levels. Low temperature, high relative humidity, and the presence of NH 3 and large
fog droplets facilitated greatly SO 4
2À formation. The SO 4
2À formation on aqueous
particles also leads to the formation of NO 3
À and secondary organic aerosol (SOA).
The abundance of these precursors could explain the continuous high production of
the secondary aerosols during the hazy events in China.
In contrary to facilitate particle formation, some studies suggest that NO x can
suppress NPF (Wildt et al. 2014) and reduce SOA formation (Sarrafzadeh et al.
2016). The photooxidation of alpha-pinene and limonene can produce SOA. Zhao
et al. (2018) investigated the roles of NO x and SO 2 on SOA formation. They found
NO x could suppress NPF and reduce SOA yield. The SOA formation depends on
specific NO x , SO 2 , VOC types, and concentrations. The presence of NO x inhibits
new particle formation and hence SOA formation, whereas SO 2 compensates for
such effects.
6.3 Contribution of Nr to PM 2.5 Pollution
6.3.1 Contribution of Inorganic Nitrogen to PM 2.5 Across
China
In general, secondary inorganic ions (SO 4
2À , NO 3
À , and NH 4
+
, hereafter referred to
as SNA), organic carbon (OC), elemental carbon (EC), and crustal species were
present as the major compositions of PM 2.5 . Yang et al. (2011) performed a PM 2.5
speciation reconstruction based on chemical species at 16 locations across China that
observed from 1999 to 2007. At both urban and rural sites in the eastern region, SNA
contributed 40–57% to the PM 2.5 mass, indicating the characteristic of regional fineparticle pollution. A similar summary was done by Zhou et al. (2016) on the basis of
chemical species data of PM 2.5 across China between 1999 and 2010. The authors
found that the average concentrations of SO 4
2À , NO 3
À , NH 4
+
, OC, and EC in PM 2.5
are 18.0 Æ 10.2, 7.7 Æ 5.7, 7.3 Æ 5.1, 19.6 Æ 14.4, and 6.2 Æ 4.7 μg m
À3 ,
respectively. They also concluded that SNA are the most abundant components
with an average contribution of 34.1% to PM 2.5 . Before 2010, the contributions of
NH 4
+ and NO 3
À to PM 2.5 are comparable or lower than SO 4
2À depending on sites.
A recent national observation network in China conducted between 2012 and
2013 shows that the dominated chemical compositions of PM 2.5 across China are
organic matter (OM), SO 4
2À , mineral dust, NO 3
À
, NH 4
+
, elemental carbon (EC),
Cl
À , and unaccounted matter (Fig. 6.1), which account 26%, 17.7%, 118%, 98%,
66%, 60%, 12%, and 20.7% to PM 2.5 , respectively (Liu et al. 2018b). Overall, the
proportion of chemical species varied significantly among the sites. At urban sites,
OM, SO 4
2À , NO 3
À
, and EC ranged from 12.6–23.3 μg∙m
À3 , 0.8–197 μg∙m
À3 ,
0.5–11.9 μg∙m
À3 , and 1.4–7.1 μg∙m
À3 , respectively. However, higher fractions of
OM (33.2%) and lower fractions of NO 3
À (8.6%) and EC (4.1%) were observed at
background sites.
6 Contribution of Atmospheric Reactive Nitrogen to Haze Pollution in China
117
fog droplets facilitated greatly SO 4
2À formation. The SO 4
2À formation on aqueous
particles also leads to the formation of NO 3
À and secondary organic aerosol (SOA).
The abundance of these precursors could explain the continuous high production of
the secondary aerosols during the hazy events in China.
In contrary to facilitate particle formation, some studies suggest that NO x can
suppress NPF (Wildt et al. 2014) and reduce SOA formation (Sarrafzadeh et al.
2016). The photooxidation of alpha-pinene and limonene can produce SOA. Zhao
et al. (2018) investigated the roles of NO x and SO 2 on SOA formation. They found
NO x could suppress NPF and reduce SOA yield. The SOA formation depends on
specific NO x , SO 2 , VOC types, and concentrations. The presence of NO x inhibits
new particle formation and hence SOA formation, whereas SO 2 compensates for
such effects.
6.3 Contribution of Nr to PM 2.5 Pollution
6.3.1 Contribution of Inorganic Nitrogen to PM 2.5 Across
China
In general, secondary inorganic ions (SO 4
2À , NO 3
À , and NH 4
+
, hereafter referred to
as SNA), organic carbon (OC), elemental carbon (EC), and crustal species were
present as the major compositions of PM 2.5 . Yang et al. (2011) performed a PM 2.5
speciation reconstruction based on chemical species at 16 locations across China that
observed from 1999 to 2007. At both urban and rural sites in the eastern region, SNA
contributed 40–57% to the PM 2.5 mass, indicating the characteristic of regional fineparticle pollution. A similar summary was done by Zhou et al. (2016) on the basis of
chemical species data of PM 2.5 across China between 1999 and 2010. The authors
found that the average concentrations of SO 4
2À , NO 3
À , NH 4
+
, OC, and EC in PM 2.5
are 18.0 Æ 10.2, 7.7 Æ 5.7, 7.3 Æ 5.1, 19.6 Æ 14.4, and 6.2 Æ 4.7 μg m
À3 ,
respectively. They also concluded that SNA are the most abundant components
with an average contribution of 34.1% to PM 2.5 . Before 2010, the contributions of
NH 4
+ and NO 3
À to PM 2.5 are comparable or lower than SO 4
2À depending on sites.
A recent national observation network in China conducted between 2012 and
2013 shows that the dominated chemical compositions of PM 2.5 across China are
organic matter (OM), SO 4
2À , mineral dust, NO 3
À
, NH 4
+
, elemental carbon (EC),
Cl
À , and unaccounted matter (Fig. 6.1), which account 26%, 17.7%, 118%, 98%,
66%, 60%, 12%, and 20.7% to PM 2.5 , respectively (Liu et al. 2018b). Overall, the
proportion of chemical species varied significantly among the sites. At urban sites,
OM, SO 4
2À , NO 3
À
, and EC ranged from 12.6–23.3 μg∙m
À3 , 0.8–197 μg∙m
À3 ,
0.5–11.9 μg∙m
À3 , and 1.4–7.1 μg∙m
À3 , respectively. However, higher fractions of
OM (33.2%) and lower fractions of NO 3
À (8.6%) and EC (4.1%) were observed at
background sites.
6 Contribution of Atmospheric Reactive Nitrogen to Haze Pollution in China
117