Study Of Atmospheric Aerosols Research Articles

Study of atmospheric aerosols by IBA techniques: The LABEC experience

Abstract At the 3 MV Tandetron accelerator of the LABEC laboratory of INFN (Florence, Italy) an external beam facility is fully dedicated to PIXE-PIGE measurements of the elemental composition of atmospheric aerosols. All the elements with Z > 10 are simultaneously detected by PIXE typically in one minute. This setup allows us an easy automatic positioning, changing and scanning of samples collected by different kinds of devices: long series of daily PM (Particulate Matter) samples can be analysed in short times, as well as size-segregated and high time-resolution aerosol samples. Thanks to the capability of detecting all the crustal elements, PIXE-PIGE analyses are unrivalled in the study of mineral dust: consequently, they are very effective in the study of natural aerosols, like, for example, Saharan dust intrusions. Among the detectable elements there are also important markers of anthropogenic sources, which allow effective source apportionment studies in polluted urban environments using a multivariate method like Positive Matrix Factorization (PMF). Examples regarding recent monitoring campaigns, performed in urban and remote areas, both daily and with high time resolution (hourly samples), as well as with size selection, are presented. The importance of the combined use of the Particle Induced Gamma Ray emission technique (PIGE) and of other complementary (non-nuclear) techniques is highlighted.

Amazon boundary layer aerosol concentration sustained by vertical transport during rainfall.

The nucleation of atmospheric vapours is an important source of new aerosol particles that can subsequently grow to form cloud condensation nuclei in the atmosphere. Most field studies of atmospheric aerosols over continents are influenced by atmospheric vapours of anthropogenic origin (for example, ref. 2) and, in consequence, aerosol processes in pristine, terrestrial environments remain poorly understood. The Amazon rainforest is one of the few continental regions where aerosol particles and their precursors can be studied under near-natural conditions, but the origin of small aerosol particles that grow into cloud condensation nuclei in the Amazon boundary layer remains unclear. Here we present aircraft- and ground-based measurements under clean conditions during the wet season in the central Amazon basin. We find that high concentrations of small aerosol particles (with diameters of less than 50 nanometres) in the lower free troposphere are transported from the free troposphere into the boundary layer during precipitation events by strong convective downdrafts and weaker downward motions in the trailing stratiform region. This rapid vertical transport can help to maintain the population of particles in the pristine Amazon boundary layer, and may therefore influence cloud properties and climate under natural conditions.

Automated aerosol Raman spectrometer for semi-continuous sampling of atmospheric aerosol

Raman spectroscopy (RS) is useful in characterizing atmospheric aerosol. It is not commonly used in studying ambient particles partly because automated instrumentation for aerosol RS has not been available. Battelle (Columbus, Ohio, USA) has developed the Resource Effective Bioidentification System (REBS) for automated detection of airborne bioagents based on RS. We use a version of the REBS that measures Raman spectra of one set of particles while the next set of particles is collected from air, then moves the newly collected particles to the analysis region and repeats. Here we investigate the use of the REBS as the core of a general-purpose automated Aerosol Raman Spectrometer (ARS) for atmospheric applications. This REBS-based ARS can be operated as a line-scanning Raman imaging spectrometer. Spectra measured by this ARS for single particles made of polystyrene, black carbon, and several other materials are clearly distinguishable. Raman spectra from a 15min ambient sample (approximately 35–50 particles, 158 spectra) were analyzed using a hierarchical clustering method to find that the cluster spectra are consistent with soot, inorganic aerosol, and other organic compounds. The ARS ran unattended, collecting atmospheric aerosol and measuring spectra for a 7hr period at 15-min intervals. A total of 32,718 spectra were measured; 5892 exceeded a threshold and were clustered during this time. The number of particles exhibiting the D-G bands of amorphous carbon plotted vs time (at 15-min intervals) increases during the morning commute, then decreases. This data illustrates the potential of the ARS to measure thousands of time resolved aerosol Raman spectra in the ambient atmosphere over the course of several hours. The capability of this ARS for automated measurements of Raman spectra should lead to more extensive RS-based studies of atmospheric aerosols.

