Aerosol Residence Time Research Articles

Influence of broadleaf forest vegetation on atmospheric deposition of airborne radionuclides

The activities of airborne radionuclides 7Be and unsupported 210Pb (210Pbus) were measured in moss samples taken from 17 different locations. The objective was to estimate the influence of the broadleaf forest vegetation on atmospheric deposition of airborne radionuclides attached to aerosols. Two moss samples were collected at each location: within the forest stand (inside the area of the tree canopy projection) and within forest openings (outside the area of the tree canopy projection). Samples were taken in the spring season, before the leaves of trees came forth and in the autumn season, right before fall defoliation. A measurement indicates an absence of variation in 210Pbus concentration, however spring/autumn ratios of 7Be concentrations in mosses showed the expected seasonal difference in 7Be deposition. It was also noted that atmospheric deposition of 7Be at the forest openings was about two times higher than deposition in the forest. Using very simplified models, these measurements can be used to get estimation at how long 7Be and aerosols can reside on the leaves before precipitation eventually wash it to the ground mosses. It was estimated that the mean residence time of aerosols in the leaves was up to 50 days.

Facile synthesis of cauliflower-like hydrophobically modified polyacrylamide nanospheres by aerosol-photopolymerization

Amphiphilic copolymers consist of hydrophilic and hydrophobic monomer units have attracted great technological attention recently, owing to their unique properties and their ability to stabilize various interfaces in aqueous systems. This paper presents a novel and facile approach to produce spherical polyacrylamide, polystyrene and hydrophobically modified polyacrylamide (HM-PAM), as one of the most important type of amphiphilic copolymers, using a continuous aerosol-photopolymerization for the first time. To this end, the monomer droplets were generated by an atomizer, then photopolymerization was initiated ‘‘in flight’’ by ultraviolet (UV) irradiation of the aerosol monomer droplets containing photoinitiator within the average aerosol residence time of 30s in the photoreactor. To control the aqueous solubility, size and morphology of the resulting HM-PAM copolymers, different styrene/acrylamide monomer concentrations were introduced to the system. The textural properties of the obtained materials were characterized by TEM, SEM and N2 adsorption-desorption isotherms. The results revealed that the copolymers and polyacrylamide have cauliflower-like morphologies, while polystyrene has a nearly smooth morphology. Moreover, chemical compositions of the obtained materials were investigated by several characterization techniques such as 1H NMR, FT-IR, TGA and elemental analysis. 1H NMR and elemental analysis of resulting copolymers microstructures displayed successful incorporation of styrene in copolymer with a good agreement compared to initial ratios. The production of amphiphilic copolymer of acrylamide and styrene using the facile aerosol-photopolymerization method might open new avenues to produce various amphiphilic copolymers with a variety of hydrophobic and hydrophilic monomers with desirable properties.

Synthesis of Spherical Carbon Nitride-Based Polymer Composites by Continuous Aerosol-Photopolymerization with Efficient Light Harvesting.

Here we report a novel, facile, and sustainable approach for the preparation of spherical submicrometer carbon nitride-based polymer composites by a continuous aerosol-photopolymerization process. In this regard, spherical mesoporous carbon nitride (SMCN) nanoparticles were initially prepared via a nanocasting approach using spray-drying synthesized spherical mesoporous silica (SMS) nanoparticles as hard templates. In addition to experimental characterization, the effect of porosity on the light absorption enhancement and consequently the generation rate of electron-hole pairs inside the SMCN was simulated using a three-dimensional finite difference time-domain (FDTD) method. To produce the carbon nitride-based polymer composite, SMCN nanoparticles exhibit excellent performance in photopolymerization of butyl acrylate (PBuA) monomer in the presence of n-methyldiethanolamine (MDEA) as a co-initiator in a continuous aerosol-based process. In this one-pot synthesis, SMCN nanoparticles act not only as photoinitiators but at the same time as fillers and templates. The average aerosol residence time in the photoreactor is about 90 s. The presented aerosol-photopolymerization process avoids the need for solvent and surfactant, operates at room temperature, and, more importantly, is suitable to produce the spherical composite with hydrophobic polymers. Furthermore, we simulated the condition of SMCN nanoparticles during illumination in the gas phase process, which can freely rotate. The results demonstrated that the hole (h(+)) density is almost equally distributed in the whole part of the SMCN nanoparticles due to their rotation, leading to efficient light harvesting and more homogeneous photoreaction. The combination of the outstanding features of environmentally friendly SMCN, photopolymerization, and aerosol processing might open new avenues, especially in green chemistry, to produce novel polymer composites with multifunctional properties.

