Man-made Aerosols Research Articles

Innovative systems for the detection of air particles in the quarries of the Western Rif, Morocco

<p>In a world where climate change looms large the spotlight often shines on greenhouse gases, but the shadow of man-made aerosols should not be underestimated. These tiny particles play a pivotal role in disrupting Earth's radiative equilibrium, yet many mysteries surround their influence on various physical aspects of our planet. The root of these mysteries lies in the limited data we have on aerosol sources, formation processes, conversion dynamics, and collection methods. Aerosols, composed of particulate matter (PM), sulfates, and nitrates, hold significant sway across the hemisphere. Accurate measurement demands the refinement of in-situ, satellite, and ground-based techniques. As aerosols interact intricately with the environment, their full impact remains an enigma. Enter a groundbreaking study in Morocco that dared to compare an internet of thing (IoT) system with satellite-based atmospheric models, with a focus on fine particles below 10 and 2.5 micrometers in diameter. The initial results, particularly in regions abundant with extraction pits, shed light on the IoT system's potential to decode aerosols' role in the grand narrative of climate change. These findings inspire hope as we confront the formidable global challenge of climate change.</p>

Low Density Interior in Supercooled Aqueous Nanodroplets Expels Ions to the Subsurface.

The interaction between water and ions within droplets plays a key role in the chemical reactivity of atmospheric and man-made aerosols. Here we report direct computational evidence that in supercooled aqueous nanodroplets a lower density core of tetrahedrally coordinated water expels the cosmotropic ions to the denser and more disordered subsurface. In contrast, at room temperature, depending on the nature of the ion, the radial distribution in the droplet core is nearly uniform or elevated toward the center. We analyze the spatial distribution of a single ion in terms of a reference electrostatic model. The energy of the system in the analytical model is expressed as the sum of the electrostatic and surface energy of a deformable droplet. The model predicts that the ion is subject to a harmonic potential centered at the droplet's center of mass. We name this effect "electrostatic confinement". The model's predictions are consistent with the simulation findings for a single ion at room temperature but not at supercooling. We anticipate this study to be the starting point for investigating the structure of supercooled (electro)sprayed droplets that are used to preserve the conformations of macromolecules originating from the bulk solution.

On the importance of nitrate for the droplet concentration in stratocumulus in the North-Sea region

Anthropogenic aerosol particles serve as extra Cloud Condensation Nuclei (CCN), increasing the cloud droplet number concentration and modifying the cloud properties. The influence of manmade aerosol is the highest in a marine environment due to a limited number of natural CCN. Marine stratocumulus-like clouds (MSC) are the most frequent cloud-type in the North Sea region. The general assumption is that sulphate is the dominant compound of the CCN. However, high levels of manmade nitrate in the area suggest a significant role for this component. We made a first assessment of how many CCN with a marine origin were dominated by nitrate via two intensive campaigns in a large flow-through cloud chamber at the coast in the Netherlands wherein the formation of stratocumulus is simulated. It was consistently observed that the CCN were virtually all in the submicron range. In marine air masses from the NW-quadrant submicron nitrate was negligible and sulphate was the dominant CCN-component; this was also the case in air masses that passed over the narrow corridor of the English Channel. In air masses from the SW quadrant, climatologically the most frequent air mass with stratus-like overcast, submicron-nitrate was the dominant compound apparently produced from sources located over southern UK and W-France/Belgium. The CCN were mostly (98%) in the size range of 100–450 nm. During the summer campaign (2007), nitrate was virtually absent in the smaller and more numerous CCN in this size range. During a, shorter, study in the first half of April (2009), all CCN were dominated by nitrate. This possible seasonal difference in the role of nitrate in SW-air was the main subject evaluated in a monitoring effort in 2008 with a total of 7 months of valid data. The mass concentration ratio of nitrate to sulphate in the “CCN”-range (the range in which 85% of the CCN number concentration is present) was used to identify the periods when nitrate was the prominent compound. In winter/early spring CCN-nitrate was the dominant compound in the CCN, while during summer the ratio of CCN-nitrate to CCN-sulphate was 0.2 and close to zero in the CCN with a diameter smaller than 150 nm. This seasonal difference can be explained by the low stability of the semi-volatile ammonium nitrate at the elevated temperatures in summer, which specifically applies for the smallest CCN due to their small mass amounts. Further data are required to obtain a reliable climatology. Note: sea salt contributed negligibly to the CCN-number; organic aerosol, measured in the April campaign, was present in significant concentrations but of minor importance because of its low hygroscopicity.

