Low Aerosol Concentrations Research Articles

Aerosol monitoring in Siberia using an 808 nm automatic compact lidar

Abstract. Our study provides new information on aerosol-type seasonal variability and sources in Siberia using observations (ground-based lidar and sun photometer combined with satellite measurements). A micropulse lidar emitting at 808 nm provided almost continuous aerosol backscatter measurements for 18 months (April 2015 to September 2016) in Siberia, near the city of Tomsk (56∘ N, 85∘ E). A total of 540 vertical profiles (300 daytime and 240 night-time) of backscatter ratio and aerosol extinction have been retrieved over periods of 30 min, after a careful calibration factor analysis. Lidar ratio and extinction profiles are constrained with sun-photometer aerosol optical depth at 808 nm (AOD808) for 70 % of the daytime lidar measurements, while 26 % of the night-time lidar ratio and AOD808 greater than 0.04 are constrained by direct lidar measurements at an altitude greater than 7.5 km and where a low aerosol concentration is found. An aerosol source apportionment using the Lagrangian FLEXPART model is used in order to determine the lidar ratio of the remaining 48 % of the lidar database. Backscatter ratio vertical profile, aerosol type and AOD808 derived from micropulse lidar data are compared with sun-photometer AOD808 and satellite observations (CALIOP space-borne lidar backscatter and extinction profiles, Moderate Resolution Imaging Spectroradiometer (MODIS) AOD550 and Infrared Atmospheric Sounding Interferometer (IASI) CO column) for three case studies corresponding to the main aerosol sources with AOD808>0.2 in Siberia. Aerosol typing using the FLEXPART model is consistent with the detailed analysis of the three case studies. According to the analysis of aerosol sources, the occurrence of layers linked to natural emissions (vegetation, forest fires and dust) is high (56 %), but anthropogenic emissions still contribute to 44 % of the detected layers (one-third from flaring and two-thirds from urban emissions). The frequency of dust events is very low (5 %). When only looking at AOD808>0.1, contributions from taiga emissions, forest fires and urban pollution become equivalent (25 %), while those from flaring and dust are lower (10 %–13 %). The lidar data can also be used to assess the contribution of different altitude ranges to the large AOD. For example, aerosols related to the urban and flaring emissions remain confined below 2.5 km, while aerosols from dust events are mainly observed above 2.5 km. Aerosols from forest fire emissions are observed to be the opposite, both within and above the planetary boundary layer (PBL).

Solar and Climatic High Performance Factors for the Placement of Solar Power Plants in Argentina Andes Sites—Comparison With African and Asian Sites

The installation of solar power plants is currently having a notable expansion. The results presented show that the Argentinean Andes range, from the central to northern latitudes, is an excellent region for the placement of these plants, due to the sum of different positive factors: very high mean annual solar irradiation, low ambient temperature and relative humidity, low precipitable water content, normal wind speeds, and extremely low aerosol content of the atmosphere. The proposed regions are nearby San Antonio de los Cobres and El Leoncito and are compared with two important locations where large solar power plants have been (or will be) built: a site in Africa (Ouarzazate, Morocco) and one in Asia (Dubai, Arab Emirates). We present the results of the possible production of electricity, supplying a total of about 21,000 GWh, which is 15.6% of the 2015 Argentinean electric consumption and, consequently, could reduce the emission of greenhouse gases in a total mass of 11.2 × 106 tons of CO2eq. The installation of this type of renewable power plant will contribute significantly to the Argentinean population due to frequent (mainly summer) cutoff of electric power supply and, in particular, to isolated (low income) populations leaving in the Argentinean Andes range.

Comparison of radioactive aerosol size distributions (Activity, number, mass, and surface area)

