Rapid increase in summer surface ozone over the North China Plain during 2013–2019: a side effect of particulate matters reduction control?

Abstract

Abstract. While the elevated ambient levels of particulate matters with aerodynamic diameter of 2.5 micrometers or less (PM2.5) are alleviated largely with the implementation of effective emission control measures, an opposite trend with a rapid increase is seen in surface ozone (O3) in the North China Plain (NCP) region over the past several years. It is critical to determine the real culprit causing such a large increase in surface O3. In this study, seven-year surface observations and satellite retrieval data are analyzed to determine the long-term change in surface O3 as well as driving factors. Results indicate that anthropogenic emission control strategies and changes in aerosol concentrations as well as aerosol optical properties such as single-scattering albedo (SSA) are the most important factors driving such a large increase in surface O3. Numerical simulations with National Center for Atmospheric Research (NCAR) Master Mechanism (MM) model suggest that reduction of O3 precursor emissions and aerosol radiative effect accounted for 45 % and 23 % of the total change in surface O3 in summertime during 2013–2019, respectively. Planetary boundary layer (PBL) height with an increase of 0.21 km and surface air temperature with an increase of 2.1 °C contributed 18 % and 12 % to the total change in surface O3, respectively. The combined effect of these factor was responsible for the rest change. Decrease in SSA or strengthened absorption property of aerosols may offset the impact of AOD reduction on surface O3 substantially. While the MM model enables quantification of individual factor's percentage contributions, it requires further refinement with aerosol chemistry included in the future investigation. The study indicates an important role of aerosol radiative effect in development of more effective emission control strategies on reduction of ambient levels of O3 as well as alleviation of national air quality standard exceedance events.

On the Relevancy of Observed Ozone Increase during COVID-19 Lockdown to Summertime Ozone and PM2.5 Control Policies in China

“… 11 During the past several years, numerous studies witnessed aggravated O 3 pollutions, especially in megacity clusters over eastern China in the context of the rapid drop of anthropogenic NO x emissions due to implementing strict emission controls nationwide. 8 , 12 − 14 The increase in O 3 during the pandemic lockdown appears to further suggest that NO x emission reductions alone might lead to additional increases in summertime O 3 , although some recent studies found an O 3 decline in summer with NO x reductions in several places of China. 15 , 16 However, NO x emission control is necessary and effective in reducing the PM 2.5 nitrate, 17 − 19 which is currently replacing sulfate in many places as the major PM 2.5 secondary constituent as SO 2 emissions from power plants and industries have been drastically reduced in recent years.…”

Changes in tropospheric air quality related to the protection of stratospheric ozone in a changing climate

“…This has led to surface brightening (e.g., by 0.70-1.16 W m −2 year −1 in eastern China over 2014-2019) [29] but also to undesirable increases in ambient O 3 [30][31][32][33] (e.g., by 2-6 µg m −3 year −1 in megacity clusters of Beijing and Shanghai over 2013-2017) [34]. Simulations with numerical models show several possible reasons including increases in UV radiation [31,[33][34][35][36][37][38][39], shifts in the VOC/NOx chemical regime resulting in increased production of O 3 efficiency [35,40], higher emissions of biogenic VOC due to rising temperatures [30], and decreased competition for gas-phase radicals by aerosol surfaces [34,40], with reality likely being a combination of these factors.…”