Statistical Thermodynamic Model for Surface Tension of Aqueous Organic Acids with Consideration of Partial Dissociation.

With statistical mechanics, an isotherm-based surface tension model for single solute aqueous solutions was derived previously (Wexler et al. J. Phys. Chem. Lett. 2013) for the entire concentration range, from infinite dilution to pure liquid solute, as a function of solute activity. In recent work (Boyer et al. J. Phys. Chem. Lett. 2015), empirical model parameters were reduced through physicochemical interpretations of both electrolyte and organic solutes, enabling surface tension predictions for systems where there is little or no data. The prior binary model is extended in the current work for the first time to treat multicomponent systems to predict surface tensions of partially dissociating organic acids (acetic, butyric, citric, formic, glutaric, maleic, malic, malonic, oxalic, propionic, and succinic acids). These organic acids are especially applicable to the study of atmospheric aqueous aerosols, due to their abundance in the atmosphere. In the model developed here, surface tension depends explicitly on activities of both the neutral organic and deprotonated components of the acid. The relative concentrations of the nondissociated and dissociated mole fractions are found using known dissociation constants. Model parameters strongly depend on molecular size, number of functional groups, O:C ratio, and number of carbons. For all organic acids in this study, fully predictive modeling of surface tensions is demonstrated.

Airborne Raman Lidar and its Applications for Atmospheric Process Studies

Although ground-base Raman lidars are widely used for atmospheric observations, the capabilities of airborne Raman lidar is not fully explored. Here we presented two recently developed airborne Raman lidar systems for the studies of atmospheric boundary layer process, aerosols, and clouds. The systems are briefly introduced. Observation examples are presented to illustrate the unique observational capabilities of airborne Raman lidar and their applications for atmospheric process studies.

The Mössbauer study of atmospheric iron-containing aerosol in the coarse and PM2.5 fractions measured in rural site

The size-resolved iron-containing atmospheric aerosol was measured by Mössbauer spectroscopy. The particulate matter (PM) was size-segregated into aerosol <2.5μm in diameter (fine fraction, PM2.5) and aerosol >2.5μm (coarse fraction).The Mössbauer spectra at room temperature show components assigned to mono- and polymeric species which are products related to hydrolysis of ferric solutions in the atmosphere. In order to extract reliable information regarding the quadrupole splittings necessary for identification of iron-containing compounds, the histogram method was used for evaluation of the Mössbauer spectra. The value and distribution of quadrupole splitting (QS) parameters obtained by this method suggests that the ultra fine particles (<10nm) identified as a ferrihydrite, hematite and goethite were observed in the spectra both in fine and coarse fraction of the collected aerosol. However, the content of the individual chemical components was different for each fraction. The least crystalline form of ferrihydrite (QS≅0.85mm) was observed in PM2.5 fraction more frequently than in the coarse fraction. The content of the ultra fine hematite particles which presence was confirmed in low temperature measurements was also larger in PM2.5 fraction than in the coarse fraction. Superparamagnetic behavior of iron-containing atmospheric aerosol was observed in low temperature Mössbauer spectra.

Observations of atmospheric water vapor, aerosol, and cloud with a Raman lidar

To realize the improvement of signal-to-noise ratio and rejection rate for elastic Mie-Rayleigh signals, a set of dichroic mirrors and narrow-band interference filters with high efficiency was proposed to constitute a new spectroscopy for atmospheric water vapor, aerosol, and cloud studies. Based on the curves of signal-to-noise ratio at three different channels, the actual rejection rates of elastic Mie-Rayleigh signals at the Raman channels were found to be higher than eight orders of magnitude with the cloudy conditions. Continuous nighttime observations showed that the statistical error of the water vapor mixing ratio was <10% at a height of 2.3 km with an aerosol backscatter ratio of 17. Temporal variations of water vapor and aerosols were obtained under the conditions of cloud and cloud-free, the change relevance between aerosol and water vapor was analyzed, and the growth characteristics of water vapor and aerosols showed a good agreement within the cloud layers. Obtained results indicate achievement of the continuous detection of water vapor, aerosol, and cloud with a high efficiency and stability by Raman lidar.

