The Role of Deep Convection in Modulating LNOx and Boundary Layer-Upper Troposphere Exchange in the Amazon

Lightning-produced nitrogen oxides (LNOx) represent a key source of reactive nitrogen in the Amazon, yet their role in regional atmospheric chemistry and transport remains poorly constrained. Beyond their role in ozone production, LNOx is a key driver of new aerosol particle formation in the upper troposphere, with earlier studies linking this process to the outflow of deep convective clouds and a downward flux of aerosol particles during precipitation events. However, recent findings highlight that ozone injections driven by LNOx from convective processes also play a crucial role in triggering in-situ particle bursts in the boundary layer. Both upper tropospheric aerosols and boundary layer particle bursts may play a pivotal role in supplying cloud condensation nuclei, promoting the development of green-ocean clouds and precipitation in the Amazon.

This study investigates the interplay between deep convective processes and LNOx production, emphasizing the vertical transport of gases and aerosols between the boundary layer and upper troposphere. Using data from the GoAmazon, ACRIDICON-CHUVA and CAFE-Brazil experiments, ATTO project, radar, satellite and lightning observations, we evaluate the temporal and spatial scales of NOx and ozone enrichment following deep convection activity. Time series of NOx and ultrafine particles are analyzed to identify peaks associated with potential LNOx emissions, contextualized with precipitation structure, divergence, mass flux at the cloud top, and lightning events. We intercompare radar-derived wind profiles and echo top heights from cloud and wind profiler radars at ATTO to determine the vertical range of mass detrainment. The height of the detrainment layer (HDL) is identified by correlating the divergence profiles with the distribution of radar reflectivity and ice water content within the anvil and convective cores. Echo tops exceeding the level of neutral buoyancy, derived from atmospheric soundings, are also used to assess the extent of vertical mass transport, with particular attention to anvil echo tops and convective tops surpassing this level. Ice water content within the anvil is used as a proxy for mass detrainment, applying a correction for ice fall speed to estimate the detrainment range. This proxy is then applied to 3D scanning radars over the Amazon. 

For the storms analyzed, all of them demonstrated enhanced ozone and NOx concentrations during downdrafts. The HDL is calculated to be near 11 km, with the detrainment range spanning 8 to 18 km. Over 15% of anvil echo tops extended beyond the neutral level of buoyancy of 16 km, and convective tops reached altitudes above 18 km. The results suggest that deep convection not only redistributes NOx and ozone but also alters the oxidative capacity and particle formation potential of the regional atmosphere. This work highlights the need to incorporate detailed convective processes into atmospheric models to improve predictions of chemical budgets and their implications for climate and air quality in tropical environments.