Our objectives are to evaluate inter-continental source-receptor relationships for fine aerosols and to identify the regions whose emissions have dominant influence on receptor continents. We simulate sulfate, black c...
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Our objectives are to evaluate inter-continental source-receptor relationships for fine aerosols and to identify the regions whose emissions have dominant influence on receptor continents. We simulate sulfate, black carbon (BC), organic carbon (OC), and mineral dust aerosols using a global coupled chemistry-aerosol model (MOZART-2) driven with NCEP/NCAR reanalysis meteorology for 1997-2003 and emissions approximately representing year 2000. The concentrations of simulated aerosol species in general agree within a factor of 2 with observations, except that the model tends to overestimate sulfate over Europe in summer, underestimate BC and OC over the western and southeastern (SE) U.S. and Europe, and underestimate dust over the SE U.S. By tagging emissions from ten continental regions, we quantify the contribution of each region's emissions on surface aerosol concentrations (relevant for air quality) and aerosol optical depth (AOD, relevant for visibility and climate) globally. We find that domestic emissions contribute substantially to surface aerosol concentrations (57-95%) over all regions, but are responsible for a smaller fraction of AOD (26-76%). We define "background" aerosols as those aerosols over a region that result from inter-continental transport, DMS oxidation, and emissions from ships or volcanoes. Transport from other continental source regions accounts for a substantial portion of background aerosol concentrations: 36-97% for surface concentrations and 38-89% for ACID. We identify the Region of Primary Influence (RPI) as the source region with the largest contribution to the receptor's background aerosol concentrations (or AOD). We find that for dust Africa is the RPI for both aerosol concentrations and AOD over all other receptor regions. For non-dust aerosols (particularly for sulfate and BC), the RPIs for aerosol concentrations and AOD are identical for most receptor regions. These findings indicate that the reduction of the emission of non-dust a
The time-dependent release of lead and zinc from rural aerosol samples has been studied in four natural lake waters and various synthetic solutions spanning a pH range of 2.99-8.02. Automatic direct measurement of the...
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The time-dependent release of lead and zinc from rural aerosol samples has been studied in four natural lake waters and various synthetic solutions spanning a pH range of 2.99-8.02. Automatic direct measurement of the released metals in the experimental vessel was performed at 1 min intervals using square wave anodic stripping voltammetry. Substantial initial release occurred within minutes. Further release was sometimes complete within 15 min but could be still continuing after 60 min depending on the nature of the aerosol and the pH of the solution. A maximum concentration of metal in solution observed after a few minutes for some aerosols was attributed to initial release followed by readsorption to the aerosol occurring as a result of a temporary pH minimum induced by the dissolution process. High concentrations (1.8 meg 1(-1)) of calcium in solution stimulated release of lead and zinc, consistent with a surface exchange mechanism. The pH dependence of the percentage of zinc released was the same for synthetic and natural waters. Complete dissolution required more acid conditions than would be expected if release was entirely controlled by a simple, reversible exchange of ions at the particle surface. The pH dependence of lead release is more dependent on solution conditions.
Infrared extinction spectroscopy has been used to monitor liquid-to-solid and solid-to-liquid phase transitions of a variety of model tropospheric aerosols over a temperature range from 298 to 238 K. Uptake and loss o...
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Infrared extinction spectroscopy has been used to monitor liquid-to-solid and solid-to-liquid phase transitions of a variety of model tropospheric aerosols over a temperature range from 298 to 238 K. Uptake and loss of water were induced by controlling the relative humidity (RH) as submicron-sized aerosols passed through a low-temperature, atmospheric pressure flow tube on a time scale of tens of seconds. Observation of the absorption features of condensed-phase liquid water showed that NaCl aerosols deliquesced at a RH within +/-2% of the thermodynamic value from 298 to 253 K, whereas efflorescence did not occur until 40 +/- 5% RH. No hydrate formation was observed. By contrast, aerosols composed of species with considerably lower deliquescence points, including MgCl2, NH4HSO4, and NH4NO3, exhibited a strong inhibition to efflorescence down to 2% RH. As aerosols, the only one of these three which began to effloresce was MgCl2, and only at relative humidities below 2%. MgCl2. 6H(2)O is the likely product. NH4HSO4 aerosols were induced to effloresce when sprayed onto an infrared window and subjected to relative humidities of less than 1 % fur periods of hours. These findings strongly suggest that, in the absence of heterogeneous nuclei, a wide variety of inorganic aerosols will exist as liquid solutions in the atmosphere regardless of relative humidity and temperature conditions.
A system has been developed for measuring the penetration of monodisperse aerosols through filters. The aerosol generator used is a Berglund-Liu generator with a liquid-feed system designed to make the particle size m...
