causes severe plant damage and its high regional localized concentration (Feng et al.
2014, 2015a). Although in some areas O 3 level was decreased, especially in the
USA and Europe (Cooper et al. 2015), ozone monitoring in China showed an
increasing trend since the 1990s (Xu et al. 2008, 2016a; Wang et al. 2009), which
became especially alarming in the last 5 years (2013–2016) (Lu et al. 2018; Zeng
et al. 2019). Ozone pollution observed during summers in China is especially
concerned. Particularly high O 3 levels were observed in multiple cities during
summer 2017: 90th percentile of a daily maximum 8-h average (MDA8) O 3 level
in 30 out of 74 major cities exceeded 200 μg/m
3 . Air with such high O 3 concentrations corresponds to grade II according to the national air quality standards for
residential areas (Lu et al. 2018). Ground-level O 3 in China strongly correlated with
emissions of NO x , which is a main contributor to O 3 formation (Wang et al. 2017).
Literature results demonstrate 10% yield decrease for major food crops (such as
potato, rice, wheat, soybeans, etc.) at O 3 concentrations in air equal to ~40 ppb in
comparison with crop yields grown in O 3 -free air (Feng and Kobayashi 2009).
Survey in Beijing and its surroundings revealed 28 plant species or cultivars with
typical O 3 symptoms (Feng et al. 2014). Thus, food security in China is being
threatened or has already been severely affected by current high ground-level O 3
concentration. Without special measures and precautions, O 3 levels will continue
to rise.
This chapter describes mechanism of ground-level O 3 formation and summarizes
recent development based on the analysis and predictions of spatial-temporal distribution patterns of NO x emission in China. It also discusses how ground-level O 3
affects the well-being of plants. Recommendations on adverse impact of groundlevel O 3 pollution as well as way for its reduction and prevention are also illustrated.
7.2 Mechanism of O 3 Formation
Ozone forms in the atmosphere as a result of visible light-assisted reaction of various
nitrogen oxides (formed in a NO x $ NO 2 + NO reaction) with volatile organic
compounds (VOCs), methane (CH 4 ) and carbon monoxide (CO). Specifically, ozone
formation is a combination reaction between molecular oxygen (O 2 ) and atomic
oxygen (O(
3 P)) (see Eq. 7.1). Atomic oxygen is obtained by O 2 decomposition upon
its exposure to short-wavelength ultraviolet (UV) radiation with wavelengths below
240 nm. These reactions are responsible for producing and maintaining protective
O 3 layer (Chapman 1930).
Troposphere does not have so much UV as other atmospheric layers; thus, NO 2
photolytic reaction occurring at wavelengths below 424 nm (as shown in Eq. 7.2) is
a primary source of atomic O(
3 P), which becomes the major O 3 -producing reaction.
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Z. Feng et al.
2014, 2015a). Although in some areas O 3 level was decreased, especially in the
USA and Europe (Cooper et al. 2015), ozone monitoring in China showed an
increasing trend since the 1990s (Xu et al. 2008, 2016a; Wang et al. 2009), which
became especially alarming in the last 5 years (2013–2016) (Lu et al. 2018; Zeng
et al. 2019). Ozone pollution observed during summers in China is especially
concerned. Particularly high O 3 levels were observed in multiple cities during
summer 2017: 90th percentile of a daily maximum 8-h average (MDA8) O 3 level
in 30 out of 74 major cities exceeded 200 μg/m
3 . Air with such high O 3 concentrations corresponds to grade II according to the national air quality standards for
residential areas (Lu et al. 2018). Ground-level O 3 in China strongly correlated with
emissions of NO x , which is a main contributor to O 3 formation (Wang et al. 2017).
Literature results demonstrate 10% yield decrease for major food crops (such as
potato, rice, wheat, soybeans, etc.) at O 3 concentrations in air equal to ~40 ppb in
comparison with crop yields grown in O 3 -free air (Feng and Kobayashi 2009).
Survey in Beijing and its surroundings revealed 28 plant species or cultivars with
typical O 3 symptoms (Feng et al. 2014). Thus, food security in China is being
threatened or has already been severely affected by current high ground-level O 3
concentration. Without special measures and precautions, O 3 levels will continue
to rise.
This chapter describes mechanism of ground-level O 3 formation and summarizes
recent development based on the analysis and predictions of spatial-temporal distribution patterns of NO x emission in China. It also discusses how ground-level O 3
affects the well-being of plants. Recommendations on adverse impact of groundlevel O 3 pollution as well as way for its reduction and prevention are also illustrated.
7.2 Mechanism of O 3 Formation
Ozone forms in the atmosphere as a result of visible light-assisted reaction of various
nitrogen oxides (formed in a NO x $ NO 2 + NO reaction) with volatile organic
compounds (VOCs), methane (CH 4 ) and carbon monoxide (CO). Specifically, ozone
formation is a combination reaction between molecular oxygen (O 2 ) and atomic
oxygen (O(
3 P)) (see Eq. 7.1). Atomic oxygen is obtained by O 2 decomposition upon
its exposure to short-wavelength ultraviolet (UV) radiation with wavelengths below
240 nm. These reactions are responsible for producing and maintaining protective
O 3 layer (Chapman 1930).
Troposphere does not have so much UV as other atmospheric layers; thus, NO 2
photolytic reaction occurring at wavelengths below 424 nm (as shown in Eq. 7.2) is
a primary source of atomic O(
3 P), which becomes the major O 3 -producing reaction.
136
Z. Feng et al.