Daily variation of radon gas and its short-lived progeny concentration near ground level and estimation of aerosol residence time**Project supported by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah (Grant No. 291/965/1434).

Atmospheric concentrations of radon (222Rn) gas and its short-lived progenies 218Po, 214Pb, and 214Po were continuously monitored every four hours at the ground level in Jeddah city, Kingdom of Saudi Arabia. The measurements were performed three times every week, starting from November 2014 to October 2015. A method of electrostatic precipitation of positively charged 218Po and 214Po by a positive voltage was applied for determining 222Rn gas concentration. The short-lived 222Rn progeny concentration was determined by using a filter holder connected with the alpha-spectrometric technique. The meteorological parameters (relative air humidity, air temperature, and wind speed) were determined during the measurements of 222Rn and its progeny concentrations. 222Rn gas as well as its short-lived progeny concentration display a daily and seasonal variation with high values in the night and early morning hours as compared to low values at noon and in the afternoon. The observed monthly atmospheric concentrations showed a seasonal trend with the highest values in the autumn/winter season and the lowest values in the spring/summer season. Moreover, and in parallel with alpha-spectrometric measurements, a single filter-holder was used to collect air samples. The deposited activities of 214Pb and the long-lived 222Rn daughter 210Pb on the filter were measured with the gamma spectrometric technique. The measured activity concentrations of 214Pb by both techniques were found to be relatively equal largely. The highest mean seasonally activity concentrations of 210Pb were observed in the autumn/winter season while the lowest mean were observed in the spring/summer season. The mean residence time (MRT) of aerosol particles in the atmospheric air could be estimated from the activity ratios of 210Pb/214Pb.

Long-term variations of radionuclides in the Bratislava air

Variations of aerosol radionuclides (2001–2015) in the ground–level air in Bratislava (Slovakia) showed 7Be maxima in spring/early summer and minima in winter, however, an inverse trend was observed for 210Pb, 137Cs and 40K. A decreasing amplitude and splitting of summer maxima for 7Be in the last years has been found. A temporal behavior of the 7Be/210Pb activity ratio showed higher levels during warm seasons due to vertical convection of air masses from higher altitudes. The 137Cs activity concentration in the surface air between 2003 and 2010 was decreasing with an effective half-life of 1.9 ± 0.3 years. The yearly average 137Cs concentrations during 2009–2014 were almost constant, disturbed only by the Fukushima accident in 2011. The increased atmospheric 137Cs and 40K levels observed during the autumn–winter season may be due to surface soil resuspension, biomass burning and radionuclide transport by winds. Seasonal variations of 222Rn activity concentrations were found with maxima at the end of autumn and in winter, and minima in spring. The variability of the average annual course of 222Rn has been larger than that of 210Pb. The 210Pb/222Rn activity ratio was highest at the end of winter and in the spring, while from June to December remained nearly constant. More intensive atmospheric mixing in spring months caused a decrease in the 222Rn activity concentration, while the aerosol component of the atmosphere has been affected mainly during the autumn and winter seasons. The mean residence time of aerosols in the atmosphere was calculated using the 210Pb/222Rn method to be 4.5 ± 0.9 days.

