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Supporting Online Material
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Implications of Low Volatility SOA and Gas-Phase Fragmentation Reactions on
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SOA Loadings, and their Spatial and Temporal Evolution in the Atmosphere
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Manish Shrivastava,
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Beranek, 1 Rahul A. Zaveri, 1 Jerome Fast 1
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Imre Consulting, Richland, WA
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Corresponding author: ManishKumar.Shrivastava@pnl.gov
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Alla Zelenyuk,
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Dan Imre,
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Richard Easter,
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Josef
Pacific Northwest National Laboratory, Richland, WA 99352
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S1.0. Kinetic mass transfer
The kinetic mass transfer model described by Koo et al. [2003] is used to compare
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model predictions of SOA particle evaporation to the laboratory and field measurements
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of Vaden et al. [2011]. The mass flux of species i (representing a given volatility bin) to
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particles of size k (Ji,k) is calculated using the equation [Seinfeld and Pandis, 1998]
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𝑒𝑞
𝐽𝑖,𝑘 = 2𝜋𝑁𝑘 𝑑𝑘 𝐷𝑖 𝑓(𝐾𝑛𝑘 , 𝛼)(𝑐𝑖 − 𝑐𝑖,𝑘
𝜂𝑘 )
1
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27
where Nk and dk are the number and diameter of particles of size k, respectively; Di is the
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diffusivity of species i; ci is the bulk gas-phase concentration of species i away from the
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particle surface; ci,keq is the equilibrium concentration of species i at the particle surface,;
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f(Kn,α) is the correction for non-continuum effects and imperfect accommodation; Knk is
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the Knudsen number; α is the accommodation coefficient; and ηk is the Kelvin effect
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correction.
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The quantity ci,keq is calculated assuming absorptive partitioning in a pseudo-ideal
solution:
𝑒𝑞
𝑐𝑖,𝑘
= 𝑥𝑖,𝑘 𝑐𝑖∗
2
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where xi,k is the mole fraction of species i in particles of size k and ci* is the effective
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saturation concentration of species i (equal to given volatility species). For all species, a
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molecular weight of 150 g mol-1, density of 1500 kg m-3, diffusion coefficient of 5×10-6
2
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m2 s-1, and surface tension of 0.05 N m-1 are assumed following Riipinen et al. [2010].
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The Livermore Solver for Ordinary Differential Equations (LSODES) in FORTRAN is
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used to solve the mass transfer equations and output instantaneous particle diameters for
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comparison to experimental data.
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For evaporation rates shown in Figure 1a of the main text, calculations are
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performed using a-7-species volatility basis set (VBS) fit from Pathak et al. [2007] for
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ozonolysis of α-pinene under low NOx conditions in the dark. Initial aerosol mass
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fractions, defining the initial particle volatility distribution used as input to the kinetic
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mass transfer code, are shown in Table S1, and are calculated for each lumped species i,
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assuming ROG=200 ppb and product distributions from the 7-species VBS fits. Particle
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evaporation rates are calculated as the sum of evaporation rates from all species i as:
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𝑛
𝑑𝑚𝑘
= ∑ 𝐽𝑖,𝑘
𝑑𝑡
3
𝑖=1
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where dmk/dt is the instantaneous rate of change of mass of particles of size k. For any
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given calculation, all particles are assumed to be of the same size. For evaporation
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calculations in main text Figure 1a, we assume that concentrations of organics in the gas-
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phase (ci in equation 1) remain zero over the entire modeling period, consistent with the
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experimental conditions of Vaden et al. [2011]. With this assumption, particles do not
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interact with each other, the particle evaporation rate does not depend on the total number
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of particles Nk, and the kinetic mass transfer equation needs only to be solved for the
3
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particle phase. Figure 1a shows calculations for two values of the mass accommodation
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coefficient: α=1 and 0.001. A smaller value of α reduces the kinetic evaporation rate of
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SOA particles. For clarity, other laboratory experiments from Vaden et al. [2011] that are
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similar to the field data are not shown in main text Figure 1.
