Influence of convection on the upper-tropospheric O3 and NOx budget in southeastern China

Thunderstorms can significantly influence the air composition via strong updraft and lightning nitrogen oxides (LNOx). In this study, the ozonesondes and TROPOMI (TROPOspheric Monitoring Instrument) nitrogen dioxide (NO2) observations for two cases are combined with a model to investigate the effects of typical strong convection on vertical redistribution of air pollutants in Nanjing, southeastern China. The ozonesonde observations show higher O-3 and water vapor mixing ratios in the upper troposphere (UT) after convection, indicating the strong updraft transporting lower-level air masses into the UT and the possible downward O-3-rich air near the top of UT over the convective period. During the whole convection life cycle, the UT O-3 production is driven by the chemistry (5-10 times the magnitude of dynamic contribution) and reduced by the LNOx (-40 %). Sensitivity tests demonstrate that neglecting LNOx in standard TROPOMI NO2 products causes over-estimated air mass factors over fresh lightning regions and the opposite for outflow and aged lightning areas. Therefore, a new high-resolution retrieval algorithm is applied to estimate the LNOx production efficiency. Our work shows the demand for high-resolution modeling and satellite observations on LNOx emissions of both active and dissipated convection, especially small-scale storms.

Automated summary

This study investigates the effects of strong convection on vertical redistribution of air pollutants in Nanjing, southeastern China, using a combination of ozonesondes, TROPOMI NO2 observations, and a model. The results show that convective updrafts transport lower-level air masses into the upper troposphere, leading to higher O-3 and water vapor concentrations in this region. The production of O-3 in the upper troposphere is mainly driven by chemistry, while LNOx reduces its formation. Neglecting LNOx in satellite observations causes overestimation of air mass factors over fresh lightning regions and underestimation over outflow and aged lightning areas.