Concentration Of Aerosol Particles Research Articles

Attachment rate characteristics of different wide used aerosol sources in indoor air.

In this work, six different aerosol sources, used in everyday life, were investigated to analyze parameters such as concentration, size distributions, and dynamics: regular and electronic cigarettes, incense, candles, mosquito coils, and cooking. During the experiments, the aerosol particle count ranged from 200 to 2·105cm-3. The number, mass, and specific surface area of the aerosol size distributions were measured by a Model 2702M diffusion aerosol spectrometer (DAS) with a range of 5nm to 10μm. The attachment rate of radon decay products to aerosol particles is calculated depending on their size distribution/ The use of household sources of aerosols (heat treatment of food, smoking, candles, etc.) result in an increase in the concentration of aerosol particles by more than an order of magnitude, mainly due to the generation of ultrafine aerosols with number median diameter 64-92nm and GSD 1.45-1.84. The mass distribution is dominated by particles with a distribution maximum in the range of 2-5μm. The attachment of radon decay products to aerosols is associated with ultrafine particles with diameter < 200nm. The median diameter of the rate of attachment to aerosols is 130nm.

Drivers of the fungal spore bioaerosol budget: observational analysis and global modeling

Abstract. Bioaerosols are produced by biological processes and directly emitted into the atmosphere, where they contribute to ice nucleation and the formation of precipitation. Previous studies have suggested that fungal spores constitute a substantial portion of the atmospheric bioaerosol budget. However, our understanding of what controls the emission and burden of fungal spores on the global scale is limited. Here, we use a previously unexplored source of fungal spore count data from the American Academy of Allergy, Asthma, and Immunology (AAAAI) to gain insight into the drivers of their emissions. First, we derive emissions from observed concentrations at 66 stations by applying the boundary layer equilibrium assumption. We estimate an annual mean emission of 62 ± 31 m−2 s−1 across the USA. Based on these pseudo-observed emissions, we derive two models for fungal spore emissions at seasonal scales: a statistical model, which links fungal spore emissions to meteorological variables that show similar seasonal cycles (2 m specific humidity, leaf area index and friction velocity), and a population model, which describes the growth of fungi and the emission of their spores as a biological process that is driven by temperature and biomass density. Both models show better skill at reproducing the seasonal cycle in fungal spore emissions at the AAAAI stations than the model previously developed by Heald and Spracklen (2009) (referred to as HS09). We implement all three emissions models in the chemical transport model GEOS-Chem to evaluate global emissions and burden of fungal spore bioaerosol. We estimate annual global emissions of 3.7 and 3.4 Tg yr−1 for the statistical model and the population model, respectively, which is about an order of magnitude lower than the HS09 model. The global burden of the statistical and the population model is similarly an order of magnitude lower than that of the HS09 model. A comparison with independent datasets shows that the new models reproduce the seasonal cycle of fluorescent biological aerosol particle (FBAP) concentrations at two locations in Europe somewhat better than the HS09 model, although a quantitative comparison is hindered by the ambiguity in interpreting measurements of fluorescent particles. Observed vertical profiles of FBAP show that the convective transport of spores over source regions is captured well by GEOS-Chem, irrespective of which emission scheme is used. However, over the North Atlantic, far from significant spore sources, the model does not reproduce the vertical profiles. This points to the need for further exploration of the transport, cloud processing and wet removal of spores. In addition, more long-term observational datasets are needed to assess whether drivers of seasonal fungal spore emissions are similar across continents and biomes.