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For the growth calculations shown in main text Figure 1b, we assumed non-
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volatile SOA and that a constant concentration gradient (ci – cieq) of 1 µg m-3 is always
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present between the gas and aerosol phases. For non-volatile SOA, cieq is zero, and the
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constant concentration gradient transforms to a single species bulk gas-phase
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concentration (ci) of 1 µg m-3. This value of ci corresponds to semi-volatile organic
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species within the range of the VBS. Figure 1b of the main text shows calculation results
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for four different values of the mass accommodation coefficient: α=1, 0.1, 0.01 and
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0.001. Similar to the evaporation rate results, a smaller value of α reduces the growth rate
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of SOA.
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In Figure 1c of the main text, the range of C* for the 5 VBS species (with lumped
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C* of 0.001, 0.01, 0.1, 1 and 10 µg m-3) was chosen to fit the measured evaporation rate
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of laboratory-generated pure α-pinene SOA and ambient particles as follows. First, a re-
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arrangement of equations 1 and 3 above, gives an expression for the instantaneous
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average vapor pressure at the particle surface (C*inst) from the measured rate of change of
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particle diameter (ddp/dt) (ms-1):
∗
𝐶𝑖𝑛𝑠𝑡
=−
𝑑𝑑𝑝
1
∗
𝑑𝑡 4𝐷𝑖 𝑓(𝐾𝑛𝑘 , 𝛼)/(𝑑𝑝 𝑝 )
4
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4
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, where p is the particle density (assumed to be 1000 kg m-3) and all other terms are as
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defined previously. Here the gas-phase concentration away from the particle surface is set
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to zero, corresponding to conditions in the evaporation chamber. Using equation 4, data
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from both laboratory and ambient measurements, and two α values of 1 and 0.05 [Pierce
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et al., 2011; Riipinen et al., 2010], we then calculate the minimum and maximum C*inst
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as 1.85 *10-3 g m-3 and 2.39 g m-3, respectively. Note that α values lower than 0.01
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resulted in almost no SOA growth shown in Figure 1b in the main text, and are most
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likely unrealistic. Our 5 components with lumped C* of 0.001, 0.01, 0.1, 1 and 10 µg m-3
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include the minimum and maximum C*inst for both laboratory and ambient datasets, and
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are thus appropriate for this study.
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S2.0 Reactions in WRF-Chem
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The
equations
governing
oxidation
of
S/IVOC
precursors
through
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functionalization reactions (Fn) are written within the KPP module of WRF-Chem, and
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were previously described by Shrivastava et al. [2011]. In this work, we also track the
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generation number of species to treat fragmentation as shown in Figure S1. The
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corresponding equations used for the VBS species undergoing only functionalization
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reactions (i.e., all generations in the Fn approach and just the first 2 generations in the
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Frag1 and Frag2 approaches) are:
𝑃𝑂𝐴(𝑔)𝑖,𝑛 + 𝑂𝐻 → 1.15 𝑆𝐼 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1
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𝑆𝐼 − 𝑆𝑂𝐴(𝑔)𝑖,𝑛 + 𝑂𝐻 → 1.15 𝑆𝐼 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1
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5
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where POA(g) represents directly emitted SIVOC organic vapors from anthropogenic or
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biomass burning sources; SI-SOA(g) represents SOA precursor species formed after
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photochemical oxidation of POA(g); i denotes any given volatility species except the
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lowest volatility one; i-1 denotes the species with C* equal to i/10; and n denotes the
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generation number indicating the number of times a given species has reacted with OH.
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The generation number n increases by 1 from the left to the right hand side of any
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equation due to reaction with OH. We assume that 15% by mass is added every
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generation, corresponding to the addition of 2 oxygen atoms to a C15H32 precursor. All
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VBS species are assumed to have a molecular weight of 250 g mole-1.
