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The e ec o a mosphe ically ele an aminium sal s on wa e up ake
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Hy inen, Noo a
Hy inen, N. (2023). The e ec o a mosphe ically ele an aminium sal s on wa e up ake.
A mosphe ic Chemis y and Physics, 23(21), 13809-13817. h ps://doi.o g/10.5194/acp-23-
13809-2023
2023
A mos. Chem. Phys., 23, 13809–13817, 2023
h ps://doi.o g/10.5194/acp-23-13809-2023
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he C ea i e Commons A ibu ion 4.0 License.
Resea ch a icle
The e ec o a mosphe ically ele an
aminium sal s on wa e up ake
Noo a Hy inen
Depa men o Chemis y, Nanoscience Cen e , Uni e si y o Jy äskylä, 40014 Jy äskylä, Finland
Co espondence: Noo a Hy inen ([email p o ec ed])
Recei ed: 26 May 2023 – Discussion s a ed: 7 June 2023
Re ised: 27 Sep embe 2023 – Accep ed: 3 Oc obe 2023 – Published: 6 No embe 2023
Abs ac . A mosphe ic new pa icle o ma ion is ini ia ed by clus e ing o gaseous p ecu so s, such as small
acids and bases. The hyg oscopic p ope ies o hose p ecu so s he e o e a ec he hyg oscopic p ope ies o
ae osol pa icles. In his wo k, he wa e up ake o di e en sal s consis ing o a mosphe ic small acids and
amines was s udied compu a ionally using he conduc o -like sc eening model o eal sol en s (COSMO-RS).
This me hod allows o he p edic ion o wa e ac i i ies in a mosphe ically ele an sal s ha ha e no been
included in o he he modynamics models. Wa e ac i i ies a e epo ed he e o bina y aqueous sal solu-
ions, as well as e na y solu ions con aining p oxies o o ganic ae osol cons i uen s. The o de o he s ud-
ied ca ion species ega ding wa e ac i i ies is simila in sul a e, ioda e, and me hylsul ona e, as well as in
bisul a e and ni a e. P edic ed wa e up ake s eng hs (in mole ac ion) con o m o he ollowing o de s: e -
ia y >seconda y >p ima y amines and guanidinos >amino acids. The addi ion o wa e -soluble o ganic o he
s udied sal s gene ally leads o weake wa e up ake compa ed o pu e sal s. On he o he hand, wa e -insoluble
o ganic likely phase sepa a es wi h aqueous sal solu ions, leading o minimal e ec s on wa e up ake.
1 In oduc ion
Wa e up ake o a mosphe ic ae osol has a la ge e ec on
he adia i e o cing h ough, e.g., cloud o ma ion. Theo-
e ical and expe imen al e idence show ha e en a small
amoun o sal has a dominan e ec on cloud condensa-
ion nucleus (CCN) ac i i y (Bilde and S enningsson, 2004;
King e al., 2012). These sal s may o igina e om sea sp ay
o om he nuclea ion and condensa ion o acidic and basic
compounds, such as sul u ic acid and amines.
The nuclea ion o gas-phase acids and bases has been
in es iga ed compu a ionally du ing ecen yea s by com-
pu ing o ma ion ene gies o clus e s ha con ain a ious
small molecules (Elm, 2021). Compu a ional s udies ha e
shown ha a ious amines can o m molecula clus e s wi h
acidic species, such as sul u ic acid (Elm e al., 2016; Myllys
e al., 2018; Kubeˇ
cka e al., 2023). Liu e al. (2022) ound
ha guanidino-con aining compounds (guanidine, agma ine)
enhance me hylsul onic-acid-d i en nuclea ion. Chen e al.
(2022) simula ed he nuclea ion o ni ic acid wi h a ious
alkylamines, alkanolamines, and polyamines. They ound
ha alkanolamines and polyamines can nuclea e wi h ni ic
acid a oom empe a u e, while ammonia and alkylamines
equi e lowe empe a u es.
The ac i i y o wa e in ae osol pa icles desc ibes he e-
sponse o he pa icles o a ia ions in RH. Some expe imen-
al s udies ha e in es iga ed wa e ac i i ies o ammonium
and aminium sul a e as well as ni a e sal s (Bonne , 1981;
Clegg e al., 2013; Saue wein e al., 2015; Ro elli e al.,
2017). Fo example, Ro elli e al. (2017) ound ha wa e
ac i i y dec eases wi h he inc easing alkyl g oup leng h and
numbe o alkyl g oups. Howe e , wa e ac i i y measu e-
men s o sal solu ions comp ising la ge amines ele an o
sal solu ions a e s ill lacking.
This s udy in es iga es he e ec o di e en amine and
acid species in ol ed in he a mosphe ic nuclea ion on wa-
e ac i i y compu a ionally. Many he modynamics models
commonly used o ac i i y coe icien calcula ions, such
as AIOMFAC (Zuend e al., 2008, 2011), a e pa ame e -
ized o only a ew a mosphe ic ions, such as NH+
4, SO2−
4,
HSO−
4, NO−
3, and IO−
3. On he con a y, he quan um-
Published by Cope nicus Publica ions on behal o he Eu opean Geosciences Union.
