Speciation of Organic Aerosols in the Tropical Mid-Pacific and Their Relationship to Light Scattering

Crahan, K.; Hegg, D́ean A.; Covert, David S.; Jonsson, Haflidi H.; Reid, Jeffrey S.; Khelif, D.; Brooks, Barbara

doi:10.1175/jas3284.1

Cited by 34 publications

(50 citation statements)

References 36 publications

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“…We have adjusted the scattering coefficients to RH dry = 40 % using a generally accepted approach (e.g., Gasso et al, 2000;Crahan et al, 2004): the dependence of aerosol scattering on RH was parameterized though aerosol hygroscopic exponent α:…”

Section: Appendix B: Relative Humidity Correctionsmentioning

confidence: 99%

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Simultaneous retrieval of effective refractive index and density from size distribution and light-scattering data: weakly absorbing aerosol

et al. 2014

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Abstract. We propose here a novel approach for retrieving in parallel the effective density and real refractive index of weakly absorbing aerosol from optical and size distribution measurements. Here we define "weakly absorbing" as aerosol single-scattering albedos that exceed 0.95 at 0.5 µm. The required optical measurements are the scattering coefficient and the hemispheric backscatter fraction, obtained in this work from an integrating nephelometer. The required size spectra come from mobility and aerodynamic particle size spectrometers commonly referred to as a scanning mobility particle sizer and an aerodynamic particle sizer. The performance of this approach is first evaluated using a sensitivity study with synthetically generated but measurementrelated inputs. The sensitivity study reveals that the proposed approach is robust to random noise; additionally the uncertainties of the retrieval are almost linearly proportional to the measurement errors, and these uncertainties are smaller for the real refractive index than for the effective density. Next, actual measurements are used to evaluate our approach. These measurements include the optical, microphysical, and chemical properties of weakly absorbing aerosol which are representative of a variety of coastal summertime conditions observed during the Two-Column Aerosol Project (TCAP; http://campaign.arm.gov/tcap/). The evaluation includes calculating the root mean square error (RMSE) between the aerosol characteristics retrieved by our approach, and the same quantities calculated using the conventional volume mixing rule for chemical constituents. For dry conditions (defined in this work as relative humidity less than 55 %) and sub-micron particles, a very good (RMSE ∼ 3 %) and reasonable (RMSE ∼ 28 %) agreement is obtained for the retrieved real refractive index (1.49 ± 0.02) and effective density (1.68 ± 0.21), respectively. Our approach permits discrimination between the retrieved aerosol characteristics of sub-micron and sub-10-micron particles. The evaluation results also reveal that the retrieved density and refractive index tend to decrease with an increase of the relative humidity.

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Section: Appendix B: Relative Humidity Correctionsmentioning

confidence: 99%

“…Gasso et al (2000) reported α values of 0.57 for polluted marine and 0.73 for clean marine aerosol; Crahan et al (2004) reported α values between 0.23 and 0.48 for marine air masses, with an average for coastal air of 0.45. Here we use value of 0.5 for parameter α.…”

Section: Appendix B: Relative Humidity Correctionsmentioning

confidence: 99%

Simultaneous retrieval of effective refractive index and density from size distribution and light-scattering data: weakly absorbing aerosol

et al. 2014

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“…Measurements made in this campaign and previous campaigns have suggested oxalic acid composes a significant portion of the resolved soluble organic mass in the marine atmosphere, and thus was chosen to represent soluble organic carbon (Kawamura and Sakaguchi, 1999;Crahan et al, 2004b). Similarly, palmitic acid was chosen to represent the insoluble portion of the organic fraction (Tervahattu et al, 2002).…”

Section: Laboratory Analysismentioning

confidence: 99%

Organics in the Northeastern Pacific and their impacts on aerosol hygroscopicity in the subsaturated and supersaturated regimes

Kaku¹,

Hegg²,

Covert³

et al. 2006

Atmos. Chem. Phys.

