Abstract
Abstract. Tropospheric ozone (O3) is one of the most important air pollutants in China and is projected to continue to increase in the near future. O3 and vegetation closely interact with each other and such interactions may not only affect plant physiology (e.g., stomatal conductance and photosynthesis) but also influence the overlying meteorology and air quality through modifying leaf stomatal behaviors. Previous studies have highlighted China as a hotspot in terms of O3 pollution and O3 damage to vegetation. Yet, few studies have investigated the effects of O3–vegetation interactions on meteorology and air quality in China, especially in the light of recent severe O3 pollution. In this study, a two-way coupled land–atmosphere model was applied to simulate O3 damage to vegetation and the subsequent effects on meteorology and air quality in China. Our results reveal that O3 causes up to 16 % enhancement in stomatal resistance, whereby large increases are found in the Henan, Hebei, and Shandong provinces. O3 damage causes more than 0.6 µmol CO2 m−2 s−1 reductions in photosynthesis rate and at least 0.4 and 0.8 g C m−2 d−1 decreases in leaf area index (LAI) and gross primary production (GPP), respectively, and hotspot areas appear in the northeastern and southern China. The associated reduction in transpiration causes a 5–30 W m−2 decrease (increase) in latent heat (sensible heat) flux, which induces a 3 % reduction in surface relative humidity, 0.2–0.8 K increase in surface air temperature, and 40–120 m increase in boundary-layer height in China. We also found that the meteorological changes further induce a 2–6 ppb increase in O3 concentration in northern and south-central China mainly due to enhanced isoprene emission following increased air temperature, demonstrating that O3–vegetation interactions can lead to strong positive feedback that can amplify O3 pollution in China. Our findings emphasize the importance of considering the effects of O3 damage and O3–vegetation interactions in air quality simulations, with ramifications for both air quality and forest management.
Highlights
Tropospheric ozone (O3) is a secondary air pollutant, which is mainly formed from the photochemical oxidation of carbon monoxide (CO), methane (CH4), and non-methane volatile organic compounds (VOCs) by hydroxyl radicals (OH) in the presence of nitrogen oxides (NOx= NO + NO2)
We found that the model simulations have better performance in northeastern China, central China, and southern China in terms of IOA and CORR as shown in these tables (Table 4)
We find that the Henan, Hebei, Shanxi, and Shandong provinces have smaller values of photosynthesis rate (PSN), leaf area index (LAI), and gross primary production (GPP) when compared with other provinces in eastern China
Summary
Tropospheric ozone (O3) is a secondary air pollutant, which is mainly formed from the photochemical oxidation of carbon monoxide (CO), methane (CH4), and non-methane volatile organic compounds (VOCs) by hydroxyl radicals (OH) in the presence of nitrogen oxides (NOx= NO + NO2). Vegetation can in turn modulate O3 concentration through influencing the sources and sinks of O3. Dry deposition of O3 onto vegetation is a major sink for O3, mainly via stomatal uptake. Stomata conductance may decrease subsequently in response to O3 exposure, reducing the dry-depositional sink of O3 (Sadiq et al, 2017; Zhou et al, 2018), but some studies suggest that O3 exposure can cause stomata to respond more sluggishly to changing environmental conditions, such as drought, with complex overall effects on stomatal behaviors and dry deposition (e.g., Huntingford et al, 2018). Transpiration, which is modulated by stomatal behaviors, significantly regulates surface meteorology including water vapor content and air temperature, which further influence the production and loss of O3. Through influencing plant ecophysiology (e.g., photosynthesis and stomata behaviors), O3–vegetation interactions can modulate boundary-layer meteorology and climate, and may further affect O3 air quality via a series of feedback mechanisms. It is essential to fully understand the O3– vegetation interactions and the following climatic and biospheric impacts especially in areas with high O3 concentrations and vegetation density
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