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

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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Calculating the aerosol asymmetry factor based on measurements from the humidified nephelometer system

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-9049-2018 ◽

2018 ◽

Vol 18 (12) ◽

pp. 9049-9060 ◽

Cited By ~ 8

Author(s):

Gang Zhao ◽

Chunsheng Zhao ◽

Ye Kuang ◽

Yuxuan Bian ◽

Jiangchuan Tao ◽

...

Keyword(s):

Radiative Forcing ◽

Field Measurements ◽

Mie Scattering ◽

Vital Role ◽

Asymmetry Factor ◽

Hygroscopic Growth ◽

Aerosol Radiative Forcing ◽

The North ◽

Ambient Relative Humidity ◽

Wide Range

Abstract. The aerosol asymmetry factor (g) is one of the most important factors for assessing direct aerosol radiative forcing. However, little attention has been paid to the measurement and parameterization of g. In this study, the characteristics of g are studied based on field measurements over the North China Plain (NCP) using the Mie scattering theory. The results show that calculated g values for dry aerosol can vary over a wide range (between 0.54 and 0.67). Furthermore, when ambient relative humidity (RH) reaches 90 %, g is significantly enhanced by a factor of 1.2 due to aerosol hygroscopic growth. For the first time, a novel method of calculating g based on measurements from the humidified nephelometer system is proposed. This method can constrain the uncertainty of g to within 2.56 % for dry aerosol populations and 4.02 % for ambient aerosols, providing that aerosol hygroscopic growth is taken into account. Sensitivity studies show that aerosol hygroscopicity plays a vital role in the accuracy of predicting g.

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

Atmospheric Measurement Techniques ◽

10.5194/amt-12-3541-2019 ◽

2019 ◽

Vol 12 (7) ◽

pp. 3541-3550 ◽

Cited By ~ 3

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.

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

10.5194/acp-2019-385 ◽

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.

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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 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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Air Quality and Climate Change, Topic 3 of the Model Inter-Comparison Study for Asia Phase III (MICS-Asia III), Part II: aerosol radiative effects and aerosol feedbacks

10.5194/acp-2019-719 ◽

2019 ◽

Author(s):

Meng Gao ◽

Zhiwei Han ◽

Zhining Tao ◽

Jiawei Li ◽

Jeong-Eon Kang ◽

...

Keyword(s):

Air Quality ◽

Radiative Forcing ◽

Eastern China ◽

Phase Iii ◽

Comparison Study ◽

Near Surface ◽

Aerosol Radiative Forcing ◽

The North ◽

Bth Region ◽

Aerosol Radiative

Abstract. Topic 3 of the Model Inter-Comparison Study for Asia (MICS-Asia) Phase III examines how online coupled air quality models perform in simulating high aerosol pollution in the North China Plain region during wintertime haze events and evaluates the importance of aerosol radiative and microphysical feedbacks. This paper discusses the estimates of aerosol radiative forcing, aerosol feedbacks, and possible causes for the differences among the models. Over the Beijing-Tianjin-Hebei (BTH) region, the ensemble mean of aerosol direct radiative forcing (ADRF) at the top of atmosphere, inside the atmosphere and at the surface are −1.9, 8.4 and −10.3 W/m2, respectively. Subdivisions of direct and indirect aerosol radiative forcing confirm the dominant roles of direct forcing. During severe haze days (January 17–19, 2010), the averaged reduction in near surface temperature for the BTH region can reach 0.3–3.0 ºC. The responses of wind speeds at 10 m (WS10) inferred from different models show consistent declines in eastern China. For the BTH region, aerosol-radiation feedback induced changes in PM2.5 range from 6.0 to 8.8 µg/m3 (

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