14 Dec 2020

14 Dec 2020

Review status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Spatial and temporal changes of the ozone sensitivity in China based on satellite and ground-based observations

Wannan Wang1,2,3, Ronald van der A3, Jieying Ding3, Michiel van Weele3, and Tianhai Cheng1 Wannan Wang et al.
  • 1Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, 100094, China
  • 2University of Chinese Academy of Sciences, Beijing, 100049, China
  • 3Royal Netherlands Meteorological Institute (KNMI), De Bilt, 3730 AE, the Netherlands

Abstract. Ground-level ozone (O3) pollution has been steadily getting worse in most part of eastern China during the past five years. The non-linearity of O3 formation with its precursors like nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs) are complicating effective O3 abatement plans. The diagnosis from space-based observations, the ratio of formaldehyde (HCHO) columns to tropospheric NO2 columns (HCHO / NO2), has previously been proved to be highly consistent with our current understanding of surface O3 chemistry. HCHO / NO2 ratio thresholds distinguishing O3 formation sensitivity depend on regions and O3 chemistry interactions with aerosol. To shed more light on current the O3 formation sensitivity over China, we have derived HCHO / NO2 ratio thresholds by directly connecting satellite-based HCHO / NO2 observations and ground-based O3 measurements over the major Chinese cities in this study. We find that a VOC-limited regime occurs for HCHO / NO2 < 2.3 and NOx-limited regime occurs for HCHO / NO2 > 4.2. The HCHO / NO2 between 2.3 and 4.2 reflects the transition between the two regimes. Our method shows that the O3 formation sensitivity tends to be VOC-limited over urban areas and NOx-limited over rural and remote areas in China. We find that there is a shift in some cities from the VOC-limited to the transitional regime that is associated with a rapid drop of anthropogenic NOx emissions owing to the widely-applied rigorous emission control strategies between 2016 and 2019. This detected spatial expansion of the transitional regime is supported by rising surface O3 concentrations. The enhanced O3 concentrations in urban areas during the COVID-19 lockdown in China indicate that a protocol with simultaneous anthropogenic NOx emissions and VOC emissions controls is essential for O3 abatement plans.

Wannan Wang et al.

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Wannan Wang et al.

Wannan Wang et al.


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Short summary
We developed a method to determine the type of photochemical regime of ozone formation by using only satellite observations of formaldehyde and nitrogen dioxide and ozone measurements on the ground. It was found that many cities in China, because of their high level of air pollution, are in the so-called VOC-limited photochemical regime. This means that the current reductions of nitrogen dioxide resulted in higher levels of photochemical smog in these cities.