6.2.2 Amines
Amines have recently been listed as an important precursor of atmospheric secondary aerosols (Kulmala et al. 2013). Amines refer to a category of organic compounds
that contain a basic nitrogen atom with a lone pair. Aliphatic amines have no
aromatic ring attached directly to the nitrogen atom, whereas aromatic amines
have a nitrogen atom connected to an aromatic ring. Amines can be further classified
into four categories according the number of hydrogen atoms that are replaced:
primary, secondary, tertiary, and cyclic amines. Amines found in the atmosphere
include mainly C1–C3 amines (Kuerten et al. 2014).
Although the concentration of amines in the atmosphere is probably 2 or 3 orders
of magnitude lower than in NH 3 (Kuerten et al. 2014), amines can significantly assist
the growth of both neutral and ionic clusters (Almeida et al. 2013; Kuerten et al.
2014). Above 3 pptv DMA can enhance particle formation rates more than 1000-fold
compared to NH 3 (Almeida et al. 2013). From the climate perspective, the trace
condensable compounds contributing to formation of secondary aerosols supply
almost half of global cloud condensation and ice nuclei (Merikanto et al. 2009).
Amines are strong stabilizers of aerosols (Kulmala et al. 2013; Kurtén et al. 2008). A
recent study investigated the mechanisms of new particle formation in Shanghai
(Yao et al. 2018a). This study consisted of long-term continuous observations and an
intensive campaign during the haze period. High concentrations of sulfuric acid
dimers were detected, which resulted most likely from the strong acid-base stabilization in H 2 SO 4 -DMA clusters. The results suggest that, despite the fact that
preexisting particles would scavenge the precursors of new particles and suppress
their formation, DMA could still enhance NPF in a highly polluted urban
atmosphere.
6.2.3 Nitrogen Oxides
The condensed water could facilitate the partition of gaseous pollutants into particle
phase and accelerate the formation of severe haze pollution by acting as a powerful
medium for multiphase reactions (Wu et al. 2018). A positive correlation between
the mass concentrations of nitrate (NO 3
À ) and SO 4
2À in PM 2.5 and the aerosol liquid
water content (ALWC) indicates that both NO 3
À and SO 4
2À determine the ALWC
(Pan et al. 2016b). However, since SO 2 emission mitigation has been successfully
achieved throughout China, NO 3
À became a dominant anthropogenic inorganic saltdriving ALWC. Moreover, Wang et al. (2016) and Xue et al. (2016) stated that the
oxidation of SO 2 by NO 2 leads to SO 4
2À formation. The combination of relatively
high pH in aqueous phase; high concentrations of NO 2 , SO 2 , and PM; and small fog
droplets can significantly improve SO 4
2À formation. It is observed that the oxidation
of SO 2 by NO x during winters in Beijing stimulates severe haze (Ma et al. 2018).
Both SO 2 and NO 2 which are produced from coal burning present in highly elevated
116
Y. Pan et al.
Amines have recently been listed as an important precursor of atmospheric secondary aerosols (Kulmala et al. 2013). Amines refer to a category of organic compounds
that contain a basic nitrogen atom with a lone pair. Aliphatic amines have no
aromatic ring attached directly to the nitrogen atom, whereas aromatic amines
have a nitrogen atom connected to an aromatic ring. Amines can be further classified
into four categories according the number of hydrogen atoms that are replaced:
primary, secondary, tertiary, and cyclic amines. Amines found in the atmosphere
include mainly C1–C3 amines (Kuerten et al. 2014).
Although the concentration of amines in the atmosphere is probably 2 or 3 orders
of magnitude lower than in NH 3 (Kuerten et al. 2014), amines can significantly assist
the growth of both neutral and ionic clusters (Almeida et al. 2013; Kuerten et al.
2014). Above 3 pptv DMA can enhance particle formation rates more than 1000-fold
compared to NH 3 (Almeida et al. 2013). From the climate perspective, the trace
condensable compounds contributing to formation of secondary aerosols supply
almost half of global cloud condensation and ice nuclei (Merikanto et al. 2009).
Amines are strong stabilizers of aerosols (Kulmala et al. 2013; Kurtén et al. 2008). A
recent study investigated the mechanisms of new particle formation in Shanghai
(Yao et al. 2018a). This study consisted of long-term continuous observations and an
intensive campaign during the haze period. High concentrations of sulfuric acid
dimers were detected, which resulted most likely from the strong acid-base stabilization in H 2 SO 4 -DMA clusters. The results suggest that, despite the fact that
preexisting particles would scavenge the precursors of new particles and suppress
their formation, DMA could still enhance NPF in a highly polluted urban
atmosphere.
6.2.3 Nitrogen Oxides
The condensed water could facilitate the partition of gaseous pollutants into particle
phase and accelerate the formation of severe haze pollution by acting as a powerful
medium for multiphase reactions (Wu et al. 2018). A positive correlation between
the mass concentrations of nitrate (NO 3
À ) and SO 4
2À in PM 2.5 and the aerosol liquid
water content (ALWC) indicates that both NO 3
À and SO 4
2À determine the ALWC
(Pan et al. 2016b). However, since SO 2 emission mitigation has been successfully
achieved throughout China, NO 3
À became a dominant anthropogenic inorganic saltdriving ALWC. Moreover, Wang et al. (2016) and Xue et al. (2016) stated that the
oxidation of SO 2 by NO 2 leads to SO 4
2À formation. The combination of relatively
high pH in aqueous phase; high concentrations of NO 2 , SO 2 , and PM; and small fog
droplets can significantly improve SO 4
2À formation. It is observed that the oxidation
of SO 2 by NO x during winters in Beijing stimulates severe haze (Ma et al. 2018).
Both SO 2 and NO 2 which are produced from coal burning present in highly elevated
116
Y. Pan et al.