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A system has been developed for measuring the penetration of monodisperse aerosols through filters. The aerosol generator used is a Berglund-Liu generator with a liquid-feed system designed to make the particle size more uniform and to reduce the incidence of orifice blockage. The generator is supplied with air at a constant rate, which ensures that the aerosol concentration does not vary. The airflow is monitored with an orifice plate and micromanometer. The filter test box has been designed to produce uniform airflow through the filter, and an identical box is used as a control. The aerosol concentration is measured with a Royco optical counter, connected to a microcomputer which records the particle counts, and which also controls the flow of aerosol through the filter test box and the control box. The microcomputer makes an initial approximate measurement of the particle concentration and penetration; and it uses these results to calculate the fraction of the total sampling time that should be devoted to the filtered aerosol, and the number of times during the experiment that the aerosol should be passed through the filter in order to reduce the likely error to a value close to the minimum possible with the chosen duration of the experiment.
The temporal and diurnal patterns of particulate-bound mutagens in the atmosphere were examined for a two-month period in the summer of 1985. Daily PM-10 samples were collected at 0900–2100 and 2100–0900 along with ...
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The temporal and diurnal patterns of particulate-bound mutagens in the atmosphere were examined for a two-month period in the summer of 1985. Daily PM-10 samples were collected at 0900–2100 and 2100–0900 along with other air quality measurements from a suburban site in southeast Michigan. The paired samples were collected daily in order to examine day/night variations. Each particulate sample was extracted and separated into 16 different fractions based on polarity before Ames tests were conducted on each fraction to determine the bacterial mutagenic activities in TA98 and TA98/DNP6. Other air quality parameters measured included fine particle mass (diameter less than 2.5 μm), sulfate, sulfur dioxide, nitrogen oxides, nitric acid, ozone, carbonaceous aerosols, some trace elements, and pertinent meteorological data. The results show that the four most polar fractions accounted for at least 70% of the *** highest levels of mutagenic activity occurred during two different types of meteorological conditions. The first type was associated with the long-range transport of coal combustion emissions from south of Michigan's border, whereas the second type was associated with stagnant atmospheric conditions and an accumulation of locally-emitted combustion products. Although nighttime mutagenic activity was slightly higher than daytime activity on some days, rigorous statistical tests indicated that the differences were not significant at the 95% confidence level. However, the mutagenicity profiles of individual paired day/night samples suggest that, under appropriate meteorological conditions, the polar mutagenic species can be formed via nighttime chemical reactions and/or degraded to less mutagenic form via photochemical reactions during the day.
Airborne transmission of SARS-CoV-2 plays a critical role in spreading COVID-19. To protect public health, we designed and fabricated electrospun nanofibrous air filters that hold promise for applications in personal ...
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Airborne transmission of SARS-CoV-2 plays a critical role in spreading COVID-19. To protect public health, we designed and fabricated electrospun nanofibrous air filters that hold promise for applications in personal protective equipment (PPE) and the indoor environment. Due to ultrafine nanofibers (similar to 300 nm), the electrospun air filters had a much smaller pore size in comparison to the surgical mask and cloth masks (a couple of micrometers versus tens to hundreds of micrometers). A coronavirus strain served as a SARS-CoV-2 surrogate and was used to generate aerosols for filtration efficiency tests, which can better represent SARS-CoV-2 in comparison to other agents used for aerosol generation in previous studies. The electrospun air filters showed excellent performance by capturing up to 99.9% of coronavirus aerosols, which outperformed many commercial face masks. In addition, we observed that the same electrospun air filter or face mask removed NaCl aerosols equivalently or less effectively in comparison to the coronavirus aerosols when both aerosols were generated from the same system. Our work paves a new avenue for advancing air filtration by developing electrospun nanofibrous air filters for controlling SARS-CoV-2 airborne transmission.
We studied photoformation of Fe(II) in the water-soluble fractions (WSFs) of bulk aerosol particles collected in Okinawa, Japan, using radiation at wavelengths of 313, 334, 366, and 405 nm. Fe(II) photoformation quick...