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For the Frag1 and Frag2 approaches, the 3rd and higher generation species undergo
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fragmentation reactions in addition to functionalization. Equations (7) and (8) below
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represent the reactions for 3rd and higher generation (n≥3) for the Frag1 and Frag2
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approaches, respectively.
𝑆𝐼 − 𝑆𝑂𝐴(𝑔)𝑖,𝑛≥3 + 𝑂𝐻
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→ 0.575 𝑆𝐼 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1 + 0.4𝑆𝐼 − 𝑆𝑂𝐴(𝑔)𝑖=1,𝑛+1
𝑆𝐼 − 𝑆𝑂𝐴(𝑔)𝑖,𝑛≥3 + 𝑂𝐻
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→ 0.1725 𝑆𝐼 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1 + 0.75𝑆𝐼 − 𝑆𝑂𝐴(𝑔)𝑖=1,𝑛+1
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The first term on the right hand side of both equations 7 and 8 denotes functionalization
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with a 15% increase in mass from added oxygen, while the second term on the right hand
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side denotes fragmentation where 40% and 75%, respectively, of VBS species in each
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volatility bin are moved to the highest volatility species of C* = 104 g m-3 (i.e. i=1).
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S3.0 Reactions in the box model
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Reactions governing oxidation of S/IVOC precursors in the box model are similar to
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those implemented in WRF-Chem, but include additional tracers to represent the non-
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oxygen and oxygen parts of each VBS species to allow simulating the O:C ratio of SOA,
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as described by Shrivastava et al. [2011]. Box-model-simulated O:C ratios are shown in
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Figure 3 of the main text and in Figure S6 for the 7-species and 4-species VBS,
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respectively. The ratios were calculated by splitting each VBS species shown in Figure
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S1 into its oxygen (O) and non-oxygen (C,H,N) parts and repeating the multi-
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dimensional representation shown in Figure S1 for non-oxygen and oxygen parts
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separately in the box model. The equations governing this process for VBS species
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undergoing only functionalization reactions (all generations in Fn and just the first 2
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generations in the Frag1 and Frag2 approaches) are:
𝑉𝑂𝐶(𝑔)𝑖,𝑛,𝑐 + 𝑂𝐻 → 𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑐 + 0.15𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑜
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𝑉𝑂𝐶(𝑔)𝑖,𝑛,𝑜 + 𝑂𝐻 → 𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑜
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𝑉 − 𝑆𝑂𝐴(𝑔)𝑖,𝑛,𝑐 + 𝑂𝐻 → 𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑐 + 0.15𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑜
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𝑉 − 𝑆𝑂𝐴(𝑔)𝑖,𝑛,𝑜 + 𝑂𝐻 → 𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑜
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where VOC(g) represents the “initial” oxidation products derived from the smog chamber
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yields; the additional subscripts c and o represent the non-oxygen and oxygen parts of the
7
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VOC species, respectively; and V-SOA(g) represents SOA precursor species formed after
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the photochemical oxidation of VOC(g). The non-oxygen component of the “initial”
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oxidation products are derived from the assumed “initial” O:C ratio of 0.2. The sum of
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non-oxygen and oxygen parts equals the total VOC(g) concentrations, thus conserving
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mass. The “initial” O:C ratio of 0.2 is similar to that of first generation alpha-pinene
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ozonolysis products [Jimenez et al., 2009]. As shown by equations (9) and (11), oxidation
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of the non-oxygen part of SOA precursor i results in formation of non-oxygen, and
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oxygen parts (15% by mass due to 2 oxygen atoms added) of V-SOA with successive
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lower volatility i-1. Equations (10) and (12) account for movement of the oxygen part of
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each VBS species to lower volatility, similar to the non-oxygen part, to satisfy mass
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conservation.
