Mechanisms of formation of differential reflectivity columns are investigated in simulations of a midlatitude summertime hailstorm with hailstones up to several centimeters in diameter. Simulations are performed using...
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Mechanisms of formation of differential reflectivity columns are investigated in simulations of a midlatitude summertime hailstorm with hailstones up to several centimeters in diameter. Simulations are performed using a new version of the Hebrew University Cloud Model (HUCM) with spectral bin microphysics. A polarimetric radar forward operator is used to calculate radar reflectivity and differential reflectivity Z(DR). It is shown that Z(DR) columns are associated with raindrops and with hail particles growing in a wet growth regime within convective updrafts. The height and volume of Z(DR) columns increases with an increase in aerosol concentration. Small hail forming under clean conditions grows in updrafts largely in a dry growth regime corresponding to low Z(DR). Characteristics of Z(DR) columns are highly correlated with vertical velocity, hail size, and aerosol concentration.
Experimental and field measurements have shown that, in the presence of both iron-containing aerosols and sunlight, oxidized mercury species such as HgCl2 and HgBr2 undergo reduction to elemental mercury (Hg degrees),...
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Experimental and field measurements have shown that, in the presence of both iron-containing aerosols and sunlight, oxidized mercury species such as HgCl2 and HgBr2 undergo reduction to elemental mercury (Hg degrees), which remains in the atmosphere longer than oxidized mercury species due to its higher volatility. We performed density functional theory (DFT, PW91 + U) calculations to elucidate the reduction mechanism for atmospheric HgCl2 and HgBr2 to Hg degrees on several iron-oxide aerosol surfaces relevant in the troposphere. On the OH-Fe-Rterminated alpha-Fe2O3 (0001) surface, predicted to be most prevalent under ambient conditions, we show that: (1) the first Hg-X bond is broken via either thermal or photolytic activation depending on the ambient temperature;(2) photons with an energy of 2.69 eV (461 nm) are required to break the second Hg-X bond;and (3) a photoinduced surface-to-adsorbate charge-transfer process can promote Hg degrees desorption with an excitation energy of 2.59 eV (479 nm). All the calculated excitation energies are below the threshold value of 3.9 eV (320 nm) for photons in the troposphere, suggesting that sunlight can facilitate mercury reduction on iron-oxide aerosol surfaces. In contrast, the gas-phase reduction of HgCl2 (HgBr2) involves photoexcitation requiring an energy of 4.98 (4.45) eV (249 (279) nm);therefore, the energy range of sunlight is not suitable for gas-phase reduction. Our computational results provide the first evidence on the detailed mechanism for the combined role of aerosols and photons in the reduction of HgCl2 and HgBr2. Our methodology can be adapted to study other photochemical heterogeneous processes in the atmosphere.
Food-cooking organic aerosols (COA) are one of the primary sources of submicron particulate matter in urban environments. However, there are still many questions surrounding source apportionment related to instrumenta...
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Food-cooking organic aerosols (COA) are one of the primary sources of submicron particulate matter in urban environments. However, there are still many questions surrounding source apportionment related to instrumentation as well as semivolatile partitioning because COA evolve rapidly in the ambient air, making source apportionment more complex. Online measurements of emissions from cooking different types of food were performed in a laboratory to characterize particles and gases. Aerosol mass spectrometer (AMS) measurements showed that the relative ionization efficiency for OA was higher (1.56-3.06) relative to a typical value of 1.4, concluding that AMS is over-estimating COA and suggesting that previous studies likely over-estimated COA concentrations. Food-cooking mass spectra were generated using AMS, and gas and particle food markers were identified with filter inlets for gases and aerosols-chemical ionization mass spectrometer (CIMS) measurements to be used in future food cooking-source apportionment studies. However, there is a considerable variability in both gas and particle markers, and dilution plays an important role in the particle mass budget, showing the importance of using these markers with caution during receptor modeling. These findings can be used to better understand the chemical composition of COA, and they provides useful information to be used in future source-apportionment studies.
Aerosol-cloud interactions represent one of the largest uncertainties in external forcings on our climate system. Compared with liquid clouds, the observational evidence for the aerosol impact on ice clouds is much mo...
