Positive and negative influences of landfalling typhoons on tropospheric ozone over southern China

Abstract

Abstract. In this study, we use an ensemble of 17 landfalling typhoons over 2014–2018 to investigate the positive and negative influences of typhoons on tropospheric ozone over southern China. Referring to the proximity to typhoons and typhoon developmental stages, we found that surface ozone is enhanced when typhoons are 400–1500 km away during the initial stages of typhoons (e.g., from 1 day before and to 1 day after typhoon genesis). The positive ozone anomaly averagely reaches 10–20 ppbv at the daytime and 9 ppbv at nighttime compared with the background ozone level. Particularly, surface ozone at radial distances of 1100–1300 km is most significantly enhanced during these initial stages. As the typhoons approach and land in southern China, the influences of typhoons change from enhancing to reducing ozone. Surface ozone concentrations decrease with a negative ozone anomaly ranging between -12 % ~ -17 % relative to the background ozone level. We explore the physical linkages between typhoons, meteorological conditions and ozone variations. Results show that during typhoon initial stages, the increasing temperature and weak winds in the atmospheric boundary layer (ABL) and dominating downward motions promote ozone production and accumulation over the outskirts of typhoons. While the deteriorating weather accompanied by dropping temperature, wind gales and convective activity reduces the production and accumulation of surface ozone when typhoons are making landfalling. Variations of tropospheric ozone profiles during the differential developmental stages of landfalling typhoons are further examined to quantify the influences of typhoon-induced stratospheric intrusions on lower troposphere and surface ozone. Using temporally dense ozone vertical observations, we found two regions of high ozone concentrations separately located in the ABL and the middle-to-upper troposphere under the influences of typhoons. Averagely, the ozone enhancement maximizes around 10–12 ppbv at 1–1.5 km altitude at the typhoon initial stages. The ozone enhancement persists over a longer period in the middle-to-upper troposphere with a positive ozone anomaly of 10 ppbv at 7–8 km altitude shortly after typhoon genesis, and 30 ppbv near 12 km altitude when typhoons reach their maximum intensity. When typhoons are landing, a negative ozone anomaly appears and extends upward with a maximum ozone reduction of 14–18 ppbv at 5 km altitude and 20–25 ppbv at 11 km altitude. Though the overall tropospheric ozone is usually reduced during typhoon landfalling, we quantify that five of eight typhoon samples deduce ozone-rich air with the stratospheric origin (80 ppbv) above 4 km altitude, and in 3 typhoon cases the ozone-rich air intrusions (60 ppbv) can sink to the ABL. This suggests that the typhoon-induced stratospheric ozone-rich air intrusions play an important role in surface ozone enhancement.

A machine learning approach to quantify meteorological drivers of recent ozone pollution in China

“…In addition, despite more OH may be available given high humidity, OH can react with NO2, forming HNO3 in highly NOxpolluted regions, which ultimately leading to less efficient O3 formation by competing with the oxidation of VOC and CO with OH (Lu et al, 2019a). The negative correlation between humidity and ozone in PRD region has been identified by previous studies (W. Yang et al, 2021;Hua et al, 2008), and the high humidity environment in southern China may be the result of moisture marine air masses transported from tropical region, South China Sea and western Pacific (W. Ding and Chen, 2005). For a non-linear learning framework using RFR, the second most important meteorological driver in PRD is again the level of surface solar radiation.…”

“…The geographical location and the intensity of typhoons can modulate the level of ozone in PRD; when typhoons are located relatively far away from PRD during their development period, ozone can be elevated by downward movement of air masses, atmospheric stagnation and lower planetary boundary layer height (Z. Chen et al, 2021), leading to suppressed dispersion of ozone and its precursors before typhoon landing (Jiang et al, 2015;.…”