Implications for air quality and the impact of financial and economic crisis in South Spain: Geochemical evolution of atmospheric aerosol in the ceramic region of Bailén

A temporal series study of atmospheric aerosol was performed over the last ten years (2003–2012) in an urban background monitoring station with ceramic industrial influence, in Bailén, SE Spain. Temporal trends of major and minor chemical components of PM10 for a long term data series were investigated, showing that PM10 concentrations have been steadily decreasing over almost a decade, with a statistical significance. Measurements indicate a reduction of elements and components related to the industrial activity of brick-ceramic production (V, Cd, Rb, La, Cr, Ni, As, Pb and SO42−). Conversely, Cu levels define an increasing trend from the beginning of the study period but with the highest step trend since 2011–2012, coinciding with the beginning of the financial and economic crisis in 2008. A similar time evolution pattern of Cu and OC, EC, and K levels may be a tracer of domestic local combustion source, and a new biomass burning source has been identified. Chemical composition of olive tree logs suggest as the combustion of wood with high concentration of Cu can imply an increase of Cu concentration in the atmospheric particles compared with other sources such as traffic.

Comparative study of ultrafine atmospheric aerosol within a city

Particle number size distributions in a mobility diameter range of 6–1000 nm and size-resolved number concentrations were determined with a time resolution of 10 min for a near-city background, city centre, street canyon and road tunnel environments in Budapest. Median N6–100 concentrations for the sites listed were 3.1 × 103, 9.3 × 103, 19.4 × 103 and 123 × 103 cm−3, respectively. Contributions of the ultrafine (UF) particles (<100 nm) to the total particle number for all locations were rather large (up to 86%), and do not seem to vary substantially in time. Diurnal variations of the mean N6–100 concentrations had different patterns for both the various urban sites, and for workdays and weekends. Nucleation strength factor (NSF) was introduced for the first time to quantify the relative importance of new particle formation with respect to all sources of UF particles. During the daytime in summer, nucleation in the near-city background was a major production process of UF particles with a daily mean relative contribution of 42%. In the city centre and street canyon, the daily mean relative contributions of nucleation to the UF particles were 30% and 23%, respectively. Median particle diameters for the background, city centre, street canyon and road tunnel environments were 61, 42, 35 and 42 nm, respectively, so they were jointly influenced with the anthropogenic impact and aerosol ageing. Monthly mean frequency of new particle formation and growth events in the background seems somewhat larger, while it appears smaller for the street canyon in comparison to the city centre.

The retrieval of optical properties from terrestrial dust devil vortices

The retrieval of the optical properties of desert aerosols in suspension within terrestrial dust devils is presented with possible future application for martian dust devils. The transmission of light through dust devil vortices was measured in situ to obtain the wavelength-dependent attenuation by the aerosols. A Monte Carlo model was applied to each dust devil with the retrieved optical properties corresponding to the set of parameters which lead to the best model representation of the observed transmission spectra. The retrieved optical properties agree well with single scattering theory and are consistent with previous studies of dust aerosols. The enhanced absorption observed for dust devils with a higher tangential wind speed, and in comparison to atmospheric aerosol studies, suggests that larger dust particles are lofted and suspended around dust devil vortices. This analysis has shown that the imaginary refractive indices (and thus the optical properties of the suspended dust) are generally overestimated when these larger dust grains entrained by dust devils are neglected. This will lead to an overestimation of the amount of solar radiation absorbed by the small particles that remain in suspension after the dust devil terminates. It is also demonstrated that a 10% uncertainty in the particle size distribution of the dust entrained in the dust devils can result in a 50% increase in the predicted amount of incident solar radiation absorbed by the dust particles once the dust devil has terminated. The method used here provides the capability to retrieve the optical properties of the dust entrained in martian dust devils by taking advantage of transits over surface spacecraft which are capable of making optical measurements at ultraviolet and visible wavelengths. Our results suggest that we would observed higher absorption at all wavelengths for dust particles entrained in dust devil vortices compared to the ubiquitous dust haze.