Comparison of Coincident Optical Particle Counter and Lidar Measurements of Polar Stratospheric Clouds Above McMurdo (77.85°S, 166.67°E) From 1994 to 1999

AbstractMacroscopic stratospheric aerosol properties such as surface area density (SAD) and volume density (VD) are required by modern chemistry climate models. These quantities are in continuous need of validation by observations. Direct observation of these parameters is not possible, but they can be derived from optical particle counters (OPCs) which provide concentration (number density) and size distributions of aerosol particles, and possibly from ground‐based and satellite‐borne lidar observations of particle backscatter coefficients and aerosol type. When such measurements are obtained simultaneously by OPCs and lidars, they can be used to calculate backscatter and extinction coefficients, as well as SAD and VD. Empirical relations can thus be derived between particle backscatter coefficient, extinction coefficient, and SAD and VD for a variety of aerosols (desert dust, maritime aerosols, stratospheric aerosols) and be used to approximate SAD and VD from lidar measurements. Here we apply this scheme to coincident measurements of polar stratospheric clouds above McMurdo Station, Antarctica, by ground‐based lidar and balloon‐borne OPCs. The relationships derived from these measurements will provide a means to obtain values of SAD and VD for supercooled ternary solutions (STS) and nitric acid trihydrate (NAT) PSCs from the backscatter coefficients measured by lidar. Coincident lidar and OPC measurements provided 15 profile comparisons. Empirical expressions of SAD and VD as a function of particle backscatter coefficient, β, were calculated from fits of the form log(SAD/VD) = A + B log(β) using β from the lidar and SAD/VD from the OPC. The PSCs were classified as STS and NAT mixtures, ice being absent.

Processes contributing to cloud dissipation and formation events on the North Slope of Alaska

Abstract. Clear-sky periods across the high latitudes have profound impacts on the surface energy budget and lower atmospheric stratification; however an understanding of the atmospheric processes leading to low-level cloud dissipation and formation events is limited. A method to identify clear periods at Utqiaġvik (formerly Barrow), Alaska, during a 5-year period (2014–2018) is developed. A suite of remote sensing and in situ measurements from the high-latitude observatory are analyzed; we focus on comparing and contrasting atmospheric properties during low-level (below 2 km) cloud dissipation and formation events to understand the processes controlling clear-sky periods. Vertical profiles of lidar backscatter suggest that aerosol presence across the lower atmosphere is relatively invariant during the periods bookending clear conditions, which suggests that a sparsity of aerosol is not frequently a cause for cloud dissipation on the North Slope of Alaska. Further, meteorological analysis indicates two active processes ongoing that appear to support the formation of low clouds after a clear-sky period: namely, horizontal advection, which was dominant in winter and early spring, and quiescent air mass modification, which was dominant in the summer. During summer, the dominant mode of cloud formation is a low cloud or fog layer developing near the surface. This low cloud formation is driven largely by air mass modification under relatively quiescent synoptic conditions. Near-surface aerosol particles concentrations changed by a factor of 2 around summer formation events. Thermodynamic adjustment and increased aerosol presence under quiescent atmospheric conditions are hypothesized as important mechanisms for fog formation.

Ventilation and air cleaning to limit aerosol particle concentrations in a gym during the COVID-19 pandemic

SARS-CoV-2 can spread by close contact through large droplet spray and indirect contact via contaminated objects. There is mounting evidence that it can also be transmitted by inhalation of infected saliva aerosol particles. These particles are generated when breathing, talking, laughing, coughing or sneezing. It can be assumed that aerosol particle concentrations should be kept low in order to minimize the potential risk of airborne virus transmission. This paper presents measurements of aerosol particle concentrations in a gym, where saliva aerosol production is pronounced. 35 test persons performed physical exercise and aerosol particle concentrations, CO2 concentrations, air temperature and relative humidity were obtained in the room of 886 m³. A separate test was used to discriminate between human endogenous and exogenous aerosol particles. Aerosol particle removal by mechanical ventilation and mobile air cleaning units was measured. The gym test showed that ventilation with air-change rate ACH = 2.2 h−1, i.e. 4.5 times the minimum of the Dutch Building Code, was insufficient to stop the significant aerosol concentration rise over 30 min. Air cleaning alone with ACH = 1.39 h−1 had a similar effect as ventilation alone. Simplified mathematical models were engaged to provide further insight into ventilation, air cleaning and deposition. It was shown that combining the above-mentioned ventilation and air cleaning can reduce aerosol particle concentrations with 80 to 90% , depending on aerosol size. This combination of existing ventilation supplemented with air cleaning is energy efficient and can also be applied for other indoor environments.