Retrieval of volcanic and man-made stratospheric aerosols from orbital polarimetric measurements.

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-μm 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.

Two pathways of how remote SST anomalies drive the interannual variability of autumnal haze days in the Beijing–Tianjin–Hebei region, China

Abstract. Analogous to the circumstances in wintertime, the increasing severity of autumnal haze pollution over the Beijing–Tianjin–Hebei (BTH) region may also lead to impairment of the socioeconomic development and human health in this region. Despite man-made aerosol emissions, the interannual variability of autumnal (September–October–November) haze days (AHDs) in the BTH region (AHDBTH) is apparently tied to the global and regional meteorological anomalies. The present study suggests that an above-normal AHDBTH is closely associated with the simultaneous sea surface temperature (SST) warming in two regions (over the North Atlantic subtropical sector, R1, and over the western North Pacific sector, R2). When the autumnal SST warming in both R1 and R2 is significant, the likelihood of a higher AHDBTH is greatly enhanced. Observational and simulation evidence demonstrated how remote SST anomalies over R1 and R2 influence variation of AHDBTH via two different pathways. Firstly, SST warming in R1 can induce a downstream midlatitudinal Rossby wave train, leading to a barotropic high-pressure and subsidence anomaly over the BTH region. Secondly, SST warming in R2 can also result in air subsidence over the BTH region through an anomalous local meridional cell. Through these two distinct pathways, localized meteorological circumstances conducive to a higher AHDBTH (i.e., repressed planetary boundary layer, weak southerly airflow, and warm and moist conditions) can be established.

An improved algorithm for retrieving the fine-mode fraction of aerosol optical thickness, part 1: Algorithm development

The fine-mode fraction (FMF) can be a useful tool to separate natural aerosols from man-made aerosols and to assist in estimating surface concentrations of particulate matter with a diameter<2.5μm. A LookUp Table-based Spectral Deconvolution Algorithm (LUT-SDA) was developed here for satellite-based applications using data such as MODerate resolution Imaging Spectroradiometer (MODIS) measurements. This method was validated against ground-based FMF retrievals from the Aerosol Robotic Network (AERONET). The LUT-SDA was then applied to two MODIS-retrieved aerosol optical thickness (AOT) products for the period of December 2013 to July 2015: the MODIS Collection 6 (C6) Dark Target (DT) AOT product and the simplified high-resolution MODIS Aerosol Retrieval Algorithm (SARA) AOT product. In comparison with the MODIS C6 FMF product in three study areas (Beijing, Hong Kong, and Osaka), FMFs estimated by the LUT-SDA agreed more closely with those retrieved from the AERONET with a very low bias. Eighty percent of the FMF values fell within the expected error range of ±0.4. The root mean square error (RMSE) was 0.168 with few anomalous values, whereas the RMSE for the MODIS FMF was 0.340 with more anomalous values. The LUT-SDA FMF estimated using SARA AOT data conveys more detailed information on urban pollution than that from MODIS C6 DT AOT data. As a demonstration, the seasonally-averaged spatial distribution of the FMF in Beijing was obtained from the LUT-SDA applied to SARA AOT data and compared with that of the AERONET-retrieved FMF. Their seasonal trends agreed well.

Evidence for an earlier greenhouse cooling effect in the stratosphere before 1980 over the Northern Hemisphere

