The Red Sea Deep Water is a potent source of atmospheric ethane and propane

Abstract

Non-methane hydrocarbons (NMHCs) such as ethane and propane are significant atmospheric pollutants and precursors of tropospheric ozone, while the Middle East is a global emission hotspot due to extensive oil and gas production. Here we compare in situ hydrocarbon measurements, performed around the Arabian Peninsula, with global model simulations that include current emission inventories (EDGAR) and state-of-the-art atmospheric circulation and chemistry mechanisms (EMAC model). While measurements of high mixing ratios over the Arabian Gulf are adequately simulated, strong underprediction by the model was found over the northern Red Sea. By examining the individual sources in the model and by utilizing air mass back-trajectory investigations and Positive Matrix Factorization (PMF) analysis, we deduce that Red Sea Deep Water (RSDW) is an unexpected, potent source of atmospheric NMHCs. This overlooked underwater source is comparable with total anthropogenic emissions from entire Middle Eastern countries, and significantly impacts the regional atmospheric chemistry.

Measurements of carbonyl compounds around the Arabian Peninsula: overview and model comparison

“…For acetone, a constant water concentration of 15 nmol L −1 is used, following the suggestion of Fischer et al (2012). The model configuration in the study is the same as the model applied in Bourtsoukidis et al (2020), where a natural non-methane hydrocarbon source (ethane and propane) was implemented. The model is at the resolution of T106L31 (i.e.…”

“…Therefore, fewer primary precursors as well as carbonyls were transported to the southern part of the Red Sea compared to the northern part. Moreover, the unexpected sources of hydrocarbons (ethane and propane) from northern Red Sea deep water reported by Bourtsoukidis et al (2020) would lead to higher carbonyl levels in the northern part compared with the southern part due to the additional precursors in the Red Sea North. However, acetaldehyde was still found to be significantly underestimated compared to the model results, even taking the deep-water source into consideration (Sect.…”

“…For further insight, we focused on a time series of selected trace gases and their inter-correlations to better identify the sources of the major aliphatic carbonyls. Meanwhile, we calculated the OH exposure ([OH] t) based on hydrocarbon ratios (Roberts et al, 1984;de Gouw et al, 2005;Yuan et al, 2012) for the polluted regions (Arabian Gulf and Suez) where primary emissions have been identified (Bourtsoukidis et al, 2019;Bourtsoukidis et al, 2020), to better understand the photochemical aging of the major carbonyls using the following equation:…”

Measurements of carbonyl compounds around the Arabian Peninsula indicate large missing sources of acetaldehyde

“…The model applied in this study is a combination of the 5 th generation of European Centre Hamburg general circulation model (ECHAM5) (Roeckner et al, 2006) and the 2 nd version of Modular Earth Submodel System (MESSy2) (Jöckel et al, 2010), where a comprehensive chemistry mechanism MOM (Mainz Organic Mechanism) was deployed (Sander et al, 2019). The model configuration in the study is the same as the model applied in Bourtsoukidis et al (2020) in the resolution of T106L31 (i.e. ~ 1.1 o × 1.1 o horizontal resolution and , 31 vertical hybrid pressure levels up to 10 hPa) and the time resolution of 10 minutes.…”

“…The model underestimation was most significant for acetaldehyde, which is underpredicted by a factor (median values) of more than 6 over the Red Sea North, ~ 4 over the Arabian Sea and Arabian Gulf and between 1 and 4 over other regions. A strong natural nonmethane hydrocarbon source from deep water in the Northern Red Sea was implemented in the model (Bourtsoukidis et al, 2020).…”