuracy was greatly improved with a measuring range of 30 kA/m, an error of 3.1%, and a high-frequency response of 50 MHz. Our study greatly increases the accuracy of measuring aircraft high-frequency lightning current. [ABSTRACT FROM AUTHOR]

Multi‐AXis Differential Optical Absorption Spectroscopy (MAX‐DOAS) observations were carried out from March 1, 2019 to February 29, 2020 in Qingdao, China, on the coast of the Yellow Sea (120.67°E, 36.35°N). Atmospheric parameters retrieved from the MAX‐DOAS instrument included vertical profiles of aerosol extinction, gaseous aerosol precursors (NO2, SO2), and H2O. First, the seasonal relationship between aerosol optical depth (AOD) and the H2O vertical column density (VCD) was analyzed. The correlation coefficients (r) between AOD and H2O VCD were largest in the winter, followed by spring, autumn, and summer. In addition, the correlation during heavily polluted weather was much higher than that during clean weather or slightly polluted weather. Then, an analysis of the wind speed and direction, and trace gas VCDs during the months with frequent pollution (December 2019 and January 2020) found that heavy pollution episodes easily occurred in Qingdao due to a combination of high H2O concentrations and low wind speeds. Out of four pollution events (P1, P2, P3, P4), both the H2O concentration and pollution were highest during the first event (P1). The H2O VCD, AOD, sulfate AOD, and total column HNO3 simultaneously increased during P1, while the NO2 and SO2 VCDs decreased. These trends are consistent with liquid phase reactions. Finally, the 1,000 m backward trajectory for the wind and the gas profiles during P1 revealed that the pollutants increased in Qingdao due to the influence of a polluted air mass from the western inland regions. Plain Language Summary: Water vapor and aerosols are important components of the atmosphere. An increase in H2O concentration will accelerate the liquid phase reactions of trace gas and aggravate haze pollution. In recent years, heavy haze pollution has frequently occurred in China, especially during the winter in the northern China. The relationship between H2O and the aerosol optical depth (AOD), and how this relationship impacts haze formation, are of great significance for understanding the mechanisms driving heavy air pollution. Multi‐AXis Differential Optical Absorption Spectroscopy (MAX‐DOAS) is a remote sensing method that can simultaneously measure H2O, aerosols, and gaseous precursors (NO2, SO2). MAX‐DOAS instruments are low‐cost, simple to operate, and provide high time resolution, making them well‐suited for atmospheric observations across large geographic regions. The ability of MAX‐DOAS observations to simultaneously constrain the vertical profiles of H2O, other trace gases, and aerosols provides a measurement framework for analyzing liquid‐phase reactions in heavily polluted conditions. When combined with a wind backward trajectory analysis, it is possible to study the transport of H2O and pollutants during haze events. This is crucial to understanding the causes of haze formation and informing regulatory policy. Key Points: H2O vertical profiles were measured using Multi‐AXis Differential Optical Absorption Spectroscopy (MAX‐DOAS)The correlation coefficient between the aerosol optical depth and the H2O VCD was higher during heavily polluted weatherHeavy air pollution easily occurred in Qingdao due to a combination of high H2O concentration and low wind speeds [ABSTRACT FROM AUTHOR]

Mobile differential optical absorption spectroscopy (mobile DOAS) has become an important tool for the quantification of emission sources, including point sources (e.g., individual power plants) and area emitters (e.g., entire cities). In this study, we focused on the error budget of mobile DOAS measurements from point sources, and we also offered recommendations for the optimum settings of such measurements via a simulation with a modified Gaussian plume model. Following the analysis, we conclude that (1) the proper sampling resolution should be between 5 and 50 m. (2) When measuring far from the source, undetectable flux (measured slant column densities (SCDs) are under the detection limit) resulting from wind dispersion is the main error source. The threshold for the undetectable flux can be lowered by larger integration time. When measuring close to the source, low sampling frequency results in large errors, and wind field uncertainty becomes the main error source of SO 2 flux (for NO x this error also increases, but other error sources dominate). More measurement times can lower the flux error that results from wind field uncertainty. The proper wind speed for mobile DOAS measurements is between 1 and 4 m s -1. (3) The remaining errors by [NO x ] / [NO 2 ] ratio correction can be significant when measuring very close. To minimize the [NO x ] / [NO 2 ] ratio correction error, we recommend minimum distances from the source, at which 5 % of the NO 2 maximum reaction rate is reached and thus NO x steady state can be assumed. (4) Our study suggests that emission rates < 30 g s -1 for NO x and < 50 g s -1 for SO 2 are not recommended for mobile DOAS measurements. Based on the model simulations, our study indicates that mobile DOAS measurements are a very well-suited tool to quantify point source emissions. The results of our sensitivity studies are important to make optimum use of such measurements. [ABSTRACT FROM AUTHOR]

