Classifying aerosol particles through the combination of optical and physical-chemical properties: Results from a wintertime campaign in Rome (Italy) (original) (raw)
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Atmospheric Chemistry and Physics, 2013
Characterizing chemical and physical aerosol properties is important to understand their sources, effects, and feedback mechanisms in the atmosphere. This study proposes a scheme to classify aerosol populations based on their spectral optical properties (absorption and scattering). The scheme is obtained thanks to the outstanding set of information on particle size and composition these properties contain. The spectral variability of the aerosol single scattering albedo (dSSA), and the extinction, scattering and absorption Angstrom exponents (EAE, SAE and AAE, respectively) were observed on the basis of two-year measurements of aerosol optical properties (scattering and absorption coefficients at blue, green and red wavelengths) performed in the suburbs of Rome (Italy). Optical measurements of various aerosol types were coupled to measurements of particle number size distributions and relevant optical properties simulations (Mie theory). These latter allowed the investigation of the role of the particle size and composition in the bulk aerosol properties observed. The combination of simulations and measurements suggested a general "paradigm" built on dSSA, SAE and AAE to optically classify aerosols. The paradigm proved suitable to identify the presence of key aerosol populations, including soot, biomass burning, organics, dust and marine particles. The work highlights that (i) aerosol populations show distinctive combinations of SAE and dSSA times AAE, these variables being linked by a linear inverse relation varying with varying SSA; (ii) fine particles show EAE > 1.5, whilst EAE < 2 is found for both coarse particles and ultrafine soot-rich aerosols; (iii) fine and coarse particles both show SSA > 0.8, whilst ultrafine urban Aitken mode and soot particles show SSA < 0.8. The proposed paradigm agrees with aerosol observations performed during past major field campaigns, this indicating that relations concerning the paradigm have a general validity.
Classifying aerosol type using in situ surface spectral aerosol optical properties
Atmospheric Chemistry and Physics Discussions
Knowledge of aerosol size and composition is important for determining radiative forcing effects of aerosols, identifying aerosol sources, and improving aerosol satellite retrieval algorithms. The ability to extrapolate aerosol size and composition, or type, from intensive aerosol optical properties can help expand the current knowledge of spatio-temporal variability of aerosol type globally, particularly where chemical composition measurements do not exist concurrently with optical property measurements. This study uses medians of scattering Ångström exponent (SAE), absorption Ångström exponent (AAE) and single scattering albedo (SSA) from 24 stations within the NOAA federated aerosol network to infer aerosol type using previously published aerosol classification schemes. <br><br> Three methods are implemented to obtain a best estimate of dominant aerosol type at each station using aerosol optical properties. The first method plots station medians into an AAE vs. SAE pl...
Classification of Aerosols in an Urban Environment on the Basis of Optical Measurements
Aerosol and Air Quality Research, 2016
The present study investigates various types of aerosol in the Lahore city of Pakistan using Aerosol Robotic Network (AERONET) data over a six year period from 2007 to 2012. Aerosol optical depths (AODs) observed was in the range 0.2-1.12. An analysis of seasonal variations in AOD has indicated that the highest AOD values occurred in summer and the lowest in winter. The urban aerosols of the study area were classified on the basis of optical parameters such as AOD, Extinction Angstrom Exponent (EAE), Absorption Angstrom Exponent (AAE), Single Scattering Albedo (SSA), Asymmetry Parameter (ASY) and Refractive Index (RI). The AAE values were in the range from 0.25 to 3.2. Real Refractive Index (RRI) and Imaginary part of the Refractive Index (IRI) values were in the range from 1.5 to 1.6 and 0 to 0.005 respectively. The major contributions to the atmospheric aerosols over Lahore were from urban industrial emissions, fossil fuel burning and road/soil dust. Higher RRI values reflected larger re-suspended road dust particles and long-range transported particles, while lower values reflected increased anthropogenic absorbing carbonaceous aerosols over the area. The AERONET retrieved SSA (0.80-0.89) and ASY (0.70-0.83) values suggested a predominance of urban industrial, vehicular and dust aerosols over Lahore. The Derivative of Angstrom Exponent (DAE) was derived at a wavelength of 500 nm and was found to indicate a predominance of fine aerosols across all seasons, particularly during summer and autumn seasons. Back-trajectory analyses using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model revealed that the major air masses over Lahore originated from India, Iran and Afghanistan.