Information regarding the number, mass, and specific surface area distributions of aerosols is extremely important for assessments of exposure to radiation due to the intake of radioactive aerosols by inhalation. In this study, these distributions were compared with the activity size distributions for radon decay products. The experiments were conducted in a radon chamber under controlled conditions for the aerosol concentrations and with size distributions in the range from 5 nm to 10 µm. The activity size distributions of the aerosols were measured by using a diffusion battery and two types of cascade impactors. The aerosol concentrations during the experiments were in the range from 2 × 103 to 2.5 × 105 cm–3. The measurements obtained with a diffusion battery demonstrated that at the low aerosol concentration, up to 80% of activity of the radon decay products was connected with aerosol particles with an activity median thermodynamic diameter (AMTD) ~1 nm (unattached fraction). After injecting the aerosols into the experimental chamber, the activity of the unattached fraction decreased to practically zero but we observed the presence of the activity of aerosols with AMTD values ~10–20 nm. After injecting the aerosols, the distribution of the aerosol specific surface area exhibited a bimodal distribution, where the median diameter in the accumulation mode was ~120 nm and the geometric standard deviation (GSD) was 1.3. The median diameter in the coarse mode changed with time due to the deposition of aerosols on the walls of the chamber, where it decreased from 5 µm (GSD = 1.6) at 15 min after injection to 2 µm (GSD = 2.5) at 120 min after injection. The distribution of the aerosol activity measured by the cascade impactor was virtually independent of the time from the moment when the aerosols were injected. The parameters used to assess the activity distribution comprised an activity median aerodynamic diameter (AMAD) ~500–650 nm and GSD = 1.5. Comparisons of the activity distributions with the distributions for the number, mass, and specific surface area showed that the closest correspondence was with the average distribution over the specific surface, whereas there were no exact correspondences with the other distributions.

Spatial variability, mixing states and composition of various haze particles in atmosphere during winter and summertime in northwest China

Pollutants, which are usually transported from urban cities to remote glacier basins, and aerosol impurities affect the earth's temperature and climate by altering the radiative properties of the atmosphere. This work focused on the physicochemical properties of atmospheric pollutants across the urban and remote background sites in northwest China. Information on individual particles was obtained using transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDX). Particle size and age-dependent mixing structures of individual particles in clean and polluted air were investigated. Aerosols were classified into eight components: mineral dust, black carbon (soot)/fly ash, sulfates, nitrates, NaCl salt, ammonium, organic matter, and metals. Marked spatial and seasonal changes in individual particle components were observed in the study area. Aerosol particles were generally found to be in the mixing state. For example, salt-coated particles in summer accounted for 31.2–44.8% of the total particles in urban sites and 37.5–74.5% of the total particles in background sites, while in winter, almost all urban sites comprised >50%, which implies a significant effect on the radiative forcing in the study area. We found that in PM2.5 section, the internally mixed black carbon/organic matter particles clearly increased with diameter. Moreover, urban cities were characterized by atmospheric particles sourced from anthropogenic activities, whereas background locations exhibited much lower aerosol concentrations and increased particle density, originating from natural crustal sources (e.g., mineral dust and NaCl salt), which, together with air mass trajectory analysis, indicates a potential spatial transport process and routes of atmospheric transport from urban cities to background locations. Thus, this work is of importance in evaluating atmospheric conditions in northwest China and northeast Tibetan Plateau regions, to discover the transport processes and facilitate improvements in climatic patterns concerning atmospheric impurities.

Impacts on cloud radiative effects induced by coexisting aerosols converted from international shipping and maritime DMS emissions

Abstract. International shipping emissions (ISE), particularly sulfur dioxide, can influence the global radiation budget by interacting with clouds and radiation after being oxidized into sulfate aerosols. A better understanding of the uncertainties in estimating the cloud radiative effects (CREs) of ISE is of great importance in climate science. Many international shipping tracks cover oceans with substantial natural dimethyl sulfide (DMS) emissions. The interplay between these two major aerosol sources on CREs over vast oceanic regions with a relatively low aerosol concentration is an intriguing yet poorly addressed issue confounding estimation of the CREs of ISE. Using an Earth system model including two aerosol modules with different aerosol mixing configurations, we derive a significant global net CRE of ISE (−0.153 W m−2 with a standard error of ±0.004 W m−2) when using emissions consistent with current ship emission regulations. This global net CRE would become much weaker and actually insignificant (−0.001 W m−2 standard error of ±0.007 W m−2) if a more stringent regulation were adopted. We then reveal that the ISE-induced CRE would achieve a significant enhancement when a lower DMS emission is prescribed in the simulations, owing to the sublinear relationship between aerosol concentration and cloud response. In addition, this study also demonstrates that the representation of certain aerosol processes, such as mixing states, can influence the magnitude and pattern of the ISE-induced CRE. These findings suggest a reevaluation of the ISE-induced CRE with consideration of DMS variability.