Haze and dust pollution have a significant impact on human production, life, and health. In order to understand the pollution process, the study of these two pollution characteristics is important. In this study, a one-year observation was carried out at the Beijing Southern Suburb Observatory using the MAX-DOAS instrument, and the pollution characteristics of the typical haze and dust events were analyzed. First, the distribution of aerosol extinction (AE) and H2O concentrations in the two typical pollution events were studied. The results showed that the correlation coefficient (r) between H2O and AE at different heights decreased during dust processes and the correlation slope (|k|) increased, whereas r increased and |k| decreased during haze periods. The correlation slope increased during the dust episode due to low moisture content and increased O4 absorption caused by abundant suspended dry crustal particles, but decreased during the haze episode due to a significant increase of H2O absorption. Secondly, the gas vertical column density (VCD) indicated that aerosol optical depth (AOD) increased during dust pollution events in the afternoon, while the H2O VCD decreased; in haze pollution processes, both H2O VCD and AOD increased. There were significant differences in meteorological conditions during haze (wind speed (WD) was <2 m/s, and relative humidity (RH) was >60%) and dust pollution (WD was >4 m/s, and RH was <60%). Next, the vertical distribution characteristics of gases during the pollution periods were studied. The AE profile showed that haze pollution lasted for a long time and changed slowly, whereas the opposite was true for dust pollution. The pollutants (aerosols, NO2, SO2, and HCHO) and H2O were concentrated below 1 km during both these typical pollution processes, and haze pollution was associated with a strong temperature inversion around 1.0 km. Lastly, the water vapor transport fluxes showed that the water vapor transport from the eastern air mass had an auxiliary effect on haze pollution at the observation location. Our results are of significance for exploring the pollution process of tropospheric trace gases and the transport of water vapor in Beijing, and provide a basis for satellite and model verification. [ABSTRACT FROM AUTHOR]

Water vapor transport affects regional precipitation and climate change. The measurement of precipitable water (PW) and water vapor flux (WVF) is of great importance for the study of precipitation and water vapor transport. This study presented a new method of computing PW and estimating WVF using the water vapor vertical column density (VCD) and profile retrieved from multi-axis differential optical absorption spectroscopy (MAX-DOAS), combined with the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 wind profiles. We applied our method to MAX-DOAS observations in the coastal (Qingdao) and inland (Xi'an) cities of China from June 2019 to May 2020 and compared the results to the ERA5 reanalysis datasets. Good agreement with ERA5 datasets was found; the correlation coefficient (r) of the PW and the zonal and meridional WVFs were r ≥ 0.92, r = 0.77, and r ≥ 0.89, respectively. The comparison results showed the feasibility and reliability of estimating PW and WVF using MAX-DOAS. Then, we analyzed the seasonal and diurnal climatology of the PW and WVFs in Qingdao and Xi'an. The results indicated that the seasonal and diurnal variations of the PW in the two cities were similar. The zonal water vapor transport of the two cities mainly involved eastward transport, Qingdao's meridional water vapor mainly involved southward transport, and that of Xi'an mainly involved northward transport. The WVFs of the two cities were higher in the afternoon than in the morning, which may be related to wind speed. The results also indicated that the WVF transmitting belts appeared at around 2 and 1.4 km above the surface in Qingdao and around 2.8, 2.6, 1.6, and 1.0 km above the surface in Xi'an. Before precipitation, the WVF transmitting belt moved from near the ground to a high level, reaching its maximum at about 2 km, and the PW and meridional vertically integrated WVF increased. Finally, the sources and transports of water vapor during continuous precipitation and torrential rain were analyzed according to a 24 h backward trajectory. The air mass from the southeast accounted for more than 84% during continuous precipitation in Xi'an, while the air mass from the ocean accounted for more than 75% during torrential rain in Qingdao and was accompanied by a high-level ocean jet stream. As an optical remote sensing instrument, MAX-DOAS has the advantages of high spatiotemporal resolution, low cost, and easy maintenance. The application of MAX-DOAS to meteorological remote sensing provides a better method for evaluating the PW and WVF. [ABSTRACT FROM AUTHOR]