Atmospheric ice nucleating particle measurements and parameterization representative for Indian region

Atmospheric ice nucleating particle (INP) concentration measurements over the Indian region are very sparse; hence more observations are required to represent heterogeneous ice nucleation processes in the regional cloud models for better accuracy. In this work, the INP ability and size of ambient aerosol particles at a tropical high altitude station were studied. Ice nucleation experiments were conducted at temperatures between −25 and −34 °C and water supersaturation conditions up to 102%. The mean INP concentrations varied from 1.1 to 9.5 L−1 and correlated well with coarse mode aerosol particle concentration (> 1 μm). Higher INP concentrations were observed when the aerosol loading was influenced by the regions such as Mumbai metro city, Gujarat, Thar desert region, and the Arabian sea region close to the Oman coast. An empirical equation was formulated to represent the INP concentrations using supercooled temperature and coarse mode aerosol particle concentration. The sensitivity of new heterogeneous ice nucleation parameterization was tested against literature INP parameterizations using Weather Research and Forecasting (WRF) model. The model results show that the new parameterization helped to simulate the rainfall amount better as compared to the old formulations. Better reproduction of convection and possible reduction of biases in the formation of cloud ice in the cloud-resolving model improved the model accuracy. These results show the importance of implementing new INP parameterization in a real-time forecast model to improve the regional climate model forecasting.

Towards parameterising atmospheric concentrations of ice-nucleating particles active at moderate supercooling

Abstract. A small fraction of freezing cloud droplets probably initiates much of the precipitation above continents. Only a minute fraction of aerosol particles, so-called ice-nucleating particles (INPs), can trigger initial ice formation at −15 ∘C, at which cloud-top temperatures are frequently associated with snowfall. At a mountaintop site in the Swiss Alps, we found that concentrations of INPs active at −15 ∘C can be parameterised by different functions of coarse (&gt; 2 µm) aerosol particle concentrations, depending on whether an air mass is (a) precipitating, (b) non-precipitating, or (c) carrying a substantial fraction of dust particles while non-precipitating. Consequently, we suggest that a parameterisation at moderate supercooling should consider coarse particles in combination with air mass differentiation.

Seasonal Trends of Organic and Elemental Carbon in PM1 Measured over an Industrial Area of Delhi, India

The present study was carried out to investigate the seasonal variation of organic carbon (OC) and elemental carbon (EC) in PM1 during 2018–2019 in the industrial area of Delhi, India. A cascade impactor was used to collect aerosol particles in four different size fractions (≥ PM10, PM2.5–10, PM2.5–1, ≤ PM1). The OC/EC analysis was performed by thermal/optical carbon analyzer (DRI 2001). The highest concentration of aerosol particles was observed in PM1 among four different size fractions (≥ PM10: 37.77 ± 16.07 µg/m3, PM2.5–10: 90.28 ± 41.84 µg/m3, PM2.5–1: 81.65 ± 43.85 µg/m3, and ≤ PM1: 151.75 ± 58.57 µg/m3). The annual average concentration of OC and EC in PM1 was found to be 34.12 ± 22.94 µg/m3 and 13.91 ± 11.45 µg/m3, respectively. Furthermore, a clear seasonal difference in the concentrations of OC and EC was observed. The highest OC and EC concentration were found during post-monsoon (OC: 59.58 ± 21.66 µg/m3) and winter season (EC: 23.90 ± 12.08 µg/m3), respectively. Although the lowest concentration of OC and EC was observed in the monsoon season (OC: 12.08 ± 6.98 µg/m3, EC: 3.88 ± 1.97 µg/m3). The annual average percentage contribution of OC and EC in PM1 was observed to be 22.48 and 9.16%, respectively. Total carbonaceous aerosol (TCA) accounted for 45.18% of PM1. The annual average OC/EC ratio was found to be 2.45, which indicates the secondary organic aerosol (SOA) formation. The OC/EC analysis reveals that OC2 and EC1 were dominant among eight carbon subfractions, which suggest a mixed source of emission. The higher value of inhalation dose of EC was observed during the winter season (309 µg), which can lead to a higher risk of cardiac and respiratory illness.