13810 N. Hy inen: Wa e up ake o aminium sal s
chemis y-based conduc o -like sc eening model o eal sol-
en s (COSMO-RS; Klam , 1995; Klam e al., 1998; Eck-
e and Klam , 2002) can be used o compu e he mody-
namic p ope ies o any a mosphe ically ele an species.
COSMO-RS and AIOMFAC p edic simila wa e ac i i ies
in (NH4)2SO4, NH4HSO4, NH4NO3and NH4IO3, wi hin a
ac o o 1.08 and 1.30 in aqueous solu ions wi h 0.1 and
0.2 mole ac ion o he sal , espec i ely (see Fig. S1 o
he Supplemen ). Though COSMO-RS calcula ions a e much
slowe (se e al hou s) han g oup con ibu ion me hods (∼
1 s), mainly due o he quan um chemis y inpu needed
o he COSMO-RS calcula ions, COSMO-RS is cu en ly
he only me hod capable o es ima ing wa e ac i i ies in
aminium sal s. Fo his eason, COSMO-RS was used he e
o p edic wa e ac i i ies o he sal solu ions o in e es .
The acids selec ed o his s udy a e abundan in he a mo-
sphe e. Sul u ic acid (H2SO4) is de i ed om an h opogenic
emissions o SO2, ni ic acid (HNO3) is p oduced om
bo h an h opogenic and na u al p ocesses, and iodic acid
(HIO3) and me hylsul onic acid (CH3SO3H) a e mo e abun-
dan in ma ine en i onmen s. In aqueous solu ions, hese
s ong acids a e dep o ona ed o o m sul a e (SO2−
4) and
bisul a e (HSO−
4), ni a e (NO−
3), ioda e (IO−
3), and me hyl-
sul ona e (CH3SO−
3), espec i ely. The ollowing a mosphe -
ically abundan alkylamines, guanidinos, and amino acids
(Di Filippo e al., 2014) we e selec ed as he bases o he
calcula ions.
–alkylamines: ammonia (AM), monome hy-
lamine (MMA), dime hylamine (DMA), ime hy-
lamine (TMA) die hyl amine (DEA), e hylene-
diamine (EDA) and e ame hyle hylenedi-
amine (TMEDA);
–guanidinos: guanidine (GUA) agma ine (AGM) and
a ginine (ARG; also an amino acid);
–amino acids: alanine (ALA), aspa ic acid (ASP), his-
idine (HIS), glu amic acid (GLU), glycine (GLY) and
se ine (SER).
These amines ha e many biogenic ( ege a ion, biomass
bu ning) and an h opogenic (pes icides, combus ion, li e-
s ock) sou ces (Ge e al., 2011). Addi ionally, he e ec o
he sal s on wa e up ake was in es iga ed in he p esence o
a hyd ophilic and a hyd ophobic o ganic.
2 Compu a ional me hods
The COSMO-RS model (Klam , 1995; Klam e al., 1998;
Ecke and Klam , 2002), implemen ed in he BIOVIA
COSMO he m p og am (BIOVIA COSMO he m, 2021a, ab-
b e ia ed COSMO he m), was used o ac i i y coe icien
and liquid–liquid equilib ium (LLE) calcula ions. Ac i i y
coe icien γo compound iis compu ed in COSMO he m
using he ollowing equa ion:
lnγi(x)=µ∗
i(x)−µ∗,
i
◦(x◦,T ,P )
RT ,(1)
whe e xis he composi ion o he mix u e, Tis he empe a-
u e (he e 298.15 K), R he gas cons an (in kJ K−1mol−1,
when µ∗is gi en in kJ mol−1), and P=105Pa e e ence
p essu e. Pseudo-chemical po en ial (Ben-Naim, 1987) µ∗is
an auxilia y quan i y de ined using he chemical po en ial a
he e e ence s a e µ◦:
µ∗
i(x)=µi◦(x◦,T ,P )+RT lnγi(x).(2)
The pu e compound (xi=1) is used as he e e ence s a e
composi ion x◦. The use o pseudo-chemical po en ial allows
o he calcula ion o ac i i y coe icien s in in ini ely dilu ed
s a es (xi→0).
The occu ence o liquid–liquid o solid–liquid phase sep-
a a ion (LLPS o SLPS, espec i ely) is no conside ed in
COSMO he m ac i i y coe icien calcula ions. Ins ead, he
mix u es a e assumed o be homogeneous. Small ae osol pa -
icles a e less likely o phase sepa a e han la ge d ople s
(F eedman, 2020). One-phase s a es a e he e o e possible in
small pa icles e en i he bulk solu ion would phase sepa-
a e.
The solubili y o he hyd ophobic o ganic in he sal solu-
ions was ound using he LLE condi ion:
γi(xα)xα
i=γi(xβ)xβ
i.(3)
He e, αand βdeno e he aqueous phase and he o ganic- ich
phase. In he LLE calcula ion, he sal is assumed o be ully
dissol ed in o he liquid phases.