Capture and long-term suspension of aerosols in an open cavity flow

The motion of non-Brownian aerosols in an open laminar cavity flow is investigated by means of numerical and asymptotic methods. The cavity is a rectangular domain where air enters through an inlet located on the top, and exits in the horizontal direction through symmetric apertures near the bottom wall. While such flows are generally used to provide a clean (particle-free) environment, the introduction of any object inside the cavity can affect the flow topology and, in return, can lead to large aerosol residence times. In addition, it is known that the unsteadiness of the flow, though weak, significantly delays the exit of aerosols from the cavity. The goal of this paper is to analyze the conditions under which these phenomena occur, for heavy inertial particles with a small response time and a finite free-fall velocity, in a laminar cavity flow. A two-dimensional situation is considered and investigated by means of numerical simulations and perturbation methods, at moderate cavity Reynolds numbers. It is observed that any obstacle placed inside the cavity (along the symmetry axis) creates large quasi-steady triangular recirculation cells stretched by the outward flow, provided the Reynolds number is not too large. In particular, streamlines near the floor are reversed, so that deposited particles are swept inward and remain in the cavity. The probability of trapping has been calculated asymptotically, for inertia-free sedimenting particles, and compared to numerical results. Trapping in the wake of obstacles is observed to persist when the flow is slightly unsteady. In addition, it is shown that the small but finite unsteadiness of the flow can lead to the temporary trapping of a significant portion of particles by large recirculation cells near the upper corners of the cavity. This phenomenon takes place in spite of gravity and centrifuge effects due to the curvature of the cell, and leads to a long-term suspension which significantly increases the residence time of aerosols. By making use of separatrix map methods, the critical aerosol diameter below which this phenomenon occurs has been obtained and compared to numerical simulation results.

Impacts of high-latitude volcanic eruptions on ENSO and AMOC

Large volcanic eruptions can have major impacts on global climate, affecting both atmospheric and ocean circulation through changes in atmospheric chemical composition and optical properties. The residence time of volcanic aerosol from strong eruptions is roughly 2-3 y. Attention has consequently focused on their short-term impacts, whereas the long-term, ocean-mediated response has not been well studied. Most studies have focused on tropical eruptions; high-latitude eruptions have drawn less attention because their impacts are thought to be merely hemispheric rather than global. No study to date has investigated the long-term effects of high-latitude eruptions. Here, we use a climate model to show that large summer high-latitude eruptions in the Northern Hemisphere cause strong hemispheric cooling, which could induce an El Niño-like anomaly, in the equatorial Pacific during the first 8-9 mo after the start of the eruption. The hemispherically asymmetric cooling shifts the Intertropical Convergence Zone southward, triggering a weakening of the trade winds over the western and central equatorial Pacific that favors the development of an El Niño-like anomaly. In the model used here, the specified high-latitude eruption also leads to a strengthening of the Atlantic Meridional Overturning Circulation (AMOC) in the first 25 y after the eruption, followed by a weakening lasting at least 35 y. The long-lived changes in the AMOC strength also alter the variability of the El Niño-Southern Oscillation (ENSO).

An empirically derived inorganic sea spray source function incorporating sea surface temperature

Abstract. We have developed an inorganic sea spray source function that is based upon state-of-the-art measurements of sea spray aerosol production using a temperature-controlled plunging jet sea spray aerosol chamber. The size-resolved particle production was measured between 0.01 and 10 μm dry diameter. Particle production decreased non-linearly with increasing seawater temperature (between −1 and 30 °C) similar to previous findings. In addition, we observed that the particle effective radius, as well as the particle surface, particle volume and particle mass, increased with increasing seawater temperature due to increased production of particles with dry diameters greater than 1 μm. By combining these measurements with the volume of air entrained by the plunging jet we have determined the size-resolved particle flux as a function of air entrainment. Through the use of existing parameterisations of air entrainment as a function of wind speed, we were subsequently able to scale our laboratory measurements of particle production to wind speed. By scaling in this way we avoid some of the difficulties associated with defining the "white area" of the laboratory whitecap – a contentious issue when relating laboratory measurements of particle production to oceanic whitecaps using the more frequently applied whitecap method. The here-derived inorganic sea spray source function was implemented in a Lagrangian particle dispersion model (FLEXPART – FLEXible PARTicle dispersion model). An estimated annual global flux of inorganic sea spray aerosol of 5.9 ± 0.2 Pg yr−1 was derived that is close to the median of estimates from the same model using a wide range of existing sea spray source functions. When using the source function derived here, the model also showed good skill in predicting measurements of Na+ concentration at a number of field sites further underlining the validity of our source function. In a final step, the sensitivity of a large-scale model (NorESM – the Norwegian Earth System Model) to our new source function was tested. Compared to the previously implemented parameterisation, a clear decrease of sea spray aerosol number flux and increase in aerosol residence time was observed, especially over the Southern Ocean. At the same time an increase in aerosol optical depth due to an increase in the number of particles with optically relevant sizes was found. That there were noticeable regional differences may have important implications for aerosol optical properties and number concentrations, subsequently also affecting the indirect radiative forcing by non-sea spray anthropogenic aerosols.