The problems associated with monitoring of main parameters of working areas and technological environments in high technology industry

The first part of the article describes the regulatory requirements related to the control of the main parameters of working areas and technological environments in high technology manufacturing: number concentration of aerosol particles and cleanrooms classification, mass concentration of aerosol particles in the premises and means for its control, number concentration of particles in liquid media and methods of its control.In the second part of the article, the trend of deterioration of the technical condition of the existing measuring instruments for disperse parameters of aerosols, suspensions and powder materials is described.In conclusion, it is proposed to create service and calibration centers for measuring instruments maintenance, as well as shared-use equipment centers based on national metrological organizations.

MeteoRead: Client Software for Inserting Observed Atmospheric Data into MySQL&amp;lt;sub&amp;gt;TM&amp;lt;/sub&amp;gt; Database and Downloading them into Different File Format

The investigation of the tendency of climate change and its effects on ecology, economy and sociology is essential for long term policy making. The long-term measurement of the physical and chemical properties of the atmosphere with state-of-the-arts instruments provides high-quality data for these studies. The evaluated data are stored in really special file structures and formats that cannot be inserted in one common database. Moreover, the observed data usually available in ASCII format and the users sometimes need to convert them in other format. The file conversion is usually time consuming procedure and can contribute to the uncertainties. MeteoRead is a client database software that imports the observed atmospheric data e.g. wind direction, wind speed, aerosol particle concentration etc. and makes them available in different file formats, which are most commonly used in climate research. This JavaTM based program applies the Structured Query Language (SQL) functions such as table creation on a database server, data or figures insertion into the table and data selection via Graphical User Interface. The selected data can be stored in NetCDF, HDF5, DataBase or TXT file formats and the figures can be available in PNG, JPG, JPNG, PDF or GIF file formats. The program was tested on Linux and Windows platforms with different JavaTM Development Kit. The MeteoRead is planned to be developed to visualizing the annual, seasonal, monthly, daily or hourly average value of the selected data and to use the functionality of the SQL database to calculate various mathematical and statistical correlations.

Concentration and variability of deposition-mode ice nucleating particles from Mt. Tai of China in the early summer

The concentration and chemical composition of aerosol particles were measured and sampled at two altitudes of Mt. Tai, North China Plain in May and June 2017. Concentrations of ice nucleating particles (INP) were analyzed with a static vacuum water vapor diffusion chamber (FRIDGE-NUIST) in deposition mode after being sampled using an electrostatic aerosol collector. The average INP concentration (1.19 to 3.45 L−1) at Mt. Tai matches with the same measured at Tai’ An (foot of the Mt. Tai, 1.57–3.49 L−1, at RHw = 95%, 97%, 99% and t = −20 °C). Correlations between concentrations of aerosol particles and INP were below 0.5 and less than simultaneous measurements made at Tai'An. Clear diurnal variations at the height of the planetary boundary layer (PBL) resulted in changes in aerosol and INP concentrations at the top of the mountain. We found that EC-Aged (aged elemental carbon) and mineral type particles are clearly associated with ice nuclei when the height of the PBL exceeds the altitude of the mountaintop. Furthermore, we found significant correlations between INP concentrations and concentrations of OC (organic carbon) and NaK (sodium/potassium salt) type aerosol particles at night (in the free troposphere). Ice nucleation active surface site densities are higher at night (22:00 LST, local standard time) than during the day (11:00 LST) due to the change in aerosol characteristics. This study shows that OC and NaK type particles may serve as sources of efficient ice nuclei at night.

