Processing of atmospheric nitrogen by clouds above a forest environment

Abstract

) and organic nitrogen (DON) were measured in cloud water samples collected over the northern lower peninsula of Michigan. Within a given cloud field, several altitudes were sampled to examine changes in concentration and speciation with altitude. Several samples were analyzed for bacterial content and activity. Convective cumulus (cumulus congestus) were more concentrated than fair weather cumulus (cumulus humilis) for all major ions and DON, with the cloudy air DON concentrations in convective cumulus being twice as large as for fair weather cumulus, and for all other ions, the droplets were 4-6 times more concentrated. The molar average distribution of nitrogen in the cloud water was 43 (±10, 1s)% ammonium, 39 (±7)% nitrate and 18 (±11)% DON. High concentrations of bacteria were observed in the clouds with an average concentration of 2.9 Â 10 5 (±1.0 Â 10 5 , 1s) bacteria m À3 of cloudy air but which contributed less than 1% of the nitrogen in the cloud water. In addition, nitrifying bacteria were identified, indicating bacterial processing of nitrogen in the cloud water may occur. Air mass origin and altitude influence observed cloud water concentrations, with the exception of DON. The correlation of ammonium and sulfate, and calcium and nitrate suggest that ammonium sulfate and calcium nitrate aerosol may be important sources of these ions.

Microbial Cell Retention in a Melting High Arctic Snowpack, Svalbard

“…The same pattern of higher final concentrations can also be seen for NO 3 -. It is known that atmospheric NO 3 -within the Arctic can occur in association with aerosols (Hara et al, 1999;Teinilä et al, 2003) and with bacteria (Hill et al, 2007). If particles and bacteria remain in the snowpack rather than following the meltwater, as our results suggest, an elevated concentration of associated chemicals (such as NO 3 -) might be expected in the remaining snow.…”

H<sub>2</sub>O<sub>2</sub> modulates the energetic metabolism of the cloud microbiome

“…A few decades ago, living microorganisms were observed in cloud water (Sattler et al, 2001;Amato et al, 2005Amato et al, , 2007aWei et al, 2017). Particularly through measurements of adenosine triphosphate (ATP) and anabolic precursors or nutrient incorporation rates, it has been shown that cloud microorganisms are metabolically active and play an important role in cloud chemical reactivity (Sattler et al, 2001;Amato et al, 2007a;Hill et al, 2007;Vaïtilingom et al, 2012Vaïtilingom et al, , 2013. Several studies performed on simplified or real microcosms have demonstrated that cloud microorganisms are able to degrade carbon compounds (Ariya et al, 2002;Amato et al, 2005Amato et al, , 2007cHusarova et al, 2011;Vaïtilingom et al, 2010Vaïtilingom et al, , 2011Vaïtilingom et al, , 2013Matulovà et al, 2014); recent studies have also shown that this could be the case in the air (Krumins et al, 2014).…”

Contribution of Microbial Activity to Carbon Chemistry in Clouds

“…This activity toward organic compounds likely participates in carbon chemistry in clouds. In addition, nitrifying bacteria have been detected in clouds and they could be involved in the transformation of atmospheric nitrogenous species (25). One key objective now is to quantify the importance of the biological oxidation pathways compared to that of chemical and photochemical processes.…”