This paper studied the method for converting the aerosol extinction to the mass concentration of particulate matter (PM) and obtained the spatio-temporal distribution and transportation of aerosol, nitrogen dioxide (NO2), sulfur dioxide (SO2), and formaldehyde (HCHO) based on multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations in Dalian (38.85°N, 121.36°E), Qingdao (36.35°N, 120.69°E), and Shanghai (31.60°N, 121.80°E) from 2019 to 2020. The PM2.5 measured by the in situ instrument and the PM2.5 simulated by the conversion formula showed a good correlation. The correlation coefficients R were 0.93 (Dalian), 0.90 (Qingdao), and 0.88 (Shanghai). A regular seasonality of the three trace gases is found, but not for aerosols. Considerable amplitudes in the weekly cycles were determined for NO2 and aerosols, but not for SO2 and HCHO. The aerosol profiles were nearly Gaussian, and the shapes of the trace gas profiles were nearly exponential, except for SO2 in Shanghai and HCHO in Qingdao. PM2.5 presented the largest transport flux, followed by NO2 and SO2. The main transport flux was the output flux from inland to sea in spring and winter. The MAX-DOAS and the Copernicus Atmosphere Monitoring Service (CAMS) models' results were compared. The overestimation of NO2 and SO2 by CAMS is due to its overestimation of near-surface gas volume mixing ratios. [ABSTRACT FROM AUTHOR]

NOX (NOX = NO + NO2) emissions measurements in Beijing are of great significance because they can aid in understanding how NOX pollution develops in mega-cities throughout China. However, NOX emissions in mega-cities are difficult to measure due to changes in wind patterns and moving sources on roads during measurement. To obtain good spatial coverage on different ring roads in Beijing over a short amount of time, two mobile differential optical absorption spectroscopy (DOAS) instruments were used to measure NOX emission flux from April 18th to 26th, 2018. In addition, a wind profile radar provided simultaneous wind field measurements for altitudes between 50 m and 1 km for each ring road measurement. We first determined NOX emission flux of different ring roads using wind field averages from measured wind data. The results showed that the NOX emission flux of Beijing's fifth ring road, which represented the urban part, varied from (19.29 ± 5.26) × 1024 molec./s to (36.46 ± 12.86) × 1024 molec./s. On April 20th, NOX emission flux for the third ring was slightly higher than the fourth ring because the two ring roads were measured at different time periods. We then analyzed the NOX emission flux error budget and error sensitivity. The main error source was the wind field uncertainty. For some measurements, the main emission flux error source was either wind speed uncertainty or wind direction uncertainty, but not both. As Beijing's NOX emissions came from road vehicle exhaust, we found that emission flux error had a more diverse sensitivity to wind direction uncertainty, which improved our knowledge on this topic. The NOX emission flux error sensitivity study indicated that more accurate measurements of the wind field are crucial for effective NOX emission flux measurements in Chinese mega-cities. Obtaining actual time and high resolved wind measurements is an advantage for mega-cities' NOX emission flux measurements. The emission flux errors caused by wind direction and wind speed uncertainties were clearly distinguished. Other sensitivity studies indicated that NOX/NO2 ratio uncertainty dominated flux errors when the NOX/NO2 ratio uncertainty was >0.4. Using two mobile-DOAS and wind profile radars to measure NOx emission flux improved the quality of the emission flux measuring results. This approach could be applied to many other mega-cities in China and in others countries. [ABSTRACT FROM AUTHOR]