Representative sampling analysis of radioactive airborne effluent for the stack system in a molten salt reactor

During the operation of the molten salt reactor, the radioactive gas and radioactive aerosol particles will be generated, and should be discharged into the atmospheric environment through ventilation ducts and stacks after filtration and adsorption. In order to determine whether the radioactive airborne effluent emissions would meet the requirements of the National management limits (ISO 2889–2010), it is necessary to calculate and monitor the radioactive airborne effluents in the stack system. Therefore, a three-dimensional computational fluid dynamics (CFD) model is built to evaluate the flowing and mixing state for radioactive airborne effluent in the stack system of the molten salt reactor. The uniformities of velocity, cyclonic flow, tracer gas concentration, and aerosol particle concentration at different sampling heights in the stack are analyzed by CFD-Fluent. The results show that, the airflow and concentration of tracer gas easily tend to blend well at high flow speed, while there is a little random distribution effect for the aerosol particles due to their large densities, which needs a longer transport process to increase the uniformity. When the sampling height is above 11 m from the bottom of the stack, the variation coefficients of velocity, cyclonic flow, tracer gas concentration, and aerosol particle concentration are below 11.6%, 4.4%, 0.4% and 20% correspondingly, which all meet the well-mixed criteria and the requirement of representativeness sampling location in ISO 2889–2010. If the variation coefficient of aerosol particle concentration can be allowed to be less than 30%, then sampling height above 6 m will satisfy the ISO standard. The results of this study provide a good reference for the detection, sampling and analysis of radioactive gases and aerosol particles in the stack of the molten salt reactor.

Sensitivity of spatial aerosol particle distributions to the boundary conditions in the PALM model system 6.0

Abstract. High-resolution modelling is needed to understand urban air quality and pollutant dispersion in detail. Recently, the PALM model system 6.0, which is based on large-eddy simulation (LES), was extended with the detailed Sectional Aerosol module for Large Scale Applications (SALSA) v2.0 to enable studying the complex interactions between the turbulent flow field and aerosol dynamic processes. This study represents an extensive evaluation of the modelling system against the horizontal and vertical distributions of aerosol particles measured using a mobile laboratory and a drone in an urban neighbourhood in Helsinki, Finland. Specific emphasis is on the model sensitivity of aerosol particle concentrations, size distributions and chemical compositions to boundary conditions of meteorological variables and aerosol background concentrations. The meteorological boundary conditions are taken from both a numerical weather prediction model and observations, which occasionally differ strongly. Yet, the model shows good agreement with measurements (fractional bias &lt;0.67, normalised mean squared error &lt;6, fraction of the data within a factor of 2 &gt;0.3, normalised mean bias factor &lt;0.25 and normalised mean absolute error factor &lt;0.35) with respect to both horizontal and vertical distribution of aerosol particles, their size distribution and chemical composition. The horizontal distribution is most sensitive to the wind speed and atmospheric stratification, and vertical distribution to the wind direction. The aerosol number size distribution is mainly governed by the flow field along the main street with high traffic rates and in its surroundings by the background concentrations. The results emphasise the importance of correct meteorological and aerosol background boundary conditions, in addition to accurate emission estimates and detailed model physics, in quantitative high-resolution air pollution modelling and future urban LES studies.

Mid-latitude atmospheric boundary layer electricity: A study by using a tethered balloon platform

In this study, we used a tethered balloon equipped with an instrumented platform to examine the altitude distribution of principal quantities of the lowest atmospheric region of the global electric circuit (GEC), radon volumetric activity, and aerosol particles concentration. Altitude soundings covered approximately 0.5 km of the lowest atmosphere and were accompanied by simultaneous ground-based measurements. This method of spaced observations allowed us to analyze the spatial and temporal changes in electrical quantities of the atmospheric boundary layer (ABL) more deeply than was possible before. Using successive balloon ascents and descents as well as holding the platform at certain heights, long-lived space charge layers were discovered and the rate of change of charge in atmospheric columns of various thickness was estimated. A charge density of small ions was determined to be enclosed in a range from −20 pC m−3 to 30 pC m−3 reaching the highest values with rare exceptions directly at the earth's surface. It was found that the electric field vertical profiles tend a decrease during the day most pronounced in the lower 100 m. Similar behavior is also demonstrated by radon and aerosol particle concentration profiles. Based on the results of soundings, columnar electrical resistance, electric potential, and electromotive force acting in the ABL in fair-weather conditions are quantified. These estimates show the significant contribution of the ABL to the GEC, which must be taken into account when considering it.