Abstract. This study provides a new look at the observed and calculated long-term temperature changes from the lower troposphere to the lower stratosphere since 1958 over the Northern Hemisphere. The data sets include the NCEP/NCAR reanalysis, the Free University of Berlin (FU-Berlin) and the RICH radiosonde data sets as well as historical simulations with the CESM1-WACCM global model participating in CMIP5. The analysis is mainly based on monthly layer mean temperatures derived from geopotential height thicknesses in order to take advantage of the use of the independent FU-Berlin stratospheric data set of geopotential height data since 1957. This approach was followed to extend the records for the investigation of the stratospheric temperature trends to the earliest possible time. After removing the natural variability with an autoregressive multiple regression model our analysis shows that the period 1958–2011 can be divided into two distinct sub-periods of long-term temperature variability and trends: before and after 1980. By calculating trends for the summer time to reduce interannual variability, the two periods are as follows. From 1958 until 1979, a non-significant trend (0.06 ± 0.06 °C decade−1 for NCEP) and slightly cooling trends (−0.12 ± 0.06 °C decade−1 for RICH) are found in the lower troposphere. The second period from 1980 to the end of the records shows significant warming (0.25 ± 0.05 °C decade−1 for both NCEP and RICH). Above the tropopause a significant cooling trend is clearly seen in the lower stratosphere both in the pre-1980 period (−0.58 ± 0.17 °C decade−1 for NCEP, −0.30 ± 0.16 °C decade−1 for RICH and −0.48 ± 0.20 °C decade−1 for FU-Berlin) and the post-1980 period (−0.79 ± 0.18 °C decade−1 for NCEP, −0.66 ± 0.16 °C decade−1 for RICH and −0.82 ± 0.19 °C decade−1 for FU-Berlin). The cooling in the lower stratosphere persists throughout the year from the tropics up to 60° N. At polar latitudes competing dynamical and radiative processes reduce the statistical significance of these trends. Model results are in line with reanalysis and the observations, indicating a persistent cooling (−0.33 °C decade−1) in the lower stratosphere during summer before and after 1980; a feature that is also seen throughout the year. However, the lower stratosphere CESM1-WACCM modelled trends are generally lower than reanalysis and the observations. The contrasting effects of ozone depletion at polar latitudes in winter/spring and the anticipated strengthening of the Brewer–Dobson circulation from man-made global warming at polar latitudes are discussed. Our results provide additional evidence for an early greenhouse cooling signal in the lower stratosphere before 1980, which appears well in advance relative to the tropospheric greenhouse warming signal. The suitability of early warning signals in the stratosphere relative to the troposphere is supported by the fact that the stratosphere is less sensitive to changes due to cloudiness, humidity and man-made aerosols. Our analysis also indicates that the relative contribution of the lower stratosphere versus the upper troposphere low-frequency variability is important for understanding the added value of the long-term tropopause variability related to human-induced global warming.

On the differences of ultraviolet and visible irradiance calculations in the Mediterranean basin due to model- and satellite-derived climatologies of aerosol optical properties

The variability of aerosol optical properties over the Mediterranean basin, in the ultraviolet (UV) and visible (VIS) spectral regions, is examined, using ground-based data from eight stations of the AErosol RObotic NETwork (AERONET), climatological values from the AeroCom (Aerosol Comparisons between Observations and Models) project and data from the MODerate resolution Imaging Spectroradiometer (MODIS) on-board the Terra and Aqua satellites. The aerosol optical properties from the three datasets are used as input data in a radiative transfer model, in order to estimate the differences in irradiance at the ground under cloud-free skies. The MODIS aerosol optical depth climatology shows better agreement with AERONET data. The highest difference in the monthly average values is equal to 0.09 at 550 nm, while the differences between the AERONET and the AeroCom climatologies reach 0.25 and 0.15 in the UV and VIS wavelengths, respectively. As a result, the AERONET modelled VIS and UV irradiances are closer to MODIS, with the absolute differences in average values reaching 15 (6%) and 2 W m–2 (6%), respectively, while absolute differences with AeroCom irradiances can reach up to 30 (12%) and 4.5 W m–2 (12%). The differences are higher in FORTH Crete, Nes Ziona, Sede Boker and Blida, which are influenced by desert dust aerosols. The separate effect on irradiances due to differences in aerosol optical depth and single scattering albedo from the three datasets has been also examined; according to results, the effect of aerosol optical depth is dominant. At this stage, the use of MODIS aerosol climatology would be recommended for calculations of UV and VIS irradiance in the Mediterranean basin. However, the AeroCom climatology, with some further improvements in the dust cycle, could be a valuable tool in future studies in this area, due to the provision of natural and manmade aerosol optical properties with higher spectral resolution.