2.1 Elec oly es in COSMO he m
The amewo k o COSMO he m calcula ions ea s elec-
oly es (i.e., sol en and one sal ) as e na y solu ions (sol-
en , ca ion, anion). This a ec s he mole ac ions (inpu )
and ac i i y coe icien s (ou pu ) o he p og am. All mole
ac ions p esen ed wi h he esul s we e con e ed o he
labo a o y-bina y amewo k (sol en , sal ) o easie com-
pa ison wi h expe imen s.
The highes le el o heo y pa ame e iza ion in
COSMO he m (BP_TZVPD_FINE_21, abb e ia ed FINE,
using BP/TZVPD//BP/TZVP le el cosmo iles) wo ks poo ly
wi h he s ong cha ges o small ions, such as a omic ions
and s ong small semi-sphe ical ions (such as SO2−
4, NH+
4)
(BIOVIA COSMO he m, 2021b). The use o an elec oly e
pa ame e iza ion (BP_TZVP_ELYTE_21; abb e ia ed
ELYTE; using BP/TZVP le el cosmo iles) is ecommended
o up o 6 mol kg−1solu ions, co esponding o a ound
0.1 mole ac ion o sal in wa e (BIOVIA COSMO he m,
2021b). Howe e , he use o ELYTE is no ecommended
o la ge ions (BIOVIA COSMO he m, 2021b). Based on
hese ecommenda ions, he use o ELYTE should be limi ed
A mos. Chem. Phys., 23, 13809–13817, 2023 h ps://doi.o g/10.5194/acp-23-13809-2023
N. Hy inen: Wa e up ake o aminium sal s 13811
o sys ems o which i was de eloped unless he calcula ed
alues can be co obo a ed by expe imen s.
The di e en COSMO he m pa ame e iza ions a e com-
pa ed in Sec . S1 o he Supplemen . O e all, he expe imen-
al wa e ac i i ies ag ee equally well wi h bo h ELYTE and
FINE pa ame e iza ions wi h he excep ion o ammonium
sul a e, wi h which FINE signi ican ly o e es ima es he ex-
pe imen s (see Figs. S2–S4). Fo some ca ions (e.g., ARG),
ELYTE esul s a e highly inconsis en wi h he esul s o
FINE and he BP_TZVP_21 pa ame e iza ion (abb e ia ed
TZVP), which o mos sal s gi e ai ly simila es ima es.
Addi ionally, he cu en elec oly e pa ame e iza ion is only
a ailable o he lowe le el o heo y BP/TZVP cosmo iles
and no o he highe le el o heo y BP/TZVPD cosmo iles,
co esponding o he FINE pa ame e iza ion. In case he e
a e sys ema ic e o s wi hin he di e en pa ame e iza ions
o le els o heo y, he compa ison o he di e en sal s is
mo e eliable when he same pa ame e iza ion is used in all
calcula ions. The FINE pa ame e iza ion is he e o e used o
all o he s udied sal s, wi h he excep ion o ammonium sul-
a e, which is calcula ed using he ELYTE pa ame e iza ion.
Using he selec ed pa ame e iza ions, COSMO he m
ag ees wi h he expe imen al wa e ac i i ies o aminium sul-
a e, bisul a e, and ni a e solu ions (xsal <0.2) wi hin ac-
o s o 1.39, 1.18, and 1.23, espec i ely. Simila unce ain-
ies can be expec ed o o he aminium sal s. Addi ionally, as
can be seen om Figs. S2–S4, he disag eemen be ween cal-
cula ions and expe imen s inc eases wi h he inc easing sal
mole ac ion in he solu ion.
2.2 Inpu iles o COSMO he m calcula ions
The inpu iles o COSMO he m calcula ions (cosmo- iles)
we e ob ained h ough a se ies o densi y unc ional heo y
calcula ions wi h inc easing le els o heo y. The p ocess has
been discussed in mo e de ail in a p e ious publica ion (Hy -
inen e al., 2020). In sho , all con o me s we e ound using
he sys ema ic con o me sea ch algo i hm in he Spa an20
p og am (Wa e unc ion Inc., 2020). The geome ies o all
con o me s we e op imized, and duplica e con o me s we e
emo ed using he BIOVIA COSMOcon p og am (BIOVIA
COSMOcon , 2021), which uses he Tu bomole p og am
(TURBOMOLE, 2020) o he quan um chemis y calcula-
ions. The inal cosmo- iles we e compu ed a he BP/de 2-
TZVPD-FINE//BP/de -TZVP le el o heo y (BP/de -TZVP
o ELYTE and TZVP calcula ions).
Many o he s udied ca ions ha e mul iple con o m-
e s. A mos he 10 lowes chemical po en ial con o me s
we e selec ed as inpu o he COSMO he m calcula ions.
