An evaluation of the ability of the Ozone Monitoring Instrument (OMI) to observe boundary layer ozone pollution across China: application to 2005–2017 ozone trends

Abstract

Abstract. Nadir-viewing satellite observations of tropospheric ozone in the UV have been shown to have some sensitivity to boundary layer ozone pollution episodes, but so far they have not yet been compared to surface ozone observations collected by large-scale monitoring networks. Here we use 2013–2017 surface ozone data from China's new Ministry of Ecology and Environment (MEE) network of ∼ 1000 sites, together with vertical profiles from ozonesondes and aircraft, to quantify the ability of tropospheric ozone retrievals from the Ozone Monitoring Instrument (OMI) and to detect boundary layer ozone pollution in China. We focus on summer when ozone pollution in China is most severe and when OMI has the strongest sensitivity. After subtracting the Pacific background, we find that the 2013–2017 mean OMI ozone enhancements over eastern China have strong spatial correlation with the corresponding multiyear means in the surface afternoon observations (R=0.73), and that OMI can estimate these multiyear means in summer afternoon surface ozone with a precision of 8 ppb. The OMI data show significantly higher values on observed surface ozone episode days (>82 ppb) than on non-episode days. Day-to-day correlations with surface ozone are much weaker due to OMI noise and are stronger for sites in southern China (<34∘ N; R=0.3–0.6) than in northern China (R=0.1–0.3) because of weaker retrieval sensitivity and larger upper tropospheric variability in the north. Ozonesonde data show that much of the variability of OMI ozone over southern China in summer is driven by the boundary layer. Comparison of 2005–2009 and 2013–2017 OMI data indicates that mean summer afternoon surface ozone in southern China (including urban and rural regions) has increased by 3.5±3.0 ppb over the 8-year period and that the number of episode days per summer has increased by 2.2±0.4 (as diagnosed by an extreme value model), generally consistent with the few long-term surface records. Ozone increases have been particularly large in the Yangtze River Delta and in the Hubei, Guangxi and Hainan provinces.

Local and synoptic meteorological influences on daily variability of summertime surface ozone in eastern China

“…Silver et al (2018) found the annual mean MDA8 ozone has increased significantly (p<0.05) at around 50% of the over 1000 stations across China from 2015 to 2017, with a median rate of 4.6 µg m -3 year -1 . The increasing trend over eastern China was also captured by the OMI satellite records of tropospheric ozone, reported by Shen et al (2019). The absolute increasing trend (in a unit of µg m -3 ) in daytime is higher than that in nighttime, whereas the relative increasing trend (in a unit of %) in daytime is lower than that in nighttime (Figures 4e-4h vs. which is probably related to the hot extremes in 2017 (Herring et al, 2019).…”

“…A rapid increasing trend in summertime surface ozone over China after 2012 was observed in recent studies (Lu et al, 2018;Silver et al, 2018;Shen et al, 2019;. We examine the regional mean trend over eastern China in daily, daytime (7:00-18:00), and nighttime (19:00-6:00) means ( Figure 4).…”

Exploring 2016–2017 surface ozone pollution over China: source contributions and meteorological influences

“…3.4. The warmer and drier weather conditions in May-August 2017 are expected to accelerate ozone production rates and also favor the thermal decomposition of peroxyacetyl nitrate (PAN, a NO x reservoir species whose decomposition is strongly temperature dependent), providing additional NO x to produce ozone (Steiner et al, 2010;Doherty et al, 2013). This is evident from the lower background PAN concentrations (model results in noCH only reflect changes in meteorology) over eastern China simulated in 2017 ( Fig.…”

Local and synoptic meteorological influences on daily variability in summertime surface ozone in eastern China

“…The increase in ozone over China may result from both meteorology and anthropogenic emissions. During 2013-2017, the anthropogenic emissions of NO x in China declined (Zheng et al, 2018), but the anthropogenic emissions of VOCs changed little (Zheng et al, 2018;Shen et al, 2019b). Li et al (2019) suggested that the ∼ 40 % decrease in fine particulate matter (PM 2.5 ) is the primary reason for the rising surface ozone in summer during 2013-2017, as the aerosol sink of hydroperoxy radicals was weakened and thus ozone production was enhanced.…”