Aerosol transport over the Andes from the Amazon Basin to the remote Pacific Ocean: A multiyear CALIOP assessment

AbstractSix years (2007–2012) of data from the Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite instrument were used to investigate the vertical distribution and transport of aerosols over the tropical South American continent and the southeast Pacific Ocean. The multiyear aerosol extinction assessment indicates that aerosols, mainly biomass burning particles emitted during the dry season in the Amazon Basin, are lifted in significant amounts over the Andes. The aerosols are mainly transported in the planetary boundary layer between the surface and 2 km altitude with an aerosol extinction maximum near the surface. During the transport toward the Andes, the aerosol extinction decreases at a rate of 0.02 km−1 per kilometer of altitude likely due to dilution and deposition processes. Aerosols reaching the top of the Andes, at altitudes typically between 4 and 5 km, are entrained into the free troposphere (FT) over the southeast Pacific Ocean. A comparison between CALIOP observations and ERA‐Interim reanalysis data indicates that during their long‐range transport over the tropical Pacific Ocean, these aerosols are slowly transported toward the marine boundary layer by the large‐scale subsidence at a rate of 0.4 cm s−1. The observed vertical/horizontal transport ratio is 0.7–0.8 m km−1. Continental aerosols linked to transport over the Andes can be traced on average over 4000 km away from the continent indicating an aerosol residence time of 8–9 days in the FT over the Pacific Ocean. The FT aerosol optical depth (AOD) above the Pacific Ocean near South American coast accounts on average for 6% and 25% of the total AOD during the season of low and high biomass burning, respectively. This result shows that, during the biomass burning season, continental aerosols largely influence the AOD over the remote southeast Pacific Ocean. Overall, FT AOD decrease exponentially with the distance to continental sources at a rate of about 10% per degree of longitude over the Pacific Ocean.

Coagulation effect on the activity size distributions of long lived radon progeny aerosols and its application to atmospheric residence time estimation techniques

The long lived naturally occurring radon progeny species in the atmosphere, namely 210Pb, 210Bi and 210Po, have been used as important tracers for understanding the atmospheric mixing processes and estimating aerosol residence times. Several observations in the past have shown that the activity size distribution of these species peaks at larger particle sizes as compared to the short lived radon progeny species – an effect that has been attributed to the process of coagulation of the background aerosols to which they are attached. To address this issue, a mathematical equation is derived for the activity-size distribution of tracer species by formulating a generalized distribution function for the number of tracer atoms present in coagulating background particles in the presence of radioactive decay and removal. A set of these equations is numerically solved for the progeny chain using Fuchs coagulation kernel combined with a realistic steady-state aerosol size spectrum that includes nucleation, accumulation and coarse mode components. The important findings are: (i) larger shifts in the modal sizes of 210Pb and 210Po at higher aerosol concentrations such as that found in certain Asian urban regions (ii) enrichment of tracer specific activity on particles as compared to that predicted by pure attachment laws (iii) sharp decline of daughter-to-parent activity ratios for decreasing particle sizes. The implication of the results to size-fractionated residence time estimation techniques is highlighted. A coagulation corrected graphical approach is presented for estimating the residence times from the size-segregated activity ratios of 210Bi and 210Po with respect to 210Pb. The discrepancy between the residence times predicted by conventional formula and the coagulation corrected approach for specified activity ratios increases at higher atmospheric aerosol number concentrations (>1010 #/m3) for smaller sizes (<1 μm). The results are further discussed.

