scholarly journals Absorbing aerosols at high relative humidity: linking hygroscopic growth to optical properties

2012 ◽  
Vol 12 (12) ◽  
pp. 5511-5521 ◽  
Author(s):  
J. Michel Flores ◽  
R. Z. Bar-Or ◽  
N. Bluvshtein ◽  
A. Abo-Riziq ◽  
A. Kostinski ◽  
...  
Keyword(s):  
Optical Properties ◽  
Growth Factors ◽  
Relative Humidity ◽  
Atmospheric Chemistry ◽  
Theoretical Calculations ◽  
Complex Refractive Index ◽  
High Relative Humidity ◽  
Mixing Rule ◽  
Hygroscopic Growth ◽  
Absorbing Aerosols

Abstract. One of the major uncertainties in the understanding of Earth's climate system is the interaction between solar radiation and aerosols in the atmosphere. Aerosols exposed to high humidity will change their chemical, physical, and optical properties due to their increased water content. To model hydrated aerosols, atmospheric chemistry and climate models often use the volume weighted mixing rule to predict the complex refractive index (RI) of aerosols when they interact with high relative humidity, and, in general, assume homogeneous mixing. This study explores the validity of these assumptions. A humidified cavity ring down aerosol spectrometer (CRD-AS) and a tandem hygroscopic DMA (differential mobility analyzer) are used to measure the extinction coefficient and hygroscopic growth factors of humidified aerosols, respectively. The measurements are performed at 80% and 90%RH at wavelengths of 532 nm and 355 nm using size-selected aerosols with different degrees of absorption; from purely scattering to highly absorbing particles. The ratio of the humidified to the dry extinction coefficients (fRHext(%RH, Dry)) is measured and compared to theoretical calculations based on Mie theory. Using the measured hygroscopic growth factors and assuming homogeneous mixing, the expected RIs using the volume weighted mixing rule are compared to the RIs derived from the extinction measurements. We found a weak linear dependence or no dependence of fRH(%RH, Dry) with size for hydrated absorbing aerosols in contrast to the non-monotonically decreasing behavior with size for purely scattering aerosols. No discernible difference could be made between the two wavelengths used. Less than 7% differences were found between the real parts of the complex refractive indices derived and those calculated using the volume weighted mixing rule, and the imaginary parts had up to a 20% difference. However, for substances with growth factor less than 1.15 the volume weighted mixing rule assumption needs to be taken with caution as the imaginary part of the complex RI can be underestimated.

scholarly journals COMPARISON BETWEEN KELVIN RADII AND BULK HYGROSCOPICITY OF MASS AND VOLUME BASED HYGROSCOPICITY PARAMETER FOR ATMOSPHERIC AEROSOLS

2020 ◽  
Vol 4 (2) ◽  
pp. 337-349
Author(s):  
Bello Saadu ◽  
B. I. Tijjani ◽  
S. Bello
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Regression Analysis ◽  
Growth Factors ◽  
Relative Humidity ◽  
Multiple Regression Analysis ◽  
Atmospheric Aerosols ◽  
Atmospheric Modeling ◽  
Hygroscopic Growth ◽  
Microphysical Properties

A mass based and volume based hygroscopicities models were applied to the data extracted from Optical Properties of Aerosols and Clouds (OPAC).The microphysical properties obtained were radii, density, refractive index, mass and volume of the atmospheric aerosols of continental average, continental clean, continental polluted, maritime tropical, maritime polluted, maritime clean, at eight different relative humidity of 0%, 50%, 70%, 80%, 90%, 95%, 98% and 99%.Using the microphysical properties, hygroscopic growth factors and effective radii of the mixtures were determined while the parameters Av and Bv for volume based and Am and Bm for mass based of the aerosols were determined using multiple regression analysis with SPSS 16.0 at each relative humidity. Although it was discovered that Bv is more dominant than Av, the R2 for all the models are greater than 90%. The significances are less than 0.05, Am>Av and Bm<Bv, therefore the two models are good for atmospheric modeling.

scholarly journals Sensitivity of aerosol radiative effects to different mixing assumptions in the AEROPT 1.0 submodel of the EMAC atmospheric-chemistry–climate model

2014 ◽  
Vol 7 (5) ◽  
pp. 2503-2516 ◽  
Author(s):  
K. Klingmüller ◽  
B. Steil ◽  
C. Brühl ◽  
H. Tost ◽  
J. Lelieveld
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Black Carbon ◽  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
Climate Model ◽  
Mixing Rule ◽  
Aerosol Optical Properties ◽  
Internal Mixing ◽  
Aerosol Radiative