Turbulence Effects on Precipitation and Cloud Radiative Properties in Shallow Cumulus: an Investigation Using the WRF-LES Model Coupled with Bin Microphysics

Using the large-eddy simulation version of the Weather Research and Forecasting (WRF) model coupled with a detailed bin microphysics scheme, the effects of turbulence-induced collision enhancement (TICE) on precipitation and cloud radiative properties in shallow cumulus are investigated. Similar to previous studies, the enhanced droplet collision results in an increase in rainwater content and surface precipitation amount. However, under low aerosol number concentration, the relative frequency of large surface precipitation amount is decreased mainly due to the decreased condensation amount. Due to TICE, the mean drop size increases and the drop number concentration decreases, which results in a decrease in evaporation and hence increasing cloud fraction. However, these changes induce a decrease in cloud optical thickness which largely offsets the increased cloud fraction when the domain-averaged albedo is calculated. Similarly, a decrease in cloud top height caused by the decreased in-cloud vertical velocity largely offsets the increased cloud fraction when the domain-averaged outgoing longwave radiation is calculated. Therefore, the effects of TICE on cloud radiative properties in shallow cumulus do not appear prominently. In addition, TICE results in a decrease in the shear production of turbulent kinetic energy, which indicates that TICE acts to produce a negative feedback.

Greenland records of aerosol source and atmospheric lifetime changes from the Eemian to the Holocene

The Northern Hemisphere experienced dramatic changes during the last glacial, featuring vast ice sheets and abrupt climate events, while high northern latitudes during the last interglacial (Eemian) were warmer than today. Here we use high-resolution aerosol records from the Greenland NEEM ice core to reconstruct the environmental alterations in aerosol source regions accompanying these changes. Separating source and transport effects, we find strongly reduced terrestrial biogenic emissions during glacial times reflecting net loss of vegetated area in North America. Rapid climate changes during the glacial have little effect on terrestrial biogenic aerosol emissions. A strong increase in terrestrial dust emissions during the coldest intervals indicates higher aridity and dust storm activity in East Asian deserts. Glacial sea salt aerosol emissions in the North Atlantic region increase only moderately (50%), likely due to sea ice expansion. Lower aerosol concentrations in Eemian ice compared to the Holocene are mainly due to shortened atmospheric residence time, while emissions changed little.

Aerosol and Urban Land Use Effect on Rainfall Around Cities in Indo‐Gangetic Basin From Observations and Cloud Resolving Model Simulations

AbstractCoupling of urban land use land cover (LULC) and aerosol loading on rainfall around cities in the Gangetic Basin (GB) is examined here. Long‐term observations illustrate more rainfall at urban core and climatological downwind regions compared to the upwind regions of Kanpur, a metropolitan area located in central GB. In addition, analysis of a 15 day cloud resolving simulation using the Weather Research and Forecasting model also illustrated similar rainfall pattern around other major cities in the GB. Interestingly, the enhancement of downwind rainfall was greater than that over urban regions, and it was positively associated with both the urban area of the city and ambient aerosol loading during the propagating storm. Further, to gain a process‐level understanding, a typical storm that propagated northwestward across Kanpur was simulated using Weather Research and Forecasting under three different scenarios. Case 1 has realistic LULC representation of Kanpur, while the grids representing the Kanpur urban region were replaced by cropland LULC pattern in Case 2. Comparison illustrated that urban heat island effect caused convergence of winds and moisture in the lower troposphere, which enhances convection over urban region and induced more rainfall over the urban core compared to upwind regions. Case 3 is similar to Case 1 but lower aerosol concentration (by a factor of 100) over the storm region. Analysis shows that aerosol‐induced microphysical changes delay the initiation of warm rain (over the upwind region) but enhance ice phase particle formation in latter stages (over the urban and downwind regions) resulting in increase in downwind rainfall.

Proposal and evaluation of subordinate standard solar irradiance spectra for applications in solar energy systems