Activity size distribution and residence time of 7Be aerosols in the Arctic atmosphere

The activity size distributions of the natural radionuclide tracer 7Be in different size range fractions (<0.39 μm, 0.39–0.69 μm, 0.69–1.3 μm, 1.3–2.1 μm, 2.1–4.2 μm, 4.2–10.2 μm and >10.2 μm) were determined in the boreal atmosphere in the Arctic Research Centre of the Finnish Meteorological Institute (FMI) at Sodankylä, Finland (67°22′ N, 26°38′ E, 180 m asl). The activity median aerodynamic diameter (AMAD) ranged from 0.54 μm to 1.05 μm (average 0.83 μm). A residence time of about 8 days applies to aerosols of 0.83 μm diameter, representing the residence of aerosol particles in arctic environment. The observed positive correlation between AMAD values and RH% can be explained by the fact that condensation during high relative humidity conditions becomes more intense, resulting in increased particle sizes of atmospheric aerosols. However, greater aerosol particle sizes means higher wet scavenging rate of aerosols and as a result lower activity concentration of 7Be in the atmosphere, explaining the anti-correlation between the AMAD values and activity concentrations of 7Be. But this associated with possibly higher scavenging rates of aerosols does not necessarily alone explain the anti-correlation between the AMAD and the 7Be activities. The air mass origin associated with synoptic scale weather phenomena may contribute to that too. The Flextra model was used to assess the transport pattern and to explain the deviation in radionuclide activity concentrations and AMAD values observed in the site of investigation.

Perspectives of aerosol-photopolymerization: Nanoscale polymer particles

Photoinitiated polymerization is employed to produce submicron polymer particles in aerosols. By ultraviolet (UV) irradiation of the aerosol monomer solution droplets, produced with the help of an atomizer, polymerization is initiated by free radical generation. The aerosol process allows the production of surfactant-free polymer particles without any solvent required, while photochemistry results in instantaneous formation of free radicals by cleavage of excited photoinitiator molecules. Furthermore, the initiation can take place independent of temperature, which provides polymerization at ambient temperature. A continuous experimental setup with a flow-through photoreactor is developed, which is characterized by a sub-minute aerosol residence time. The experiments reveal that spherical nanopolymers can be formed as 1-to-1 copy from the monomer droplets.

Impact of the modal aerosol scheme GLOMAP-mode on aerosol forcing in the Hadley Centre Global Environmental Model

Abstract. The Hadley Centre Global Environmental Model (HadGEM) includes two aerosol schemes: the Coupled Large-scale Aerosol Simulator for Studies in Climate (CLASSIC), and the new Global Model of Aerosol Processes (GLOMAP-mode). GLOMAP-mode is a modal aerosol microphysics scheme that simulates not only aerosol mass but also aerosol number, represents internally-mixed particles, and includes aerosol microphysical processes such as nucleation. In this study, both schemes provide hindcast simulations of natural and anthropogenic aerosol species for the period 2000–2006. HadGEM simulations of the aerosol optical depth using GLOMAP-mode compare better than CLASSIC against a data-assimilated aerosol re-analysis and aerosol ground-based observations. Because of differences in wet deposition rates, GLOMAP-mode sulphate aerosol residence time is two days longer than CLASSIC sulphate aerosols, whereas black carbon residence time is much shorter. As a result, CLASSIC underestimates aerosol optical depths in continental regions of the Northern Hemisphere and likely overestimates absorption in remote regions. Aerosol direct and first indirect radiative forcings are computed from simulations of aerosols with emissions for the year 1850 and 2000. In 1850, GLOMAP-mode predicts lower aerosol optical depths and higher cloud droplet number concentrations than CLASSIC. Consequently, simulated clouds are much less susceptible to natural and anthropogenic aerosol changes when the microphysical scheme is used. In particular, the response of cloud condensation nuclei to an increase in dimethyl sulphide emissions becomes a factor of four smaller. The combined effect of different 1850 baselines, residence times, and abilities to affect cloud droplet number, leads to substantial differences in the aerosol forcings simulated by the two schemes. GLOMAP-mode finds a present-day direct aerosol forcing of −0.49 W m−2 on a global average, 72% stronger than the corresponding forcing from CLASSIC. This difference is compensated by changes in first indirect aerosol forcing: the forcing of −1.17 W m−2 obtained with GLOMAP-mode is 20% weaker than with CLASSIC. Results suggest that mass-based schemes such as CLASSIC lack the necessary sophistication to provide realistic input to aerosol-cloud interaction schemes. Furthermore, the importance of the 1850 baseline highlights how model skill in predicting present-day aerosol does not guarantee reliable forcing estimates. Those findings suggest that the more complex representation of aerosol processes in microphysical schemes improves the fidelity of simulated aerosol forcings.

