Carbonyl sulfide (OCS) exchange between soils and the atmosphere affected by soil moisture and compensation points

Abstract

Abstract. Carbonyl sulfide (OCS) is a chemically quite stable gas in the troposphere (lifetime ~2-6 years) and consequently some of it is transported up to the stratosphere where it contributes to the stratospheric sulfate layer. Due to the similarities in uptake mechanism between OCS and CO2, the use of OCS as a proxy for CO2 in ecosystem gross primary production (GPP) has been proposed. For this application a good understanding of uptake (UOCS) and production (POCS) processes of OCS in an 15 ecosystem is required. A new OCS quantum cascade laser coupled with an automated soil chamber system enabled us to measure the soil-atmosphere OCS exchange of four different soil samples with high precision. The adjustment of the chamber air to different OCS mixing ratios (50, 500, and 1000 ppt) allowed us to separate production and consumption processes and to estimate compensation points (CPs) for the OCS exchange. At an atmospheric mixing ratio of 1000 ppt, the maximum UOCS was of the order of 22 to 110 pmol g -1 h -1 for needle forest soil samples and of the order of 3 to 5 pmol g -1 h -1 20 for an agricultural mineral soil, both measured at moderate soil moisture. Uptake processes (UOCS) were dominant at all soil moistures for the forest soils, while POCS exceeded UOCS at higher soil moistures for the agricultural soil, resulting in net emission. Hence, our results indicate that in (spruce) forests UOCS might be the dominant process, while in agricultural soils POCS at higher soil moisture and UOCS under moderate soil moisture seem to dominate the OCS exchange. The OCS compensation points (CPs) were highly dependent on soil water content and extended over a wide range of 130 ppt to 1600 25 ppt for the forest soils and 450 ppt to 5500 ppt for the agricultural soil. The strong dependency between soil water content and the compensation point value must be taken into account for all further analyses. The lowest CPs were found at about 20% water filled pore space (WFPSlab), implying the maximum of UOCS under these soil moisture conditions and excluding OCS emission under such conditions. We discuss our results in view of other studies about compensation points and the potential contribution of microbial groups. 30

Enumeration of Chemoorganotrophic Carbonyl Sulfide (COS)-degrading Microorganisms by the Most Probable Number Method

“…These results are useful for understanding the ecological distribution of COS-degrading microorganisms and estimating the potential of soil to degrade COS. The high MPN values observed in forest soils are consistent with previous findings reported by Bunk et al (2018) showing larger COS uptake rates in forest soils than in other soils (Bunk et al, 2018). In most samples, the MPN values of COS degraders were similar to or slightly lower than those of chemoorganotrophs, indicating that high percentages of culturable and numerically dominant chemoorganotrophs in soils degrade COS. COS degradation by soil samples roughly depends on the biomass (Yi et al, 2007), and soils do not need to acclimatize to COS in order to uptake COS irrespective of its concentration (Saito et al, 2002).…”

Charge-Shifted Weak Noncovalent Interactions in the Atmospherically Important OCS Microhydrates

“…The most abundant and stable sulfur-containing gas is carbonyl sulfide (OCS), which maintains the global sulfur cycle. Being one of the primary greenhouse gases involved in stratospheric aerosol formation, OCS substantially affects the earth’s radiation balance and is one of the main drivers of climate change. − Therefore, understanding the properties and behavior of OCS is crucial to realizing its impact on climate change. , Numerous studies have been conducted to understand the source and the sink of OCS promoting aerosol formation in the stratosphere. ,, The existence of other S-containing species and their water clusters in the stratosphere were observed both theoretically and experimentally. ,,, In fact, water was shown to catalyze the hydrolysis reaction of the S-containing compounds. , It was observed that the atmospheric hydrolysis of OCS is the most efficient pathway among other physicochemical processes through which S-containing compounds get removed from the atmosphere. , The atmospheric hydrolysis depends on the relative humidity and water content, suggesting that the water hydration structure plays a pivotal role in the process. ,,, Therefore, a detailed molecular-level understanding of the OCS microhydrated cluster is crucial to unraveling the underlying relationship between its hydrolysis and corresponding solvation properties in the atmospheric condition.…”

“…7,8 Numerous studies have been conducted to understand the source and the sink of OCS promoting aerosol formation in the stratosphere. 1,2,4 The existence of other S-containing species and their water clusters in the stratosphere were observed both theoretically and experimentally. 4,7,9,10 In fact, water was shown to catalyze the hydrolysis reaction of the S-containing compounds.…”

“…1,2,4 The existence of other S-containing species and their water clusters in the stratosphere were observed both theoretically and experimentally. 4,7,9,10 In fact, water was shown to catalyze the hydrolysis reaction of the S-containing compounds. 11,12 It was observed that the atmospheric hydrolysis of OCS is the most efficient pathway among other physicochemical processes through which S-containing compounds get removed from the atmosphere.…”

Microbial community responses determine how soil–atmosphere exchange of carbonyl sulfide, carbon monoxide, and nitric oxide responds to soil moisture

“…In turn, this information may provide insights into pathways of P OCS and U OCS in a way that allows prediction of net OCS fluxes across a range of soils and moisture contents. Ultimately the ability to understand the role of soils in net ecosystem exchange of OCS is relevant to enabling the estimation of canopy fluxes of OCS and their interpretation as a proxy for gross primary production, GPP (Campbell et al, 2017(Campbell et al, , 2008Blonquist et al, 2011;Berry et al, 2013).…”