[Journal of Geophysical Research - Atmosphere]
Supporting Information for
Enhanced sulfate formation by nitrogen dioxide: Implications from in-situ
observations at the SORPES Station
Yuning Xie1,2, Aijun Ding1,2,*, Wei Nie1,2, Huiting Mao1,4, Ximeng Qi1,2, Xin Huang1,2, Zheng
Xu1,2, Veli-Matti Kerminen3, Tuukka Petäjä3, Xuguang Chi1,2, Aki Virkkula1,2,3, Michael Boy1,2.3,
Likun Xue5, Jia Guo5, Jianning Sun1,2, Xiuqun Yang1,2, Markku Kulmala,3 and Congbin Fu1,2
1Institute
for Climate and Global Change Research & School of Atmospheric Sciences, Nanjing University, 210023,
China
2
Collaborative Innovation Center of Climate Change, Jiangsu Province, China
3
Department of Physics, University of Helsinki, 00014 Helsinki, Finland
4
Department of Chemistry, State University of New York, College of Environmental Science and Forestry, Syracuse,
New York, U.S.A.
5
Department of Civil and Environment Engineering, The Hong Kong Polytechnic University, Hong Kong
Contents of this file
Text S1 to S2
Figures S1
This part describes the methods that we used to estimate the aerosol acidity and
for HONO(g)-Nitrite partition.
Text S1. Calculate of aerosol acidity based on ISOPROPIA-II model
Previous studies show that the ion balance and mole ratio method could not represent the
real acidity in atmospheric particles while thermodynamics model constrained by gas and
1
aerosol measurement could provide reasonable results of the aerosol liquid water acidity
[Yao et al., 2006; Hennigan et al,. 2015]. In this study, we used thermodynamics models
ISORROPIA-II [Clegg et al., 1998; Clegg et al., 2003; Nenes et al., 1999; Fountoukis and
Nenes, 2007] to estimate the acidity of the observed episode for the Case 2. The
ISORROPIA II model uses concentration of gases and ions and relevant meteorological
parameters to drive the forward model to establish an equilibrium aerosol mixture (solid
plus liquid) and output the pH. The performance of the model was well described in Bian
et
al
(2014).
We
obtained
the
model
from
ISORROPIA
webpage
(http://nenes.eas.gatech.edu/ISORROPIA).
MARGA measured gas and ions concentrations, such as ammonia, ammonium,
sulfate, sodium, calcium, potassium, magnesium, chloride, and nitrate, and air
temperature, relative humidity were used as inputs for the model. The calculated pH
value is 3.94, and liquid water content is 209 μg m-3.
Text S2. Calculation of HONO-Nitrite partition
The distribution factor of HONO, fHONO, is defined as the ratio of HONO aqueous phase
to its gas-phase (i.e. NO2-/HONO), which could be estimated in the ideal solution
according to the Henry`s law [Seinfeld and Pandis, 2006; VandenBoer et al., 2014]. It
was shown as below:
𝑓𝐻𝑂𝑁𝑂 = 10−6 𝐻𝐻𝑂𝑁𝑂 𝑅𝑇𝐿
(1),
where R is the ideal-gas constant equal to 0.08205 atm L mol-1K-1, T is the temperature in
K, L is the water content of aerosol in g m-3, HHONO is the effective henry`s law constant
which is defined as below:
∗
𝐻𝐻𝑂𝑁𝑂
= 𝐻𝐻𝑂𝑁𝑂 (1 +
𝑘𝑎
𝐻+
)
(2),
𝑘𝑎
𝐻𝑂𝑁𝑂(𝑎𝑞) + 𝐻2 𝑂 ⇔ 𝐻 + + 𝑁𝑂2− (3)
In the eq(2), we use Henry`s law constant (HHONO) in 298 K as 49 M atm-1 [Seinfeld and
Pandis, 2006]，the acid dissociation constant (ka) in 298 k as 5.1*10-4 M atm-1[Schwartz
and White, 1981]. For liquid water content, we used the ISORROPIA II model calculated
2
value, i.e. 209 µg m-3. Then the fHONO dependence on the pH at 298 k was determined by
substituting eq(1) and eq(2) and shown in Figure S1. The fHONO is about 0.04 at pH value
of 6 and about 4.5x10-4 for pH value of 4.
Figure S1 The dependence of fHONO to pH value calculated for the peak of Case 2
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