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Optical Property Measurements and Single Particle Analysis of Secondary Organic Aerosol Produced from the Aqueous Phase Reaction of Ammonium Sulfate with Methylglyoxal Deokhyeon Kwon, Victor Or, Matthew J. Sovers, Mingjin Tang, Paul D. Kleiber, Vicki H. Grassian, and Mark Alan Young ACS Earth Space Chem., Just Accepted Manuscript • DOI: 10.1021/ acsearthspacechem.8b00004 • Publication Date (Web): 27 Feb 2018 Downloaded from http://pubs.acs.org on February 27, 2018

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ACS Earth and Space Chemistry

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Optical Property Measurements and Single Particle Analysis of Secondary

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Organic Aerosol Produced from the Aqueous Phase Reaction of Ammonium

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Sulfate with Methylglyoxal

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Deokhyeon Kwon,1 Victor W. Or,2 Matthew J. Sovers,1 Mingjin Tang,1 Paul D. Kleiber,3 Vicki

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H. Grassian,2,4 Mark A. Young1*

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1 Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA

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2 Departments of Chemistry and Biochemistry, University of California, San Diego, La Jolla,

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CA 92093, USA

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3 Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA

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4 Departments of Nanoengineering and Scripps Institution of Oceanography, University of

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California, San Diego, La Jolla, CA 92093, USA

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*Corresponding author: Mark A. Young (Telephone: 319-335-2099, E-mail: mark-

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[email protected])

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Keywords: atmospheric chemistry; secondary organic aerosol; brown carbon; optical constants;

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refractive index; atomic force microscopy; cavity ring down spectroscopy

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ACS Paragon Plus Environment

ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Abstract

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Reactions involving the dicarbonyl species, methylglyoxal (MG), have been suggested as

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an important pathway for the production of secondary organic aerosol (SOA) in the atmosphere.

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Reaction in an aqueous, inorganic salt solution, such as ammonium sulfate (AS), leads to the

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formation of light absorbing brown carbon (BrC) product. We report on an investigation of the

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optical properties of BrC aerosol generated from the aqueous phase reaction between MG and

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AS as a function of aging time, using calibrated cavity ring-down spectroscopy (CRDS) at a

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wavelength of 403 nm. The retrieved real index of refraction at 403 nm is n = 1.558 ± 0.021 with

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an imaginary index value of k = 0.002 ± 0.004; these values do not appear to change significantly

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with aging time over the course of 22 days and are similar to the AS aerosol values. The small

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complex index suggests BrC aerosol formed from this pathway may not significantly impact

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radiative forcing. Measurements of the aerosol optical properties show significant deviation from

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Mie theory simulations for particles with diameters ≳ 500 nm, probably due to non-spherical

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particle shape effects. In addition to the CRDS study, we use ultraviolet-visible (UV-vis)

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spectroscopy to measure the mass absorption coefficient (MAC) of the solution phase reaction

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products as a function of aging. We also employ atomic force microscopy-based infrared (AFM-

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IR) spectroscopy to investigate the morphology and chemical composition of single SOA

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particles. AFM analysis of particle morphology shows that a significant fraction of BrC particles

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with diameters ≳ 500 nm are non-spherical in shape, consistent with our observed breakdown in

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the applicability of Mie theory for larger particles.

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1

Introduction

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Atmospheric aerosol can affect the Earth’s climate by altering the radiative forcing

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through the direct absorption and scattering of radiation from the infrared (IR) to the ultraviolet

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(UV).1-2 Aerosol can also affect the climate indirectly by serving as nucleation sites for cloud

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condensation, which can then influence the radiative energy balance. Knowledge of the optical

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properties of atmospheric aerosol, which dictate the scattering and absorption properties, is

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critical for understanding the role of aerosol in climate.

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Carbonaceous aerosol, comprised of black carbon (BC) and organic carbon (OC), is an

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especially important component of the total atmospheric aerosol load from the perspective of

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climate since a significant fraction can absorb solar radiation.2-4 Until recently, BC, which shows

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strong absorption from the IR to the UV, was thought to be responsible for most of the light

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absorption by carbonaceous aerosol. However, there has been increasing interest in the light

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absorption properties of a class of organic aerosol termed brown carbon (BrC), which generally

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has an absorption cross-section that increases smoothly from the visible to the near UV.3-6

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There are many possible primary and secondary sources of BrC aerosol which are well

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described and summarized elsewhere in the literature.5 One proposed pathway to BrC formation

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that has received significant attention is the aqueous phase reaction of ammonium sulfate (AS)

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with methylglyoxal (MG), yielding secondary organic products that absorb in the visible region

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of the spectrum.7-12 This pathway is considered potentially important because of the atmospheric

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abundance and high water solubility of MG and the ubiquitous presence of deliquesced

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ammonium salt aerosol.5, 13-14

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Most previous laboratory studies of BrC from the reaction of AS with MG have focused

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on measurements of the ultraviolet-visible (UV-vis) absorption or NMR spectra of the bulk

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products in solution, or on mass spectrometric measurements of the particle-phase reaction

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products.7-12 However, it is important to measure the properties of aerosolized BrC samples as

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the optical properties may depend on details of the reaction mechanism, and may be altered by

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effects such as particle drying. Aerosolization can mimic environmentally relevant processes,

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such as a drying cycle, that are not replicated when preparing bulk solution samples.15-16 In

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addition, non-spherical particle shape effects can significantly alter aerosol optical properties and

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these can only be elucidated by investigating the aerosolized sample. Furthermore, deriving the

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complex index of refraction from bulk absorption spectra requires knowledge of the particle

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density, which can generally only be estimated.17

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One study by Tang et al. of the aerosol optical properties of BrC produced from the bulk,

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solution phase reaction of AS with MG has been carried out using visible light scattering (532

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nm and 402 nm) and Fourier transform IR (7000 – 800 cm-1) absorption spectroscopy.18

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Following up on that work, the present study is focused on investigating the optical properties

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and measuring the complex index of refraction of SOA product from the aqueous phase reaction

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of AS with MG, as a function of aging time, using calibrated cavity ring-down spectroscopy

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(CRDS) at a wavelength of 403 nm. The CRDS method has previously been used to investigate

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the optical properties of a closely related chemical system, BrC SOA formed from the reaction of

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AS with glyoxal.12 Quantitative measurement of the optical properties of BrC aerosol, either

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suitable laboratory proxies, such as in the current work, or authentic samples, is required for a

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more detailed assessment of potential radiative forcing effects.

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The principles and history of the application of the CRDS technique to aerosol extinction

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measurements can be found in the extensive literature in this area.19-22 While gas phase CRDS is

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known to be a self-calibrating and highly sensitive technique,20 CRDS in its application to the

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measurement of aerosol extinction requires careful calibration to correct for various instrumental

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factors, such as difficulties in accurately measuring the particle concentration.22-23 A recently

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reported method for calibrating cavity ring-down (CRD) spectrometers using an organic oil with

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well characterized optical constants, squalane (SQ), demonstrated excellent measurement

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accuracy.22 The SQ calibration approach has been adapted for use in the current investigation

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where the methodology has been applied to index retrieval for an unknown aerosol sample.

