scholarly journals A new parameterization scheme of the real part of the ambient aerosols refractive index

2019 ◽  
Author(s):  
Gang Zhao ◽  
Tianyi Tan ◽  
Weilun Zhao ◽  
Song Guo ◽  
Ping Tian ◽  
...  
Keyword(s):  
Refractive Index ◽  
Radiative Forcing ◽  
Field Measurements ◽  
Effective Density ◽  
Parameterization Scheme ◽  
Chemical Components ◽  
Ambient Aerosols ◽  
Ambient Aerosol ◽  
The Real ◽  
Aerosol Radiative

Abstract. The refractive index of ambient aerosols, which directly determines the aerosol optical properties, is widely used in atmospheric models and remote sensing. Traditionally, the real part of the refractive index (RRI) is mainly parameterized by the measurement of ambient aerosol main inorganic components. In this paper, the characteristics of the ambient aerosol RRI are studied based on the field measurement in the East China. Results show that the ambient aerosol RRI varies significantly between 1.36 and 1.56. The direct aerosol radiative forcing is estimated to vary by 40 % corresponding to the variation of the measured aerosol RRI. We find that the ambient aerosol RRI is highly related with the aerosol effective density (ρeff) rather than the main chemical components. However, parameterization schemes of the ambient aerosol RRI by ρeff are not available due to the lack of corresponding simultaneous field measurements. For the first time, the size-resolved ambient aerosol RRI and ρeff are measured simultaneously by our designed measurement system. A new parameterization scheme of the ambient aerosols RRI using ρeff is proposed. The measured and parameterized RRI agree well with the correlation coefficient of 0.76. Knowledge of the ambient aerosol RRI would improve our understanding of the ambient aerosol radiative effects.

scholarly journals A new parameterization scheme for the real part of the ambient urban aerosol refractive index

2019 ◽  
Vol 19 (20) ◽  
pp. 12875-12885 ◽  
Author(s):  
Gang Zhao ◽  
Tianyi Tan ◽  
Weilun Zhao ◽  
Song Guo ◽  
Ping Tian ◽  
...  
Keyword(s):  
Refractive Index ◽  
Radiative Forcing ◽  
Field Measurements ◽  
Urban Environments ◽  
Effective Density ◽  
Parameterization Scheme ◽  
Chemical Components ◽  
Ambient Aerosol ◽  
The Real ◽  
Aerosol Radiative

Abstract. The refractive index of ambient aerosols, which directly determines the aerosol optical properties, is widely used in atmospheric models and remote sensing. Traditionally, the real part of the refractive index (RRI) is parameterized by the measurement of ambient aerosol main inorganic components. In this paper, the characteristics of the ambient aerosol RRI are studied based on field measurements in East China. The results show that the measured ambient aerosol RRI varies significantly between 1.36 and 1.56. The direct aerosol radiative forcing is estimated to vary by 40 % when the RRI values were varied between 1.36 and 1.56. We find that the ambient aerosol RRI is highly correlated with the aerosol effective density (ρeff) rather than the main chemical components. However, the parameterization of the ambient aerosol RRI by ρeff is not available due to the lack of corresponding simultaneous field measurements. For the first time, the size-resolved ambient aerosol RRI and ρeff are measured simultaneously by our designed measurement system. A new parameterization scheme for the ambient aerosol RRI using ρeff is proposed for urban environments. The measured and parameterized RRI values agree well, with a correlation coefficient of 0.75 and slope of 0.99. Knowledge of the ambient aerosol RRI would improve our understanding of ambient aerosol radiative effects.

scholarly journals Method to measure the size-resolved real part of aerosol refractive index using differential mobility analyzer in tandem with single-particle soot photometer

