6.3.2 Organic Nitrogen in Atmospheric Aerosols
The analysis of organic nitrogen in aerosols is extremely important for global
organic nitrogen estimation, nitrogen cycling, and atmospheric nitrogen deposition
(Kanakidou et al. 2012). The inorganic nitrogen (IN ¼ NH 4
+ + NO 3
À + NO 2
À ) in the
aerosol sample is usually subtracted from total nitrogen (TN) to obtain organic
nitrogen (ON): ON ¼ TN-IN (Kundu et al. 2010). In recent years, it has been
found that the elemental analyzer can effectively measure the content of TN in
aerosols and IN can be accurately determined by ion chromatography. Studies have
shown that the ratio of ON to TN in atmospheric aerosols is 12–64% (Calvo et al.
2013; Putaud et al. 2010). For the quantification of water-soluble organic nitrogen
(WSON), the aerosol sample can be dissolved and extracted into water and then
determined by wet oxidation, ultraviolet oxidation, or high-temperature catalytic
oxidation. For example, Miyazaki et al. (2014) first reported the inter-annual variation of WSON in the forest atmosphere and found that high concentrations of
WSON appeared in early summer (378 Æ 260 ng N∙m
À3 ). Studies in different
regions have found that the ratio of WSON/TN in particulate matter is approximately
30%, which is comparable to the ratio of that in precipitation (Miyazaki et al. 2011;
Zamora et al. 2011). Based on the accurate analysis of WSON, water-insoluble
organic nitrogen (WION) can be calculated based on the difference between WSON
and ON. Many studies have illustrated that the concentration of WION in aerosols is
low (Cape et al. 2011), but in some areas such as the North Pacific Ocean, which is
greatly affected by marine activities, WION (112 Æ 61 ng NÁm
À3 ) accounted for
55 Æ 16% of TN, accounting for approximately 93% of ON, indicating that WION
has an important contribution to TN in these areas (Miyazaki et al. 2011).
The chemical composition of organic nitrogen is more complicated than the
inorganic components in the particles. Organic nitrogen consists of hundreds of
organic compounds with different physical and chemical properties, and there are
various analytical methods. So far, no analytical method has been able to measure all
organic nitrogen components in particulate matter. Despite this, there have been
many studies on the formation of aerosol organic nitrogen and its chemical
characteristics.
On the one hand, reduced organic nitrogen includes urea, amino acids, amines,
heterocyclic compounds, etc. Urea and amino acids are mainly from primary sources
such as agricultural and livestock activities, soil discharge, and the ocean surface,
mainly in coarse particles. Urea is also found in fine particles. For example, Fu et al.
(2014) showed that there is a large amount of fine-grained urea in the troposphere
(over 2 km) from East China to the Sichuan Basin and suggested that atmospheric
chemistry may be one of the main sources. Amines have both primary and secondary
sources; secondary sources mainly include biomass burning and motor vehicle
exhaust. Recently, studies have found that amines exist in ultrafine particles and
6 Contribution of Atmospheric Reactive Nitrogen to Haze Pollution in China
119
The analysis of organic nitrogen in aerosols is extremely important for global
organic nitrogen estimation, nitrogen cycling, and atmospheric nitrogen deposition
(Kanakidou et al. 2012). The inorganic nitrogen (IN ¼ NH 4
+ + NO 3
À + NO 2
À ) in the
aerosol sample is usually subtracted from total nitrogen (TN) to obtain organic
nitrogen (ON): ON ¼ TN-IN (Kundu et al. 2010). In recent years, it has been
found that the elemental analyzer can effectively measure the content of TN in
aerosols and IN can be accurately determined by ion chromatography. Studies have
shown that the ratio of ON to TN in atmospheric aerosols is 12–64% (Calvo et al.
2013; Putaud et al. 2010). For the quantification of water-soluble organic nitrogen
(WSON), the aerosol sample can be dissolved and extracted into water and then
determined by wet oxidation, ultraviolet oxidation, or high-temperature catalytic
oxidation. For example, Miyazaki et al. (2014) first reported the inter-annual variation of WSON in the forest atmosphere and found that high concentrations of
WSON appeared in early summer (378 Æ 260 ng N∙m
À3 ). Studies in different
regions have found that the ratio of WSON/TN in particulate matter is approximately
30%, which is comparable to the ratio of that in precipitation (Miyazaki et al. 2011;
Zamora et al. 2011). Based on the accurate analysis of WSON, water-insoluble
organic nitrogen (WION) can be calculated based on the difference between WSON
and ON. Many studies have illustrated that the concentration of WION in aerosols is
low (Cape et al. 2011), but in some areas such as the North Pacific Ocean, which is
greatly affected by marine activities, WION (112 Æ 61 ng NÁm
À3 ) accounted for
55 Æ 16% of TN, accounting for approximately 93% of ON, indicating that WION
has an important contribution to TN in these areas (Miyazaki et al. 2011).
The chemical composition of organic nitrogen is more complicated than the
inorganic components in the particles. Organic nitrogen consists of hundreds of
organic compounds with different physical and chemical properties, and there are
various analytical methods. So far, no analytical method has been able to measure all
organic nitrogen components in particulate matter. Despite this, there have been
many studies on the formation of aerosol organic nitrogen and its chemical
characteristics.
On the one hand, reduced organic nitrogen includes urea, amino acids, amines,
heterocyclic compounds, etc. Urea and amino acids are mainly from primary sources
such as agricultural and livestock activities, soil discharge, and the ocean surface,
mainly in coarse particles. Urea is also found in fine particles. For example, Fu et al.
(2014) showed that there is a large amount of fine-grained urea in the troposphere
(over 2 km) from East China to the Sichuan Basin and suggested that atmospheric
chemistry may be one of the main sources. Amines have both primary and secondary
sources; secondary sources mainly include biomass burning and motor vehicle
exhaust. Recently, studies have found that amines exist in ultrafine particles and
6 Contribution of Atmospheric Reactive Nitrogen to Haze Pollution in China
119