Aerosol optical depth trends over different regions of India

Abstract Seasonal and annual mean trends in aerosol optical depths (AODs) for the last decade are derived using MODerate resolution Imaging Spectroradiometer (MODIS) Level 2 10 km × 10 km remote sensing data over different locations in India. AODs have increased across India in the last decade. AOD trends exhibit spatial, seasonal and annual mean variations. Annual mean AODs have increased by >40% during 2000–2009 in Jaipur, Hyderabad and Bengaluru. The increase in AODs over Hyderabad and Bengaluru, major high-tech cities, can be ascribed to the increase in urbanization. An increase in AODs over New Delhi where manmade aerosols are dominant can be attributed to an increase in the amount of aerosols from fossil fuel and biomass burning, while an increasing trend in AODs in the northeast, indicates an increase in the amount of aerosols produced from biomass burning and forest fires. AODs decreased in the high altitude sites of Shimla and Dehradun. AODs and wind speeds increased over Jaipur, while they decreased in Trivandrum during the last decade. An increase in wind speeds led to an increase in soil derived dust particles over Jaipur, an arid site, while a decrease in wind speeds over Trivandrum, contributed to a decrease in sea spray aerosols thereby causing a decrease in AOD. Annual rainfall increased by ≤1% in most locations. Both AODs and rainfall have increased in the last decade over most study locations. These findings become important and useful in the context of regional and global climate change due to aerosols.

Characteristic Analyses of Plasma Air Cleaning Systems for the Removal of Indoor Air Pollutants

Tobacco smoke is one of the most common manmade aerosols. Yellow sand dust and pollen are the particular and regional pollutants generated by natural phenomena. These pollutants have different removal characteristics, respectively, when the air cleaning system is operated. It is well known that tobacco smoke particles are removed effectively with electrostatic precipitators. But it is necessary to evaluate whether the plasma air cleaning system has good performance of removing Yellow sand dusts and pollens simultaneously and also to establish the operation modes for efficient removal of those particular air pollutants by controlling the air flow rates passing the electrostatic precipitator and operating times of air cleaning system. In this study, the performance evaluation of plasma air cleaning systems is investigated with tobacco smoke particles, Yellow sand dusts, and pollens. For the multi-pass test in occupied spaces of 150 m3, the operation time required to reduce dust concentration from the initial concentration of 300 µg/m3 to 150 µg/m3, the criteria of indoor air quality in Korea, are 40 min for tobacco smoke, 28 min for Yellow sand dust, and 5 min for pollen when the flow rate is 17 m3/min. Also, the optimal operation modes for each pollutant are suggested for the efficient removal of indoor air pollutants. At first, most particles are removed by maximum flow operation. Second, the rest of the particles are removed by medium flow operation. Next, the plasma air cleaning systems are maintained by minimum flow for tobacco smoke mode and by repeating minimum flow and medium flow for Yellow sand and pollen modes. Edit to “Because the Yellow sand dust and the pollen flow into the room continuously and settle down … noise reduction.” Because the Yellow sand dust and the pollen flow into the room continuously and settle down. The plasma air cleaning system is suitable for the removal of the tobacco smoke, the Yellow sand dust, and the pollen for maintaining suitable indoor air quality, and, if it is operated through the suitable operation mode, energy efficiency will improve noise reduction.

Photometric measurements of spring aerosol optical properties in dust and non-dust periods in China

Aerosol observational data spanning three years (2005–2007) from the Chinese Sun Hazemeter Network (CSHN) were analyzed to characterize the optical properties of spring aerosol particles in dust and non-dust weather conditions. The measurements were segregated and the dates of dust period were chosen by ground-based observations and the National Sand-dust Weather Almanac. Observational data obtained under suitable weather conditions and averaged over 15 sites in the CSHN. The data indicated that the mean spring aerosol optical depth (AOD) increased by 33% in dust weather than in non-dust weather over the three years under study. Further, the angstrom exponent ( α) decreased by 24% in dust weather compared to in non-dust weather. At dust-source sites, AOD increased by 31% and α decrease by 20%. The atmosphere of dust-source sites is relatively clean, and is generally only contaminated with small quantities of dust particles. Atmospheric aerosols of this region were primarily in the form of coarse mode. Aside from being influenced by dust storms, the atmosphere of both near-source and distant sites displayed a large proportion of man-made aerosols, resulting in a large increase in the AOD and α values. Due to the contribution of sand-dust, the AOD of near-source and distant sites increased by 53% and 23%, respectively, while the value of α was reduced by 22% and 25%, respectively. Due to the content differences of man-made aerosols, and the fact that some observational data cannot be obtained under heavy dust storm weather conditions, the mean AOD and α were highest at distant sites (0.69 and 0.91), intermediate at near-source sites (0.51 and 0.86), and lowest at the dust-source sites (0.36 and 0.48). In addition, if we take into account the impact of strong dust storms in which AOD can't be observed by sunphotometer, the AOD probably become greater the farther form the dust-source region in non-dust periods, and while it is opposite in dust periods. Data were also obtained for both urban and ecology background sites. AOD and α values were both significantly higher at urban sites than at neighboring natural ecology background sites during both dust and non-dust periods, but the occurrence of dust process made the multiplier slightly larger.