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Aerosol-cloud interactions represent one of the largest uncertainties in external forcings on our climate system. Compared with liquid clouds, the observational evidence for the aerosol impact on ice clouds is much more limited and shows conflicting results, partly because the distinct features of different ice cloud and aerosol types were seldom considered. Using 9-year satellite retrievals, we find that, for convection-generated (anvil) ice clouds, cloud optical thickness, cloud thickness, and cloud fraction increase with small-to-moderate aerosol loadings (<0.3 aerosol optical depth) and decrease with further aerosol increase. For in situ formed ice clouds, however, these cloud properties increase monotonically and more sharply with aerosol loadings. An increase in loading of smoke aerosols generally reduces cloud optical thickness of convection-generated ice clouds, while the reverse is true for dust and anthropogenic pollution aerosols. These relationships between different cloud/aerosol types provide valuable constraints on the modeling assessment of aerosol-ice cloud radiative forcing. Plain Language Summary Aerosol-cloud interactions represent one of the largest uncertainties in external forcings on our climate system. Compared with liquid clouds, the observational evidence for the aerosol impact on ice clouds is much more limited and shows conflicting results, partly because the distinct features of different ice cloud and aerosol types were seldom considered. Using 9-year satellite retrievals, we find that the responses of ice cloud properties to aerosols differ according to the types of cloud/aerosols. For convection-generated (anvil) ice clouds, the thickness, optical thickness, and amount of clouds increase with small-to-moderate aerosol loadings and decrease with further aerosol increase. For in situ formed ice clouds, however, these cloud properties increase monotonically and more sharply with aerosol loadings. An increase in loading of smoke aerosols
In this study, we investigate the impacts of aerosols on tropical cyclone (TC) precipitation that occurred from 1980 to 2014 over China mainland. The TC-induced precipitation is objectively identified based on Western...
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In this study, we investigate the impacts of aerosols on tropical cyclone (TC) precipitation that occurred from 1980 to 2014 over China mainland. The TC-induced precipitation is objectively identified based on Western North Pacific (WNP) TC historical track data and daily precipitation data from meteorological stations. Aerosol optical depth (AOD) from the Second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) is used to represent the amount of aerosol pollution. The long-term variations in AOD and TC precipitation from the past 35 years are analyzed. A significant increasing trend is found for both the relative percentage of TC rainstorm days and the amount of aerosol loading. Together with the decreasing trend in the annual number of TCs affecting China, this indicates that aerosols are invigorating TC precipitation. For the TC precipitation during the study period, the relative occurrence of light rain shows a decreasing trend, while the proportion of heavy rain and rainstorms shows an increasing trend. Meanwhile, the intensity of the TC daily precipitation increases with the elevated pollution level, particularly during the TC initial period and for heavy TC rainfall. These statistical results based on long-term observations suggest that aerosols have a substantial impact on TC precipitation through microphysical effects and have the potential to impact the track, intensity, size, and lifespan of TCs over Southeast Asia.
This paper presents the results of a detailed study on the size characteristics of aerosols at the tropical coastal site Thiruvananthapuram based on the in-situ measurements of size resolved aerosol number density usi...
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This paper presents the results of a detailed study on the size characteristics of aerosols at the tropical coastal site Thiruvananthapuram based on the in-situ measurements of size resolved aerosol number density using an aerosol spectrometer, covering a period of 28 months from September 2011 to December 2013. The diurnal pattern of aerosol number density is characterized by day time low and a two-fold increase during nighttime and these changes are closely associated with the strong mesoscale features namely the sea breeze and land breeze prevailing at the site. Aerosol Number Size Distribution (NSD) depicts a multi-modal nature with two prominent modes, one <= 0.1 mu m and other similar to 1 mu m. Two other less pronounced modes are also observed in the NSD, one similar to 0.3-0.5 mu m and other similar to 5-8 mu m. The NSDs also exhibited strong seasonal changes linked with the synoptic meteorological feature of this region namely the South Asian monsoon. The seasonal NSDs were parameterized and analyzed. In addition to this, the effects of meteorological parameters temperature, relative humidity, and wind speed and airflow patterns on aerosol number density as revealed by partial correlation analysis were found to be aerosol size dependent.
Stratospheric aerosols that are caused by a major volcanic eruption can serve as a valuable test of global climate models, as well as severely complicate tropospheric-aerosol monitoring from space. In either case, it ...
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Stratospheric aerosols that are caused by a major volcanic eruption can serve as a valuable test of global climate models, as well as severely complicate tropospheric-aerosol monitoring from space. In either case, it is highly desirable to have accurate global information on the optical thickness, size, and composition of volcanic aerosols. We report sensitivity study results, which reveal the implications of making precise multi-angle photopolarimetric measurements in a 1.378-mu m spectral channel residing within a strong water-vapor absorption band. We demonstrate that, under favorable conditions, such measurements would enable near-perfect retrievals of the optical thickness, effective radius, and refractive index of stratospheric aerosols. Besides enabling accurate retrievals of volcanic aerosols, such measurements can also be used to monitor man-made particulates injected in the stratosphere for geoengineering purposes. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
The Regional Atmospheric Modeling System (RAMS) is used to investigate the effect of aerosols acting as ice nuclei (IN) on the formation and growth of hydrometeor particles as well as on the dynamics and precipitation...
