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

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.

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

10.5194/amt-2018-399 ◽

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.

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

10.5194/acp-2019-250 ◽

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.

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Opportunistic Experiments to Constrain Aerosol Effective Radiative Forcing

10.5194/acp-2021-559 ◽

2021 ◽

Author(s):

Matthew Christensen ◽

Andrew Gettelman ◽

Jan Cermak ◽

Guy Dagan ◽

Michael Diamond ◽

...

Keyword(s):

Forest Fires ◽

Radiative Forcing ◽

Volcanic Eruptions ◽

Point Sources ◽

Natural Experiments ◽

Experimental Conditions ◽

Anthropogenic Aerosol ◽

Aerosol Radiative Forcing ◽

Wide Range ◽

Aerosol Radiative

Abstract. Aerosol-cloud interactions (ACI) are considered to be the most uncertain driver of present-day radiative forcing due to human activities. The non-linearity of cloud-state changes to aerosol perturbations make it challenging to attribute causality in observed relationships of aerosol radiative forcing. Using correlations to infer causality can also be challenging when meteorological variability also drives both aerosol and cloud changes independently. Natural and anthropogenic aerosol perturbations from well defined sources provide “opportunistic experiments” (also known as natural experiments) to investigate ACI in cases where causality may be more confidently inferred. These perturbations cover a wide range of locations and spatio-temporal scales, including point sources such as volcanic eruptions or industrial sources, plumes from biomass burning or forest fires, and tracks from individual ships or shipping corridors. We review the different experimental conditions and conduct a synthesis of the available satellite data sets and field campaigns to place these opportunistic experiments on a common footing, facilitating new insights and a clearer understanding of key uncertainties in aerosol radiative forcing. Strong liquid water path increases due to aerosol perturbations are largely ruled out by averaging across experiments. Cloud albedo perturbations are strongly sensitive to background meteorological conditions. Opportunistic experiments have significantly improved process level understanding of ACI, but it remains unclear how reliably the relationships found can be scaled to the global level, thus, demonstrating a need for deeper investigation in order to improve assessments of aerosol radiative forcing and climate change.

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Composition Dependence of Stratospheric Aerosol Radiative Forcing

10.5194/egusphere-egu21-13162 ◽

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

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. In situ 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. In situ 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.

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Origins of a relatively tight lower bound on anthropogenic aerosol radiative forcing from Bayesian analysis of historical observations

Journal of Climate ◽

10.1175/jcli-d-21-0167.1 ◽

2021 ◽

pp. 1-51

Author(s):

Anna Lea Albright ◽

Cristian Proistosescu ◽

Peter Huybers

Keyword(s):

Lower Bound ◽

Climate Sensitivity ◽

Radiative Forcing ◽

Credible Interval ◽

Ocean Heat Uptake ◽

Aerosol Radiative Forcing ◽

Joint Inference ◽

Aerosol Forcing ◽

Wide Range ◽

Aerosol Radiative

AbstractA variety of empirical estimates have been published for the lower bounds on aerosol radiative forcing, clustered around -1.0 Wm−2 or -2.0 Wm−2. The reasons for obtaining such different constraints are not well understood. In this study, we explore bounds on aerosol radiative forcing using a Bayesian model of aerosol forcing and Earth’s multi-timescale temperature response to radiative forcing. We first demonstrate the ability of a simple aerosol model to emulate aerosol radiative forcing simulated by ten general circulation models. A joint inference of climate sensitivity and effective aerosol forcing from historical surface temperatures is then made over 1850–2019. We obtain a maximum likelihood estimate of aerosol radiative forcing of -0.85 Wm−2 [5-95% credible interval -1.3 to -0.50 Wm−2] for 2010–2019 relative to 1750 and an equilibrium climate sensitivity of 3.4°C [5-95% credible interval 1.8 to 6.1°C]. The wide range of climate sensitivity reflects difficulty in empirically constraining long-term responses using historical temperatures, as noted elsewhere. A relatively tight bound on aerosol forcing is nonetheless obtained from the structure of temperature and aerosol precursor emissions and, particularly, from the rapid growth in emissions between 1950–1980. Obtaining a fifth-percentile lower bound on aerosol forcing around -2.0 Wm−2 requires prescribing internal climate variance that is a factor of five larger than the CMIP6 mean and assuming large, correlated errors in global temperature observations. Ocean heat uptake observations may further constrain aerosol radiative forcing but require a better understanding of the relationship between time-variable radiative feedbacks and radiative forcing.

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Method to calculate the aerosol asymmetry factor based on measurements from the humidified nephelometer system

10.5194/acp-2017-1148 ◽

2018 ◽

Author(s):

Gang Zhao ◽

Chunsheng Zhao ◽

Ye Kuang ◽

Yuxuan Bian ◽

Jiangchuan Tao ◽

...

Keyword(s):

Radiative Forcing ◽

Field Measurements ◽

Mie Scattering ◽

Asymmetry Factor ◽

Hygroscopic Growth ◽

Aerosol Radiative Forcing ◽

The North ◽

Ambient Relative Humidity ◽

Wide Range ◽

Aerosol Radiative

Abstract. The aerosol asymmetry factor (g) is one of the most important factors for assessing direct aerosol radiative forcing. So far, few studies have focused on the measurements and parameterization of g. The characteristics of g are studied based on field measurements over the North China Plain by using the Mie scattering theory. The results show that calculated g values can vary over a wide range (between 0.54 and 0.67). When ambient relative humidity (RH) reaches 90 %, g is significantly enhanced by a factor of 1.2 due to aerosol hygroscopic growth. Direct aerosol radiative forcing can be reduced by 40 % when g increases by 20 %. For the first time, a novel method to calculate g based on measurements from the humidified nephelometer system is proposed. This method can constrain the uncertainty of g within 2 % for dry aerosol populations and 4 % for ambient aerosols, taking into account aerosol hygroscopic growth. Sensitivity studies show that ambient RH and aerosol hygroscopicity are the most important factors that influence the accuracy of predicting g.

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