Input of particulate heavy metals from rivers and associated sedimentary deposits on the Gulf of Lion continental shelf

Fluxes of the heavy metals chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), lead (Pb), cadmium (Cd) and zinc (Zn) delivered by rivers to the Gulf of Lion (NW Mediterranean Sea) were estimated over a three year study of the River Rhone and its smaller tributaries. Most of the particulate metal fluxes (80–90%) delivered by these rivers occurred within a very short period of time (less than 12%), a typical trend for the Mediterranean environment, where highly contrasting hydrological regimes were observed over the year. Temporal and spatial variations in the fluxes of these particulate metals were driven by the fluxes in both water discharge and suspended particulate matter load. On the shelf, these particulate metal fluxes, largely arising from the Rhone watershed, were two to ten times more important than those resulting from atmospheric deposition. Co, Cr and Ni in the rivers and on the shelf surface sediments were mainly natural and associated with the finest particles. Cd and Phosphorus appeared to be associated with the silt fraction and to be enriched in the prodelta areas. Pb, Zn and Cu were more closely associated with the organic matter content and also showed enrichment in the organic rich prodeltaic sediments. Anthropogenic influences diminished offshore, except for Pb and Zn which could be supplied from the atmosphere by man-made aerosols. Although most of the metals tended to be enriched in the prodelta areas, these did not constitute a permanent sink due to resuspension processes affecting these shallow depths. A resuspension experiment conducted on sediment cores from the Rhone prodelta demonstrated that metal deposited on the surface layer, especially those associated with the organic matter, may be resuspended; this should be taken into account for a complete understanding of the biogeochemical cycle of these metals.

Sources and sinks of sediment-bound contaminants in the Gulf of Lions (NW Mediterranean Sea): A multi-tracer approach

Surficial sediments collected in 2002 throughout the Gulf of Lions continental shelf (NW Mediterranean) were analysed for trace metals (Cd, Co, Cr, Cs, Cu, Ni, Pb, Sr, Zn and Zr), major elements (Al, Ca, Fe, P and Ti) and the sewage marker coprostanol. In addition, particle size distribution, organic carbon (OC) and carbonates were also determined. Results showed that the metal contamination (Cd, P, Cu, Pb and Zn) is mainly introduced by the local rivers and accumulates—via a regulation by OC and silt fraction (2–63 μm)—in the direct vicinity of the mouths, in high shear stress environments. Here also the signal of sewage contamination is the best preserved, especially off the eastern point sources where local sedimentation rates save the faecal marker from biodegradation processes. It is demonstrated that the shallow prodeltas are the first repository areas for land-derived particles, exposing local ecosystems to both inorganic and organic contaminations. When going seaward, however, sediment dilution, particle sorting and biodegradation processes make that most riverborne contaminants rapidly reach natural levels. Only some metals (i.e. Pb and Zn)—closely associated with the clay fraction—still depict anthropogenic enrichment, which seems to be inherited from man-made aerosols.

Small-scale patterns of sulfate aerosol climate forcing simulated with a high-resolution regional climate model

