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

Abstract

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.

Effect of Synoptic‐Scale Dynamics on the Vertical Distribution of Tropospheric Ozone Over the Arabian Sea and the Indian Ocean During the Boreal Winter of 2018

“…(2016)) are repeatedly reported over the major Oceanic regions like Pacific Ocean, Atlantic and Indian Ocean by many researchers during several campaigns. Though a common causative mechanism for the formation of this layer cannot be assigned, as it varies depending on the location, time and background meteorology, several possible pathways are proposed; continental transport (e.g., Boylan et al., 2015), stratospheric intrusions and transport from mid‐latitude UT (e.g., Hayashi et al., 2008; Tao et al., 2018; Zachariasse et al., 2000, 2001), transport from biomass burning sites (e.g., Anderson et al., 2016; Taupin et al., 1999) or both stratospheric intrusions and transport from biomass burning locations or continents (e.g., Chatfield et al., 2007; Daskalakis et al., 2022; Weller et al., 1996).…”

“…Generally, in the marine region low ozone concentrations are expected due to the lower availability of precursors for production and increased destruction via OH and halogen photochemistry (Kley et al., 1996; Liu et al., 1983; Read et al., 2008; Sarwar et al., 2015). However, continental influence, long‐range transport and prevailing meteorological conditions can significantly affect the ozone distribution over the ocean (e.g., Anderson et al., 2016; Boylan et al., 2015; Daskalakis et al., 2022; Jenkins et al., 2008, 2015; Lelieveld et al., 2001 and references there in). This makes any in situ measurements of ozone over the oceanic region a valuable asset; as the scope of satellite‐borne observations over these regions are limited in their quality of data.…”

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

“…Data availability. Data used in this manuscript can be found here: https://doi.org/10.5281/zenodo.6391170 (Daskalakis and Kanakidou, 2022b).…”