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In this study, we employ CRDS to measure the light extinction of size selected SOA

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particles formed from the aqueous phase reaction of AS and MG. The experimental extinction

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data is fit to Mie theory to extract the complex index of refraction of the sample. These

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measurements were carried out as a function of aging time over the course of 22 days. The

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measurement accuracy of the instrument was also tested and confirmed by determining the

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optical constants of two well characterized test aerosol samples: a scattering material, AS, and a

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highly absorbing material, nigrosin. Extracted optical constants for these test samples agree well

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with previously published results, validating the instrument performance.

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In addition to the CRDS study, we further characterized the MG/AS reaction products.

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UV-vis spectroscopy was used to determine the mass absorption coefficient (MAC) of the bulk

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products of the aqueous phase reaction as a function of aging time. Also, we employed atomic

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force microscopy–based infrared (AFM-IR) spectroscopy to investigate the size dependence of

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the shape and structure of isolated BrC particles, and to examine the chemical composition

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within selected particles.

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2

Experimental section

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2.1 Overview

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Descriptions of CRDS operating principles and methods have been given elsewhere.19-22

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A schematic diagram for our CRDS system is presented in Figure 1. The experimental methods

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and the instrument are discussed more fully in the following sections.

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Figure 1. Schematic diagram of the cavity ring-down spectrometer and aerosol generation

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system.

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2.2 Materials and sample preparation

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SQ (99 %, Sigma-Aldrich), an organic oil with a well-characterized refractive index, was

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used without dilution as the calibrant for the CRDS system. The complex refractive index, m, for

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SQ has been studied by several groups24-25 and based on their results, the average refractive

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index for SQ near 403 nm was taken to be m = (1.46 ± 0.01) + i0. AS (≥ 99.0 %, Sigma-Aldrich)

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aerosol was used as one test material to validate the CRD instrument calibration procedure and

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consequent accuracy. AS, which mainly scatters in the wavelength region of interest, was chosen

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because it has been well studied and the particles are known to be near spherical for diameters

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less than ~ 500 – 600 nm.26 The latter attribute makes AS well suited to modeling with Mie

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theory, which assumes spherical particles. An AS stock solution in 18 MΩ-cm deionized (DI)

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water was prepared and then diluted down to 0.15 M for aerosolization, yielding a maximum

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particle concentration of ~ 2000 – 3000 cm-3 at the smaller particle diameters, approximately 350

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nm. A second compound, nigrosin (198285, Sigma-Aldrich), was also studied in order to test the

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CRD instrument with a strong absorber. For these measurements, a 16 g/L aqueous solution of

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nigrosin was used, producing a maximum particle concentration of ~ 4500 cm-3.

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MG (40% w/w solution, Alfa Aesar) was mixed with a saturated AS solution to prepare

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the BrC stock solution, which had 3.1 M AS and 1.0 M MG as initial concentrations.11, 18 The

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stock solution was aged in sealed bottles over the course of 35 days under dark conditions and at

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room temperature. For the CRDS measurements, an aliquot of the BrC stock was diluted with DI

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water to an equivalent 0.15 M AS solution, based on the initial 3.1 M AS concentration.

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Maximum particle concentrations in the ring-down cavity ranged from ~ 1000 – 3000 cm-3,

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depending on the sample age.

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2.3 Aerosol generation and flow system

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For most of this work, aerosols were generated using a constant output atomizer (3076,

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TSI) operated with dry air at ~ 30 psig to achieve an output flow rate of ~ 2.8 liters per minute

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(LPM). All of the dry air used in the system was generated by a commercial purge gas generator.

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The aerosol flow passed through one or more diffusion dryers to reduce the relative humidity

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(RH) and was then directed to a glass flask for dilution with additional dry air, which allowed for

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better control over the particle number density and RH. An aerosol flow of 0.34 LPM was pulled

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from the flask into the DMA (3081, TSI) through an inlet impactor (nozzle diameter of 0.0508

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cm) using the CPC (3775, TSI) in high flow mode. The impactor cut-off at larger diameters

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helped to mitigate the effects of multiply charged particles on the data analysis. Excess flow was

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vented through one of the exhaust ports labeled in Fig. 1 in order to achieve the optimum

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conditions for particle number density and RH. A second flask was used to mix with the

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necessary make-up air (~ 1.11 LPM) to match the input flow of the CPC. A further ~ 0.1 LPM of

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nitrogen was added inside the cavity from the mirror purge flows. The RH in the ring-down

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cavity was always < 10 %, negligibly different than the RH in the DMA, and well below the

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efflorescence relative humidity (ERH) of AS or the BrC aerosol.18,

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diameters do not noticeably change between the selection and measurement sections of the

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aerosol flow stream.

27-28

Thus, the particle

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Typically, the DMA was adjusted to pass selected particles over the diameter range ~ 340

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– 690 nm, where the specific range depended on the sample. For each sample, the lower limit

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was chosen to minimize contributions from multiply charged particles, while the upper limit was

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generally restricted by statistical fluctuation in the number of particles in the laser beam volume,

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the cut-off diameter of the impactor, or the range of the DMA.20, 22, 29-30

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The SQ calibration measurements (as described in more detail below), which were

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carried out each day, employed a parallel flow system consisting of a nebulizer (C700d, Savillex)

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and a cyclonic spray chamber (300-30, Precision Glassblowing). The ~ 0.7 LPM output flow

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from the nebulizer was directed to the first dilution flask, after which the flow system was

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identical to that described above.

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2.4 CRD measurements

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Our instrument utilizes a continuous wave diode laser (Stradus 405-100, Vortran Laser)

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with a measured operating wavelength of 403 nm. The laser was digitally modulated to produce

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a square wave output (50 % duty cycle at 2 kHz) of ∼50 mW and the beam was spatially filtered

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before being directed into the stainless steel ring-down cavity. The cavity was sealed with

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commercial mirror mounts and high reflectivity mirrors with a 1 m radius of curvature (R >

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99.995%, CRD Optics). Light exiting the cavity was detected by a photomultiplier tube (PMT)

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fiber-optic coupled to one of the cavity mirrors. The ring-down signal was averaged by an 8-bit

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digitizer (U1082A-001, Keysight Technologies) in the instrument computer. Typically, 1000

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ring-down events were averaged by the digitizer and then fitted to a single exponential decay to

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determine the ring-down times, τ, with, and τ0, without particles in the cavity.

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Extinction coefficients (αext) and cross-section (σext) values at the different particle mobility diameters were calculated according to Equation 1,

α ext =

L 1 1 1  = σ ext N − d c  τ τ 0 

(1)

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where c is the speed of light, L (= 78 cm) is the cavity length, d (= 62 cm) is the distance

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between the cavity aerosol inlet and outlet, and N is the number density of particles in the

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cavity.19, 22, 30-31 The number density was measured by the CPC using the supplied instrument

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software (AIM, TSI) at intervals of one second. The acquisition time, including fitting of the

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ring-down decay, was about 1.2 s for each data point and for each selected diameter, data were

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collected and averaged for two minutes (ca. 100 points). The background ring-down time, τ0,

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ranged from 14.4 – 16.8 µs depending on the cleanliness of the CRD mirrors. The corresponding

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range for the minimum detectable extinction coefficient was 2.89 × 10-9 – 1.79 × 10-9 cm-1.21, 30,

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186

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calculations.