A high-resolution, regional climate model (RCA2) is employed to evaluate direct and indirect radiative forcing patterns due to man-made sulfate aerosols over Europe and to examine the sensitivity of the results to the choice of model resolution. A simulation encompassing the whole year of 1993 is performed. The model includes an explicit parameterization of the atmospheric sulfur cycle where predicted cloud and precipitation parameters are utilized at each time step. The overall pattern of the monthly mean direct climate effect simulated by the regional climate model is similar to that obtained using global climate models. Calculations over 0.4 and 4.0° spatial resolution indicate that, for the climatic conditions simulated by the RCA2, correlations between small-scale variations of relative humidity and aerosol loading do not contribute substantially to the magnitude of the monthly mean optical thickness.For the monthly mean indirect climate effect, the finer grid spacing in the RCA2 results in a pronounced spatial variability, not visible in global climate model simulations. An interesting question is whether this variability affects the estimated magnitude of the indirect climate effect. Calculations of the effective droplet radius (re) for 0.4 and 4° spatial resolution indicate a minor importance over the RCA2 model domain (the difference in re is less than 7%). The model generally underestimates the sulfate concentration within the boundary layer, whereas the magnitude of the simulated CDNC and re agrees well with aircraft measurements. Despite an underestimate of the absolute magnitude, the regional pattern of the modeled re resembles that observed by satellite. A number of sensitivity simulations demonstrate that the magnitude of the indirect radiative forcing is highly uncertain. In order to reduce the uncertainty, different parameterizations of the indirect effect should be evaluated in more detail versus measurements of, e.g., aerosol concentration and properties, CDNC, and re at various locations.

Activities and osmotic coefficients of tropospheric aerosols: (NH4)2SO4(aq) and NaCl(aq)

The theory of multilayer adsorption for concentrated aqueous electrolytes developed by Ally and Braunstein (1998) is used to calculate the thermodynamic activities and osmotic coefficients of supersaturated solutions of (NH4)2SO4(aq) and NaCl (aq) which are among man-made aerosols of atmospheric importance. The basis of the model is the postulate of Stokes and Robinson that concentrated aqueous electrolytes may be viewed as an irregular ionic lattice structure. Application to the electrolytes mentioned above is a special case of the generalized results which are proven (Ally and Braunstein, Braunstein and Ally) to be consistent with the Gibbs–Duhem equation. Calculated thermodynamic properties are compared against experimental data from isopiestic and electrodynamic balance (EDB) measurements.

Atmospheric science. Reshaping the theory of cloud formation.

Man-made aerosols are believed to have a strong influence on cloud optical properties and albedo, with a radiative forcing opposite in sign to that exerted by greenhouse gases. The uncertainties associated with this indirect aerosol forcing are, however, very large. In their Perspective, Charlson et al. discuss recent insights into cloud formation. The results indicate that current estimates of both the magnitude and the uncertainty of indirect aerosol forcing may be too low.

Human impact on the atmospheric sulfur balance

The paper reviews the development in our understanding of the atmospheric part of the globalsulfur cycle, including the role played by C.-G. Rossby and his colleagues in the 1950s, andpresents a brief assessment of the current knowledge. Measurements of the concentrations ofsulfur compounds in air, precipitation, ice cores and sea water during the past 25 years, togetherwith recent development in three-dimensional tracer transport modeling, have resulted in areasonably consistent picture of the burdens and fluxes of the main sulfur compounds in theatmosphere. It is clear that man’s activities, in particular the burning of fossil fuels, are havinga large impact on the atmospheric sulfur balance. Even on a global scale, the man-madeemissions of gaseous sulfur compounds are likely to be two to three times as large as the naturalsources. In and around the most heavily industrialized regions this ratio exceeds ten overextended areas. Nevertheless, there are several important issues that need to be resolved. Someof these are directly linked to the urgent problem of reducing the uncertainty in the estimateof direct and, in particular, indirect climate forcing due to man-made sulfate aerosols. One suchissue is the magnitude of the wet scavenging of SO2 and aerosol sulfate during upward transportinto and within the free troposphere in connection with convective and frontal cloud systemswhich has a decisive influence on the sulfate concentrations in the upper troposphere. Anotheruncertain process is the rate of oxidation of SO2 in cloud droplets and on aerosol particles. Afundamental question that remains to be answered is to what degree man-made sulfur emissionshave increased the number of aerosol particles that can act as cloud condensation nuclei.

