Effect of the air pollution on atmospheric visibility in Beijing-Tianjin area

Simultaneous measurements of air pollutant concentrations and atmospheric visibility were made in Beijing and Tianjin areas in 1983-1985. The relationship between air pollution and visibility was studied. It was found that atmospheric particulates have the most high contribution to visibility decreasing. The percentages of contributions of sulfates and soot are 52-58% and 22-29% respectively. According to the results, we suggest that the emission of SO2 and particulates must be controlled in order to improve the atmospheric visibility.

Effect of non-spherical atmospheric charged particles and atmospheric visibility on performance of satellite-ground quantum link and parameters simulation

In order to study the relationship between the non-spherical atmospheric charged particles and satellite-ground quantum links attenuation. The relationship among the particle concentration, equivalent radius, charge density of the charged particle, the attenuation coefficient and entanglement of the satellite-ground quantum link can be established first according to the extinction cross section and spectral distribution function of the non-spherical atmospheric charged particles. The quantitative relationship between atmospheric visibility and communication fidelity of satellite-ground quantum link were analyzed then. Simulation results show that the ellipsoid, Chebyshev atmospheric charged particle influences on attenuation of the satellite-ground quantum link increase progressively. When the equivalent particle radius is 0.2 gm and the particle concentration is 50 μg/m^3, the attenuation coefficient and entanglement of the satellite-ground quantum link is 9.21 dB/km, 11.46 dB/km and 0.453, 0.421 respectively; When the atmospheric visibility reduces from 8 km to 2 kin, the communication fidelity of satellite-ground quantum link decreases from 0.52 to 0.08. It is shown that the non-spherical atmospheric charged particles and atmospheric visibility influence greatly on the performance of the satellite-ground quantum link communication system. Therefore, it is necessary to adjust the parameters of the quantum-satellite communication system according to the visibility values of the atmosphere and the shapes of the charged particles in the atmosphere to improve reliability of the satellite-ground quantum link.

Retrieval of Atmospheric Horizontal Visibility by Statistical Regression from NOAA/AVHRR Satellite Data

Based on the atmospheric horizontal visibility data from forty-seven observational stations along the eastern coast of China near the Taiwan Strait and simultaneous NOAA/AVHRR multichannel satellite data during January 2001 to December 2002, the spectral characters associated with visibility were investigated. Successful retrieval of visibility from multichannel NOAA/AVHRR data was performed using the principal component regression （PCR） method. A sample of retrieved visibility distribution was discussed with a sea fog process. The correlation coefficient between the observed and retrieved visibility was about 0.82, which is far higher than the 99.9% confidence level by statistical test. The rate of successful retrieval is 94.98% of the 458 cases during 2001 2002. The error distribution showed that high visibilities were usually under-estimated and low visibilities were over-estimated and the relative error between the observed and retrieved visibilities was about 21.4%.

On Spatiotemporal Characteristics of Sea Fog Occurrence over the Northern Atlantic from 1909 to 2008

In this paper, the International Comprehensive Ocean and Atmosphere Data Set(ICOADS) is utilized to investigate the horizontal distribution of sea fog occurrence frequency over the Northern Atlantic as well as the meteorological and oceanic conditions for sea fog formation. Sea fog over the Northern Atlantic mainly occurs over middle and high latitudes. Sea fog occurrence frequency over the western region of the Northern Atlantic is higher than that over the eastern region. The season for sea fog occurrence over the Northern Atlantic is generally from April to August. When sea fogs occur, the prevailing wind direction in the study area is from southerly to southwesterly and the favorable wind speed is around 8 m s-1. It is most favorable for the formation of sea fogs when sea surface temperature(SST) is 5℃ to 15℃. When SST is higher than 25℃, it is difficult for the air to get saturated, and there is almost no report of sea fog. When sea fogs form, the difference between sea surface temperature and air temperature is mainly-1 to 3℃, and the difference of 0℃ to 2℃ is the most favorable conditions for fog formation. There are two types of sea fogs prevailing in this region: advection cooling fog and advection evaporating fog.

ANALYSIS OF PARTICULATE MASS CONCENTRATION,AEROSOL NUMBER CONCENTRATION AND VISIBILITY IN BEIJING

Particulate mass concentration (PM10, PM2.5), aerosol number concentration (NOPC), aerosol size distribu-tion and atmospheric visibility were simultaneously measured in Beijing in the summer and winter of 2001. From the profuse data collected, the following conclusions can be drown: (1) there are two peaks for the average diurnal variations of PM10 and NOPC in the summer, an obvious valley can be seen between 12:30 and 15:00 for their average diurnal variation in the winter; (2) there is one single peak for the average diurnal variation of atmospheric visibility in the summer, while there are two peaks in the winter; (3) PM10 and NOPC are usually smaller in the summer than those in the winter; (4) the average visibility is much lower during 00:00~09:00 in the summer than that in the winter, because of the very high relative humidity and higher concentration of the large particles (r>1.25 mm) in the summer during the period; (5) aerosol size distributions usually depend closely on season and relative humidity at the same place.