2019 ◽  
Vol 12 (7) ◽  
pp. 3541-3550 ◽  
Author(s):  
Gang Zhao ◽  
Weilun Zhao ◽  
Chunsheng Zhao
Keyword(s):  
Refractive Index ◽  
Single Particle ◽  
Radiative Forcing ◽  
Differential Mobility ◽  
Ambient Aerosols ◽  
Aerosol Radiative Forcing ◽  
Abstract Knowledge ◽  
Wide Range ◽  
Aerosol Radiative Effects ◽  
Aerosol Radiative

Abstract. Knowledge on the refractive index of ambient aerosols can help reduce the uncertainties in estimating aerosol radiative forcing. A new method is proposed to retrieve the size-resolved real part of the refractive index (RRI). The main principle of deriving the RRI is measuring the scattering intensity by a single-particle soot photometer (SP2) of size-selected aerosols. This method is validated by a series of calibration experiments using the components of the known RRI. The retrieved size-resolved RRI covers a wide range, from 200 to 450 nm, with uncertainty of less than 0.02. Measurements of the size-resolved RRI can improve the understanding of the aerosol radiative effects.

Spatial and temporal heterogeneity in aerosol radiative effects over ecological area in south China: Composition and transmission implications

2020 ◽  
Author(s):  
Ma Yining ◽  
Xin Jinyuan
Keyword(s):  
Organic Carbon ◽  
Radiative Forcing ◽  
Dry Season ◽  
Water Soluble ◽  
Chemical Components ◽  
Radiative Effects ◽  
Wet Season ◽  
Cooling Effects ◽  
Ecological Region ◽  
Aerosol Radiative

<p><strong>Abstract:</strong> Ecological region in southern China has been perennially affected by monsoon climate and anthropogenic emissions, resulting in complex aerosol components and frequent long-range transport. In this study, a Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model is applied to estimate aerosol radiative forcing (ARF) and multiple aerosol observation datasets is used to estimate the aerosol chemical components and optical properties. The aerosol loading and the radiative effects in the ecological region exhibited strong seasonal changes. The average major components (NH<sub>4</sub><sup>+</sup>, NO<sub>3</sub><sup>−</sup>, SO<sub>4</sub><sup>2−</sup>) in Total water soluble ionic (TWSI) ,organic carbon (OC) concentration, the ratio of organic carbon to element carbon (OC/EC) and biogenic secondary organic aerosol (BSOA) tracers were 3.20±1.22 μg·m<sup>-3</sup>, 2.19±1.39 μg·m<sup>-3</sup>, 3.17 and 74.00±35.23 ng·m<sup>-3 </sup>in the dry season and 2.22±0.91 μg·m<sup>-3</sup>, 3.14±1.62 μg·m<sup>-3</sup>, 7.13 and 186.34±113.82 ng·m<sup>-3</sup> in the wet season, respectively. The average radiative forcing at the top of atmosphere (TOA) is -11.73±11.36 W/m<sup>2</sup> and -0.41±10.08 W/m<sup>2</sup> in dry and wet season. When the aerosol single scattering albedo (SSA) less than 0.9, the retrieve frequency in wet season reached account for 75%. The increase of OC and BSOA transformed by forests in the wet season weaken the cooling effects. However, the dry season is mainly composed of anthropogenic inorganic aerosols, which enhances the scattering effect. The aerosol observation baseline also verified the seasonal variation of ARF in the ecological region. Driven by multiple factors such as meteorological conditions, emission sources, and the mixed state of particulate matter, the transport patterns of air masses in ecological area exhibits completely opposite affects to ARF.</p>

scholarly journals Role of black carbons mass size distribution in the direct aerosol radiative forcing

2019 ◽  
Author(s):  
Gang Zhao ◽  
Jiangchuan Tao ◽  
Ye Kuang ◽  
Chuanyang Shen ◽  
Yingli Yu ◽  
...  
Keyword(s):  
Size Distribution ◽  
Radiative Forcing ◽  
Climate Models ◽  
Field Measurements ◽  
Radiative Effects ◽  
Aerosol Radiative Forcing ◽  
Mass Size Distribution ◽  
Mass Size ◽  
Mixing States ◽  
Aerosol Radiative