2021
Improvements in air quality and Earth's climate predictions require improvements of the aerosol speciation in chemical transport models, using observational constraints. Aerosol speciation (e.g., organic aerosols, black carbon, sulfate, nitrate, ammonium, dust or sea salt) is typically determined using in situ instrumentation. Continuous, routine aerosol composition measurements from ground-based networks are not uniformly widespread over the globe. Satellites, on the other hand, can provide a maximum coverage of the horizontal and vertical atmosphere but observe aerosol optical properties (and not aerosol speciation) based on remote sensing instrumentation. Combinations of satellite-derived aerosol optical properties can inform on air mass aerosol types (AMTs). However, these AMTs are subjectively defined, might often be misclassified and are hard to relate to the critical parameters that need to be refined in models. In this paper, we derive AMTs that are more directly related to sources and hence to speciation. They are defined, characterized and derived using simultaneous in situ gas-phase, chemical and optical instruments on the same aircraft during the Study of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC 4 RS, an airborne field campaign carried out over the US during the summer of 2013). We find distinct optical signatures for AMTs such as biomass burning (from agricultural or wildfires), biogenic and polluted dust. We find that all four AMTs, studied when prescribed using mostly airborne in situ gas measurements, can be successfully extracted from a few combinations of airborne in situ aerosol optical properties (e.g., extinction Ångström exponent, absorption Ångström exponent and real refractive index). However, we Published by Copernicus Publications on behalf of the European Geosciences Union. 3714 M. S. F. Kacenelenbogen et al.: Bridging aerosol chemistry and physics find that the optically based classifications for biomass burning from agricultural fires and polluted dust include a large percentage of misclassifications that limit the usefulness of results related to those classes. The technique and results presented in this study are suitable to develop a representative, robust and diverse source-based AMT database. This database could then be used for widespread retrievals of AMTs using existing and future remote sensing suborbital instruments/networks. Ultimately, it has the potential to provide a much broader observational aerosol dataset to evaluate chemical transport and air quality models than is currently available by direct in situ measurements. This study illustrates how essential it is to explore existing airborne datasets to bridge chemical and optical signatures of different AMTs, before the implementation of future spaceborne missions (e.g., the next generation of Earth Observing System (EOS) satellites addressing Aerosols, Cloud, Convection and Precipitation (ACCP) designated observables).
Aerosol and Air Quality Research
Atmospheric aerosol characterization experiments were conducted, for the first time, over AC-Ahmednagar, a semi-urban location in southwest India, using a multi-spectral solar radiometer from January 2016 to May 2018. The MODIS/Terra retrieved Level-2 daily swath AOD550 nm data sets during 2011-2021 were also used to infer long-term behaviour of columnar aerosols at AC-Ahmednagar. The daily-averaged, Microtops II Sun photometer measured AOD500 nm and AOD1020 nm and MODIS retrieved AOD550 nm reveal a discernible wide spectrum of variability in their magnitudes. Magnitude-wise, AODs at both the wavelengths depict an increasing trend of about 0.05 year-1 (AOD500 nm) and 0.03 year-1 (AOD1020 nm). However, MODIS AOD550 nm illustrates statistically insignificant increasing trend of about 0.007 year-1. Microtops II Sun photometer derived Angstrom exponent (AE) depicts a noticeable day-today variability with respect to its overall mean value (1.06 ± 0.30) indicating the presence of diverse-sized aerosols. The AOD500 nm against AE440-870 nm contour density map analysis qualitatively characterizes different aerosol types prevalent in the atmospheric column. The weighted PSCF (WPSCF)
One-year measurements (October 2016-September 2017) of aerosol optical properties in the Athens urban environment were analyzed; for closure purposes, the results were supported by data of chemical composition of the non-refractory submicron aerosol fraction acquired with an Aerosol Chemical Speciation Monitor (ACSM). Both the spectral scattering (b sca) and absorption (b abs) coefficients exhibit a pronounced annual variability with higher values (63.6 Mm-1 at 550 nm and 41.0 Mm-1 at 520 nm, respectively) in winter, due to domestic heating releasing increased carbonaceous emissions and the shallow mixing layer trapping aerosols near the surface. Much lower values (33.5 Mm-1 and 22.9 Mm-1 for b sca and b abs , respectively) are found during summer, indicating rather aged aerosols from regional sources. The estimations of the dry spectral single scattering albedo (SSA), scattering (SAE) and absorption (AAE) Ångström exponents focus on the seasonality of the urban aerosols. The high SAE (~2.0) and low SSA (0.62 ± 0.11) values throughout the year indicate the dominance of fine-absorbing aerosols from fossil-fuel combustion, while the high AAE (~1.5) in winter suggests enhanced presence of biomass-burning aerosols. Pronounced morning and late evening/night peaks are found in both b sca and b abs during winter, coinciding with the morning traffic rush hour and increased residential wood burning in the evening, while in the other seasons, the diurnal patterns flatten out. The wind speed strongly affects the aerosol loading and properties in winter, since for winds below 3 m s-1 , a high increase in b sca and b abs is observed, consistent with low dilution processes and hazy/smoggy conditions. Our closure experiments indicate a good agreement (R 2 = 0.91, slope = 1.08) between the reconstructed and measured b sca values and reveal that organic matter contributes about half of the sub-micron mass in winter, followed by sulfate (~40%) and nitrate (10%, only in winter) aerosols.
Journal of the …, 2002
Aerosol radiative forcing is a critical, though variable and uncertain, component of the global climate. Yet climate models rely on sparse information of the aerosol optical properties. In situ measurements, though important in many respects, seldom provide measurements of the undisturbed aerosol in the entire atmospheric column. Here, 8 yr of worldwide distributed data from the AERONET network of ground-based radiometers were used to remotely sense the aerosol absorption and other optical properties in several key locations. Established procedures for maintaining and calibrating the global network of radiometers, cloud screening, and inversion techniques allow for a consistent retrieval of the optical properties of aerosol in locations with varying emission sources and conditions. The multiyear, multi-instrument observations show robust differentiation in both the magnitude and spectral dependence of the absorption-a property driving aerosol climate forcing, for desert dust, biomass burning, urban-industrial, and marine aerosols. Moreover, significant variability of the absorption for the same aerosol type appearing due to different meteorological and source characteristics as well as different emission characteristics are observed. It is expected that this aerosol characterization will help refine aerosol optical models and reduce uncertainties in satellite observations of the global aerosol and in modeling aerosol impacts on climate.
Temporal Variation of Aerosol Optical Properties at Măgurele, Romania
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 Å ngströ m parameter, and the aerosol optical depth from Ma˘gurele (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 Å ngströ m exponent were observed. The size-increase tendency, over 1 mm, 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 Ma˘gurele area showed visible differences between the maximal and minimal values for the spring and summer seasons.
Aerosol climatology: on the discrimination of aerosol types over four AERONET sites
Aerosols have a significant regional and global effect on climate, which is about equal in magnitude but opposite in sign to that of greenhouse gases. Nevertheless, the aerosol climatic effect changes strongly with space and time because of the large variability of aerosol physical and optical properties, which is due to the variety of their 5 sources, which are natural, and anthropogenic, and their dependence on the prevailing meteorological and atmospheric conditions. Characterization of aerosol properties is of major importance for the assessment of their role for climate. In the present study, 3-year AErosol RObotic NETwork (AERONET) data from ground-based sunphotometer measurements are used to establish climatologies of aerosol optical depth (AOD) 10 andÅngström exponent α in several key locations of the world, characteristic of different atmospheric environments. Using daily mean values of AOD at 500 nm (AOD 500 ) andÅngström exponent at the pair of wavelengths 440 and 870 nm (α 440−870 ), a discrimination of the different aerosol types occurring in each location is achieved. For this discrimination, appropriate thresholds for AOD 500 and α 440−870 are applied. The 15 discrimination of aerosol types in each location is made on an annual and seasonal basis. It is shown that a single aerosol type in a given location can exist only under specific conditions (e.g. intense forest fires or dust outbreaks), while the presence of well-mixed aerosols is the accustomed situation. Background clean aerosol conditions (AOD 500 <0.06) are mostly found over remote oceanic surfaces occurring on average 20 in ∼56.7% of total cases, while this situation is quite rare over land (occurrence of 3.8-13.7%). Our analysis indicates that these percentages change significantly from season to season. The spectral dependence of AOD exhibits large differences between the examined locations, while it exhibits a strong annual cycle.