Abstract. The modelling of aerosol radiative forcing is a major cause of uncertainty in the assessment of global and regional atmospheric energy budgets and climate change. One reason is the strong dependence of the aerosol optical properties on the mixing state of aerosol components, such as absorbing black carbon and, predominantly scattering sulfates. Using a new column version of the aerosol optical properties and radiative-transfer code of the ECHAM/MESSy atmospheric-chemistry–climate model (EMAC), we study the radiative transfer applying various mixing states. The aerosol optics code builds on the AEROPT (AERosol OPTical properties) submodel, which assumes homogeneous internal mixing utilising the volume average refractive index mixing rule. We have extended the submodel to additionally account for external mixing, partial external mixing and multilayered particles. Furthermore, we have implemented the volume average dielectric constant and Maxwell Garnett mixing rule. We performed regional case studies considering columns over China, India and Africa, corroborating much stronger absorption by internal than external mixtures. Well-mixed aerosol is a good approximation for particles with a black-carbon core, whereas particles with black carbon at the surface absorb significantly less. Based on a model simulation for the year 2005, we calculate that the global aerosol direct radiative forcing for homogeneous internal mixing differs from that for external mixing by about 0.5 W m−2.

scholarly journals Optical particle counter measurement of marine aerosol hygroscopic growth

2007 ◽  
Vol 7 (4) ◽  
pp. 12381-12415 ◽  
Author(s):  
J. R. Snider ◽  
M. D. Petters
Keyword(s):  
Growth Factors ◽  
Relative Humidity ◽  
Scattered Light ◽  
Particle Diameter ◽  
Mie Scattering ◽  
Size Spectrum ◽  
Hygroscopic Growth ◽  
Marine Stratocumulus ◽  
Ambient Relative Humidity ◽  
Light Scattering Detection

Abstract. A technique is developed for the determination of the hygroscopic growth factor of dry particles with diameter between 0.3 and 0.6 µm and is applied to measurements made during the second Dynamics and Chemistry of Marine Stratocumulus experiment. Two optical particle counters are utilized, one measures the aerosol size spectrum at ambient relative humidity and the other simultaneously dries the aerosol prior to light scattering detection. Growth factors are based on measurements made in the region of the Mie scattering curve where scattered light intensity increases monotonically with dry and wet particle diameter, i.e. D<0.9 µm. Factors influencing the accuracy of the measurement are evaluated, including particle drying, refractive index and shape. Growth factors at 90±3% ambient relative humidity in marine airmasses 400 km west of San Diego, California range between 1.5 and 1.8. This suggests that a significant fraction of the particle mass, between 40 and 70%, is either non-hygroscopic or weakly hygroscopic.

scholarly journals Single particle analysis of amines in ambient aerosol in Shanghai

2012 ◽  
Vol 9 (3) ◽  
pp. 202 ◽  
Author(s):  
Yuanlong Huang ◽  
Hong Chen ◽  
Lin Wang ◽  
Xin Yang ◽  
Jianmin Chen
Keyword(s):  
Relative Humidity ◽  
Atmospheric Chemistry ◽  
Single Particle ◽  
Reaction Pathway ◽  
Mass Spectrometric ◽  
High Relative Humidity ◽  
Particle Analysis ◽  
Organic Mass ◽  
High Concentration ◽  
Acid Base

Environmental contextAmines, a group of basic organic compounds, play important roles in atmospheric chemistry. We studied their distribution in ambient aerosols at the single particle level, and found that high relative humidity and strong particle acidity can attract more amines from the gas phase to particles. Amines may account for a significant part of organic mass in aerosols in areas with high emissions of sulfur dioxide and nitrogen oxides. AbstractAn aerosol time-of-flight mass spectrometer was deployed in urban Shanghai to analyse amine-containing particles during two separate sampling periods, 1–9 August 2007 and 22–27 December 2009. Amine-containing particles are identified by a mass spectrometric marker at m/z 86 [NCH2(C2H5)2+] and classified into six major particle types to explore their possible origins. The number fraction of amine-containing particles in winter was much higher than in summer (23.4 v. 4.4 %), which can be explained by preferred gas-to-particle partitioning of gaseous amines at lower temperatures. Mass spectrometric patterns show the strong acidity of particles collected in December 2009, suggesting the acid–base reaction pathway might also contribute to the high concentration of amine aerosol in winter. Two fog episodes and two after-rain episodes of amine-containing particle bursts were observed in August 2007. Tightly correlated number fractions of sulfate- and amine-containing particles in all these episodes reveal that high relative humidity greatly enhances particulate amine formation based on acid–base reaction and subsequent particle growth. Our observations suggest that amines may account for significant parts of secondary organic mass in heavily polluted areas.