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2.5 Mie theory calculations

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A custom Matlab code was used to control the digitizer and perform all of the fitting and

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We have employed Mie theory to model all of the CRDS results using a custom Matlab

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code based on previously published code and algorithms.19, 33-35 In order to accurately model the

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experimental results, it was critical to account for the finite width of the DMA transfer function.

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We have assumed that the output size distribution of the DMA can be described by a log-normal

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function characterized by a geometric standard deviation (GSD) of 1.05. This value is consistent

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with what other studies have suggested for similar instruments22,

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measurements of the output distribution using monodisperse polystyrene latex (PSL) spheres.

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We defined the theoretical, weighted, Mie extinction cross-section, σ Mie ( D p ) , centered at

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diameter, Dp, according to Equation 2,

σ Mie ( D p ) =

∫ f ( D, D , GSD ) σ ( D ) dD ∫ f ( D, D , GSD ) dD p

Mie

36-37

and with our own

(2)

p

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where f(D,Dp,GSD) is the log-normal function centered at diameter, Dp, and with a width

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characterized by the GSD, σ Mie ( D ) is the Mie cross-section at diameter, D, and the integration

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is over the total particle size distribution.22

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The experimentally measured extinction cross-sections, calculated from Eqn. 1, were

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corrected according to the SQ calibration procedure described below and then fit to Mie theory

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using a grid-search method with the complex indices, n and k, as adjustable parameters.22 The

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grid spacing was 0.001 for both the real and complex indices. The best-fit values were

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determined by minimizing χ2, which was defined as,

10


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χ

2

{C σ ( D ) − σ ( D )} =∑ f

ext

i

Mie

ε

i

2

i

(3)

2 i

( )

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where Cf is the calibration factor, σ ext Di and σ Mie ( Di ) are the experimental and weighted Mie

207

cross-sections, respectively, for diameter Di, and εi is the error in the measured cross-section.

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Unless stated otherwise, the indicated errors in the retrieved optical constants correspond to one

209

2 standard deviation (SD), determined by the criterion, χ 2 < χ min + 2.2958 .31, 38-40

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2.6 MAC measurements

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The BrC stock solution described in section 2.2 was used to record a series of UV-vis

212

spectra as a function of aging time. Aliquots of the stock were suitably diluted and the absorption

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spectra recorded (Cary 5000, Agilent Technologies). All BrC spectra were corrected for the

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small contribution from AS absorption at shorter wavelengths. An aqueous AS spectrum, scaled

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to account for the dilution of the BrC stock solution, was used for the subtraction. The

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absorbance values were converted to the MAC (cm2 g-1) using Equation 4,

MAC ( λ ) =

A ( λ ) ln (10 ) b Cmass

(4)

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where A(λ) is the wavelength specific decadic absorbance, b is the sample cell path length (1 cm),

218

and Cmass (g cm-3) is the calculated mass concentration of MG in the diluted sample.15, 17 Using

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this value for Cmass assumes that the organic (MG) mass is conserved and neglects incorporation

220

of water (e.g. via hydrolysis) or nitrogen from AS in the formation of the BrC product species.

221

2.7 AFM-IR measurements

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The AFM-IR (nanoIR2, Anasys Instruments) spectrometer uses a photothermal induced

223

resonance (PTIR) technique to acquire topographical and chemical information.41-42 Well-aged

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224

BrC solution (24 days) was aerosolized and then isolated particles were collected on silicon

225

substrates placed in each stage of a cascade impactor (Sioutas impactor, SKC). Imaging of the

226

BrC particles was conducted at atmospheric pressure and a temperature of 298 K. The

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experimental RH was ~ 20 %, well below the estimated DRH of the BrC aerosol.18 AFM images

228

were collected in tapping mode at a scan rate of 0.5 Hz using a silicon nitride probe (Anasys)

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with a spring constant and resonant frequency of 13 – 77 N·m-1 and 300 ± 200 kHz, respectively.

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Height images were obtained by detecting changes in the probe amplitude while phase images,

231

which are chemical maps of the spatial distribution of species within individual particles, were

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collected by detecting shifts in the phase angle of the oscillating probe interacting with the

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sample surface.43-45

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For AFM-PTIR analysis, images were collected in tapping mode at a scan rate of 0.5 Hz

235

with a gold coated silicon nitride probe (Anasys) with spring constant and contact resonant

236

frequency of 1 – 7 N·m-1 and 75 ± 15 kHz, respectively. PTIR spectra were obtained by bringing

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the tip into contact with the sample and irradiating with a pulsed, tunable IR laser. Spectra were

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recorded with a resolution of 4 cm-1, averaging 128 laser pulses at each wavelength. The signal

239

was divided by the background level of the IR source at each wavelength to normalize for the

240

effects of laser power variation across the spectral range.

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3

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3.1 Calibration procedure

Results and discussion

243

A calibration factor, Cf, was determined from SQ measurements taken before and/or after

244

sample measurements on a given day. Typical results are shown in Figure 2. In this example, the

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experimental SQ extinction cross-section data (black squares, Fig. 2), lie above the weighted Mie

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curve calculated using the known SQ optical constants (vide supra). The best-fit value, Cf =

247

0.882, is determined by minimizing χ2, as defined in Eqn. 3. Multiplication of the experimental

248

cross-sections by the calibration factor shifts the experimental data (red circles, Fig. 2) to better

249

align with the Mie calculation. The calibration factor accounts for several instrumental

250

parameters: the effective aerosol path length (which can vary with flow conditions), the CPC

251

counting efficiency, and other factors.22-23, 46-47

252 253

Figure 2. Example SQ calibration data. Fitting yields a calibration factor of, Cf = 0.882.

254

The Cf values in this study fell in the range, 0.704 – 1.010, with an average of 0.885 ±

255

0.090. While the variation in Cf values over periods of weeks can be significant, the variation

13



256

during the course of a given day’s measurements is much less, typically a few percent. Measured

257

extinction cross-sections for AS, BrC, and nigrosin aerosols were corrected by multiplying by

258

the average of the corresponding Cf values determined before and/or after each day’s

259

measurement. The complex index for each sample was then retrieved by fitting the calibrated

260

experimental cross-sections with Mie theory, as described above in section 2.5.

261

The possible role of multiply charged particles in the SQ aerosol extinction data was

262

determined to be negligible because of the very low particle number densities at larger diameters

263

(which would contribute to doubly charged, and higher, particles).

264

3.2 AS and nigrosin optical constants

265

A validation of the retrieved indices from the CRD spectrometer was performed using

266

measurements of a scattering material, AS, and a strongly absorbing compound, nigrosin.