Spectra Aerosol Light Scattering and Absorption for Laboratory and Urban Aerosol
Atmospheric aerosols considerably influence the climate, reduce visibility, and cause problems in human health. Aerosol light absorption and scattering are the important factors in the radiation transfer models. However, these properties are associated with large uncertainties in climate modeling. In addition, atmospheric aerosols widely vary in composition and size; their optical properties are highly wavelength dependent. This work presents the spectral dependence of aerosol light absorption and scattering throughout the ultraviolet to near-infrared regions. Data were collected in Reno, NV from 2008 to 2010. Also presented in this study are the aerosol optical and physical properties during carbonaceous aerosols and radiative effects study (CARES) conducted in Sacramento area during 2010. Measurements were made using photoacoustic instruments (PA), including a novel UV 355 nm PA of our design and manufacture. Comparative analyses are presented for three main categories: (1) aerosols produced by wildfires and traffic emissions, (2) laboratory-generated and wintertime ambient urban aerosols, and (3) urban plume and biogenic emissions. In these categories, key questions regarding the light absorption by secondary organic aerosols (SOA), so-called brown carbon (BrC), and black carbon (BC) will be discussed. An effort is made to model the emission and aging of urban and biomass burning aerosol by applying shell-core calculations. Multispectral PA measurements of aerosols light absorption and scattering coefficients were used to calculate the Ångström exponent of absorption (AEA) and single scattering albedo (SSA). The AEA and SSA values were analyzed to differentiate the aerosol sources. The California wildfire aerosols exhibited strong wavelength dependence of Glossary of Acronyms (in order of appearance) PA-Photoacoustic instrument SOA-Secondary organic aerosol BrC-Brown carbon BC-Black carbon AEA-Angström exponent of absorption SSA-Single scattering albedo OA-Organic aerosol POA-Primary organic aerosol CARES-Carbonaceous aerosol and radiative effects study SMPS-Scanning mobility particle sizer HR-AMS-High resolution aerosol mass spectrometer ASL-Above sea level UV-Ultraviolet VIS-Visible IR-Infrared LAOC-Light absorbing organic carbon ALAOC-Apparent light absorbing organic carbon NSF-National Science Foundation DOE-Department of energy ASP-Atmospheric science program xiv PM 2.5-Particulate matter with aerodynamic diameters less than 2.5 µm PM 10-Particulate matter with aerodynamic diameters less than 10 µm SOA-Secondary organic aerosol RI-Refractive index Nd:YAG-Neodymium-doped yttrium aluminum garnet PMT-Photomultiplier tube AES-Angström exponent of scattering AESSA-Angström exponent of single scattering albedo BAM-Beta attenuation monitor FRM-Federal reference method CE-Combustion efficiency LT-Local time BL-Boundary layer AEE-Angström exponent of extinction CRD-Cavity ring down PM 1-Particulate matter with aerodynamic diameters less than 1 µm Site T0-American River College campus Site T1-Northside School campus in Cool NW-Northwest DMA-Differential mobility analyzer CPC-Condensation particle counter SW-Southwest xv VOC-Volatile organic carbon OOA-Oxygenated organic aerosol HOA-Hydrogenated organic aerosol APS-Aerosol particle sizer