Howe e , only con o me s wi h chemical po en ials wi hin
2 kcal mol−1o he lowes chemical po en ial we e used in
o de o a oid including con o me s wi h low COSMO en-
e gies bu high chemical po en ials (Hy inen, 2023b). Mo e
speci ically, COSMO he m gi es high weigh s o con o m-
e s con aining in amolecula H bonds (Hy inen and P isle,
2020) because in amolecula H bonds a e a o ed in he
COSMO ene gies (Ku én e al., 2018). The e is an excellen
co ela ion be ween chemical po en ials in wa e and in elec-
oly e solu ions (see Fig. S7). This indica es ha con o me
dis ibu ions a e simila in pu e wa e and elec oly es. The
con o me se s o elec oly e calcula ions can he e o e be
selec ed using he chemical po en ials o he ions in wa e .
3 Resul s and discussion
3.1 Sal –wa e solu ions
Wa e ac i i ies we e calcula ed in solu ions anging om
pu e wa e o 0.2 mole ac ion o sal . I should be no ed ha
he wa e solubili y o some sal s a 298.15 K may be below
0.2 mole ac ion. Howe e , all sal was assumed o be dis-
sol ed in he sol en wa e as ions. Addi ionally, all ca ions
in he calcula ions a e singly cha ged o simple compa i-
son, e en i some con ain mul iple amine g oups. Figu e 1
shows COSMO he m-de i ed wa e ac i i ies in selec ed sal
solu ions a 298.15 K. The alues a e gi en in Tables S1–S16
in he Supplemen and in Fig. S8. Un o una ely, de e min-
ing eliable e o es ima es o wa e ac i i ies in hese sal s
is no possible due o he lack o expe imen al da a o sim-
ila sal s. Howe e , he e o s a e likely o be sys ema ic o
simila compounds, such as aminium ions. The o de o he
ca ions may he e o e be mo e eliable han he o de o he
anions.
Figu e 1 shows ha bo h he anion and ca ion a ec he
wa e ac i i y o he solu ions. Assuming ha he ions in-
es iga ed he e ollow he Ho meis e se ies, he o de o
ca ions should be simila ega dless o coun e ion. Based
on COSMO he m es ima es, he o de o he ca ions is
ai ly simila in sul a e (Fig. 1d), ioda e and me hylsul ona e
(Fig. 1 ) sal s. Simila ly, bisul a e and ni a e (Fig. 1e) sal s
ha e a simila o de o he ca ions. This indica es ha he
e ec o he ca ion on wa e up ake also pa ially depends on
he anion. Addi ionally, he o de o he s udied anions is no
he same o all o he ca ions.
Some pa e ns can be seen be ween he di e en unc-
ional g oups o he ca ions. Fo example, wa e up ake is
enhanced in he ollowing o de : e ia y amine >seconda y
amine >p ima y amine (Fig. 1a). This o de ollows
he hyg oscopici y o aminium sul a e sal s (Ro elli
e al., 2017) and is he same as Dawson e al. (2014)
ound o wa e up ake o aminium me hylsul ona e sal s
(TMA >DMA >MMA). Addi ionally, wo amine g oups in
he ca ion lead o lowe wa e ac i i y han one amine g oup,
e en hough only one o he amine g oups is p o ona ed. This
is seen in he compa ison be ween TMA and TMEDA, as
well as MMA and EDA (Fig. 1a).
Ca boxylic acid g oups ha e inconsis en e ec s on wa e
ac i i y. Amino acids ha e lowe wa e ac i i ies han MMA
in some sal s (bisul a e, ni a e; Fig. 1 ) and highe in o he s
(sul a e; Fig. 1d, ioda e, me hylsul ona e; Fig. 1e). Addi ion-
h ps://doi.o g/10.5194/acp-23-13809-2023 A mos. Chem. Phys., 23, 13809–13817, 2023
13812 N. Hy inen: Wa e up ake o aminium sal s
Figu e 1. COSMO he m-de i ed wa e ac i i ies (aw) in aqueous (a) amine, (b) guanidino, and (c) amino acid bisul a e solu ions, as well
as selec ed (d) sul a e, (e) me hylsul ona e, and ( ) ni a e solu ions a 298.15 K. Ac i i ies we e calcula ed in 0.01 in e als o sal mole
ac ion (xsal ) and plo ed as lines o cla i y. The black line ep esen s ideali y aw=xw.
ally, he e is no clea end be ween he s udied amino acids
wi h one (ALA, GLY, SER) o wo (GLU, ASP) acid g oups.
On he o he hand, wa e ac i i y is lowe in all i e ARG
(one ca boxylic acid g oup) sal s han in he co esponding
AGM (no ca boxylic acid g oup) sal s (Fig. 1d– ).
In sul a e solu ions, he wa e ac i i ies ha e he la ges de-
pendence on he ca ion compa ed o he o he s udied anions.
Addi ionally, GLY and ASP sul a es a e p edic ed o inhibi
wa e up ake a low sal concen a ions (wa e ac i i y coe i-
cien s abo e one, see Tables S12 and S14). I should be no ed
ha he ionic s eng h o he sul a e solu ions is 3 imes he
ionic s eng h o he o he s udied solu ions wi h he same
sal mole ac ion.