267

Typical cross-section data for AS and nigrosin aerosols are presented in Figure 3. The large

268

particle limit for AS was chosen to minimize errors associated with non-spherical particles at

269

diameters greater than ~ 500 – 600 nm.26 For both AS and nigrosin, the small particle limit was

270

selected in order to mitigate the effects of multiply charged particles on the data analysis since

271

such errors are more significant for smaller particles. Truncating the Mie fits at successively

272

larger minimum particle diameters did not significantly change the best-fit values for the optical

273

constants, indicating that extinction due to multiply charged particles was negligible over the

274

chosen size range.

275

The average (8 measurements) retrieved complex refractive index for AS was m = (1.522

276

± 0.019) + i(0.011 ± 0.016), while for nigrosin (5 measurements) the value was m = (1.625 ±

277

0.030) + i(0.130 ± 0.037). The results for both of these compounds are in generally good

14


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278

agreement with the literature values,18, 40, 48-50 as illustrated by the comparison summarized in

279

Table 1, confirming the accuracy of the calibration procedure and the general experimental

280

approach for both absorbing and scattering samples. We will also note that our experimental

281

error is comparable with the reported errors from other studies employing related techniques.

Figure 3. Typical cross-section curves for AS, (a), and nigrosin aerosol, (b). The average Cf values are 0.726 and 0.982, respectively. 282

Table 1. Summary of the retrieved complex index values for AS and nigrosin aerosol studied in

283

the current work, along with a comparison to previously reported results using related methods at

284

similar wavelengths. Errors for values determined in this study are given as ± 1SD. Literature

285

values are either as reported or are estimated from published figures.

286

n (± 1SD) k (± 1SD) Methoda Ref. 1.522 ± 0.019 0.011 ± 0.016 1 this study 49 1.496 ± 0.016 < 0.020 2 40 AS 1.537 ± 0.004 < 0.001 2 18 1.505 ± 0.013 < 0.010 3 50 1.53 ± 0.01 < 0.001 4 1.625 ± 0.030 0.130 ± 0.037 1 this study 40 1.658 ± 0.021 0.184 ± 0.056 2 Nigrosin 48 1.625 ± 0.006 0.153 ± 0.008 5 50 1.57 ± 0.03 0.133 ± 0.014 4 a Method: 1 = CRDS, 2 = BBCES, 3 = light scattering, 4 = CRD-PAS, 5 = ellipsometry Material

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287

3.3 BrC optical constants

288

The optical constants for BrC aerosol from the aqueous phase reaction of AS with MG

289

were similarly measured as a function of reaction time over the course of 22 days. Typical

290

extinction cross-section data for a well-aged (22 days) sample are shown in Figure 4 for two

291

particle diameter ranges. A summary of the retrieved optical constants as a function of aging

292

time is presented in Figure 5. Measurements of AS aerosol extinction were taken each day along

293

with the BrC aerosol measurements to confirm instrument performance and the results are

294

included in Fig. 5.

295

The diameter range used for fitting the AS and BrC extinction data in these studies was

296

340 – 520 nm. The lower limit was chosen to minimize the effects of multiply charged particles,

297

which was confirmed by truncating the range of diameters used in the fit, as described above.

298

The upper limit was determined by the need to minimize errors associated with non-spherical

299

particle shape effects. In particular, the AFM studies described in Section 3.5 demonstrate that a

300

significant fraction of BrC particles with diameters ≳ 500 nm are agglomerates or have non-

301

spherical shapes. The poor fit to Mie theory for larger particles is evident in Fig. 4a where

302

significant deviations between experiment and the theoretical curve are observed for particles

303

with diameters > 550 nm.

16


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304 305

Figure 4. Measured extinction cross-section data for BrC aerosol, calibrated data, and best-fit

306

Mie curve illustrating deviations from theory when attempting to fit particles with larger

307

diameters, (a). Similar, representative data used to extract the reported complex index for BrC

308

aerosol, (b), aged 22 days with a calibration factor of Cf = 0.726.

309 310

Figure 5. Real, (a), and imaginary, (b), retrieved refractive indices for BrC aerosol as a function

311

of solution aging time. Data for AS, recorded on the same day, is also shown

17



312

The data in Fig. 5 indicate that there was no meaningful change in the retrieved index

313

values, n or k, for BrC aerosols over the course of 22 days. The average complex index for the

314

BrC aerosol data set is m = (1.558 ± 0.021) + i(0.002 ± 0.004). This can be compared with the

315

average value for the AS aerosol data set, m = (1.522 ± 0.019) + i(0.011 ± 0.016). The mean n

316

value for BrC is slightly larger than that for AS at the 68 % confidence limit (±1 SD). The results,

317

however, do overlap at the 95 % confidence limit (±2 SD). Measurements of k for both AS and

318

BrC aerosol show that the values are consistent with k = 0.

319

Related experiments have shown that aging, or browning, of organics by reaction with

320

AS can be accelerated by drying the bulk sample.15-16, 51 The diffusion dryers in the aerosol flow

321

stream might facilitate a similar mechanism in the AS/MG system. As a consequence, it may not

322

be surprising that we observe no dependence of the BrC index of refraction on reaction time.

323

However, since our results show that the retrieved complex index for the BrC is the same as that

324

of AS, we cannot definitively determine whether a similar drying-induced mechanism is relevant

325

for the AS/MG sample.

326

It is interesting to compare the BrC optical constants obtained from the CRDS extinction

327

measurements with those determined previously from light scattering measurements.18 Tang et al.

328

determined the BrC optical constants by simultaneously fitting the light scattering phase function

329

and polarization data at a wavelength of 402 nm to find an average of n = 1.497 ± 0.017 with an

330

upper limit of k ≤ 0.01. The value for n is slightly lower than the results obtained in the current

331

study and the difference falls outside the ±1 SD uncertainty range (although it lies within the ±2

332

SD range). The reasons for the small difference between the two experiments are not entirely

333

clear. However, we note that in the CRDS results, the optical constants were determined by

334

fitting the extinction data for size selected particles over the diameter range 340 – 520 nm. In the

18


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335

light scattering experiments, there was no particle size selection and larger particles, including

336

those with diameters ≥ 500 nm, generally dominate the scattering signal. Thus, it is possible that

337

the difference results from a breakdown of the Mie theory assumption of spherical particles for

338

larger particles, with diameters ≳ 500 nm, that were present in the light scattering experiment.

339

Further support for this hypothesis is found in the AFM-IR results described in Section 3.5.

340

3.4 MAC measurements

341

Selected UV-vis spectra of AS/MG bulk solutions as a function of aging time are

342

collected in Figure 6a. The absorbance data has been converted to MAC according to Eqn. 4,

343

taking into account the sample dilution. Qualitatively, the spectra show a strong peak centered at

344

280 nm and a shoulder at about 335 nm that both increase in intensity as the sample ages. In

345

addition, there is a long tail extending to approximately 500 nm that also grows with reaction

346

time and is responsible for the increasingly dark color of the bulk solution. These observations

347

are similar to what has previously been reported in the literature.9-11 In Figure 6b, MAC values at

348

two specific wavelengths, the peak at 280 nm and at the CRDS wavelength of 403 nm, are

349

shown as a function of aging out to 35 days. Fig. 6b includes data from two separate trials to

350

verify the reproducibility of the results. The absorption of the BrC product is observed to grow

351

steadily at both wavelengths and saturate after approximately 30 days reaction time. A pseudo-

352

first order analysis indicates a characteristic aging time of 11 – 12 days.