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For the Frag1 and Frag2 approaches, 3rd and higher generation species undergo
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fragmentation reactions in addition to functionalization. Reactions 13 and 14 represent
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the movement of non-oxygen and oxygen species, respectively, for the Frag1 approach.
𝑉 − 𝑆𝑂𝐴(𝑔)𝑖,𝑛≥3,𝑐 + 𝑂𝐻
→ 0.5 𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑐 + 0.075 𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑜
13
+ 0.4𝑉 − 𝑆𝑂𝐴(𝑔)𝑖=1,𝑛+1,𝑐
𝑉 − 𝑆𝑂𝐴(𝑔)𝑖,𝑛≥3,𝑜 + 𝑂𝐻
14
→ 0.5 𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑜 + 0.4𝑉 − 𝑆𝑂𝐴(𝑔)𝑖=1,𝑛+1,𝑜
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8
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The first 2 terms on the right hand side of equation 13 represent functionalization
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reactions in the VBS for n≥3 of each non-oxygen-containing causing formation of 50%
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non-oxygen species and 15% of oxygen species of successively lower volatility. The
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third term represents fragmentation leading to 40% of the non-oxygen part being assigned
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to the highest volatility species with C* = 104 g m-3 (i.e., i=1). Equation 14 represents
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movement of the n≥3 oxygen parts similar to the n≥3 non-oxygen-containing partts, i.e.
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50% of the oxygen part moves to successively lower volatility, while 40% moves to the
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highest volatility bin where C* = 104 g m-3 (i.e., i=1).
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Similarly, equations 15 and 16 represent the movement of non-oxygen-containing and
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oxygen-containing species for the Frag2 approach.
𝑉 − 𝑆𝑂𝐴(𝑔)𝑖,𝑒,𝑛≥3,𝑐 + 𝑂𝐻
→ 0.15 𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑐 + 0.0225 𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑜
15
+ 0.75𝑉 − 𝑆𝑂𝐴(𝑔)𝑖=1,𝑛+1,𝑐
𝑉 − 𝑆𝑂𝐴(𝑔)𝑖,𝑛≥3,𝑜 + 𝑂𝐻
16
→ 0.15 𝑉 − 𝑆𝑂𝐴(𝑔)𝑖−1,𝑛+1,𝑜 + 0.75𝑉 − 𝑆𝑂𝐴(𝑔)𝑖=1,𝑛+1,𝑜
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Thus after every generation of oxidation, both the non-oxygen and oxygen parts of each
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VBS species functionalize and fragment, moving to either the lower or the highest
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volatility species respectively, thus satisfying mass conservation.
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S4.0 Comparing 7-species and 4-species VBS
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In section 3.2 of the main text, using an initial volatility distribution based on the
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7-species VBS fits from Pathak et al. [2007] (low NOx, dark, low RH), we demonstrated
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how details of aging parameterization, background OA concentrations, and treatment of
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SOA as SVSOA or NVSOA affect the evolution of SOA and the O/C ratio. However,
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because of the limited range of experimental conditions in Pathak et al. [2007], the yield
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of the highest C* species (104 µg m-3) is not constrained by measurements. Donahue et al.
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[2012] suggested recently that gas-phase OH reactions with semi-volatile SOA vapors
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enhance SOA concentrations by a factor of 2-4 and that the volatility distribution of 1st
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generation α-pinene ozonolysis products is comprised of a pool of organics whose C* are
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104 to 106 g m-3, which serve as precursor for SOA formation during aging. In our
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simulations, the stoichiometric yield coefficient αi for species with C* of 104 µg m-3 is
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1.64 times the sum of corresponding yield coefficients αi for species with C* = 0.01 to
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103 µg m-3 for the 7-species VBS in Pathak et al. [2007], which by comparison to
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Donahue et al. [2012] is reasonable. There is clearly need for more robust
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experimentally-based parameterizations; nevertheless, the point of this study is to
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investigate the differences in predicted SOA loadings and O/C ratio as we introduce
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approaches involving fragmentation and non-volatile SOA.