In hei expe imen s, Saue wein e al. (2015) obse ed
simila osmo ic coe icien s o aqueous AM, MMA, DMA,
TMA, and DEA bisul a e solu ions, indica ing simila wa-
e ac i i ies independen o he ca ion. Simila ly, he
COSMO he m-de i ed wa e ac i i ies in he bisul a e solu-
ions a e simila (wi hin a ac o o 1.1 in xsal =0.1 solu-
ions) o all s udied ca ions. Due o unce ain ies in he cal-
cula ed alues, i is possible ha he e a e no eal di e ences
be ween he wa e ac i i ies o he di e en aminium bisul-
a e solu ions. Con e sely, MMA, DMA, TMA, and DEA
sul a e solu ions had lowe expe imen al wa e ac i i ies han
he co esponding bisul a e solu ions, while wa e ac i i ies
in AM bisul a e solu ions we e simila o hose in AM sul a e
solu ions (Saue wein e al., 2015). A simila end is seen in
he COSMO he m-de i ed wa e ac i i ies.
Myllys (2023) s udied he e ec o wa e on he g ow h
o acid–guanidine clus e s in he gas phase compu a ion-
ally. A he molecula le el, wa e was seen o enhance pa -
icle o ma ion a 298 K in sys ems con aining ni ic acid
and me hylsul onic acid a ela i ely low acid concen a ions.
No signi ican e ec was seen in sul u ic acid sys ems. The
same o de in hese h ee acids is seen in COSMO he m
bulk-phase calcula ions. Ni a e enhances wa e up ake o
he aqueous phase mo e han he o he wo anions, me hyl-
sul ona e enhances wa e up ake sligh ly less han ni a e,
and he bisul a e has he weakes enhancing e ec . How-
e e , COSMO he m p edic s he lowes wa e ac i i y in so-
lu ions con aining sul a e ions, indica ing he s onges wa-
e up ake. Howe e , since he concen a ion o guanidine
was lowe han he sul u ic acid concen a ion in he sim-
ula ions o Myllys (2023), he sul u ic acid is expec ed o
o m bisul a e ions and no sul a e ions. I he co ela ion be-
ween COSMO he m-es ima ed wa e ac i i ies and he en-
hancemen on clus e o ma ion a high RH holds o o he
acid–base pai s, he ela i e e ec o RH on pa icle o ma-
A mos. Chem. Phys., 23, 13809–13817, 2023 h ps://doi.o g/10.5194/acp-23-13809-2023

N. Hy inen: Wa e up ake o aminium sal s 13813
Table 1. COSMO he m-p edic ed equilib ium wa e mass ac ions
(mw) a 70 % RH (aw=0.7) and 298.15 K.
SO2−
4HSO−
4NO−
3IO−
3CH3SO−
3
AM 0.393 0.521 0.563 0.206 0.424
MMA 0.454 0.454 0.551 0.328 0.486
DMA 0.568 0.449 0.554 0.398 0.519
TMA 0.636 0.462 0.562 0.448 0.544
DEA 0.573 0.440 0.516 0.415 0.501
EDA 0.448 0.396 0.494 0.343 0.461
TMEDA 0.551 0.404 0.487 0.416 0.482
GUA 0.491 0.469 0.552 0.354 0.491
AGM 0.410 0.343 0.413 0.321 0.394
ARG 0.388 0.359 0.412 0.318 0.388
ALA 0.303 0.409 0.457 0.257 0.381
GLY 0.257 0.427 0.479 0.231 0.369
SER 0.300 0.385 0.441 0.244 0.355
ASP 0.229 0.383 0.419 0.191 0.311
GLU 0.250 0.369 0.402 0.209 0.320
HIS 0.329 0.306 0.371 0.290 0.352
ion could be es ima ed using he compu a ionally simple wa-
e ac i i y calcula ions ins ead o he mo e ime-consuming
molecula clus e calcula ions.
Highe equilib ium wa e con en in ae osol pa icles in-
dica es a highe hyg oscopic g ow h ac o . Because he sal s
ha e di e en mola masses, mass ac ion wa e con en p o-
ides a mo e di ec compa ison o he hyg oscopic g ow h
ac o s o he sal s. Table 1 shows he mass ac ion wa e
con en o each o he s udied sal s a 70 % RH as an example.
Compa ing he anions, he highes wa e con en is ound in
ei he he sul a e o he ni a e sal o all s udied ca ions. Fo
mos o he s udied ca ions (all excep TMEDA), he lowes
wa e con en in e ms o mass ac ion is in he ioda e sal .
COSMO he m p edic ed wa e mass ac ions a 70 % RH
a y be ween 0.19 (ASP-IO3) and 0.64 (TMA2-SO4) o he
s udied sal s.
