Measurement of relative humidity dependent light scattering of aerosols

Fierz-Schmidhauser, R.; Zieger, Paul; Wehrle, G.; Jefferson, Anne; Ogren, J. A.; Baltensperger, Urs; Weingärtner, E.

doi:10.5194/amt-3-39-2010

Cited by 95 publications

(130 citation statements)

References 32 publications

(33 reference statements)

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“…Garland et al (2007) parameterized the relative humidity dependence of light extinction at 532 nm for inorganic ammonium sulfate aerosols, Baynard et al (2006) looked at mixtures of NaCl and ammonium sulfate with a few dicarboxylic acids, and Fierz-Schmidhauser et al (2010) measured the scattering dependence of ammonium sulfate and sodium chloride. Conversely, we could only find two recent studies (Hasenkopf et al, 2011;Lewis et al, 2009) which dealt with the optical growth of slightly absorbing particles.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2012

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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 (f RH ext (%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 f RH(%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.

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Section: Introductionmentioning

confidence: 99%

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

et al. 2012

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“…It should be noted that different authors used various reference RHs, ranging from 10 to 45% for the "dry" value, and 62 to 90% for the "wet" value (Kotchenruther and Hobbs 1998;Sheridan et al 2002;Howell et al 2006;Fierz-Schmidhauser et al 2010), which makes direct comparison of the results difficult and/or confusing. The scattering factor F can also be assessed from the two or three parameter fit (Equation (1)); here, we will base our assessment of F on the most frequently used "dry" and "wet" RH values of 40 and 85% respectively, and the three parameter model:…”

Section: Instrumentation and System Designmentioning

confidence: 99%

“…Note that the Aurora nephelometers utilize a LED light source with improved angular intensity and integration characteristics (Müller et al 2011). LED-based light sources do not increase the sample temperature and thus do not affect the RH of the sample air, which has been a common problem in humidigraph systems using nephelometers with incandescent light sources (Fierz-Schmidhauser et al 2010).…”

Section: Instrumentation and System Designmentioning

confidence: 99%

“…Aerosol water uptake and subsequent changes in aerosol properties have been studied in three categories: (1) change in size (Chan and Chan 2005), (2) light scattering enhancement (Covert et al 1972;Fierz-Schmidhauser et al 2010), and (3) change in physical and chemical properties, such as refractive index (Wang and Rood 2008). The current state of f(RH) studies pertaining to climate research is summarized nicely in Yan et al (2009).…”

Section: Introductionmentioning

confidence: 99%

“…The impact of humidity on aerosol light scattering has been traditionally studied with the help of humidigraphs or humidographs (Covert et al 1972;Carrico et al 2003;Hegg et al 2008;Fierz-Schmidhauser et al 2010) where one or several nephelometers combined with a humidity conditioning system measures the dependence of the aerosol scattering coefficient σ sp on relative humidity (RH). Several groups have extensively deployed humidigraphs on airborne platforms in numerous field campaigns; two central groups are noted here: the University of Washington (Hegg et al 2008) and NOAA (Sheridan et al 2012).…”

Section: Introductionmentioning

confidence: 99%

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Development of a New Airborne Humidigraph System

Pekour

Schmid

Chand

et al. 2013

Aerosol Science and Technology

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The hygroscopic behavior of atmospheric aerosols complicates modeling and measurements of aerosol properties adding significant uncertainty to our best estimates of the direct effect aerosols exert on the radiative balance of the atmosphere. Airborne measurements of aerosol hygroscopicity are particularly challenging but critically needed. This motivated the development of a new system designed to measure the dependence of the aerosol light scattering coefficient (σ sp ) on relative humidity (RH), known as f(RH), in real-time on an aerial platform.The new instrument has several advantages over existing systems. It consists of three integrating nephelometers and humidity conditioners for simultaneous measurement of the σ sp at three different RHs. The humidity is directly controlled in exchanger cells without significant temperature disturbances and without particle dilution, heating, or loss of volatile compounds. The singlewavelength nephelometers are illuminated by LED-based light sources thereby minimizing heating of the sample stream. The flexible design of the RH conditioners, consisting of a number of specially designed exchanger cells (driers or humidifiers), enables us to measure f(RH) under hydration or dehydration conditions (always starting with the aerosol in a known state) with a simple system reconfiguration. These exchanger cells have been characterized for losses of particles using latex spheres and laboratory generated ammonium sulfate aerosols. The performance of this instrument has been assessed aboard DOE's G-1 research aircraft during test flights over California, Oregon, and Washington.

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Bistable effect of organic enrichment on sea spray radiative properties

Vaishya

Ovadnevaitė

Białek

et al. 2013

Geophysical Research Letters

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[1] Primary-produced sea spray aerosol, typically comprising sea-salt, but also enriched with organic matter (OM) in biologically active oceanic regions, impacts the global radiative budget through contributions to aerosol optical depth. We show that sea spray light-scattering enhancement, f(RH), as a function of relative humidity (RH) is suppressed when enriched with OM. A new hygroscopic growth factor parameterization reveals a dual hygroscopicity state, flipping from high hygroscopicity and high f(RH) to low hygroscopicity and low f(RH) as the OM mixing volume percentage exceeds~55% in sea spray. Under elevated wind speeds, this affects the Top-of-atmosphere direct radiative forcing (ΔF) by reducing the cooling contribution of sea spray by~5.5 times compared to pure sea-salt spray. These results suggest a positive feedback coupling between the marine biosphere, sea spray aerosol, and the direct radiative budget.

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Measurement of relative humidity dependent light scattering of aerosols

Cited by 95 publications

References 32 publications

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

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

Development of a New Airborne Humidigraph System

Bistable effect of organic enrichment on sea spray radiative properties

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