scholarly journals Sensitivity of aerosol extinction to new mixing rules in the AEROPT submodel of the ECHAM5/MESSy1.9 atmospheric chemistry (EMAC) model

2014 ◽  
Vol 7 (3) ◽  
pp. 3367-3402
Author(s):  
K. Klingmüller ◽  
B. Steil ◽  
C. Brühl ◽  
H. Tost ◽  
J. Lelieveld
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Black Carbon ◽  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
Strong Dependence ◽  
Mixing Rule ◽  
Aerosol Optical Properties ◽  
Volume Average ◽  
Internal Mixing

Abstract. The modelling of aerosol radiative forcing is a major cause of uncertainty in the assessment of global and regional atmospheric energy budgets and climate change. One reason is the strong dependence of the aerosol optical properties on the mixing state of aerosol components like black carbon and sulphates. Using a new column version of the aerosol optical properties and radiative transfer code of the atmospheric chemistry-climate model EMAC, we study the radiative transfer applying various mixing states. The aerosol optics code builds on the AEROPT submodel which assumes homogeneous internal mixing utilising the volume average refractive index mixing rule. We have extended the submodel to additionally account for external mixing, partial external mixing and multi-layered particles. Furthermore, we have implemented the volume average dielectric-constant and Maxwell Garnett Mixing rule. We performed regional case studies considering columns over China, India and Africa, corroborating much stronger absorption by internal than external mixtures. Well mixed aerosol is a good approximation for particles with a black carbon core, whereas particles with black carbon at the surface absorb significantly less. Based on a model simulation for the year 2005 we calculate that the global aerosol direct radiative-forcing for homogeneous internal mixing differs from that for external mixing by about 0.5 W m−2.

Surface Organic Monolayers Control the Hygroscopic Growth of Submicrometer Particles at High Relative Humidity

2014 ◽  
Vol 118 (22) ◽  
pp. 3952-3966 ◽  
Author(s):  
Christopher R. Ruehl ◽  
Kevin R. Wilson
Keyword(s):  
Relative Humidity ◽  
High Relative Humidity ◽  
Hygroscopic Growth ◽  
Organic Monolayers

scholarly journals New representation of water activity based on a single solute specific constant to parameterize the hygroscopic growth of aerosols in atmospheric models

2012 ◽  
Vol 12 (12) ◽  
pp. 5429-5446 ◽  
Author(s):  
S. Metzger ◽  
B. Steil ◽  
L. Xu ◽  
J. E. Penner ◽  
J. Lelieveld
Keyword(s):  
Relative Humidity ◽  
Water Activity ◽  
Atmospheric Chemistry ◽  
Reference Model ◽  
Climate Modeling ◽  
Cloud Condensation Nuclei ◽  
Hygroscopic Growth ◽  
Wide Range ◽  
Kohler Theory ◽  
Key Factor

Abstract. Water activity is a key factor in aerosol thermodynamics and hygroscopic growth. We introduce a new representation of water activity (aw), which is empirically related to the solute molality (μs) through a single solute specific constant, νi. Our approach is widely applicable, considers the Kelvin effect and covers ideal solutions at high relative humidity (RH), including cloud condensation nuclei (CCN) activation. It also encompasses concentrated solutions with high ionic strength at low RH such as the relative humidity of deliquescence (RHD). The constant νi can thus be used to parameterize the aerosol hygroscopic growth over a wide range of particle sizes, from nanometer nucleation mode to micrometer coarse mode particles. In contrast to other aw-representations, our νi factor corrects the solute molality both linearly and in exponent form x · ax. We present four representations of our basic aw-parameterization at different levels of complexity for different aw-ranges, e.g. up to 0.95, 0.98 or 1. νi is constant over the selected aw-range, and in its most comprehensive form, the parameterization describes the entire aw range (0–1). In this work we focus on single solute solutions. νi can be pre-determined with a root-finding method from our water activity representation using an aw−μs data pair, e.g. at solute saturation using RHD and solubility measurements. Our aw and supersaturation (Köhler-theory) results compare well with the thermodynamic reference model E-AIM for the key compounds NaCl and (NH4)2SO4 relevant for CCN modeling and calibration studies. Envisaged applications include regional and global atmospheric chemistry and climate modeling.