Atmospheric extinction properties in Shenyang,China

Atmospheric visibility impairment due to human activities is becoming increasingly significant in metropolitan 8henyang, China. In this study, hourly data of relevant factors throughout the year 2010 in Shenyang were used to evaluate the local atmospheric extinction properties. The results show that the average coefficient of total extinction and aerosol single-scattering albedo in 2010 were 622.72 Mm^-1 and 0.87, respectively, values that are characteristic of the ＂municipal pollution type＂. Visibility is most impaired during winter and especially in January. The coefficient of total extinction exhibits a single daily cycle with a maximum at 5-6 am and a minimum at 3 pm. The mean extinction contributions of the constituents, from high to low, were particle scattering （87.49%）, particle absorption, gas absorption, and gas scattering. The extinction contribution of gas molecules was little more than 4.5%, far smaller than that of particles. Scattering by particles was the main contributor to extinction, especially in the morning and around midnight.

Analysis and Modeling of a Long-Lasting Fog Event over Beijing in February 2007

The evolution characteristics of a long-lasting fog investigated using the 5-min automatic visibility data analysis results reveal that there is a close relationship and the weather conditions such as high humidity, light event over Beijing during 20-22 February 2007 are and conventional meteorological observations. Data between the development/evolution of this fog event wind, and low temperature in the lower troposphere. Furthermore, numerical simulations of this event are carried out by using the Advanced Research WRF （ARW） V2.2 Noah LSM land-atmosphere coupled model. The model is two-way and two-nested with improvement in the description of the interface between the urban underlying surface and the atmospheric boundary layer. The horizontal grid spacings are 9 and 3 km for the two domains. The ground-based GPS precipitable water vapor content and automatic and conventional meteorological observations at the initial time are assimilated. The simulation results indicate that the control experiment with local data assimilation has successfully captured the spatial-temporal evolution of this fog event, especially the synoptic patterns and characteristics of the weather conditions （high humidity, light wind, and lower temperature）. The results are well consistent with observations. Comparison of two experiments （with and without local data assimilation） shows that the model initial conditions are considerably modified with the WRF 3DVAR. The assimilation of local observations leads to significant improvement in the prediction of this event with better representation of static stability, enhanced southeasterly winds, concomitant warmer moisture in the south of Beijing, intensified temperature inversion between the lower and upper troposphere, and generally decreasing environmental temperature.

Multilevel air quality evolution in Shenyang:Impact of elevated point emission reduction

Visibility observed at different altitudes is favorable to understand the causes of air pol-lution.We conducted 4-years of observations of visibility at 2.8 and 60 m and particulate matter(PM)concentrations from 2015 to 2018 in Shenyang,a provincial city in Northeast China.The results indicated that visibility increased with the increasing height in winter(especially at night),and decreased with height in summer(especially at the daytime).PM concentration exhibited opposite vertical variation to visibility,reflecting that visibility de-grades with the increase of aerosol concentration in the air.The radiosonde meteorological data showed that weak turbulence in the planetary boundary layer(PBL)in winter favored aerosols'accumulation near the surface.Whereas in summer,unstable atmospheric con-ditions,upper-level moister environment,and regional transport of air pollutants resulted in the deterioration of upper-level visibility.Inter-annual variation in the two-level visibility indicated that the upper-level visibility improved more significantly than low-level visibil-ity,much likely due to the reduction in emission of elevated point sources in Shenyang.Our study suggested that strengthening the control of surface non-point emissions is a promis-ing control strategy to improve Shenyang air quality.

An observational and modeling study of a sea fog event over the yellow and east China seas on 17 March 2014

The Moderate Resolution Imaging Spectroradiometer(MODIS)satellite imagery,weather charts,objectively reanalyzed data,the observational data and station sounding data were analyzed to investigate a sea fog event occurred over the Yellow and East China Seas on March 17,2014.The sounding profiles,weather situations and the related meteorological factors during the development and dissipation stages of this sea fog event were documented.Weather Research Forecast(WRF)model was applied to simulate this sea fog case.The simulated horizontal atmospheric visibility,cloud water,humidity,and vertical wind profile during the different stages of this fog event were analyzed.During the development stage of this sea fog,a southerly lower-jet with 16-18 ms-1,an inversion layer and a cold center over the Yellow Sea were detected.The relative humidity in the fog area was above 95%.The specific humidity over the East China Sea was higher than that over the Yellow Sea.Southerly was dominated in fog area.However,during the dissipation stage of this sea fog,westerly replaced the southerly and at the lower level,southerly jet disappeared.A dry air area formed over the Shandong Peninsula and moved eastwards.Moreover,the WRF modeling result showed that the simulated atmospheric horizontal visibility and cloud water were approximately consistent with the MODIS satellite imagery.Most of cloud water concentrated below 200-400 m,and the cloud water in the southern part of fog area extended to a higher height than the northern part.While both of air temperature and dew-point temperature were close to sea surface temperature.

Fabrication of multi-wavelength visible and infrared filter for solar atmosphere tomographic imaging

To simultaneously obtain high-resolution multi-wavelength （from visible to near infrared） tomographic images of the solar atmosphere, a high-performance multi-wavelength optical filter has to be used in solar imaging telescopes. In this Letter, the fabrication of the multi-wavelength filter for solar tomographic imaging is described in detail. For this filter, Ta2O5 and SiO2 are used as high- and low-index materials, respectively, and the multilayer structure is optimized by commercial Optilayer software at a 7.5° angle of incidence. Experimentally, this multi-wavelength optical filter is prepared by a plasma ion-assisted deposition technique with optimized deposition parameters. High transmittance at 393.3, 396.8, 430.5, 525, 532.4, 656.8, 705.8, 854.2, 1083, and 1565.3 nm, as well as high reflectance at 500 and 589 nm are achieved. Excellent environmental durability, demonstrated via temperature and humidity tests, is also established.