Reference solar irradiance spectra are needed to specify key parameters of solar technologies such as photovoltaic cell efficiency, in a comparable way. The IEC 60904-3 and ASTM G173 standards present such spectra for Direct Normal Irradiance (DNI) and Global Tilted Irradiance (GTI) on a 37° tilted sun-facing surface for one set of clear-sky conditions with an air mass of 1.5 and low aerosol content. The IEC/G173 standard spectra are the widely accepted references for these purposes. Hence, the authors support the future replacement of the outdated ISO 9845 spectra with the IEC spectra within the ongoing update of this ISO standard.The use of a single reference spectrum per component of irradiance is important for clarity when comparing and rating solar devices such as PV cells. However, at some locations the average spectra can differ strongly from those defined in the IEC/G173 standards due to widely different atmospheric conditions and collector tilt angles. Therefore, additional subordinate standard spectra for other atmospheric conditions and tilt angles are of interest for a rough comparison of product performance under representative field conditions, in addition to using the main standard spectrum for product certification under standard test conditions. This simplifies the product selection for solar power systems when a fully-detailed performance analysis is not feasible (e.g. small installations). Also, the effort for a detailed yield analyses can be reduced by decreasing the number of initial product options.After appropriate testing, this contribution suggests a number of additional spectra related to eight sets of atmospheric conditions and tilt angles that are currently considered within ASTM and ISO working groups. The additional spectra, called subordinate standard spectra, are motivated by significant spectral mismatches compared to the IEC/G173 spectra (up to 6.5%, for PV at 37° tilt and 10–15% for CPV). These mismatches correspond to potential accuracy improvements for a quick estimation of the average efficiency by applying the appropriate subordinate standard spectrum instead of the IEC/G173 spectra.The applicability of these spectra for PV performance analyses is confirmed at five test sites, for which subordinate spectra could be intuitively selected based on the average atmospheric aerosol optical depth (AOD) and precipitable water vapor at those locations.The development of subordinate standard spectra for DNI and concentrating solar power (CSP) and concentrating PV (CPV) is also considered. However, it is found that many more sets of atmospheric conditions would be required to allow the intuitive selection of DNI spectra for the five test sites, due in particular to the stronger effect of AOD on DNI compared to GTI.The matrix of subordinate GTI spectra described in this paper are recommended to appear as an option in the annex of future standards, in addition to the obligatory use of the main spectrum from the ASTM G173 and IEC 60904 standards.

Aerosol indirect effects on summer precipitation in a regional climate model for the Euro-Mediterranean region

Abstract. Aerosols affect atmospheric dynamics through their direct and semi-direct effects as well as through their effects on cloud microphysics (indirect effects). The present study investigates the indirect effects of aerosols on summer precipitation in the Euro-Mediterranean region, which is located at the crossroads of air masses carrying both natural and anthropogenic aerosols. While it is difficult to disentangle the indirect effects of aerosols from the direct and semi-direct effects in reality, a numerical sensitivity experiment is carried out using the Weather Research and Forecasting (WRF) model, which allows us to isolate indirect effects, all other effects being equal. The Mediterranean hydrological cycle has often been studied using regional climate model (RCM) simulations with parameterized convection, which is the approach we adopt in the present study. For this purpose, the Thompson aerosol-aware microphysics scheme is used in a pair of simulations run at 50 km resolution with extremely high and low aerosol concentrations. An additional pair of simulations has been performed at a convection-permitting resolution (3.3 km) to examine these effects without the use of parameterized convection. While the reduced radiative flux due to the direct effects of the aerosols is already known to reduce precipitation amounts, there is still no general agreement on the sign and magnitude of the aerosol indirect forcing effect on precipitation, with various processes competing with each other. Although some processes tend to enhance precipitation amounts, some others tend to reduce them. In these simulations, increased aerosol loads lead to weaker precipitation in the parameterized (low-resolution) configuration. The fact that a similar result is obtained for a selected area in the convection-permitting (high-resolution) configuration allows for physical interpretations. By examining the key variables in the model outputs, we propose a causal chain that links the aerosol effects on microphysics to their simulated effect on precipitation, essentially through reduction of the radiative heating of the surface and corresponding reductions of surface temperature, resulting in increased atmospheric stability in the presence of high aerosol loads. Keywords. Atmospheric composition and structure (aerosols and particles)

Chemical characteristics of submicron particles at the central Tibetan Plateau: insights from aerosol mass spectrometry