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We studied photoformation of Fe(II) in the water-soluble fractions (WSFs) of bulk aerosol particles collected in Okinawa, Japan, using radiation at wavelengths of 313, 334, 366, and 405 nm. Fe(II) photoformation quickly reached a steady state within 5 min of irradiation at all wavelengths. The steady-state Fe(II) concentrations were 85 +/- 13% (n = 39) of the total dissolved Fe (TDFe) concentrations in the WSF solutions. Apparent quantum yields of Fe(II) photoformation were determined based on total absorbance of the WSF solutions, and the means (+/- 1 S.D.) were 0.019 (+/- 0.034), 0.021 (+/- 0.031), 0.014 (+/- 0.023), and 0.010 (+/- 0.025) at 313, 334, 366, and 405 nm, respectively. Comparison of the observed rates of Fe(II) photoformation for the WSF solutions and the calculated rates from the known Fe(II)-forming compounds suggested that Fe(oxalate)(2) could account for the observed Fe(II) photoformation rates if the Fe(oxalate)(2)(-) concentration is sufficiently high (> 20% of [Fe(III)](0)). Furthermore, our study showed that the calculated wavelength dependence of Fe(II) photoformation from Fe(oxalate)(2)(-) was consistent with that of Fe(II) photoformation observed in the WSF solutions. The results obtained here have implications to daytime Fe(III)/Fe(II) cycles in the atmospheric water droplet.
This study is an attempt to assess atmospheric modulations of the radiometric ratio of ultraviolet-B (UVB) to broadband solar radiation (G). It examines the role of the atmosphere as a filter, absorbing and scattering...
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This study is an attempt to assess atmospheric modulations of the radiometric ratio of ultraviolet-B (UVB) to broadband solar radiation (G). It examines the role of the atmosphere as a filter, absorbing and scattering portions of the solar spectrum, shielding the biosphere from damaging doses of UVB. The diurnal variability of UVB/G at the Earth's surface has been evaluated by analysing 10-year hourly measurements of UVB and G on a horizontal surface at Qena, Egypt. The results show that, throughout the whole period, the values of hourly UVB/G varied from 0.03 to 0.73%, with an average value of 0.27%. This average represents only 17% of the corresponding value outside the atmosphere (1.56%). Moreover, the study quantifies the impact of ozone, water vapour, and aerosols on UVB/G under cloudless conditions. An analysis of the relationship between this ratio and the slant total ozone column (Z) was also carried out. It showed that the ratio decreased with increasing Z. For Z=537 DU, the average UVB/G was almost 53.47% lower than that at low Z (277 DU). The influence of precipitable water (W) on UVB/G was determined under limited change in Z (<8.72%) and almost constant turbidity level (angstrom ngstrom turbidity coefficient, , of 0.19). The values of UVB/G increased with increasing W. For an average W=1.13cm, the average UVB/G was approximately 3.93% lower than at high W (2.82cm). Moreover, the study illustrated the effect of aerosols on UVB/G when their influence on this ratio is greater than the impact of other atmospheric factors such as ozone and water vapour. It can be concluded that the ratio of the change in UVB/G to the change in varies from 0.16 to 0.59%, with an average value of 0.33%.
作者：
VINCENT, JHPhysics Branch
Institute of Occupational Medicine 8 Roxburgh Place Edinburgh EH8 9SU U.K.
Evidence from experiments with humans and animals suggests that the lung deposition of inhaled particles is enhanced if the particles are electrically charged. Simple analysis has been carried out by which the practic...
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Evidence from experiments with humans and animals suggests that the lung deposition of inhaled particles is enhanced if the particles are electrically charged. Simple analysis has been carried out by which the practical significance of the problem can be assessed, based on consideration of the physical factors which influence particle movement under electrostatic image forces in the confined spaces of the alveolar region of the lung. The results support the observations in animal studies that electrostatic enhancement of lung deposition is small for inhaled isometric polydisperse mineral dusts, but potentially large for similarly dispersed fine fibrous asbestos aerosols. From measurements of the levels of electrostatic charging of workplace aerosols, it is concluded that the same will be true for human subjects occupationally exposed to airborne dust.
作者：
PIOCH, MMADOZESCANDE, CInstitut de Protection et de Sûreté Nucléaire
Département de Protection de l'Environnement ete des Installations Service d'Etudes et de Recherches sur les transferts dans l'Environnement IPSN/CEA C.E. de Cadarache Bât. 159 13108 St. Paul Lez Durance France
An accident in a PWR could lead to discharge of radioactive aerosols into the atmosphere. The present study consisted of establishing, under laboratory conditions, how the caesium and strontium contained in such aeros...
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An accident in a PWR could lead to discharge of radioactive aerosols into the atmosphere. The present study consisted of establishing, under laboratory conditions, how the caesium and strontium contained in such aerosols are remobilized by rainwater after dry deposition in an urban environment. aerosols representative of those discharged in a PWR accident were generated and deposited on five building materials used in France. A rainfall simulator was used to provide varying intensities of rain. The percentages remobilized, both as particles and dissolved in rainwater, were then measured. Remobilization is dependent on the nature of the material, the radioelement and the intensity of the rain. It varies from 5 to 60% for caesium and from 5 to 30% for strontium. Remobilization increases as rain intensity decreases. Caesium is mainly remobilized in dissolved form while strontium is remobilized in the form of particles.
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