353

The MAC values determined in the current work, ∼2.5 m2 g-1 and ∼0.25 m2 g-1 at 280 nm

354

and 400 nm, respectively, are relatively large compared to other examples of NH3/NH4+ aged

355

SOA, such as that produced from the ozonolysis of limonene.5-6,

356

comparable to the higher absorption found for wood burning aerosols.5, 10, 17 Prior work with

357

lower initial concentrations of AS and MG found smaller values for the MAC.10, 53-54 Our own

19


15, 52

The BrC MAC is


Page 20 of 31

358

trial with an equimolar, 0.25 M, AS/MG mixture, identical to the conditions studied by Powelson

359

et al., determined MAC values at 400 nm that were approximately 20 times smaller than for our

360

normal stock solution.10

361 362

The MAC values can be used to estimate the wavelength specific complex index, k(λ), of the BrC solution through Equation 5,5, 17, 33, 55-56

k (λ ) =

MAC ( λ ) ρ λ 4π

(5)

363

where ρ is the density of the organic material. Using a typical, estimated density for the organic

364

product of 1.4 g cm-3, we calculate a value of k at 403 nm that is ≤ 0.01 for the fully aged sample,

365

which is roughly consistent with the CRDS results where, essentially, k = 0 at this wavelength.

Figure 6. Wavelength resolved MAC spectra of aged BrC solution, (a), and wavelength specific MAC values at 280 nm and 403 nm for two separate trials, (b).

366

3.5 AFM-IR results

367

An AFM shape analysis for BrC particles deposited in two stages of the cascade impactor

368

corresponding to particle diameter ranges of ∼250 – 500 nm and ∼500 – 1000 nm, respectively,

20


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369

was completed. The results are summarized in Figure 7. For the smaller diameter particle range,

370

nearly all the imaged particles were spherical in shape. These particle sizes correspond to the

371

particle diameter range used in the Mie fits to extract optical constants for BrC aerosol. Image

372

analysis for the larger particle diameter range, albeit for fewer total particles, revealed that

373

approximately half of the particles were non-spherical in shape, largely consisting of

374

agglomerated particle types. These results are consistent with previous studies that have shown

375

that AS particles with diameters ≳ 500 – 600 nm appear to deviate from spherical morphology.26

376

Phase separation of particles in both size ranges, using phase imaging, was also examined

377

and results are summarized in Figure 8. Approximately two-thirds of the particles with diameters

378

≳ 500 nm evinced core-shell phase separation. In contrast, there were no phase separated

379

particles observed in the 250 – 500 nm size regime. Phase separation has been observed in other,

380

similar, mixed organic-inorganic systems.44, 57-59 The AFM results reinforce the current CRDS

381

work where attempts to include larger particle diameters in the data analysis yielded poor fits to

382

Mie theory for both AS and BrC aerosol due to non-spherical particle shapes.

250-500 nm (N = 359) 500-1000 nm (N = 71)

Shape (%) Non-spherical 0.6 8.5

Spherical 98.9 49.3

Aggregated 0.6 42.3

Figure 7. Results of AFM shape analysis for BrC aerosol in the size ranges 250-500 nm and 500-1000 nm, corresponding to two stages in the cascade impactor. The number of particles analyzed, N, is indicated. Representative 3D height images for spherical, non-spherical, and

21



agglomerated particles types are also shown. 383

Figure 8. Results for AFM phase imaging analysis of BrC aerosols in the size range ∼500 – 1000 nm. Of the particles examined (number, N = 71), approximately two-thirds displayed a phase separated morphology. Representative phase images for homogenous and phase separated particles are shown. 384

Figures 9a and 9b show height and phase images, respectively, for a homogenous BrC

385

particle, ~ 800 nm in diameter. In addition to the AFM image analysis, PTIR spectra were

386

collected from two locations on the particle and the resultant spectra are shown in Figure 9c.

387

Reference spectra for pure AS and MG are included and labeled red and purple, respectively.

388

Since this particular particle does not demonstrate phase separation, variations in the peak

389

intensities arise primarily due to differences in the height of the particle between the two probe

390

locations. Peaks associated with the organic component of the particle are evident at 1678, 2972,

391

and 3020 cm-1. The broad 1678 cm-1 feature is assigned to the C=N and C=O stretches in the

392

aged BrC product species with a contribution from carbonyl moieties in unreacted MG, ν(C=O)

393

at 1720 cm−1. The higher frequency feature at 2972 cm-1 is assigned to a C-H stretching mode

394

and the peak at 3020 cm-1 is assigned to an O-H bond stretching mode. The shoulder at

22


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395

approximately 3350 cm-1 may also be due to O-H modes in the organic product, as well as

396

unreacted MG. In addition, there are distinct bands corresponding to the ammonium sulfate

397

content of the particle; ν3(NH4+) at 2848, 3064, and 3228 cm-1; ν4(NH4+) at 1418 cm−1; and

398

ν3(SO42−) at 1097 cm−1. The PTIR data confirm that aerosolization of the BrC solution yields

399

particles that contain AS as well as organic compounds consistent with expected organic

400

products of the AS/MG reaction.7, 9, 11, 60-61

Figure 9. AFM 3D height image, (a), and phase image, (b), for a BrC particle with a diameter of ∼800 nm. PTIR spectra, (c), for two particle locations. Spectra are color coded to the corresponding target locations indicated in image (a). Reference PTIR spectra for AS and MG are also shown in red and purple, respectively. 401

23



402

4

Conclusions

403

We have developed a CRDS instrument operating at 403 nm that is calibrated using an

404

organic oil, squalane, with well-known optical constants to account for various instrumental

405

uncertainties. The calibrated instrument was tested with AS, a scattering material at the relevant

406

wavelength, and nigrosin, a strongly absorbing compound. The optical constants derived from a

407

Mie theory fit to the corrected experimental extinction cross-section data agree well with

408

literature values.

409

We studied BrC aerosol produced from the aqueous phase reaction of MG and AS. The

410

retrieved optical constants from CRDS showed no systematic trend over the course of 22 days of

411

reaction. The MAC of the bulk solution is observed to greatly increase over this time period, in

412

addition to the qualitative changes apparent in the absorption spectrum. The average complex

413

index, determined by CRDS, m = (1.558 ± 0.021) + i(0.002 ± 0.004), is not greatly different from

414

AS. The value for the real part of the index is slightly larger than that of AS, with the difference

415

just outside the 1 SD limit.