Climate‐induced changes in sea salt aerosol number emissions: 1870 to 2100

AbstractGlobal climate model output is combined with an emission parameterization to estimate the change in the global and regional sea salt aerosol number emission from 1870 to 2100. Global average results suggest a general increase in sea salt aerosol number emission due to increasing surface wind speed. However, the emission changes are not uniform over the aerosol size spectrum due to an increase in sea surface temperature. From 1870 to 2100 the emission of coarse mode particles (dry diameter DP&gt;655 nm) increase by approximately 10 % (global average), whereas no significant change in the emission of ultrafine mode aerosols (dry diameter Dp&lt;76 nm) was found over the same period. Significant regional differences in the number emission trends were also found. Based on CAM‐Oslo global climate model output, no straight‐forward relationship was found between the change in the number emissions and changes in the sea salt aerosol burden or optical thickness. This is attributed to a change in the simulated residence time of the sea salt aerosol. For the 21st century, a decrease in the residence time leads to a weaker sea salt aerosol‐climate feedback that what would be inferred based on changes in number emissions alone. Finally, quantifying any potential impact on marine stratocumulus cloud microphysical and radiative properties due to changes in sea salt aerosol number emissions is likely to be complicated by commensurate changes in anthropogenic aerosol emissions and changes in meteorology.

Synthesis of nanosized metallic particles from an aerosol

The synthesis of metallic nanoparticles from the precursor solution of salts using the ultrasonic spray pyrolysis method was considered in this work. During the control of process parameters (surface tension and density, the concentration of solution, residence time of aerosol in the reactor, presence of additives, gas flow rate, decomposition temperature of aerosol, type of precursor and working atmosphere) it is possible to guide the process in order to obtain powders with such a morphology which satisfies more complex requirements for the desired properties of advanced engineering materials. Significant advance in the improvement of powder characteristics (lower particles sizes, better spheroidity, higher surface area) was obtained by the application of the ultrasonic generator for the preparation of aerosols. Ultrasonic spray pyrolysis is performed by the action of a powerful source of ultrasound on the corresponding precursor solution forming the aerosol with a constant droplet size, which depends on the characteristics of liquid and the frequency of ultrasound. The produced aerosols were transported into the hot reactor, which enables the reaction to occur in a very small volume of a particle and formation of nanosized powder. Spherical, nanosized particles of metals (Cu, Ag, Au, Co) were produced with new and improved physical and chemical characteristics at the IME, RWTH Aachen University. The high costs associated with small quantities of produced nanosized particles represent a limitation of the USP-method. Therefore, scale up of the ultrasonic spray pyrolysis was performed as a final target in the synthesis of nanosized powder.

A new method for monitoring the average residence time of atmospheric particulate matter

The long life decay products 210Pb, 210Bi and 210Po of 222Rn are adsorbed in atmospheric particulate matters, thus making it possible to estimate the average residence time by measuring the specific activity or activity ratio of radon daughters. However, the existing research results are rather bad in consistency and the contradictory phenomena cannot be reasonably explained, which makes it inapplicable to atmospheric environmental monitoring. For this reason, starting with the basic attributes of lower atmosphere, based on the decay characteristics, transfer rates and other related information of radioactive nuclides in atmospheric particulates, a mathematical model is built to reflect the relationship among the particle numbers of the absorbed, decayed and transferred. Then, a new method is presented to estimate the average residence time of atmospheric aerosol. The method can solve the confusion that have appeared in the current research, reveal that the atmosphere has limited self-purification function, and provide the condition for nuclides in the same decaying chain to decay to the activity balance and the way to reduce the average residence time. All these conclusions will provide a scientific basis for further study and exploitation in atmospheric environment monitoring.