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In this section, we investigate the sensitivity of the model to yield of the highest
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C* species (104 µg m-3) by comparing results from 7-species VBS with the 4-species VBS
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fits from Pathak et al. [2007]. Note that the 4-species VBS fit in Pathak et al. [2007] only
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covers the C* range from 1-1000 µg m-3; thus, there is zero yield for C* = 104 µg m-3.
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Because the 4-species VBS does not include a C* = 104 µg m-3 species, we added it to the
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4-species VBS, but assigned a zero initial yield to be consistent with Pathak et al. [2007].
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Addition of this species facilitates the movement of fragmented material from the lower
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volatility species, similar to the 7-species VBS formulation. Note that due to its high
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volatility this species does not affect SOA partitioning.
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Figure S5 shows the gas-particle distribution for the FnSVSOA and FnNVSOA
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approaches after 2 hours, 4 hours and 8 hours of simulation time. Figure S5a and S5b
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show that gas phase concentrations are higher in FnNVSOA compared to FnSVSOA after
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2 hours of aging, while S5e and S5f show lower gas phase concentrations in FnNVSOA
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compared to FnSVSOA due to the combined effects of gas phase functionalization
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reactions and likely particle phase processes. Importantly, Figure S5 shows that
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calculated SOA loadings in the FnNVSOA and the FnSVSOA simulations are nearly the
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same throughout the simulation (also evident from Figure S6b).
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Figure S6 shows the temporal evolution of SOA concentration and O:C ratios for
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the 4-species VBS. In the “non-aging SIVOC” parameterization (Figure S6a) the
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RevNVSOA configuration produces no SOA, because the initial volatility distribution of
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SOA is high than the 7-species VBS. In the “aging SIVOC” parameterizations, the
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calculated peak SOA loadings in the Fn and Frag1 configurations are factor of 2.2 and
200
1.4 lower, respectively, compared with corresponding 7-species VBS calculated SOA
201
loadings presented in the main paper. In contrast, the calculated peak SOA loadings in the
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Frag2 configurations using 4 or 7-species VBS (Figures S6d and 3d) yield nearly the
203
same results. Similarly, the calculated O:C ratios using the two VBS representations are
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comparable.
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In summary, the absolute SOA loadings are sensitive to the mass in the C* of 104
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g m-3 species, but the relative differences between model configurations show similar
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trends varying with fragmentation and volatility in both the 7-species and the 4-species
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VBS.
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S5.0 Effect of initial precursor concentration
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So far all our box model simulations using both 4-species and 7-species VBS used
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ROG = 2 ppbv. Here, we investigate the behavior under increased precursor
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concentration. Figure S7 shows box model results with the 7-species VBS using ROG =
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50 ppbv at a constant background OA of 0.5 µg m-3.
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The non-aging SIVOC (Figure S7a) produces much higher peak SOA loadings as
216
compared to the corresponding results for ROG = 2 ppbv (Figure 3a in the main text)
217
and the large difference between SVSOA and NVSOA seen in the main text Figure 3a
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are significantly reduced. In addition, the aging configurations (Fn, Frag1 and Frag2)
219
produce only a factor of 2 higher SOA loading compared to the non-aging configuration
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during the first day (e.g., compare Figure S7b with Figure S7a). In comparison, at ROG
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= 2 ppbv, the aging configurations increased SOA loadings by 1-2 orders of magnitude
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(Figure 3b versus Figure 3a in main text). Figures S7b to S7d show that the O:C ratio
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increases with aging in both the SVSOA and NVSOA approaches, consistent with Figure
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3. In addition, Figure S7e shows the NVSOA to SVSOA ratio rapidly approaches 1 early
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in the day. In the non-aging case (orange line in Figure S7e), this ratio continuously
226
increases as SVSOA evaporates due to dilution and because there is no additional SOA
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227
formation beyond the fixed yields. In the aging cases the ratio remains close to 1
228
throughout the 3 day simulation.