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Abstract. Aerosol samples were collected by aircraft during the summer of 2004 in the Northeastern Pacific and compared to measurements of aerosol hygroscopicity. Chemical speciation analyses of the samples revealed that a significant portion of the marine aerosols was organic, and on average 8% of the total aerosol mass was insoluble organic material, tentatively attributed to natural marine emissions. Two chemical models were explored in an attempt to achieve closure between the marine aerosol chemical and physical properties through reproduction of the observed aerosol growth, both in the subsaturated and supersaturated regimes. Results suggest that at subsaturated relative humidities, the nonideal behavior of water activity with respect to aerosol chemistry has an important effect on aerosol growth. At supersaturations, the underprediction of critical supersaturations by all models suggests the hypothesis that formation of a complete monolayer by the insoluble organics may inhibit the activation of aerosols to form cloud droplets.

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“…The organic composition of aerosols has been shown to be highly variable [16], but several different chemical species including alkanes [17,18], alcohols [19], polycyclic aromatic hydrocarbons (PAHs) [20], sterols [21], free fatty acids (FFAs) [22][23][24], and carbohydrates [25] have been detected. Of these species FFAs are commonly identified.…”

Section: Introductionmentioning

confidence: 99%

“…Cerebrosides, a type of glycosphingolipid, are a typical component of membranes in marine organisms [45], but, to our knowledge, have yet to be detected on the ocean surface microlayer or in marine aerosols. However, recent studies have revealed that lipopolysaccharides are found within the ocean surface microlayer [46] and in atmospheric aerosols, where the majority of organic content in aerosol particles is composed of polysaccharides or sugar-like lipids (glycolipids) [25,47,48], and that these species are more abundant in the water insoluble fraction [49]. Cerebrosides are the simplest water insoluble lipids with a saccharide group.…”

Section: Introductionmentioning

confidence: 99%

Palmitic Acid on Salt Subphases and in Mixed Monolayers of Cerebrosides: Application to Atmospheric Aerosol Chemistry

Adams

Allen

2013

Atmosphere

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Palmitic acid (PA) has been found to be a major constituent in marine aerosols, and is commonly used to investigate organic containing atmospheric aerosols, and is therefore used here as a proxy system. Surface pressure-area isotherms (π-A), Brewster angle microscopy (BAM), and vibrational sum frequency generation (VSFG) were used to observe a PA monolayer during film compression on subphases of ultrapure water, CaCl 2 and MgCl 2 aqueous solutions, and artificial seawater (ASW). π-A isotherms indicate that salt subphases alter the phase behavior of PA, and BAM further reveals that a condensation of the monolayer occurs when compared to pure water. VSFG spectra and BAM images show that Mg . π-A isotherms and BAM were also used to monitor mixed monolayers of PA and cerebroside, a simple glycolipid. Results reveal that PA also has a condensing effect on the cerebroside monolayer. Thermodynamic analysis indicates that attractive interactions between the two components exist; this may be due to hydrogen bonding of the galactose and carbonyl headgroups. BAM images of the collapse structures show that mixed monolayers of PA and cerebroside are miscible at all surface pressures. These results suggest that the surface morphology of organic-coated aerosols is influenced by the chemical composition of the aqueous core and the organic film itself.

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Speciation of Organic Aerosols in the Tropical Mid-Pacific and Their Relationship to Light Scattering

Cited by 34 publications

References 36 publications

Simultaneous retrieval of effective refractive index and density from size distribution and light-scattering data: weakly absorbing aerosol

Simultaneous retrieval of effective refractive index and density from size distribution and light-scattering data: weakly absorbing aerosol

Organics in the Northeastern Pacific and their impacts on aerosol hygroscopicity in the subsaturated and supersaturated regimes

Palmitic Acid on Salt Subphases and in Mixed Monolayers of Cerebrosides: Application to Atmospheric Aerosol Chemistry

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