416

The particle size range used for Mie fitting was chosen to mitigate the effects of multiply

417

charged particles at smaller sizes and non-spherical shape effects at larger sizes. AFM image

418

analysis confirms that larger particles, ≥ 500 nm, consist of a significant fraction of particles that

419

are non-spherical in shape, while smaller particles are almost entirely spherical and, hence,

420

amenable to a Mie theory analysis. The observed breakdown of Mie theory for modeling the

421

extinction of larger BrC particles due to particle shape effects suggests that care must be taken

422

when applying Mie theory to characterize BrC radiative transfer effects in the atmosphere. AFM-

423

IR data also confirms that the aerosolized particles consist of AS and an organic component

424

consistent with the identified reaction products of the AS/MG reaction.

24


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425

The bulk AS/MG solution is strongly absorbing with a measured MAC of approximately

426

0.25 m2 g-1 at 400 nm. However, BrC aerosols produced from the solution are found to have an

427

index of refraction that is virtually the same as the AS seed. Specifically, the measured complex

428

index from CRDS is consistent with a value of zero, with an approximate upper limit of k ≤

429

0.006. These results are relevant to considerations of the potential forcing of related BrC aerosol

430

in the atmosphere. Although we determined the index at only one wavelength, 403 nm, the value

431

at relevant solar wavelengths will be even less since the MAC is observed to decrease

432

monotonically to longer wavelengths. Similar results showing a low value for the imaginary

433

refractive index of BrC product from the reaction of AS with glyoxal at a wavelength of 350 nm

434

have been reported.12 Related studies also suggest that photobleaching of the BrC chromophores

435

in the atmosphere may further reduce the potential for warming.62-63 In contrast, the complex

436

index values used to account for BrC in global models of radiative transfer can be much larger.64-

437

65

438

which incorporates other information, such as aerosol loading, in addition to the optical property

439

data for a range of BrC samples, to reach a more definitive conclusion.

Of course, a detailed examination of the impact of BrC on climate requires complex modeling

440

441

Acknowledgement

442

This manuscript is based on work supported by the National Science Foundation under

443

Grant ATC-1439045. Any opinions, findings, and conclusions or recommendations expressed in

444

this material are those of the authors and do not necessarily reflect the views of National Science

445

Foundation.

25



446

References

447

448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488

1. IPCC, Climate Change 2013: The Physical Science Basis. Cambridge University Press: Cambridge, United Kingdom and New York, NY, USA, 2013; p 1535. 2. Seinfeld, J. H.; Pandis, S. N., Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. John Wiley & Sons, Ltd: 2006. 3. Andreae, M. O.; Gelencsér, A., Black Carbon or Brown Carbon? The Nature of LightAbsorbing Carbonaceous Aerosols. Atmos. Chem. Phys. 2006, 6 (10), 3131-3148. 4. Pöschl, U., Atmospheric Aerosols: Composition, Transformation, Climate and Health Effects. Angew. Chem., Int. Ed. 2005, 44 (46), 7520-7540. 5. Laskin, A.; Laskin, J.; Nizkorodov, S. A., Chemistry of Atmospheric Brown Carbon. Chem. Rev. 2015, 115 (10), 4335-4382. 6. Moise, T.; Flores, J. M.; Rudich, Y., Optical Properties of Secondary Organic Aerosols and Their Changes by Chemical Processes. Chem. Rev. 2015, 115 (10), 4400-4439. 7. De Haan, D. O.; Hawkins, L. N.; Kononenko, J. A.; Turley, J. J.; Corrigan, A. L.; Tolbert, M. A.; Jimenez, J. L., Formation of Nitrogen-Containing Oligomers by Methylglyoxal and Amines in Simulated Evaporating Cloud Droplets. Environ. Sci. Technol. 2011, 45 (3), 984-991. 8. Kampf, C. J.; Filippi, A.; Zuth, C.; Hoffmann, T.; Opatz, T., Secondary Brown Carbon Formation via the Dicarbonyl Imine Pathway: Nitrogen Heterocycle Formation and Synergistic Effects. Phys. Chem. Chem. Phys. 2016, 18 (27), 18353-18364. 9. Lin, P.; Laskin, J.; Nizkorodov, S. A.; Laskin, A., Revealing Brown Carbon Chromophores Produced in Reactions of Methylglyoxal with Ammonium Sulfate. Environ. Sci. Technol. 2015, 49 (24), 14257-14266. 10. Powelson, M. H.; Espelien, B. M.; Hawkins, L. N.; Galloway, M. M.; De Haan, D. O., Brown Carbon Formation by Aqueous-Phase Carbonyl Compound Reactions with Amines and Ammonium Sulfate. Environ. Sci. Technol. 2014, 48 (2), 985-993. 11. Sareen, N.; Schwier, A. N.; Shapiro, E. L.; Mitroo, D.; McNeill, V. F., Secondary Organic Material Formed by Methylglyoxal in Aqueous Aerosol Mimics. Atmos. Chem. Phys. 2010, 10 (3), 997-1016. 12. Trainic, M.; Abo Riziq, A.; Lavi, A.; Flores, J. M.; Rudich, Y., The optical, physical and chemical properties of the products of glyoxal uptake on ammonium sulfate seed aerosols. Atmos. Chem. Phys. 2011, 11 (18), 9697-9707. 13. Betterton, E. A.; Hoffmann, M. R., Henry's Law Constants of Some Environmentally Important Aldehydes. Environ. Sci. Technol. 1988, 22 (12), 1415-1418. 14. Fu, T.-M.; Jacob, D. J.; Wittrock, F.; Burrows, J. P.; Vrekoussis, M.; Henze, D. K., Global Budgets of Atmospheric Glyoxal and Methylglyoxal, and Implications for Formation of Secondary Organic Aerosols. J. Geophys. Res.: Atmos. 2008, 113 (D15), D15303. 15. Nguyen, T. B.; Lee, P. B.; Updyke, K. M.; Bones, D. L.; Laskin, J.; Laskin, A.; Nizkorodov, S. A., Formation of Nitrogen- and Sulfur-Containing Light-Absorbing Compounds Accelerated by Evaporation of Water from Secondary Organic Aerosols. J. Geophys. Res.: Atmos. 2012, 117 (D1), D01207. 16. Nguyen, T. B.; Laskin, A.; Laskin, J.; Nizkorodov, S. A., Brown carbon formation from ketoaldehydes of biogenic monoterpenes. Faraday Discuss. 2013, 165 (0), 473-494.