Optimizing the detection, ablation, and ion extraction efficiency of a single-particle laser ablation mass spectrometer for application in environments with low aerosol particle concentrations

Abstract. The aim of this study is to show how a newly developed aerodynamic lens system (ALS), a delayed ion extraction (DIE), and better electric shielding improve the efficiency of the Aircraft-based Laser ABlation Aerosol MAss spectrometer (ALABAMA). These improvements are applicable to single-particle laser ablation mass spectrometers in general. To characterize the modifications, extensive size-resolved measurements with spherical polystyrene latex particles (PSL; 150–6000 nm) and cubic sodium chloride particles (NaCl; 400–1700 nm) were performed. Measurements at a fixed ALS position show an improved detectable particle size range of the new ALS compared to the previously used Liu-type ALS, especially for supermicron particles. At a lens pressure of 2.4 hPa, the new ALS achieves a PSL particle size range from 230 to 3240 nm with 50 % detection efficiency and between 350 and 2000 nm with 95 % detection efficiency. The particle beam divergence was determined by measuring the detection efficiency at variable ALS positions along the laser cross sections and found to be minimal for PSL at about 800 nm. Compared to measurements by single-particle mass spectrometry (SPMS) instruments using Liu-type ALSs, the minimum particle beam divergence is shifted towards larger particle sizes. However, there are no disadvantages compared to the Liu-type lenses for particle sizes down to 200 nm. Improvements achieved by using the DIE and an additional electric shielding could be evaluated by size-resolved measurements of the hit rate, which is the ratio of laser pulses yielding a detectable amount of ions to the total number of emitted laser pulses. In particular, the hit rate for multiply charged particles smaller than 500 nm is significantly improved by preventing an undesired deflection of these particles in the ion extraction field. Moreover, it was found that by using the DIE the ion yield of the ablation, ionization, and ion extraction process could be increased, resulting in up to 7 times higher signal intensities of the cation spectra. The enhanced ion yield results in a larger effective width of the ablation laser beam, which in turn leads to a hit rate of almost 100 % for PSL particles in the size range from 350 to 2000 nm. Regarding cubic NaCl particles the modifications of the ALABAMA result in an up to 2 times increased detection efficiency and an up to 5 times increased hit rate. The need for such instrument modifications arises in particular for measurements of particles that are present in low number concentrations such as ice-nucleating particles (INPs) in general, but also aerosol particles at high altitudes or in pristine environments. Especially for these low particle number concentrations, improved efficiencies help to overcome the statistical limitations of single-particle mass spectrometer measurements. As an example, laboratory INP measurements carried out in this study show that the application of the DIE alone increases the number of INP mass spectra per time unit by a factor of 2 to 3 for the sampled substances. Overall, the combination of instrument modifications presented here resulted in an increased measurement efficiency of the ALABAMA for different particle types and particles shape as well as for highly charged particles.

Measured Constraints on Cloud Top Entrainment to Reduce Uncertainty of Nonprecipitating Stratocumulus Shortwave Radiative Forcing in the Southern Ocean

AbstractStratocumulus cloud top entrainment has a significant effect on cloud properties, but there are few observations quantifying its impact. Using explicit 0‐D parcel model simulations, initialized with below‐cloud in situ measurements, and validated with in situ measurements of cloud properties, the shortwave cloud radiative forcing (SWCF) was reduced by up to 100 W m−2 by cloud top entrainment in the Southern Ocean. The impact of entrainment‐corrected SWCF is between 2 and 20 times that of changes in the aerosol particle concentration or updraft at cloud base. The variability in entrainment‐corrected SWCF accounts for up to 50 W m−2 uncertainty in estimating cloud forcing. Measurements necessary for estimating the impact of entrainment on cloud properties can be constrained from existing airborne platforms and provide a first‐order approximation for cloud radiative properties of nonprecipitating stratocumulus clouds. These measurement‐derived estimates of entrainment can be used to validate and improve parameterizations of entrainment in Global Climate Models.