3.2 Addi ion o wa e soluble o ganic
Nex , an o ganic compound was added o he aqueous sal
solu ions o in es iga e he e ec o he sal s on wa e ac i -
i y in he p esence o an o ganic componen . An isop ene-
de i ed epoxydiol ( ans-β-IEPOX; C5H10O3) was selec ed
as he o ganic compound because o i s high es ima ed gas-
phase p oduc ion a e in he a mosphe e (100 Tg C pe yea ;
S . Clai e al., 2016). Addi ionally, COSMO he m p edic s
miscibili y be ween wa e and IEPOX and only sligh de ia-
ion om ideali y in all mixing a ios (Hy inen e al., 2020).
This is impo an , as limi ed solubili y be ween wa e and he
chosen o ganic would lead o s ong de ia ion om ideali y
o wa e by he o ganic. In such cases, liquid–liquid phase
Figu e 2. COSMO he m-de i ed wa e con en s (xwin mole
ac ion) in aqueous solu ions o h ee me hylsul ona e sal s and
IEPOX. The alues we e calcula ed wi h 0.1 in e als o sal mole
ac ion in he d y mix u e (xsal , d y).
sepa a ion should be aken in o accoun in he ac i i y coe -
icien calcula ions.
3.2.1 Wa e con en
Figu e 2 shows he wa e ac i i ies in e na y sal –IEPOX–
wa e solu ions o h ee di e en me hylsul ona e sal s. The
wa e ac i i ies we e compu ed wi h 0.025 xwin e als, and
he xw alues o each aw(0.99, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4)
we e in e pola ed using he spline in e pola ion me hod o
MATLAB (MATLAB, 2019). The di e ence be ween in e -
pola ed xw alues using 0.025 and 0.01 in e als was less
han 10−6mole ac ion, indica ing ha spline inds a good i
o COSMO he m-es ima ed wa e ac i i ies calcula ed wi h
0.025 mole ac ion in e als.
Ammonia, GLY, and TMEDA ha e he weakes , he
second-weakes , and s onges e ec on wa e up ake o
he s udied me hylsul ona e sal s, espec i ely (see Fig. 1e).
Va ying he mole a io o sal and IEPOX shows a maximum
equilib ium wa e mole ac ion (xw) in he AM me hylsul-
ona e solu ions a ixed RH (i.e., aw). This indica es ha
adding an o ganic componen may enhance wa e up ake
compa ed o some pu e sal pa icles. On he con a y, GLY
and TMEDA me hylsul ona e solu ions each hei highes
wa e con en a a ixed RH in he pa icles con aining no
IEPOX.
Figu e 3 shows a compa ison be ween wa e con en s (in
mass ac ion mw) a equilib ium unde 70 % RH condi-
ions (aw=0.7) in pu e sal ( alues in Table 1) and sal –
IEPOX mix u es. He e, he sal : IEPOX a io was kep con-
s an a 1 :1, co esponding o xsal ,d y =0.5 in Fig. 2. Fig-
u e S9 shows simila compa ison a 90 % RH, and Figs. S10
and S11 show compa isons o wa e mole ac ions a 70 %
and 90 % RH, espec i ely. Wa e ac i i ies in all s udied
h ps://doi.o g/10.5194/acp-23-13809-2023 A mos. Chem. Phys., 23, 13809–13817, 2023
13814 N. Hy inen: Wa e up ake o aminium sal s
Figu e 3. COSMO he m-de i ed equilib ium wa e con en s (mw
in mass ac ion) in 70 % RH a 298.15 K. The do ed black line
shows he 1 :1 co ela ion, and he dashed blue lines a e o mw=
0.262, co esponding o equilib ium wa e mass ac ion in IEPOX
a 70 % RH.
sal –IEPOX mix u es wi h 1 :1 mole a io o sal and IEPOX,
up o 0.1 mole ac ion o sal , a e shown in Fig. S12.
The p edic ed equilib ium wa e con en o pa icles con-
aining small amines is he highes ou o he s udied
amines, mainly due o hei low mola mass compa ed o he
polyamines. The equilib ium wa e con en in IEPOX is p e-
dic ed o be 0.699 mole ac ion (0.262 mass ac ion; dashed
blue lines in Fig. 3) in 70 % RH. The addi ion o sal o
IEPOX wi h 1 :1 mole a io inc eases wa e up ake by 14 %
o 30 % in mole ac ion depending on he sal . In mass ac-
ion, he co esponding wa e up akes inc ease by up o a ac-
o o 2.2 (yaxis in Fig. 3). Pu e sal s ha e up o 36 % highe
wa e con en in mole ac ion, and 142 % in mass ac ion,
han pu e IEPOX in 70 % RH (xaxis in Fig. 3).
3.2.2 Ac i i y o he o ganic
The ac i i ies o IEPOX we e compu ed in mix u es ha con-
ain equal mole ac ions o IEPOX and sal . O e all, he
IEPOX ac i i ies a e highe in sal solu ions han in pu e wa-
e , indica ing ha all o he sal s ha e a sal ing ou e ec
on IEPOX. The solubili y o IEPOX, and likely o he hy-
d ophilic o ganics, is educed by aminium sal s in he ae osol
pa icles compa ed o pu e o ganic pa icles. Simila sal ing
ou beha io has been obse ed in COSMO he m calcula-
ions o ammonium sul a e and a mosphe ically ele an o -
ganics (Toi ola e al., 2017; Hy inen e al., 2020).