Activation properties of ambient aerosol in the Netherlands

A cloud chamber has been used to study the cloud activation of ambient aerosol in The Netherlands. The large dimensions and throughput of the chamber allowed unperturbed collection of aerosol and droplets with cascade impactors and on-line measurements with cloud monitors (FSSP) inside the facility. The study provided maxima for the number of man-made aerosol acting as cloud nuclei in marine clouds in The Netherlands. Emphasis was given to the investigation of cloud formation in marine air, since sensitivity studies had shown that such clouds are most effectively influenced by the (extra) anthropogenic aerosol particles. For this reason the supersaturations in the study were low (on average 0.12%), similar to those in actual marine stratus. The effect of the anthropogenic aerosols on cloud formation was determined by comparing the number of droplets formed in “clean” arctic marine air to the number of droplets formed in “polluted” marine air (air which had travelled over the U.K.). Air masses with the total aerosol number concentration of the order of 100 cm −3 were considered as “clean” marine air. Air masses with higher aerosol concentrations were divided into “moderately” and “heavily” polluted with total aerosol concentrations of the order of 1000 and 10,000 cm −3, respectively. In the clean marine air all potential cloud nuclei (particles larger than the threshold size of the smallest reference particles that were activated at a given supersaturation) were activated and the number of cloud droplets formed was on average 45 cm −3. In the moderately polluted air 72% of potential cloud nuclei were activated and the average droplet number was 190 cm −3. The difference in the actual cloud droplet number and the number of potential cloud nuclei could be explained by the presence of water-insoluble particles which do not activate. In the heavily polluted air the average droplet concentration was around 320 cm −3. which is, on average, 24% of the number of potential cloud nuclei.

Ozone Depletion Update

Stratospheric ozone depletion due to chlorofluorocarbons an d increased ultraviolet radiation penetration has long been predicted. To determine if predictions of ozone depletion are correct and, if so, the significance of this depletion. Review of the English literature regarding ozone depletion and solar ultraviolet radiation. The ozone layer is showing definite thinning. Recently, significantly increased ultraviolet radiation transmission has been detected at ground level at several metering stations. It appears that man-made aerosols (air pollution) block increased UVB transmission in urban areas. Recent satellite measurements of stratospheric fluorine levels more directly implicate chlorofluorocarbons as a major source of catalytic stratospheric chlorine, although natural sources may account for up to 40% of stratospheric chlorine. Stratospheric chlorine concentrations, and resultant increased ozone destruction, will be enhanced for at least the next 70 years. The potential for increased transmission of ultraviolet radiation will exist for the next several hundred years. While little damage due to increased ultraviolet radiation has occurred so far, the potential for long-term problems is great.

Handling safety of antimony trioxide

Water-soluble and insoluble, organic and inorganic, natural and man-made aerosol particles participate in vapor-liquid, vapor-solid (ice), and liquid-solid phase transitions in the atmosphere. Hydrosol particles (aerosol particles that have been transferred into water droplets) nucleate ice through freezing. A small without scavenging or being scavenged by another aerosol particle. It is also difficult to imagine that pure mineral particles can be lifted from soil surfaces. In view of this, an ice-nucleating site may be a much smaller particle attached to a larger clay particle. To this category belong, e.g., silver iodide-clay mixed particles. Limited studies indicate that decaying leaves and forest litter under the surface of soils are a potential source of biogenic ice-forming nuclei but that their contribution to the atmosphere is very limited. Research should be directed to study possible relations between cloud condensation nuclei and ice-forming nuclei derived from natural organic compounds (terpenes, leaf-derived nuclei, bacteria, etc.).A balance must be maintained between large cloud chambers, in which duplication of in-cloud processes is possible, and the special instrumentation which provides information about the modes of ice nucleation on aerosol particles. The two modes of instrumentation should supplement each other.The greatest difficulty in attempting to make a comparison between the number of ice-forming nuclei estimated in the laboratory and the number in a cloud is the lack of knowledge of the time-temperature-humidity history of the aerosol particles. In nature, the ability of an aerosol particle to nucleate ice may be destroyed or“poisoned“ in the presence of pollutants. An aerosol particle may, on the other hand, become an activated or warmer ice-forming nucleus, e.g.,after the sublimation of ice once formed on it. The temperature of ice nucleation is not a singular property of a particle; the warmest temperatures of ice nucleation of, e.g., particles of a certain soil 10cm in diameter are-15°C,-10°C, and-8°C for nucleation through freezing, condensation followed by freezing and contact, respectively (ref.26). The progress made in instrumentation permits studies of the modes of ice nucleation. Understanding the physical and chemical processes taking place in clouds makes estimates of the rates of ice particle formation more realistic (Young [ref.157]).The reader should examine two previous reviews written by Mossop (1963) and Montefinale . (1971) for a more complete list of references.