Abstract. Recent studies have revealed a significant influx of anthropogenic aerosol from South Asia to the Himalayas and Tibetan Plateau (TP) during pre-monsoon period. In order to characterize the chemical composition, sources, and transport processes of aerosol in this area, we carried out a field study during June 2015 by deploying a suite of online instruments including an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-AMS) and a multi-angle absorption photometer (MAAP) at Nam Co station (90∘57′ E, 30∘46′ N; 4730 m a.s.l.) at the central of the TP. The measurements were made at a period when the transition from pre-monsoon to monsoon occurred. The average ambient mass concentration of submicron particulate matter (PM1) over the whole campaign was ∼ 2.0 µg m−3, with organics accounting for 68 %, followed by sulfate (15 %), black carbon (8 %), ammonium (7 %), and nitrate (2 %). Relatively higher aerosol mass concentration episodes were observed during the pre-monsoon period, whereas persistently low aerosol concentrations were observed during the monsoon period. However, the chemical composition of aerosol during the higher aerosol concentration episodes in the pre-monsoon season was on a case-by-case basis, depending on the prevailing meteorological conditions and air mass transport routes. Most of the chemical species exhibited significant diurnal variations with higher values occurring during afternoon and lower values during early morning, whereas nitrate peaked during early morning in association with higher relative humidity and lower air temperature. Organic aerosol (OA), with an oxygen-to-carbon ratio (O ∕ C) of 0.94, was more oxidized during the pre-monsoon period than during monsoon (average O ∕ C ratio of 0.72), and an average O ∕ C was 0.88 over the entire campaign period, suggesting overall highly oxygenated aerosol in the central TP. Positive matrix factorization of the high-resolution mass spectra of OA identified two oxygenated organic aerosol (OOA) factors: a less oxidized OOA (LO-OOA) and a more oxidized OOA (MO-OOA). The MO-OOA dominated during the pre-monsoon period, whereas LO-OOA dominated during monsoon. The sensitivity of air mass transport during pre-monsoon with synoptic process was also evaluated with a 3-D chemical transport model.

Ultraviolet radiation modelling from ground-based and satellite measurements on Reunion Island, southern tropics

Abstract. Surface ultraviolet radiation (SUR) is not an increasing concern after the implementation of the Montreal Protocol and the recovery of the ozone layer (Morgenstern et al., 2008). However, large uncertainties remain in the prediction of future changes of SUR (Bais et al., 2015). Several studies pointed out that UV-B impacts the biosphere (Erickson et al., 2015), especially the aquatic system, which plays a central part in the biogeochemical cycle (Hader et al., 2007). It can affect phytoplankton productivity (Smith and Cullen, 1995). This influence can result in either positive or negative feedback on climate (Zepp et al., 2007). Global circulation model simulations predict an acceleration of the Brewer-Dobson circulation over the next century (Butchart, 2014), which would lead to a decrease in ozone levels in the tropics and an enhancement at higher latitudes (Hegglin and Shepherd, 2009). Reunion Island is located in the tropics (21° S, 55° E), in a part of the world where the amount of ozone in the ozone column is naturally low. In addition, this island is mountainous and the marine atmosphere is often clean with low aerosol concentrations. Thus, measurements show much higher SUR than at other sites at the same latitude or at midlatitudes. Ground-based measurements of SUR have been taken on Reunion Island by a Bentham DTMc300 spectroradiometer since 2009. This instrument is affiliated with the Network for the Detection of Atmospheric Composition Change (NDACC). In order to quantify the future evolution of SUR in the tropics, it is necessary to validate a model against present observations. This study is designed to be a preliminary parametric and sensitivity study of SUR modelling in the tropics. We developed a local parameterisation using the Tropospheric Ultraviolet and Visible Model (TUV; Madronich, 1993) and compared the output of TUV to multiple years of Bentham spectral measurements. This comparison started in early 2009 and continued until 2016. Only clear-sky SUR was modelled, so we needed to sort out the clear-sky measurements. We used two methods to detect cloudy conditions: the first was based on an observer's hourly report on the sky cover, while the second was based on applying Long and Ackerman (2000)'s algorithm to broadband pyranometer data to obtain the cloud fraction and then discriminating clear-sky windows on SUR measurements. Long et al. (2006)'s algorithm, with the co-located pyranometer data, gave better results for clear-sky filtering than the observer's report. Multiple model inputs were tested to evaluate the model sensitivity to different parameters such as total ozone column, aerosol optical properties, extraterrestrial spectrum or ozone cross section. For total column ozone, we used ground-based measurements from the SAOZ (Système d'Analyse par Observation Zénithale) spectrometer and satellite measurements from the OMI and SBUV instruments, while ozone profiles were derived from radio-soundings and the MLS ozone product. Aerosol optical properties came from a local aerosol climatology established using a Cimel photometer. Since the mean difference between various inputs of total ozone column was small, the corresponding response on UVI modelling was also quite small, at about 1 %. The radiative amplification factor of total ozone column on UVI was also compared for observations and the model. Finally, we were able to estimate UVI on Reunion Island with, at best, a mean relative difference of about 0.5 %, compared to clear-sky observations.