The o de o IEPOX ac i i ies om he low-
es o highes in he sal mix u es is bisul-
a e <ni a e <me hylsul ona e <ioda e <sul a e sal s.
The sal ing ou e ec o sul a e is much s onge han ha
o he o he anions, likely due o he highe ionic s eng h.
The o de o he s udied ca ions a ies depending on bo h
he coun e ion and he sal mole ac ion.
3.2.3 O ganosul a e o ma ion
Aoki e al. (2020) ound ha sul a e ions eac wi h he
epoxide g oup o IEPOX in he condensed phase o o m an
o ganosul a e species. Howe e , he eac ion be ween IEPOX
and bisul a e was ound o be slow, indica ing ha o ganosul-
a es a e less likely o o m in solu ions con aining equal
mole ac ions o sul u ic acid and amines (Aoki e al., 2020).
Reac i e up ake o IEPOX in o aqueous sul a e ae osols may
coun e ac he s ong sal ing ou e ec o sul a e sal s o
o ganic compounds ha can o m ionic species by eac ing
wi h he sul a e ion.
Since o ganosul a es a e likely o o m om he selec ed
o ganic (IEPOX), addi ional wa e ac i i ies we e compu ed
o mix u es con aining equal mole ac ions o aminium
o ganosul a e sal and neu al amine. This mix u e may a ise
i 1 :1 mole a io o sul a e sal and IEPOX eac , neu aliz-
ing hal o he aminium ions in he p ocess:
epoxide +SO2−
4+2RNH+
3→o ganosul a e−
+RNH+
3+RNH2.(R1)
While he elemen al con en o he mix u e emains he same,
o ganosul a e o ma ion eac ion educes he ionic s eng h
o he mix u e by neu alizing hal o he amines and con e -
ing he doubly cha ged sul a e in o singly cha ged o ganosul-
a e.
Wa e ac i i ies we e addi ionally compu ed o o ganosul-
a e solu ions ha do no con ain neu al amines. These mix-
u es co espond o ei he o ganosul a e o ma ion om an
epoxide eac ion wi h bisul a e ion, o e apo a ion o he neu-
al amines a e he o ganosul a e o ma ion om a eac ion
wi h sul a e ion.
Figu e 4 shows he COSMO he m-de i ed wa e mass
ac ion in he bisul a e, sul a e (xaxis), and o ganosul-
a e (yaxis) mix u es a 70 % RH. Simila wa e con en
is p edic ed o aminium bisul a e–IEPOX and aminium
o ganosul a e mix u es (magen a ci cles in Fig. 4). On
he o he hand, la ge di e ences a e seen be ween
aminium sul a e–IEPOX and he co esponding aminium
o ganosul a e–amine mix u es. Fo mos o he s udied
ca ions, wa e up ake is p edic ed o be s onge o he
aminium sul a e–IEPOX mix u e han o he co espond-
ing aminium o ganosul a e–amine mix u e. One eason may
be he di e ence in ionic s eng h be ween sul a e and
o ganosul a e. Addi ionally, he COSMO he m es ima es o
sul a e sal s may be less accu a e han he o sal s comp is-
ing singly cha ged non-sphe ical ions, such as bisul a e and
o ganosul a e.
While amines can also eac wi h epoxides in hei neu al
o ms, hey a e likely o exis in p o ona ed o ms in acidic
seconda y o ganic ae osol. The nucleophilic s eng hs o p o-
ona ed amines a e much weake han hose o neu al amines
(S opoli and El od, 2015). This makes eac ions be ween he
s udied aminiums and IEPOX unlikely. The ni a e ion can
also ac as a nucleophile and eac wi h he epoxy g oup.
A mos. Chem. Phys., 23, 13809–13817, 2023 h ps://doi.o g/10.5194/acp-23-13809-2023
N. Hy inen: Wa e up ake o aminium sal s 13815
Figu e 4. COSMO he m-p edic ed equilib ium wa e con en (mw
in mass ac ion) in mix u es con aining IEPOX (xaxis) and
o ganosul a e (yaxis) unde 70 % RH condi ions. The 1 :1 a io
is shown as he dashed black line.
Howe e , he p oduc e ia y o ganoni a e is no as s able
as he co esponding o ganosul a e, leading o wa e subs i-
u ing he ni a e g oup o o m a me hyl e ol (Da e e al.,
2011). The o ma ion o an o ganoni a e species was he e-
o e no conside ed he e.