Evaluation of Residence Time of Dust Aerosols during the Harmattan Season in Sokoto Area of Northwestern Nigeria, Using Visibility Data

Sokoto (13.01 0 N, 5.15 0 E) lies within the hot /dry semi desert climate type i.e. Sahel Savannah climate zone and is identified as one of the regions in West Africa that is severely affected by the dust particles originating from Sahara desert. In this paper, we computed the residence time of dust aerosol in Sokoto region using visibility data for 20 years (1991-2010) obtained from Nigeria Meteorological Agency (NIMET). The method used yielded results which show variations in the values of the monthly and annual mean residence time of values 2.4-12.9 and 5.21 days respectively for the Harmattan months (November to March). These values are in general agreed with measurable values and similar to other naturally occurring aerosols in the atmosphere. Reasons are adduced for the variations.

Generation and characterization of radiolabelled nanosized carbonaceous aerosols for human inhalation studies

New insights on the output of a commercial Technegas generator were proposed in order to optimize the generation of a radioactive nanosized aerosol for human inhalation studies. Parameters influencing Technegas generated aerosols (i.e. gaseous atmosphere, generation temperature and storage duration) were analyzed by a combination of size-fractionation and gamma-scintigraphy detection to determine the aerosol aerodynamic-related distributions. It was found that the total radioactivity per mass and number concentrations of aerosols was mostly influenced by the burn temperature, while the radiolabelling of particles was mostly driven by their surface area. 99mTc labeled nanosized carbonaceous primary particles appear mainly to result from nucleation/condensation of the supersaturated vapor during the burning step, and then coalesce into larger particles due to coagulation processes during the residence time in the expansion chamber. We showed that the burn temperature and the aerosol residence time were the main parameters influencing the particle size distribution. Under optimized operating conditions, the amount of radiolabelled nanoparticles substantially increased since the radioactivity median aerodynamic diameter was reduced by half (250nm—GSD of 2.5) compared with the standard operating conditions of the Technegas generator (450nm—GSD of 3.4).

Determination of the mean aerosol residence times in the atmosphere and additional 210Po input on the base of simultaneous determination of 7Be, 22Na, 210Pb, 210Bi and 210Po in urban air.

The significant differences in the activities of 210Pb, 210Bi, 210Po and cosmogenic 7Be and 22Na radionuclides in the urban aerosol samples collected in the summers 2010 and 2011 in the Lodz city of Poland were observed. Simultaneous measurement of these radionuclides, after a simple modification of the one compartment model, allows us to calculate both: the corrected aerosol residence times in the troposphere (1 ÷ 25 days) and in the lower stratosphere (103 ÷ 205 days). The relative input of the additional sources (beside of the 222Rn decay in the air) to the total activity concentrations of 210Pb, 210Bi and 210Po radionuclides in the urban air, plays a substantial role (up to 97% of the total activity) only in the case of 210Po.

How does the atmospheric variability drive the aerosol residence time in the Arctic region?

This paper aims at characterising the impact of the atmospheric variability on the aerosol burden and residence time in the Arctic region. For this purpose, a global simulation using an emissions inventory from the year 2000 is performed for the period 2000–2005. The model thus describes a 6-yr evolution of sulphate, black carbon (BC) and mineral dust, whose variability is driven by the atmosphere only. Our simulation is validated, thanks to comparisons with surface observations. The aerosol residence time takes minimum values in fall: 4 d for sulphate and 8 d for BC and dust. It takes maximum values in June: 10 d for sulphate and 16 d for BC and dust. However, from one spring to another, it can vary by about 50% for sulphate, 40% for BC and 100% for dust, depending on the atmospheric variability. In June, sulphate, BC and dust burden averaged over the Arctic region reach respectively maximums of 1.9 mg[S] m−2, 0.2 mg m−2 and 6 mg m−2, characteristic of the so-called Arctic haze. From one year to another, these values can vary by 20% for sulphate, 10% for BC and 60% for dust.