A comparison between PIXE and ICP-AES measurements of metals in aerosol particulate collected in urban and marine sites in Italy

PIXE and ICP-AES techniques are largely used in atmospheric aerosol studies. Since PIXE is able to provide the total elemental concentrations, while ICP-AES results depend on the extraction conditions, parallel PIXE and ICP-AES measurements of Fe, Al, Cu, Pb, Mn, Cr, Ni, V, As on PM10 and PM2.5 samples were compared. Two extraction procedures were applied to samples from 5 sites at different anthropization level in Italy: a “weak” extraction (HNO3 at pH=1.5) and a “strong” extraction (micro-wave oven in HNO3 and H2O2 – following EU rules).The amount of the metal extracted in the different conditions resulted to be strongly dependent on the sampling site, on the main sources of the particle (crustal or anthropic) containing the metal and on the sampled size class.

Communication: Fourier-transform infrared probing of remarkable quantities of gas trapped in cold homogeneously nucleated nanodroplets

Studies of catalyzed all-vapor gas-hydrate formation on a sub-second timescale have been extended with a special focus on liquid-droplet compositions at the instant of hydrate crystallization. This focus has been enabled by inclusion of methanol in the all-vapor mixture. This slows droplet to gas-hydrate conversion near 200 K to a time scale suited for standard FTIR sampling. Such droplet data are sought as a guide to ongoing efforts to reduce the amount of guest catalyst required for instant formation of the gas hydrates. For the same reason, all-vapor sampling has also been extended to the generation of long-lived liquid droplets with reduced or no water content. Observations of single-solvent droplets show that surprising quantities of gas molecules are trapped during rapid droplet growth. For example, CO2 is trapped at levels near 50 mol. % in droplets of acetone, tetrahydrofuran, or trimethylene oxide formed under CO2 pressures of several Torr in a cold-chamber at 170 K. Less but significant amounts of gas are trapped at higher temperatures, or in methanol or water-methanol droplets. The droplet metastability appears to commonly lead to formation of bubbles larger than the original nanodroplets. Besides serving as a guide for the all-vapor gas-hydrate studies, the semiquantitative evidence of extensive trapping of gases is expected to have a role in future studies of atmospheric aerosols.

Size-segregated chemical composition of aerosol emissions in an urban road tunnel in Portugal

An atmospheric aerosol study was performed in 2008 inside an urban road tunnel, in Lisbon, Portugal. Using a high volume impactor, the aerosol was collected into four size fractions (PM0.5, PM0.5–1, PM1–2.5 and PM2.5–10) and analysed for particle mass (PM), organic and elemental carbon (OC and EC), polycyclic aromatic hydrocarbons (PAH), soluble inorganic ions and elemental composition. Three main groups of compounds were discriminated in the tunnel aerosol: carbonaceous, soil component and vehicle mechanical wear. Measurements indicate that Cu can be a good tracer for wear emissions of road traffic. Cu levels correlate strongly with Fe, Mn, Sn and Cr, showing a highly linear constant ratio in all size ranges, suggesting a unique origin through sizes. Ratios of Cu with other elements can be used to source apportion the trace elements present in urban atmospheres, mainly on what concerns coarse aerosol particles.

Design and analysis of new spectroscopic system of Raman lidar for detection of atmospheric water vapor

A new ultraviolet Raman lidar system is proposed and developed for detecting atmospheric water vapor and aerosol study. The combination of dichroic mirrors and narrow-band interference filters is used as high-performance spectroscopic system to obtain the fine-separation and high-efficiency extraction of Mie-Rayleigh scattering signals, the vibrational Raman scattering signal of H2O and N2. By the American standard model and a set of atmospheric scattering signal model, the signal-to-noise ratio (SNR) and the water vapor measurement error are simulated and analyzed. The preliminary experiments are carried out at nighttime in Xi'an area for detecting the atmospheric water vapor and aerosols. Taking a set of the atmospheric returned signals measured under cloudy weather for example, the profiles of atmospheric backscatter ratio and water vapor mixing ratio are retrieved, and the SNR profiles of the three channels are discussed and verify that this configuration can achieve a high rejection rate (10-7) to Mie-Rayleigh scattering. The theoretical and experimental results show that water vapor detection error of less than 15% can be obtained under a backscatter ratio of 17, which demonstrates the feasibility of the system for the atmospheric aerosol and water vapor measurements.