26


Page 26 of 31

Page 27 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532


17. Chen, Y.; Bond, T. C., Light Absorption by Organic Carbon from Wood Combustion. Atmos. Chem. Phys. 2010, 10 (4), 1773-1787. 18. Tang, M.; Alexander, J. M.; Kwon, D.; Estillore, A. D.; Laskina, O.; Young, M. A.; Kleiber, P. D.; Grassian, V. H., Optical and Physicochemical Properties of Brown Carbon Aerosol: Light Scattering, FTIR Extinction Spectroscopy, and Hygroscopic Growth. J. Phys. Chem. A 2016, 120 (24), 4155-4166. 19. Abo Riziq, A.; Erlick, C.; Dinar, E.; Rudich, Y., Optical Properties of Absorbing and Non-Absorbing Aerosols Retrieved by Cavity Ring Down (CRD) Spectroscopy. Atmos. Chem. Phys. 2007, 7 (6), 1523-1536. 20. Berden, G.; Engeln, R., Cavity Ring-Down Spectroscopy: Techniques and Applications. John Wiley & Sons, Ltd: 2009. 21. Brown, S. S., Absorption Spectroscopy in High-Finesse Cavities for Atmospheric Studies. Chem. Rev. 2003, 103 (12), 5219-5238. 22. Toole, J. R.; Renbaum-Wolff, L.; Smith, G. D., A Calibration Technique for Improving Refractive Index Retrieval from Aerosol Cavity Ring-Down Spectroscopy. Aerosol Sci. Technol. 2013, 47 (9), 955-965. 23. Singh, S.; Fiddler, M. N.; Smith, D.; Bililign, S., Error Analysis and Uncertainty in the Determination of Aerosol Optical Properties Using Cavity Ring-Down Spectroscopy, Integrating Nephelometry, and the Extinction-Minus-Scattering Method. Aerosol Sci. Technol. 2014, 48 (12), 1345-1359. 24. Painter, L. R.; Attrey, J. S.; Jr., H. H. H.; Birkhoff, R. D., Vacuum Ultraviolet Optical Properties of Squalane and Squalene. J. Appl. Phys. 1984, 55 (3), 756-759. 25. Schuldt, K. J. Application of a Calibrated Aerosol Cavity Ring Down Spectrometer at 355 nm for the Measurement of Scattering and Absorbing Homogeneous Aerosols and Aerosol Mixtures. Thesis, The University of Georgia, Athens, Georgia, 2014. 26. William, D. D.; Paul, J. Z.; Po-Fu, H.; Peter, H. M., Optical Shape Fraction Measurements of Submicrometre Laboratory and Atmospheric Aerosols. Meas. Sci. Technol. 1998, 9 (2), 183. 27. Onasch, T. B.; Siefert, R. L.; Brooks, S. D.; Prenni, A. J.; Murray, B.; Wilson, M. A.; Tolbert, M. A., Infrared Spectroscopic Study of the Deliquescence and Efflorescence of Ammonium Sulfate Aerosol as a Function of Temperature. J. Geophys. Res.: Atmos. 1999, 104 (D17), 21317-21326. 28. Smith, M. L.; Bertram, A. K.; Martin, S. T., Deliquescence, Efflorescence, and Phase Miscibility of Mixed Particles of Ammonium Sulfate and Isoprene-Derived Secondary Organic Material. Atmos. Chem. Phys. 2012, 12 (20), 9613-9628. 29. Butler, T. J. A.; Mellon, D.; Kim, J.; Litman, J.; Orr-Ewing, A. J., Optical-Feedback Cavity Ring-Down Spectroscopy Measurements of Extinction by Aerosol Particles. J. Phys. Chem. A 2009, 113 (16), 3963-3972. 30. Pettersson, A.; Lovejoy, E. R.; Brock, C. A.; Brown, S. S.; Ravishankara, A. R., Measurement of Aerosol Optical Extinction at 532nm with Pulsed Cavity Ring Down Spectroscopy. J. Aerosol Sci. 2004, 35 (8), 995-1011. 31. Michel Flores, J.; Bar-Or, R. Z.; Bluvshtein, N.; Abo-Riziq, A.; Kostinski, A.; Borrmann, S.; Koren, I.; Koren, I.; Rudich, Y., Absorbing Aerosols at High Relative Humidity: Linking Hygroscopic Growth to Optical Properties. Atmos. Chem. Phys. 2012, 12 (12), 5511-5521.

27



533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578

32. Brown, S. S.; Stark, H.; Ciciora, S. J.; McLaughlin, R. J.; Ravishankara, A. R., Simultaneous in situ Detection of Atmospheric NO3 and N2O5 via Cavity Ring-Down Spectroscopy. Rev. Sci. Instrum. 2002, 73 (9), 3291-3301. 33. Bohren, C. F.; Huffman, D. R., Absorption and Scattering of Light by Small Particles. John Wiley & Sons, Ltd: 1983. 34. Mätzler, C. MATLAB Functions for Mie Scattering and Absorption, Version 2; Institute of Applied Physics, University of Bern: Bern, Switzerland, August 2002, 2002; p 26. 35. Hinds, W. C., Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles. 2nd ed.; John Wiley & Sons, Ltd: New York, 1999; p xx, 483 p. 36. Anttila, T.; Vaattovaara, P.; Komppula, M.; Hyvärinen, A. P.; Lihavainen, H.; Kerminen, V. M.; Laaksonen, A., Size-Dependent Activation of Aerosols into Cloud Droplets at a Subarctic Background Site During the Second Pallas Cloud Experiment (2nd PaCE): Method Development and Data Evaluation. Atmos. Chem. Phys. 2009, 9 (14), 4841-4854. 37. Hering, S. V.; McMurry, P. H., Optical Counter Response to Monodisperse Atmospheric Aerosols. Atmos. Environ., Part A 1991, 25 (2), 463-468. 38. Dinar, E.; Abo Riziq, A.; Spindler, C.; Erlick, C.; Kiss, G.; Rudich, Y., The Complex Refractive Index of Atmospheric and Model Humic-Like Substances (HULIS) Retrieved by a Cavity Ring Down Aerosol Spectrometer (CRD-AS). Faraday Discuss. 2008, 137 (0), 279-295. 39. Press, W. H., Numerical Recipes in Pascal (First Edition): The Art of Scientific Computing. Cambridge University Press: 1989. 40. Washenfelder, R. A.; Flores, J. M.; Brock, C. A.; Brown, S. S.; Rudich, Y., Broadband Measurements of Aerosol Extinction in the Ultraviolet Spectral Region. Atmos. Meas. Tech. 2013, 6 (4), 861-877. 41. Bondy, A. L.; Kirpes, R. M.; Merzel, R. L.; Pratt, K. A.; Banaszak Holl, M. M.; Ault, A. P., Atomic Force Microscopy-Infrared Spectroscopy of Individual Atmospheric Aerosol Particles: Subdiffraction Limit Vibrational Spectroscopy and Morphological Analysis. Anal. Chem. 2017, 89 (17), 8594-8598. 42. Dazzi, A.; Prater, C. B., AFM-IR: Technology and Applications in Nanoscale Infrared Spectroscopy and Chemical Imaging. Chem. Rev. 2017, 117 (7), 5146-5173. 43. Chernoff, D. A. In High Resolution Chemical Mapping Using Tapping Mode AFM with Phase Contrast, Bailey, G. W.; Ellisman, M. H.; Henniger, R. A.; Zaluzec, N. J., Eds. Jones and Begell: 1995; pp 888-889. 44. Estillore, A. D.; Morris, H. S.; Or, V. W.; Lee, H. D.; Alves, M. R.; Marciano, M. A.; Laskina, O.; Qin, Z.; Tivanski, A. V.; Grassian, V. H., Linking hygroscopicity and the surface microstructure of model inorganic salts, simple and complex carbohydrates, and authentic sea spray aerosol particles. Phys. Chem. Chem. Phys. 2017, 19 (31), 21101-21111. 45. Garcı́a, R.; Pérez, R., Dynamic atomic force microscopy methods. Surf. Sci. Rep. 2002, 47 (6), 197-301. 46. Hudson, P. K.; Gibson, E. R.; Young, M. A.; Kleiber, P. D.; Grassian, V. H., A Newly Designed and Constructed Instrument for Coupled Infrared Extinction and Size Distribution Measurements of Aerosols. Aerosol Sci. Technol. 2007, 41 (7), 701-710. 47. Weis, D. D.; Ewing, G. E., Infrared Spectroscopic Signatures of (NH4)2SO4 Aerosols. J. Geophys. Res.: Atmos. 1996, 101 (D13), 18709-18720. 48. Bluvshtein, N.; Flores, J. M.; He, Q.; Segre, E.; Segev, L.; Hong, N.; Donohue, A.; Hilfiker, J. N.; Rudich, Y., Calibration of a Multi-Pass Photoacoustic Spectrometer Cell Using Light-Absorbing Aerosols. Atmos. Meas. Tech. 2017, 10 (3), 1203-1213.