Transmission of ultrafine particles through separating systems of dust samplers

Abstract In underground mines there is a radiation hazard associated with natural radioactive nuclides. The main sources of radiation exposure in Polish mines are short-lived radon decay products, radioactive mine water containing radium and the sediments precipitated from these waters. For miners, the most common hazard is usually the short-lived radon decay products. Aspirators, equipped with separation systems, are mostly used in order to control this hazard. Inside these aspirators there are meters which measure the radiation emitted by radioactive aerosols collected on the filter. The purpose of these systems is to remove particles from the air stream that do not form the respirable fraction. At the same time, however, a deposition of small-size aerosols takes place in them because of the high values of their corresponding diffusion coefficients. This excludes the possibility of their proper detection by radiation meters. In this paper, the transmission of particles up to 100 nm in size by the separating systems is evaluated. The evaluated transmission ranged from about 60% for sizes of 7 nm, reaching up to 95% at the boundary values of the tested range. The influence of the particle distribution of the aerosols on the radiation calibration coefficients was also investigated in a radon chamber, through their exposure to conditions where the air contained low aerosol concentrations of about 4.0 × 108 particles/m3 and also when it was nearly 100-times higher. In the first case, the measured sensitivity of the meters was about 20–30% lower, which was probably due to a higher number of small aerosols and, as a result, particle transmission decreased. However, at higher aerosol concentrations, the sensitivity of the meters remained practically the same, regardless of whether the air reached the filters by the separation systems or if they were omitted.

Multi-objective optimization of green powder-mixed electrical discharge machining of tungsten carbide alloy

Machining of difficult-to-machine materials produces huge amount of slurry and harmful aerosol concentration in the atmosphere, which are investigated in this work. In this study, an integrated framework was designed for the multi-response parametric optimization of powder-mixed electrical discharge machining of tungsten carbide alloy keeping into account both manufacturing and environmental aspects. Experiments were conducted using Taguchi L27 orthogonal array (OA), and process optimization was achieved using grey, grey-fuzzy, and grey-adaptive neuro fuzzy inference system–integrated approach. The multi-objective optimization techniques provide optimal parameter settings, i.e. medium pulse-on time (50 µs), low dielectric level (40 mm), medium current intensity (6 A), and high flushing pressure (0.6 kg/cm2). Results conclude that medium input discharge energies (pulse-on time and current intensity) are optimal for machining difficult-to-machine materials to produce low aerosol concentration. The comparison between the grades was performed to show the effectiveness of optimization approaches relative to each other. Finally, confirmation experiments were also conducted to indicate the effectiveness of the adopted optimization approach.

Field Measurement of Amine Aerosol by FTIR and Phase Doppler Interferometry

The emission of volatile compounds is an environmental and economic concern for CO2 capture by amine scrubbing. The condensation of amine species into aerosol is the main cause of volatile amine emissions. Current mitigation methods, including water wash, are not effective at preventing the atmospheric release of aerosol. This study focuses on the observation of aerosol at three amine scrubbing pilot plants.Fourier Transform Infrared Spectrometry (FTIR) sampling was performed in a pilot plant at the University of Texas at Austin. SO2 injection increased the emission of PZ solvent at a 1:1 molar ratio, and the injection of vaporized sulfuric acid increased amine emissions at a rate of 3 mols PZ/mol H2SO4. The slipstream pilot plant operated by the University of Kentucky utilized MEA to scrub CO2 from the flue gas stream of a coal-fired power plant. Bypassing caustic pretreatment and allowing SO2 to enter the absorber column increased MEA emissions. A 4% increase in the outlet CO2 resulted in a 10% reduction of amine emissions. A simplified water wash system was found to be ineffective at curtailing aerosol emissions.Phase Doppler Interferometry (PDI) and FTIR sampling were performed simultaneously at the National Carbon Capture Center. Using a blower between the water wash and absorber column instead of upstream of the absorber column resulted in a decrease in MEA emissions. The use of the intermediate blower instead of the upstream blower resulted in fewer, smaller aerosol drops. Decreasing the CO2 removal resulted in reduced amine aerosol emissions. Lower CO2 correlated with a lower aerosol concentration in the treated flue gas, but the aerosol sizes were significantly larger and resulted in overall increased amine emissions. Increasing the water wash temperature was found to increase average aerosol size and the amine concentration within the aerosol phase, resulting in an overall increase in amine emissions. By using the particle size distribution and aerosol concentration observed by PDI, the total liquid volume in the aerosol phase was calculated. Comparing this calculated quantity with the amine emissions observed using the FTIR allowed the approximate amine concentration in the aerosol phase to be determined.