Interactions of mineral dust with pollution and clouds: An individual-particle TEM study of atmospheric aerosol from Saudi Arabia

Aerosol particles from desert dust interact with clouds and influence climate on regional and global scales. The Riyadh (Saudi Arabia) aerosol campaign was initiated to study the effects of dust particles on cloud droplet nucleation and cloud properties. Here we report the results of individual-particle studies of samples that were collected from an aircraft in April 2007. We used analytical transmission electron microscopy, including energy-dispersive X-ray spectrometry, electron diffraction, and imaging techniques for the morphological, chemical, and structural characterization of the particles.Dust storms and regional background conditions were encountered during four days of sampling. Under dusty conditions, the coarse (supermicrometer) fraction resembles freshly crushed rock. The particles are almost exclusively mineral dust grains and include common rock-forming minerals, among which clay minerals, particularly smectites, are most abundant. Unaltered calcite grains also occur, indicating no significant atmospheric processing. The particles have no visible coatings but some contain traces of sulfur. The fine (submicrometer) fraction is dominated by particles of anthropogenic origin, primarily ammonium sulfate (with variable organic coating and some with soot inclusions) and combustion-derived particles (mostly soot). In addition, submicrometer, iron-bearing clay particles also occur, many of which are internally mixed with ammonium sulfate, soot, or both. We studied the relationships between the properties of the aerosol and the droplet microphysics of cumulus clouds that formed above the aerosol layer. Under dusty conditions, when a large concentration of coarse-fraction mineral particles was in the aerosol, cloud drop concentrations were lower and droplet diameters larger than under regional background conditions, when the aerosol was dominated by submicrometer sulfate particles.

Temporal Variation of Aerosol Optical Properties at Măgurele, Romania

Abstract Even though much research has been conducted regarding the study of atmospheric aerosols, significant uncertainties still exist in this direction. The uncertainties are related to different physical and microphysical properties of these fine particles, but they are also related to the complex processes of interactions between aerosols and other atmospheric components, such as water droplets in the clouds or gaseous molecules. Therefore, it is mandatory to understand aerosol physics with maximum precision in real time all over the world. In this paper, the results of the statistical analysis of atmospheric aerosol optical properties as the total scattering and the backscattering coefficients, the Ångström parameter, and the aerosol optical depth from Măgurele (Ilfov, Romania) are presented. The analysis covers the period between 1 June 2008 and 31 December 2009. The results showed significant differences in temporal variations of the optical parameters for the winter of 2008 and 2009. From spring 2009 to the winter of this year, a decreasing tendency of the total scattering coefficient and an increasing trend for the Ångström exponent were observed. The size-increase tendency, over 1 μm, appears during the spring of 2008 and the summers of 2008 and 2009, coinciding with the local pollution or Saharan dust intrusion episodes. From the seasonal analysis, a certain monthly variation of the optical parameters was noticed. The results of the diurnal optical properties variations for the Măgurele area showed visible differences between the maximal and minimal values for the spring and summer seasons.

Study of atmospheric aerosols over the central Himalayan region using a newly developed Mie light detection and ranging system: preliminary results

A LIDAR system to receive Mie backscattered photons has been developed at the Manora peak, Nainital, India and it is the first of its kind in the central Himalayan region. The system is sensitive to receive backscattered photons from heights up to ∼20 km (above ground level). The atmospheric extinction profiles using Mie LIDAR have been estimated for the first timeatthissiteinJanuary(winter)andMarch(spring)seasonsinthreecampaignsandmaximum valuesarefoundtobe ∼0.01,0.03,and0.08km −1 ,respectively.Theaerosolopticaldepth(AOD) values are found to be ∼0.051, 0.098, and 0.233 in three campaigns, respectively, showing enhancement from January (winter) to March (spring) indicating a seasonal variation. AOD values of LIDAR, aerosol robotic network, and moderate resolution imaging spectroradiometer were found within the standard deviations. The aerosol loading at the site has increased during the last decade as evident from previous studies. C 2011 Society of Photo-Optical Instrumentation

