31 Aug 2021

31 Aug 2021

Review status: this preprint is currently under review for the journal ACP.

Impact of biomass burning and stratospheric intrusions in the remote South Pacific Ocean troposphere

Nikos Daskalakis1, Laura Gallardo2, Maria Kanakidou1,3,4, Rasmus Nüß1, Camilo Menares2, Roberto Rondanelli2, Anne M. Thompson5, and Mihalis Vrekoussis1,6,7 Nikos Daskalakis et al.
  • 1Laboratory for Modeling and Observation of the Earth System (LAMOS), Institute of Environmental Physics (IUP), University of Bremen, Bremen, Germany
  • 2Center for Climate and Resilience Research (CR2) & Department of Geophysics, Faculty of Physical and Mathematical Sciences, University of Chile, Santiago, Chile
  • 3Environmental Chemical Processes Laboratory (ECPL), Department of Chemistry, University of Crete, 70013 Heraklion, Greece
  • 4CSTACC, ICE-HT, FORTH, Patras, Greece
  • 5NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
  • 6Center of Marine Environmental Sciences (MARUM), University of Bremen, Germany
  • 7Climate and Atmosphere Research Center (CARE-C), The Cyprus Institute, Cyprus

Abstract. The ozone mixing ratio spatio-temporal variability in the pristine southern Pacific Ocean is studied, for the first time, using 21-year long ozone (O3) records from the entire southern tropical and subtropical Pacific, between 1994 and 2014. The analysis considered regional O3 vertical observations from ozonesondes, surface carbon monoxide (CO) observations from flasks and three-dimensional chemistry-transport model simulations of the global troposphere. Two 21-year long numerical simulations, with and without biomass burning emissions, were performed to disentangle the importance of biomass burning relative to stratospheric intrusions for ambient ozone levels in the region. Tagged tracers of O3 from the stratosphere and CO from various biomass burning regions have been used to track the impact of these different regions on the southern tropical Pacific O3 and CO levels. Patterns have been analyzed based on atmospheric dynamics variability.

Considering the interannual variability in the observations, the model can capture the observed ozone gradients in the troposphere with a positive bias of 7.5 % in the upper troposphere/low stratosphere (UTLS), as well as near the surface. Remarkably, even the most pristine region of the global ocean is affected by distant biomass burning emissions by convective outflow through the mid and high troposphere and subsequent subsidence over the pristine oceanic region. Therefore, the biomass burning contribution to tropospheric CO levels maximizes in the UTLS. The Southeast Asian open fires have been identified as the major contributing source to CO from biomass burning in the tropical southern Pacific, contributing on average for the study period about 8.5 and 13 ppbv of CO at Rapa Nui and Samoa, respectively, at an altitude of around 12 km during the burning season in the spring of the Southern Hemisphere. South America is the second most important biomass burning source region that influences the study area. Its impact maximizes in the lower troposphere (6.5 ppbv for Rapa Nui and 3.8 ppbv for Samoa). All biomass burning sources contribute about 15–23 ppbv of CO, accounting for about 25 % of the total CO in the entire troposphere of the tropical and subtropical South Pacific. This impact is also seen on tropospheric O3, to which biomass burning O3 precursor emissions contribute only a few ppbv during the burning period, while the stratosphere-troposphere exchange is the most important source of O3 for the mid-troposphere of the south Pacific Ocean, contributing about 15–20 ppbv in the subtropics.

Nikos Daskalakis et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-640', Anonymous Referee #1, 05 Nov 2021
  • RC2: 'Comment on acp-2021-640', Anonymous Referee #2, 14 Nov 2021

Nikos Daskalakis et al.

Nikos Daskalakis et al.


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Short summary
Forest fires emit carbon monoxide (CO) that can be transported in the atmosphere far from the sources and reacts to produce ozone (O3) that affects climate, ecosystems and health. O3 is also produced in the stratosphere and can be transported downwards. Using a global numerical model, we found that forest fires can affect CO and O3 even the southern Pacific, the most pristine region of the global ocean but transport from the stratosphere is a more important O3 source than fires in this region.