Aerosol concentration measurements and correlations with air mass trajectories at the Pierre Auger Observatory

Aerosols play an important role in radiative transfer processes involved in different fields of study. In particular, their influence is crucial in the attenuation of light at astronomical and astrophysical observatories, and has to be taken into account in light transfer models employed to reconstruct the signals. The Andean Argentinean region is increasingly being considered as a good candidate to host such facilities, as well as the ones for solar-energy resources, and an adequate knowledge of aerosols characteristics there is needed, but it is not always possible due to the vast area involved and the scarce atmospheric data at ground. The aim of this work is to find correlations between aerosol data and particle trajectories that can give an insight into the origin and behaviour of aerosols in this zone and can be employed in situations in which one does not have local aerosol measurements. For this purpose, an aerosol spectrometer and dust monitor (Grimm 1.109) was installed at the Pierre Auger Observatory of ultra-high-energy cosmic rays, to record aerosol concentrations in different size intervals, at surface level. These measurements are analysed and correlated with air mass trajectories obtained from HYSPLIT (NOAA) model calculations. High aerosol concentrations are registered predominantly when air masses have travelled mostly over continental areas, mainly from the NE direction, while low aerosol concentrations are found in correspondence with air masses coming from the Pacific Ocean, from the NW direction. Different size distribution patterns were found for the aerosols depending on their origin: marine or continental. This work shows for the first time the size distribution of aerosols registered at the Pierre Auger Observatory. The correlations found between mass and particle concentrations (total and for different size ranges) and HYSPLIT air mass trajectories, confirm that the latter can be employed as a useful tool to infer the sources, evolution and characteristics of the aerosols.

Deposition and spatial variation of thoron decay products in a thoron experimental house using the Direct Thoron Progeny Sensors

Experiments have been carried out using the deposition-based Direct Thoron Progeny Sensors (DTPS) in a thoron experimental house. The objective was to study the thoron decay product characteristics such as the deposition velocities, spatial variability and dependence on aerosol particle concentrations. Since the deposition velocity is an important characteristic in the calibration of the DTPS, it is very important to study its dependence on aerosol concentration in a controlled environment. At low aerosol concentration (1500 particles/cm3) the mean effective deposition velocity was measured to be 0.159 ± 0.045 m h−1; at high aerosol concentration (30 000 particles/cm3) it decreased to 0.079 ± 0.009 m h−1. The deposition velocity for the attached fraction of the thoron decay products did not change with increasing aerosol concentration, showing measurement results of 0.048 ± 0.005 m h−1 and 0.043 ± 0.014 m h−1, respectively. At low particle concentration, the effective deposition velocity showed large scattering within the room at different distances from center. The attached fraction deposition velocity remained uniform at different distances from the wall. The measurements in the thoron experimental house can be used as a sensitivity test of the DTPS in an indoor environment with changing aerosol concentration. The uniform spatial distribution of thoron decay products was confirmed within the experimental house. This indicates that direct measurement of thoron decay product concentration should be carried out instead of inferring it from thoron gas concentration, which is very inhomogeneous within the experimental house.

Estimating optical turbulence of atmospheric surface layer at Antarctic Taishan station from meteorological data

Turbulence intensity in the near-surface layer and its decrease rate with height are closely related to the quality of potential sites. Astronomers have been pursuing a perfect astronomical site to place the large-aperture telescopes. Compared with the best mid-latitude sites, Antarctic plateau inevitably becomes an ideal site for building the next-generation large optical and infrared telescopes, which is because of its low infrared sky emission, low atmospheric precipitable water vapour content, low aerosol and dust content of the atmosphere, and light pollution. In this paper, we establish a model of the atmospheric optical turbulence in surface layer, and use it to estimate Cn2 at Antarctic Taishan station for the first time. The meteorological parameters of the model input are the data measured by a mobile atmospheric parameter measurement system at Antarctic Taishan station from 30 December 2013 to 10 February 2014. The values of Cn2, estimated by the model and measured by a micro-thermometer, are compared. Sensitivity analysis of the estimation method is also carried out. The measurement results and analyses show that Cn2 obtained at Taishan station has obvious diurnal variation characteristics, with well-behaved peaks in the daytime and nighttime, and minima near sunrise and sunset. Cn2 obtained in the nighttime is stronger than that in daytime, more specifically, it is on the order of 210-14 m-2/3. The comparison between model predictions and experimental data demonstrates that it is feasible to estimate Cn2 in Antarctic by using this model. The biggest differences between Cn2 values obtained from the model and measurement usually emerge at sunrise and sunset, respectively. Considering the fact that Antarctic atmosphere is in a stable state most of the time, the values of Cn2 estimated by different nondimensional structure parameter functions are nearly the same. Thus, the measurement accuracy of air temperature difference from one height to another is the main factor that affects the estimated value of Cn2.