scholarly journals Effects of SO<sub>2</sub> on optical properties of secondary organic aerosol generated from photooxidation of toluene under different relative humidity

2019 ◽  
Author(s):  
Wenyu Zhang ◽  
Weigang Wang ◽  
Junling Li ◽  
Chao Peng ◽  
Kun Li ◽  
...  
Keyword(s):  
Climate Change ◽  
Optical Properties ◽  
Relative Humidity ◽  
Secondary Organic Aerosol ◽  
Complex Refractive Index ◽  
Organic Aerosol ◽  
Conjugated Oligomers ◽  
Atmospheric Conditions ◽  
Multiphase Reaction ◽  
532 Nm

Abstract. Secondary organic aerosol (SOA) have great impacts on air quality, climate change and human health. The composition and physicochemical properties of SOA differ a lot for they originated under different atmospheric conditions and from various precursors and oxidations. In this work, photooxidation experiments of toluene were performed under four conditions (dry, dry with SO2, wet, and wet with SO2) to investigate the effect of SO2 under different relative humidity on the composition and optical properties of SOA at the wavelength of 375 nm and 532 nm. According to our results, the increase of humidity enhances not only light absorption, but also scattering property of SOA. Highly conjugated oligomers formed through multiphase reaction might be the reasons of this phenomenon. Adding SO2 slightly lower the real part of complex refractive index (n) of SOA: ndry, SO2 

scholarly journals The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southern West Africa

2019 ◽  
Vol 19 (3) ◽  
pp. 1505-1520 ◽  
Author(s):  
Sophie L. Haslett ◽  
Jonathan W. Taylor ◽  
Konrad Deetz ◽  
Bernhard Vogel ◽  
Karmen Babić ◽  
...  
Keyword(s):  
Optical Properties ◽  
Chemical Composition ◽  
Relative Humidity ◽  
West Africa ◽  
Monsoon Season ◽  
Hygroscopic Growth ◽  
Aerosol Direct Effect ◽  
Humidity Measurements ◽  
Original Size ◽  
Solid Liquid

Abstract. Water in the atmosphere can exist in the solid, liquid or gas phase. At high humidities, if the aerosol population remains constant, more water vapour will condense onto the particles and cause them to swell, sometimes up to several times their original size. This significant change in size and chemical composition is termed hygroscopic growth and alters a particle's optical properties. Even in unsaturated conditions, this can change the aerosol direct effect, for example by increasing the extinction of incoming sunlight. This can have an impact on a region's energy balance and affect visibility. Here, aerosol and relative humidity measurements collected from aircraft and radiosondes during the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) campaign were used to estimate the effect of highly humid layers of air on aerosol optical properties during the monsoon season in southern West Africa. The effects of hygroscopic growth in this region are of particular interest due to the regular occurrence of high humidity and the high levels of pollution in the region. The Zdanovskii, Stokes and Robinson (ZSR) mixing rule is used to estimate the hygroscopic growth of particles under different conditions based on chemical composition. These results are used to estimate the aerosol optical depth (AOD) at λ=525 nm for 63 relative humidity profiles. The median AOD in the region from these calculations was 0.36, the same as that measured by sun photometers at the ground site. The spread in the calculated AODs was less than the spread from the sun photometer measurements. In both cases, values above 0.5 were seen predominantly in the mornings and corresponded with high humidities. Observations of modest variations in aerosol load and composition are unable to explain the high and variable AODs observed using sun photometers, which can only be recreated by accounting for the very elevated and variable relative humidities (RHs) in the boundary layer. Most importantly, the highest AODs present in the mornings are not possible without the presence of high RH in excess of 95 %. Humid layers are found to have the most significant impact on AOD when they reach RH greater than 98 %, which can result in a wet AOD more than 1.8 times the dry AOD. Unsaturated humid layers were found to reach these high levels of RH in 37 % of observed cases. It can therefore be concluded that the high AODs present across the region are driven by the high humidities and are then moderated by changes in aerosol abundance. Aerosol concentrations in southern West Africa are projected to increase substantially in the coming years; results presented here show that the presence of highly humid layers in the region is likely to enhance the consequent effect on AOD significantly.

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