3.3 Addi ion o wa e -insoluble o ganic
A hyd ophobic wa e -insoluble o ganic ma e (WIOM;
CC(=O)C1OC2OC(OC2(C)O1)C1=CC(C)=CC(C)=C1)
p oposed by Kalbe e e al. (2004) has o en been used as a
p oxy in COSMO-RS calcula ions o a mosphe ic ae osol
p ope ies (Wania e al., 2014; Wang e al., 2017; Ku én
e al., 2016; Hy inen e al., 2021; Lumia o e al., 2021).
COSMO he m-p edic ed solubili y o wa e in WIOM is
low (0.07 mole ac ion; Hy inen, 2023b), indica ing ha
ela i ely high RH is needed o inc ease he wa e con en in
pu e WIOM pa icles. Fo example, a equilib ium in 70 %
and 90 % RH, he p edic ed wa e mole ac ion in WIOM
is only 0.047 and 0.065, espec i ely. Adding a sal o he
mix u e inc eases equilib ium wa e con en compa ed o
pu e WIOM. Howe e , high mole ac ions o sal lead o
he sal ing ou o WIOM om he aqueous sal solu ion.
When he sal –WIOM–wa e mix u es phase sepa a e in o
an aqueous phase and a o ganic- ich phase, he aqueous
phase will con ain mos ly wa e and sal , while he o ganic-
ich phase is almos pu e WIOM. The COSMO he m-de i ed
solubili y o WIOM in wa e a 298.15 K is e y low, only
2.5×10−5mole ac ion. The solubili y o WIOM u he de-
c eases wi h he addi ion o sal (sal ing ou o WIOM). The
p edic ed wa e ac i i y in he aqueous phase is e y close o
ha o he bina y sal –wa e mix u es (see Fig. S13). The e -
ec o e y hyd ophobic o ganics on wa e ac i i y o sal s is
he e o e expec ed o be negligible, as wa e ac i i y in bo h
phases a equilib ium is equal acco ding o he LLE condi-
ion o Eq. (3).
4 Conclusions
Sal s a e expec ed o ha e a la ge e ec on wa e ac i i y and
equilib ium wa e con en han neu al o ganic compounds.
Addi ionally, he c i ical supe sa u a ion is lowe ed h ough
dec eased wa e ac i i y in sal -con aining pa icles. The wa-
e con en o a mosphe ic ae osol also a ec s he ae osol a-
dia i e o cing, which is a c ucial ac o in clima e models.
I is he e o e impo an o know how each ionic species in
a mosphe ic ae osol a ec s wa e ac i i y.
Wa e ac i i ies can be used o de e mine he hyg oscopic
g ow h and CCN ac i a ion o a mosphe ic ae osol pa icles.
Knowledge o how di e en a mosphe ic ions a ec wa e
up ake and CCN ac i a ion o ae osol pa icles will help im-
p o e clima e models. COSMO he m calcula ions show how
he di e en a mosphe ic anions and ca ions a ec wa e ac-
i i y. Mos o he sal s o his s udy enhance wa e up ake
ela i e o ideal solu ions (e.g., pu e wa e ).
O ganosul a e and bisul a e–o ganic mix u es ha e simila
e ec s on he equilib ium wa e con en . Howe e , wa e up-
ake may be slowe in o ganosul a e han in sul a e–o ganic
mix u es. This indica es ha he o ma ion o o ganosul a e
may educe he wa e up ake abili y compa ed o pa icles
ha do no con ain o ganic compounds. This should be con-
side ed in models ha use expe imen al hyg oscopici ies o
pu e sul a e sal s o desc ibe he hyg oscopici ies o mixed
sal –o ganic pa icles. Fu u e s udies a e needed o u he
in es iga e o he ionic species and highly oxygena ed mul i-
unc ional o ganics.
Da a a ailabili y. The esea ch da a (cosmo iles) can be ac-
cessed h ough he Jy äskylä Uni e si y Digi al Reposi o y (JYX)
a h ps://doi.o g/10.17011/jyx/da ase /89238 (Hy inen, 2023a).
Supplemen . The supplemen ela ed o his a icle is a ailable
online a : h ps://doi.o g/10.5194/acp-23-13809-2023-supplemen .
Compe ing in e es s. The au ho has decla ed ha he e a e no
compe ing in e es s.
Disclaime . Publishe ’s no e: Cope nicus Publica ions emains
neu al wi h ega d o ju isdic ional claims made in he ex , pub-
lished maps, ins i u ional a ilia ions, o any o he geog aphical ep-
esen a ion in his pape . While Cope nicus Publica ions makes e -
e y e o o include app op ia e place names, he inal esponsibili y
lies wi h he au ho s.
h ps://doi.o g/10.5194/acp-23-13809-2023 A mos. Chem. Phys., 23, 13809–13817, 2023
13816 N. Hy inen: Wa e up ake o aminium sal s
Acknowledgemen s. I hank he CSC – IT Cen e o Science,
Finland, o compu a ional esou ces.
Financial suppo . This esea ch has been suppo ed by he Re-
sea ch Council o Finland (g an no. 338171).
Re iew s a emen . This pape was edi ed by Thomas Be kemeie
and e iewed by wo anonymous e e ees.
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