Comparison of in situ and columnar aerosol spectral measurements during TexAQS-GoMACCS 2006: testing parameterizations for estimating aerosol fine mode properties

Abstract. During the 2006 Texas Air Quality Study and Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS-GoMACCS 2006), the optical, chemical and microphysical properties of atmospheric aerosols were measured on multiple mobile platforms and at ground based stations. In situ measurements of the aerosol light extinction coefficient (σep) were performed by two multi-wavelength cavity ring-down (CRD) instruments, one located on board the NOAA R/V Ronald H. Brown (RHB) and the other located at the University of Houston, Moody Tower (UHMT). An AERONET sunphotometer was also located at the UHMT to measure the columnar aerosol optical depth (AOD). The σep data were used to extract the extinction Ångström exponent (åep), a measure of the wavelength dependence of σep. There was general agreement between the åep (and to a lesser degree σep) measurements by the two spatially separated CRD instruments during multi-day periods, suggesting a regional scale consistency of the sampled aerosols. Two spectral models are applied to the σep and AOD data to extract the fine mode fraction of extinction (η) and the fine mode effective radius (Reff,f). These two parameters are robust measures of the fine mode contribution to total extinction and the fine mode size distribution, respectively. The results of the analysis are compared to Reff,f values extracted using AERONET V2 retrievals and calculated from in situ particle size measurements on the RHB and at UHMT. During a time period when fine mode aerosols dominated the extinction over a large area extending from Houston/Galveston Bay and out into the Gulf of Mexico, the various methods for obtaining Reff,f agree qualitatively (showing the same temporal trend) and quantitatively (pooled standard deviation = 28 nm).

Development of a variable configuration cascade impactor for aerosol size distribution measurement

In atmospheric aerosol studies, it is often required to use two different impactors, namely, the normal pressure and the low-pressure impactor, to measure the mass-size distribution over a wide size range. From the perspective of rendering the system compact for such measurements, it may be more advantageous to combine the two features in a single instrument. In an effort towards exploring this option, a variable configuration cascade impactor (VCCI) comprising of 7 normal pressure and 4 low-pressure stages has been designed and developed. In configuration-1, it operates as a low-pressure impactor, with a sampling flow rate of 10 L min −1 and classifies the particles from 0.1 to 21 μm in eleven size classes. In configuration-2, it operates as a normal pressure impactor, with a sampling flow rate of 45 L min −1, and classifies the particles from 0.53 to 10 μm in seven size classes. As part of performance evaluation of the system, the deposit patterns and the integral performance have been studied. For integral performance, a comparative mass-size distribution measurement between VCCI and standard Andersen impactor was carried out. Its performance was also evaluated against the GRIMM Scanning Mobility Particle Sizer (SMPS) in the common size range of both these instruments and against GRIMM Optical Particle Counter (OPC). In addition to this, VCCI was evaluated for its performance in the PM x configuration obtained by removing a few of the impactor stages sequentially and measuring corresponding size distribution for every stage removed. Changes in the distribution parameters due to spillover of the deposits of previous stage to remaining stages were within 10%. This variation is well within the generally accepted value for all environmental measurement related applications.

Study of atmospheric aerosols and mixing layer by LIDAR

The LIDAR (laser radar) is an active remote sensing technique, which allows for the altitude-resolved observation of several atmospheric constituents. A typical application is the measurement of the vertically resolved aerosol optical properties. By using aerosol particles as a marker, continuous determination of the mixing layer height (MLH) can also be obtained by LIDAR. Some examples of aerosol extinction coefficient profiles and MLH extracted from a 1-year LIDAR data set collected in Milan (Italy) are discussed and validated against in situ data (from a balloon-borne optical particle counter). Finally a comparison of the observation-based MLH with relevant numerical simulations (mesoscale model MM5) is provided.