Aerosols, clouds, and precipitation in the North Atlantic trades observed during the Barbados aerosol cloud experiment – Part 1: Distributions and variability

Abstract. Shallow marine cumulus clouds are by far the most frequently observed cloud type over the Earth's oceans; but they are poorly understood and have not been investigated as extensively as stratocumulus clouds. This study describes and discusses the properties and variations of aerosol, cloud, and precipitation associated with shallow marine cumulus clouds observed in the North Atlantic trades during a field campaign (Barbados Aerosol Cloud Experiment- BACEX, March–April 2010), which took place off Barbados where African dust periodically affects the region. The principal observing platform was the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter (TO) research aircraft, which was equipped with standard meteorological instruments, a zenith pointing cloud radar and probes that measured aerosol, cloud, and precipitation characteristics.The temporal variation and vertical distribution of aerosols observed from the 15 flights, which included the most intense African dust event during all of 2010 in Barbados, showed a wide range of aerosol conditions. During dusty periods, aerosol concentrations increased substantially in the size range between 0.5 and 10 µm (diameter), particles that are large enough to be effective giant cloud condensation nuclei (CCN). The 10-day back trajectories showed three distinct air masses with distinct vertical structures associated with air masses originating in the Atlantic (typical maritime air mass with relatively low aerosol concentrations in the marine boundary layer), Africa (Saharan air layer), and mid-latitudes (continental pollution plumes). Despite the large differences in the total mass loading and the origin of the aerosols, the overall shapes of the aerosol particle size distributions were consistent, with the exception of the transition period.The TO was able to sample many clouds at various phases of growth. Maximum cloud depth observed was less than ∼ 3 km, while most clouds were less than 1 km deep. Clouds tend to precipitate when the cloud is thicker than 500–600 m. Distributions of cloud field characteristics (depth, radar reflectivity, Doppler velocity, precipitation) were well identified in the reflectivity–velocity diagram from the cloud radar observations. Two types of precipitation features were observed for shallow marine cumulus clouds that may impact boundary layer differently: first, a classic cloud-base precipitation where precipitation shafts were observed to emanate from the cloud base; second, cloud-top precipitation where precipitation shafts emanated mainly near the cloud tops, sometimes accompanied by precipitation near the cloud base. The second type of precipitation was more frequently observed during the experiment. Only 42–44 % of the clouds sampled were non-precipitating throughout the entire cloud layer and the rest of the clouds showed precipitation somewhere in the cloud, predominantly closer to the cloud top.

Quantification of Airborne Biological Contaminants Associated with Land-Applied Biosolids

Greater than 50% of all class B biosolids produced in the US are reused by application to agricultural land. The goal of this research was to pair a comprehensive literature review with a field aerosol sampling campaign to characterize aerosols emitted during the land application process and provide a simplified framework for evaluating exposure to on-site workers and off-site residents. Three aerosolization scenarios for dewatered biosolids were considered and include spreading biosolids onto land by side slinging, disk incorporating into soils, and aerosolization of land applied biosolids due to high wind events. Particulate mater, metal aerosols, and biological aerosols of biosolids origin were in the respirable size range and were markedly greater downwind of land application than in upwind ambient control sites. Low level aerosolization of field applied biosolids were detected during high wind events, and biosolids derived aerosols were detected at 170 meters downwind of disk incorporation. The ability to reconstruct source aerosol concentration from PM10 measurements and the linear correlations made between bulk biosolids concentrations and source emission rates serve as a framework for determining relevant aerosol concentrations without the requirement of biological or chemical aerosol sampling. Application of this framework eliminates the inherent limitations and costs associated with monitoring low aerosol concentration of toxic compounds and pathogens. This title belongs to WERF Research Report Series ISBN: 9781843397700 (eBook)