Comment on essd-2021-246

doi:10.5194/essd-2021-246-rc3

Abstract

Abstract. Methane, ethane, and propane are among the most abundant hydrocarbons in the atmosphere. These compounds have many emission sources in common and are all primarily removed through OH oxidation. Their mixing ratios and long-term trends in the upper troposphere and stratosphere are rarely reported due to the paucity of measurements. In this study, we present long-term (2006â2016) northern hemispheric ethane, propane, and methane data from airborne observation in the upper troposphere-lower stratosphere (UTLS) region from the IAGOS-CARIBIC project. The methane and propane observations provide additional information for understanding northern hemispheric ethane trends, which is the major focus of this study. The linear trends, moving averages, nonlinear trends and monthly variations of ethane, methane and propane in 2006â2016 are presented for the upper troposphere and lower stratosphere over 5 regions (whole Northern Hemisphere, Europe, North America, Asia and the rest of the world). The growth rates of ethane, methane, and propane in the upper troposphere are â2.24â%âyrâ1, 0.33â%âyrâ1, and â0.78â%âyrâ1, respectively, and in the lower stratosphere they are â3.27â%âyrâ1, 0.26â%âyrâ1, and â4.91â%âyrâ1, respectively, in 2006â2016. This dataset is of value to future global ethane budget estimates and the optimization of current ethane inventories. The data are publicly accessible at https://doi.org/10.5281/zenodo.6536109 (Li et al., 2022a).

Highlights

Ethane (C2H6) is among the most abundant non-methane hydrocarbons (NMHC) present in the atmosphere
Ethane oxidation forms acetaldehyde, which in turn contributes to the formation of peroxyacetyl nitrate (PAN) or peracetic acid depending on the levels of nitrogen oxides (NOx) (Millet et al, 2010)
Franco et al (2015) showed the ethane trend at Jungfraujoch to be -0.92%/yr during 1994-2008, followed by a strong positive trend of 4.9%/yr during 2009-2014, which may be related to the growth of shale gas exploitation in North America

Summary

Introduction

Ethane (C2H6) is among the most abundant non-methane hydrocarbons (NMHC) present in the atmosphere. 84% of its total emissions are from the Northern Hemisphere (NH) (Xiao et al, 2008). Oxidation by hydroxyl (OH) radicals is the major atmospheric loss process for tropospheric ethane while in the stratosphere the reaction with chlorine (Cl) radicals provides an additional loss processes (Li et al, 2018). Due to the seasonal variation of ethane emissions and the photochemically generated OH radicals, ethane 35 has a clear annual cycle in concentration, showing higher levels in winter. Ethane oxidation forms acetaldehyde, which in turn contributes to the formation of PAN (peroxyacetyl nitrate) or peracetic acid depending on the levels of NOx (Millet et al, 2010). PAN acts as a reservoir species of nitrogen oxides (NOx) 40 and can strongly affect tropospheric ozone distributions by transporting NOx from the point of emission to remote locations. PAN is known to be a secondary pollutant like ozone with negative impacts on regional air quality and human health (Dalsøren et al, 2018; Fischer et al, 2014; González Abad et al, 2011; Kort et al, 2016; Monks et al, 2018; Pozzer et al, 2020; Rudolph, 1995; Tzompa-Sosa et al, 2017)

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