Abstract
The first Tropospheric Ozone Assessment Report (TOAR) provides information on present-day distributions and long-term trends of ozone metrics relevant for climate change, human health, and vegetation. However, only few results are available in TOAR for China due to limited long-term ozone observations. Here, we present an integrated analysis of long-term measurements of surface ozone from eight sites distributed in the North China Plain (NCP) and Yangtze River Delta (YRD), the relatively underdeveloped region Northeast China, and the remote regions in Northwest and Southwest China. Trends and present-day values for seven annual and five seasonal ozone metrics were calculated following the TOAR methodologies. We compare the seasonal and diurnal cycles of ozone concentrations as well as the present-day values of ozone among sites and discuss the long-term trends in the ozone metrics. Large and significant increases of ozone are detected at the background site in the NCP, moderate increases at the global baseline site in western China, significant decreases at the northwestern edge of China, and nearly no trend at other sites. Extremely high values of ozone occurred in the NCP and YRD, particularly in warmer seasons. The present-day levels of summer ozone metrics in the NCP are much higher than the thresholds set in TOAR for the highest value groups of ozone metrics. The summer ozone metrics at the Shangdianzi background site in the NCP indicate increases at rates of more than 2%/yr during 2004–2016. In contrast, ozone at the Lin’an background site in the YRD was constant over the period 2006–2016. Our results fill some knowledge gaps in spatiotemporal changes of ozone in China and may be of useful in the assessment of ozone impacts on human health and vegetation.
Highlights
Ozone is a ubiquitous trace gas in the stratosphere and troposphere, with the stratosphere and troposphere containing about 90% and 10% of atmospheric ozone, respectively
In previous studies we found that there were periodicities of ozone at WLG during 1994–2013, with 2–4-year, 7-year, and 11-year cycles (Xu et al, 2018), which were linked to the periodic variations of the quasi-biennial oscillation (QBO), the East Asian summer monsoon (EASM), etc
Summary and conclusions In this work, we present for the first time an integrated analysis of long-term measurements of surface ozone at six background sites (WLG, SDZ, LA, LFS, XGLL, and AKDL), a rural site (GCH), and an urban site (CMA) in mainland China
Summary
Ozone is a ubiquitous trace gas in the stratosphere and troposphere, with the stratosphere and troposphere containing about 90% and 10% of atmospheric ozone, respectively. Stratospheric ozone protects life on the Earth’s surface from harmful solar ultraviolet radiation. Tropospheric ozone is one of the key greenhouse gases (IPCC, 2013; Monks et al, 2015) and very important in sustaining the atmospheric oxidation capacity (Monks et al, 2005; Lelieveld et al, 2008). Surface ozone is a pollutant detrimental to human health and vegetation (REVIHAAP, 2013; CLRTAP, 2016). Atmospheric ozone can only be formed in photochemical reactions. Ozone is produced and sustained by the Chapman mechanism and catalytically destroyed by active species, such as OH, NO, and halogenated species (Solomon, 1999). A simulation study by Lelieveld and Dentener (2000) suggests that more than 85% of tropospheric ozone originates from photochemical oxidation of volatile organic compounds (VOCs), CO, and CH4, catalyzed by NOx, with
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