Abstract. Large uncertainties exist when estimating radiative effects of ambient black carbon (BC) aerosol. Previous studies about the BC aerosol radiative forcing mainly focus on the BC aerosols’ mass concentrations and mixing states, while the effects of BC mass size distribution (BCMSD) were not well considered. In this paper, we developed a method by measuring the BCMSD by using a differential mobility analyzer in tandem with an aethalometer. A comprehensive method of multiple charging corrections is proposed and implemented in measuring the BCMSD. Good agreement is obtained between the BC mass concentration integrated from this system and that measured in bulk phase, demonstrating the reliability of our proposed method. Characteristics of the BCMSD and corresponding radiative effects are studied based on field measurements conducted in the North China Plain by using our own designed measurement system. Results show that the BCMSD have two modes and the mean peak diameters of the two modes are 150 nm and 503 nm respectively. The BCMSD of coarser mode varies significantly under different pollution conditions with peak diameter varying between 430 nm and 580 nm, which gives rise to significant variation in aerosol buck optical properties. The aerosol direct aerosol radiative forcing is estimated to vary by 22.5 % for different measured BCMSDs, which shares the same magnitude to the variation associated with assuming different aerosol mixing states (21.5 %). Our study reveals that the BCMSD matters as well as their mixing state in estimating the direct aerosol radiative forcing. Knowledge of the BCMSD should be fully considered in climate models.

Composition Dependence of Stratospheric Aerosol Radiative Forcing

2021 ◽  
Author(s):  
Yaowei Li ◽  
John Dykema ◽  
Frank Keutsch
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Radiative Forcing ◽  
Complex Refractive Index ◽  
Stratospheric Aerosol ◽  
Organic Component ◽  
Aerosol Optical Properties ◽  
Aerosol Radiative Forcing ◽  
Aerosol Radiative

<p>Model results suggest organic aerosol represents a significant fraction of total stratospheric aerosol radiative forcing, which in itself could represent as much as a quarter of global radiative forcing. Other model investigations suggest that the radiative influence of organic aerosols and dust must be included to obtain consistency with satellite measurements of stratospheric aerosols. <em>In situ</em> observations suggest that stratospheric aerosol composition is strongly vertically dependent and contains a significant organic component in the lower stratosphere. Laboratory studies suggest a range of possible values for the complex refractive index of organic aerosols in the stratosphere. The real part of the refractive index could vary over a range that brackets the value of the real refractive index for pure sulfuric acid/water aerosols. The imaginary part of the refractive index of the organic component is highly uncertain, suggesting aerosols that range from being purely refractive to significantly absorbing (eg, brown carbon). The mixing state of these mixed composition aerosols is also uncertain; depending on the complex refractive index of the organic component, morphological variation could have a significant influence on aerosol radiative properties. In this work we perform a sensitivity study of shortwave radiative forcing of stratospheric aerosols, examining the influence of different plausible values of complex refractive index and particle morphologies. <em>In situ</em> measurements of aerosol size and composition are used to represent the size distribution, vertical profile, and organic mass fraction for the computation of aerosol optical properties. These profiles of aerosol optical properties are used as inputs to a radiative transfer model to calculate profiles of shortwave fluxes and radiative heating rates for standard model atmospheres. The implications of the variations in aerosol optical depth and resulting radiative forcing are interpreted in terms of implications for satellite measurements of stratospheric radiative forcing. The various radiative forcing results and remote sensing implications for different scenarios of organic complex refractive index and morphology call for better understandings of the effects of chemical evolution and transport dynamics on the aerosol optical properties in the stratosphere.</p>

Larger than expected variation range in the real part of the refractive index for ambient aerosols in China

2021 ◽  
Vol 779 ◽  
pp. 146443
Author(s):  
Gang Zhao ◽  
Min Hu ◽  
Xin Fang ◽  
Tianyi Tan ◽  
Yao Xiao ◽  
...  
Keyword(s):  
Refractive Index ◽  
Ambient Aerosols ◽  
The Real ◽  
Variation Range

scholarly journals Method to measure the size-resolved real part of aerosol refractive index