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S6.0 Temperature effects
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The effect of temperature on C* is given by the Clausius-Clapeyron equation,
231
parameterized by the enthalpy of vaporization Hv. In this study, we select Hv values
232
varying with C* as described by Donahue et al. [2006]. Figure S8a illustrates the effect of
233
temperature on SOA formation and evolution for the Frag1 approach, with constant
234
background OA concentration of 0.5 µg m-3. Peak SOA concentrations increase by a
235
factor of 3 as temperature is reduced from 313 K to 273 K in both the SVSOA (dashed
236
lines) and NVSOA (solid lines) approaches, because of the reduction in C* with
237
temperature. Some of the differences in SOA loadings are also due to higher OH
238
concentrations at higher temperatures simulated by the gas-phase chemistry mechanism
239
in the box model, but this impact is secondary to the effect of reducing C* on SOA
240
formation. Figure S8b demonstrates that with time, dilution plays a more important role
241
and the SVSOA evaporates while the NVSOA does not.
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243
244
245
246
247
248
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Table S1. Initial aerosol mass fractions (AMF) in each volatility bin corresponding to the
250
7-species VBS stoichiometric coefficients in Pathak et al. [2007]. These values were
251
used as inputs to the kinetic mass transfer code.
Parameter
C* at 298 K
Lumped species
10-2
10-1
100
101
102
103
104
7-species VBS AMF 0.003 0.038 0.118 0.274 0.251 0.222 0.094
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
14
270
271
272
273
Table S2: Initial conditions for gas phase species in box model simulations implementing
the CBM-Z photochemical mechanism as defined in Zaveri et al. [1999]. Other variables
used for model initialization (chemistry and photolysis) include relative humidity (RH) =
85% and latitude = 40 N. The model simulates a day in the month of March.
Species
Mixing ratio (ppb)
H2SO4
1
HNO3
0.2
HCl
0.1
NH3
1.2
NO
2
NO2
5
O3
60
H2O2
1
CO
70
SO2
1
CH4
1800
HCHO
2
PAN
1
PAR
50
OLET
1
OLEI
1
TOL
2
XYL
2
API
2
LIM
2
274
275
15
276
277
278
279
280
281
282
283
284
285
286
287
Figure S1: Schematic illustrating the assumed gas phase oxidation reactions of
VBS species with OH as discussed in the text. The generation number indicates
the number of times a given species has reacted with OH. Since generations 3 and
higher undergo the same functionalization and fragmentation reactions, they are
lumped together to simplify their representation in models. Fragmentation
reactions are assumed to move 40% or 75% of the mass of each VBS species to
the highest volatility species (C* of 104 g m-3), while 10% of the mass of each
VBS species is lost to highly volatile organic species outside the VBS range.
288
289
290
291
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292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
Figure S2: Box model simulations showing the temporal evolution of SOA
concentrations using the 7-species VBS fits from Pathak et al. (2007) with
ROG = 2 ppbv. Results are presented as dilution-corrected SOA
concentrations above background. DF represents the dilution factor, calculated
as the ratio of the concentration of a non-volatile non-reactive tracer species
before dilution to its concentration after dilution. Atmospheric SOA evolution
compares traditional absorptive partitioning SVSOA (blue line) to our revised
approach with formation of NVSOA (red line). (a) “Non-aging SIVOC”
parameterization. (b), (c) and (d) “Aging SIVOC” parameterizations as defined
in main text Table 1 for the Fn, Frag1, and Frag2 approaches. e) dilution factor
and OH concentrations. The solid and dashed lines in (a-d) denote simulations
assuming background SOA concentrations of 0.5 µg m-3 and 0.1 µg m-3,
respectively.