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The Regional Atmospheric Modeling System (RAMS) is used to investigate the effect of aerosols acting as ice nuclei (IN) on the formation and growth of hydrometeor particles as well as on the dynamics and precipitation of a severe storm in Northern China. The focus of this study is to determine how the overall dynamics and microphysical structure of deep convective clouds are influenced if IN concentrations are somehow altered in a storm environment that is otherwise unchanged. Ice mixing ratios tend to increase and liquid mixing ratios tend to decrease with increasing IN concentrations. High concentrations of IN reduce the mean hail diameter and hail particles with smaller diameters melt more easily, which leads to a decrease in ground hailfall and an increase in surface rainfall. Liquid water plays a more important role in the process of hail formation, while the role of ice particles in the process of hail formation decreases with higher IN concentrations. The role of small cloud droplets in the formation of raindrops is increased and the role of hail melting in the process of raindrops formation is weakened with enhanced IN concentrations. Both latent heat release and absorption significantly increase with increasing IN concentrations. Increasing the concentration of IN by an appropriate amount is beneficial for increasing the total water content and strengthening the updraft, leading to enhancement of a storm, but excessive IN concentrations will inhibit the development of a storm.
As the SO3 emissions from coal-fired flue gas have received increasing concerns, experiments on the removal characteristics of sulfuric acid aerosols in the wet electrostatic precipitator (WESP) system were carried ou...
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As the SO3 emissions from coal-fired flue gas have received increasing concerns, experiments on the removal characteristics of sulfuric acid aerosols in the wet electrostatic precipitator (WESP) system were carried out by using a pilot plant. The physical properties of sulfuric acid aerosols before the WESP system were analyzed as also the removal performance in the WESP system. Moreover, the effects of operating parameters on the removal and the effect of sulfuric acid aerosols on PM2.5 removal were discussed. The results displayed that plenty of submicron sulfuric acid aerosols exited before the WESP system, and the majority ones were smaller than 0.1 mu m. The corresponding removal efficiencies were mainly from 30 to 65%, and the fractional removal efficiency had a distinct decline for aerosols with sizes from 0.1 to 1 mu m. Furthermore, with the increase of the operating voltage and the decline of the inlet gas temperature and the inlet concentration of sulfuric acid aerosols, the removal effect was promoted. Besides, the existence of sulfuric acid aerosols was beneficial for the PM2.5 removal in the WESP system, especially for submicron ones. The tendency was more obvious when the inlet concentration was increased.
In this study a chemical kinetic model which converts sodium oxide aerosols to sodium carbonate aerosols as a function of CO2 and humidity is implemented in the FLEXPART atmospheric dispersion model for impact assessm...
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In this study a chemical kinetic model which converts sodium oxide aerosols to sodium carbonate aerosols as a function of CO2 and humidity is implemented in the FLEXPART atmospheric dispersion model for impact assessment during sodium fire accidents in sodium cooled fast reactors. The model is validated with open environment aerosol dispersion experiments conducted at Kalpakkam coastal site. Simulated total aerosol concentrations and deposition agree with experimental data. Simulations indicate rapid conversion of NaOH to Na2CO3 during atmospheric transport under high humidity levels (57-80%) at Kalpakkam. Parametric tests with different particle size indicated that a particle diameter of 5 mu m produced realistic aerosol deposition closely comparing with observations. A series of simulations were conducted for various meteorological conditions to assess the chemical impact in a range of 25 km during a postulated accident. Simulations for extended 8-h release scenarios in different seasonal flow conditions indicate the concentrations beyond 1.5 km fall to very low values (<= 0.1 mg/m(3) for NaOH and <= 4 mg/m(3) for Na2CO3) indicating no chemical impact. Short-duration (1 h) releases during worst environmental conditions (sea breeze, low winds) indicate that the aerosol concentrations during sea breeze are about 4-5 times high compared to winter time calm winds due to wide diffusion of aerosols in winter. The concentrations in these two cases are found to be higher (similar to 0.2 mg/m(3) for NaOH and 6 mg/m(3) for Na2CO3) in the site distance range but thereafter rapidly fall, thus indicating no inhalation hazard during sodium fire scenarios at the coastal site.
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