2018 ◽  
Author(s):  
Gang Zhao ◽  
Chunsheng Zhao ◽  
Weilun Zhao
Keyword(s):  
Refractive Index ◽  
Single Particle ◽  
Radiative Forcing ◽  
Main Principle ◽  
Scattering Intensity ◽  
Aerosol Radiative Forcing ◽  
Abstract Knowledge ◽  
Wide Range ◽  
Aerosol Radiative Effects ◽  
Aerosol Radiative

Abstract. Knowledge on the refractive index of ambient aerosol can help reduce the uncertainties in estimating aerosol radiative forcing. A new method is proposed to retrieve the size-resolved real part of RI (RRI). Main principle of deriving the RRI is measuring the scattering intensity by single particle soot photometer of size-selected aerosol. This method is validated by a series of calibration experiments using the components of known RI. The retrieved size-resolved RRI cover a wide range from 200nm to 450nm with uncertainty less than 0.02. Measurements of the size resolved real part of the aerosol refractive index can improve the understanding of the aerosol radiative effects.

scholarly journals Variability of the infrared complex refractive index of African mineral dust: experimental estimation and implications for radiative transfer and satellite remote sensing

2014 ◽  
Vol 14 (20) ◽  
pp. 11093-11116 ◽  
Author(s):  
C. Di Biagio ◽  
H. Boucher ◽  
S. Caquineau ◽  
S. Chevaillier ◽  
J. Cuesta ◽  
...  
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Radiative Transfer ◽  
Radiative Forcing ◽  
Mineral Dust ◽  
Complex Refractive Index ◽  
Mineralogical Composition ◽  
Asymmetry Factor ◽  
Large Variability ◽  
The Real

Abstract. Experimental estimations of the infrared refractive index of African mineral dust have been retrieved from laboratory measurements of particle transmission spectra in the wavelength range 2.5–25 μm. Five dust samples collected at Banizoumbou (Niger) and Tamanrasset (Algeria) during dust events originated from different Western Saharan and Sahelian areas have been investigated. The real (n) and imaginary (k) parts of the refractive index obtained for the different dust samples vary in the range 1.1–2.7 and 0.05–1.0, respectively, and are strongly sensitive to the mineralogical composition of the particles, especially in the 8–12 and 17–25 μm spectral intervals. Dust absorption is controlled mainly by clays (kaolinite, illite, smectite) and, to a lesser extent, by quartz and calcium-rich minerals (e.g. calcite, gypsum). Significant differences are obtained when comparing our results with existing experimental estimations available in the literature, and with the values of the OPAC (Optical Properties of Aerosols and Clouds) database. The different data sets appear comparable in magnitude, with our values of n and k falling within the range of variability of past studies. However, literature data fail in accurately reproducing the spectral signatures of the main minerals, in particular clays, and they significantly overestimate the contribution of quartz. Furthermore, the real and the imaginary parts of the refractive index from some literature studies are found not to verify the Kramers–Kronig relations, thus being theoretically incorrect. The comparison between our results, from western Africa, and literature data, from different locations in Europe, Africa, and the Caribbean, nonetheless, confirms the expected large variability of the dust infrared refractive index. This highlights the necessity for an extended systematic investigation of dust properties at infrared wavelengths. For the five analysed dust samples, aerosol intensive optical properties relevant to radiative transfer (mass extinction efficiency, kext, single scattering albedo, ω, and asymmetry factor, g) have been calculated, by using the Mie theory, based on the estimated refractive index and measured particle size distribution. The optical properties show a large sample-to-sample variability, with kext, ω, and g varying in the range 0.05–0.35, 0.25–1.0, and 0.05–0.75. This variability is expected to significantly impact satellite retrievals of atmospheric and surface parameters (e.g. from the Infrared Atmospheric Sounding Interferometer, IASI) and estimates of the dust radiative forcing.

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