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49. Lavi, A.; Bluvshtein, N.; Segre, E.; Segev, L.; Flores, M.; Rudich, Y., Thermochemical, Cloud Condensation Nucleation Ability, and Optical Properties of Alkyl Aminium Sulfate Aerosols. J. Phys. Chem. C 2013, 117 (43), 22412-22421. 50. Ugelow, M. S.; Zarzana, K. J.; Day, D. A.; Jimenez, J. L.; Tolbert, M. A., The Optical and Chemical Properties of Discharge Generated Organic Haze Using in-situ Real-Time Techniques. Icarus 2017, 294 (Supplement C), 1-13. 51. Lee, A. K. Y.; Zhao, R.; Li, R.; Liggio, J.; Li, S.-M.; Abbatt, J. P. D., Formation of Light Absorbing Organo-Nitrogen Species from Evaporation of Droplets Containing Glyoxal and Ammonium Sulfate. Environ. Sci. Technol. 2013, 47 (22), 12819-12826. 52. Updyke, K. M.; Nguyen, T. B.; Nizkorodov, S. A., Formation of Brown Carbon via Reactions of Ammonia with Secondary Organic Aerosols from Biogenic and Anthropogenic Precursors. Atmos. Environ. 2012, 63 (Supplement C), 22-31. 53. Aiona, P. K.; Lee, H. J.; Leslie, R.; Lin, P.; Laskin, A.; Laskin, J.; Nizkorodov, S. A., Photochemistry of Products of the Aqueous Reaction of Methylglyoxal with Ammonium Sulfate. ACS Earth Space Chem. 2017, 1 (8), 522-532. 54. Zhao, R.; Lee, A. K. Y.; Huang, L.; Li, X.; Yang, F.; Abbatt, J. P. D., Photochemical processing of aqueous atmospheric brown carbon. Atmos. Chem. Phys. 2015, 15 (11), 6087-6100. 55. Flores, J. M.; Washenfelder, R. A.; Adler, G.; Lee, H. J.; Segev, L.; Laskin, J.; Laskin, A.; Nizkorodov, S. A.; Brown, S. S.; Rudich, Y., Complex Refractive Indices in the NearUltraviolet Spectral Region of Biogenic Secondary Organic Aerosol Aged with Ammonia. Phys. Chem. Chem. Phys. 2014, 16 (22), 10629-10642. 56. Lambe, A. T.; Cappa, C. D.; Massoli, P.; Onasch, T. B.; Forestieri, S. D.; Martin, A. T.; Cummings, M. J.; Croasdale, D. R.; Brune, W. H.; Worsnop, D. R.; Davidovits, P., Relationship between Oxidation Level and Optical Properties of Secondary Organic Aerosol. Environ. Sci. Technol. 2013, 47 (12), 6349-6357. 57. Bertram, A. K.; Martin, S. T.; Hanna, S. J.; Smith, M. L.; Bodsworth, A.; Chen, Q.; Kuwata, M.; Liu, A.; You, Y.; Zorn, S. R., Predicting the relative humidities of liquid-liquid phase separation, efflorescence, and deliquescence of mixed particles of ammonium sulfate, organic material, and water using the organic-to-sulfate mass ratio of the particle and the oxygen-to-carbon elemental ratio of the organic component. Atmos. Chem. Phys. 2011, 11 (21), 10995-11006. 58. You, Y.; Renbaum-Wolff, L.; Carreras-Sospedra, M.; Hanna, S. J.; Hiranuma, N.; Kamal, S.; Smith, M. L.; Zhang, X.; Weber, R. J.; Shilling, J. E.; Dabdub, D.; Martin, S. T.; Bertram, A. K., Images reveal that atmospheric particles can undergo liquid–liquid phase separations. Proc. Natl. Acad. Sci. 2012. 59. Laskina, O.; Morris, H. S.; Grandquist, J. R.; Qin, Z.; Stone, E. A.; Tivanski, A. V.; Grassian, V. H., Size Matters in the Water Uptake and Hygroscopic Growth of Atmospherically Relevant Multicomponent Aerosol Particles. J. Phys. Chem. A 2015, 119 (19), 4489-4497. 60. Schwier, A. N.; Sareen, N.; Mitroo, D.; Shapiro, E. L.; McNeill, V. F., GlyoxalMethylglyoxal Cross-Reactions in Secondary Organic Aerosol Formation. Environ. Sci. Technol. 2010, 44, 6174-6182. 61. Noziere, B.; Dziedzic, P.; Cordova, A., Products and Kinetics of the Liquid-Phase Reaction of Glyoxal Catalyzed by Ammonium Ions (NH4+). J. Phys. Chem. A 2009, 113, 231237. 62. Sareen, N.; Moussa, S. G.; McNeill, V. F., Photochemical Aging of Light-Absorbing Secondary Organic Aerosol Material. J. Phys. Chem. A 2013, 117 (14), 2987-2996.

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63. Woo, J. L.; Kim, D. D.; Schwier, A. N.; Li, R.; McNeill, V. F., Aqueous aerosol SOA formation: impact on aerosol physical properties. Faraday Discuss. 2013, 165, 357-367. 64. Hammer, M. S.; Martin, R. V.; van Donkelaar, A.; Buchard, V.; Torres, O.; Ridley, D. A.; Spurr, R. J. D., Interpreting the ultraviolet aerosol index observed with the OMI satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effects. Atmos. Chem. Phys. 2016, 16 (4), 2507-2523. 65. Wang, X.; Heald, C. L.; Liu, J.; Weber, R. J.; Campuzano-Jost, P.; Jimenez, J. L.; Schwarz, J. P.; Perring, A. E., Exploring the observational constraints on the simulation of brown carbon. Atmos. Chem. Phys. 2018, 18 (2), 635-653.

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TOC graphic 215x120mm (300 x 300 DPI)


Optical Property Measurements and Single Particle Analysis of

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