Physical and chemical properties of atmospheric aerosols in Moscow and its suburb for climate assessments

The paper presents results of experimental study of the physicochemical properties of surface aerosols in the Moscow region in the summer of 2019. Microphysical parameters, mass concentration and elemental composition of submicron and micron aerosol particles are considered, and their morphological structure is described. The features of variability of aerosol characteristics under atypical weather conditions prevailing in June-July 2019 are shown. The spatial distribution of the elemental composition of aerosols is established, a significant degree of their enrichment with heavy metals and metalloids is revealed. Geochemical analysis of aerosols and soils in Moscow was performed, and the coefficients of local aerosol concentration were calculated. The obtained experimental data will be useful for the refinement and verification of climate models.

UNATTACHED 212PB FRACTION IN THE WORKER'S BREATHING ZONE AT HIGH THORON CONCENTRATIONS.

Classical aerosol physics predicts that it is impossible to observe noticeable values of the unattached fraction of decay products of thoron at typical concentrations of aerosol particles. The experimental data have shown that the unattached fraction of the thoron decay products in a monazite storage facility is in the range 0.3-0.6. This effect is caused by local increase in air exchange near the inlet of the sampling device at high 220Rn concentrations. It was found that a dynamic shift between the unattached and attached thoron decay products is also observed in the worker's breathing zone at a high concentration of thoron. The 212Pb unattached fraction in worker's breathing zone was ~0.4. It demonstrates that when evaluating inhalation exposure to the products of the decay of thoron, it is necessary to take into account the increase of the 212Pb unattached fraction in the worker's breathing zone.

Placing a mask on COVID-19 patients during high-flow nasal cannula therapy reduces aerosol particle dispersion.

Wearing a surgical/procedure mask over high-flow nasal cannula (HFNC) reduces aerosol particle concentrations in the patients’ vicinity. Wearing a mask over HFNC should be encouraged to reduce risks of aerosol transmission. #COVID19 https://bit.ly/2HLg5cE

Activation properties of aerosol particles as cloud condensation nuclei at urban and high-altitude remote sites in southern Europe

Understanding the activation properties of aerosol particles as cloud condensation nuclei (CCN) is important for the climate and hydrological cycle, but their properties are not fully understood. In this study, the CCN activation properties of aerosols are investigated at two different sites in southern Spain: an urban background station in Granada and a high altitude mountain station in the Sierra Nevada National Park, with a horizontal separation of 21 km and vertical separation of 1820 m.CCN activity at the urban environment is driven by primary sources, mainly road traffic. Maximum CCN concentrations occurred during traffic rush hours, although this is also when the activation fraction is lowest. This is due to the characteristics of the rush hour aerosol consisting of ultrafine and less hygroscopic particles. In contrast, the mountain site exhibited larger and more hygroscopic particles, with CCN activity driven by the joint effect of new particle formation (NPF) and vertical transport of anthropogenic particles from Granada urban area by orographic buoyant upward flow. This led to the maximum concentrations of CCN and aerosol particles occurring at midday at the mountain site. Clear differences in the diurnal evolution of CCN between NPF events and non-event days were observed at the Sierra Nevada station, demonstrating the large contribution of NPF to CCN concentrations, especially at high supersaturations. The isolated contribution of NPF to CCN concentration has been estimated to be 175% higher at SS = 0.5% relative to what it would be without NPF. We conclude that NPF could be the major source of CCN at this mountain site.Finally, two empirical models were used to parameterize CCN concentration in terms of aerosol optical or physical parameters. The models can explain measurements satisfactorily at the urban station. At the mountain site both models cannot reproduce satisfactorily the observations at low SS.