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Figure S3: SOA volatility distribution (excluding background OA) after 24
hours for (a) TradSVSOA, (b) FnSVSOA, (c) Frag1SVSOA, and (d)
Frag2SVSOA configurations at background SOA concentration of 0.5 µg m-3
with ROG = 2 ppbv. See main text Table 1 for configuration definitions.
Species are distributed according to their effective saturation concentration (C*,
g m-3), presented as a logarithmically-distributed volatility basis set. Also
indicated are total gas and particle phase concentrations calculated as sum of
all volatility species.
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Figure S4: Box model simulations of the SOA volatility distribution (excluding
background OA) after 24 hours for (a) TradNVSOA, (b) FnNVSOA, (c)
Frag1NVSOA, and (d) Frag2NVSOA configurations at a background SOA
concentration of 0.5 µg m-3 with ROG = 2 ppbv. See main text Table 1 for
configuration definitions. Species are distributed according to their effective
saturation concentration (C*, g m-3), presented as a logarithmically-distributed
volatility basis set. Also indicated are total gas and particle phase concentrations
calculated as sum of all volatility species.
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Figure S5: Box model evolution of SOA volatility distributions due to dilution
and OH oxidation for (a), (c), (e) FnSVSOA and (b), (d), (e) FnNVSOA after 2, 4
and 8 hours, respectively, with ROG = 2 ppbv. Panels (a) and (b) show that gas
phase concentrations are higher in the FnNVSOA configuration compared to the
FnSVSOA configuration after 2 hours of aging, while panels (e) and (f) show
lower gas phase concentrations in FnNVSOA compared to FnSVSOA due to the
combined effects of gas phase functionalization reactions and likely particle phase
processes continuously moving material to the non-volatile species. See main text
and supplemental material for more details.
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Figure S6. Box model calculations showing the temporal evolution of absolute
SOA concentrations above background (bkg), using the 4-species VBS from
Pathak et al. [2007] as described in the text with ROG = 2 ppbv. Atmospheric
SOA evolution compares traditional absorptive partitioning SVSOA (blue line) to
our revised approach with formation of NVSOA (red line). (a) “Non-aging
SIVOC” parameterization. (b), (c) and (d) “Aging SIVOC” parameterization as
defined in main text Table 1. (e) ratio of NVSOA to SVSOA approaches for the
Fn, Frag1 and Frag2 configurations as defined in main text Table 1. f) dilution
factor and OH concentrations. The solid and dashed lines in (a-e) denote
calculations assuming background SOA concentrations of 0.5 µg m-3, and 0.1 µg
m-3, respectively. The black and green lines in (a), (b), (c) and (d) denote O:C
ratios (right-hand vertical axis) for the SVSOA and NVSOA approaches
respectively.
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Figure S7. Box model calculations showing the temporal evolution of absolute SOA
concentrations above background (bkg), using the 7-species VBS from Pathak et al.
[2007]. This figure is similar to Figure 3 in the main text except that it is initialized with a
higher ROG concentration of 50 ppbv. All results are based on a constant background
concentration of 0.5 g m-3. (a) “Non-aging SIVOC” parameterization. (b) Fn, (c) Frag1
and (d) Frag2 configurations using the “aging SIVOC” parameterization as defined in
main text Table 1. (e) ratio of NVSOA to SVSOA approaches for Fn, Frag1 and Frag2
configurations, defined in main text Table 1. The blue and red lines denote SVSOA and
NVSOA loadings, while the black and green lines denote O:C ratios for the SVSOA and
NVSOA approaches, respectively.
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Figure S8: Effects of temperature on the temporal evolution of absolute SOA
concentrations (above background) for the Frag1 configuration assuming a
constant background SOA concentration of 0.5 µg m-3 at ROG = 2 ppbv. The
dashed and solid lines represent SVSOA and NVSOA approaches, respectively,
for temperatures of 273 K (black), 298 K (blue) and 313 K (green).
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S7.0 References
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