Microbes emit nitrogen oxides—perhaps more than you think

August 4, 2022 by Science China Press Microbes emit nitrogen oxides, or NO x . This is important because it involves surface-earth nitrogen (N) cycle, which strongly interacts with environmental quality, food production, biosphere and climate changes. A study led by Drs.

Wei Song and Xue-Yan Liu from Tianjin University, China, shows that NO x emissions from the microbial N cycle account for about 24%, 58%, and 31% of the total NO x emissions in the land, ocean, and globe, equivalent to 0. 5, 1. 4, and 0.

6 times of the corresponding fossil fuel NO x emissions. This study fills the data gap of NO x emissions from microbial N cycle in the ocean and updates fluxes of NO x emissions from microbial N cycle in the land and globe. “We confirm the significant contribution of microbial N cycle to global NO x emissions.

It should be considered into current and future atmospheric NO x emission reduction policy formulation and eco-environmental and climatic effects assessment,” Liu says. googletag. cmd.

push(function() { googletag. display(‘div-gpt-ad-1449240174198-2’); }); Over the past century, atmospheric N loading has become a major driver of air pollution, ozone-layer destruction, elevated N deposition, and associated negative impacts on ecosystem structure and functions (e. g.

, biodiversity, acidification, eutrophication, and carbon balance). Nitrogen oxides (NO x ) are major components of reactive N pollutants. Its concentrations and deposition fluxes have been remarkably elevated since the industrial revolution , which has been attributed to fossil fuel NO x emissions dominated by coal and oil combustion.

Recently, non-fossil fuel NO x emissions from biomass burning and microbial N cycle have been recognized as important sources of atmospheric NO x . However, due to the incomplete or missing NO x emissions from the microbial N cycle in the land and ocean , there is great uncertainty in global NO x emissions. “To accurately constrain global NO x emissions is pivotal to mitigate NO x emissions, budget nitrate (NO 3 – ) deposition fluxes, and evaluate the eco-environmental and climatic effects of atmospheric NO x loading,” Liu says.

In the land environment, there have been observations and simulations of NO x emissions from microbial N cycle in natural and agricultural soils. However, it remains challenging to observe NO x emissions accurately and comprehensively from microbial N cycle from other substrates (e. g.

, the surface water of rivers, lakes, swamps, etc. ) and emission sources (e. g.

, wastewater, water treatment systems, solid wastes, etc. ). In the ocean environment, there are very sporadic observations of NO x emissions from seawater and thus lack of an estimate on the ocean microbial NO x emission.

Previously, the oil combustion of marine traffic transportation has been considered as the dominant source of ocean NO x emissions. “Stable isotope methods have been successfully used to trace global water and many other biogeochemical cycles. We need to explore new N isotope methods to comprehensively constrain ocean and land NO x emissions from microbial N cycle,” Song says.

Based on the above issues and background, the nitrogen isotope research team of Tianjin University collected and analyzed the global observation data on nitrogen isotopes of NO 3 – in atmospheric particulates. By using its ocean-land differences, they constrained the nitrogen isotope signals of particulate NO 3 – that were purely derived from ocean NO x emissions. Furthermore, they constructed a new N isotope method to quantify the relative contributions of major NO x emission sources by constraining N isotope effects of atmospheric NO x transformations to particulate NO 3 – and combining the N isotope ratios of NO x from dominant emission sources, including coal combustion, oil combustion, biomass burning, and microbial N cycle.

Then, combining the known fossil fuel NO x emissions, they accomplished estimates on NO x emissions from microbial N cycle in the land and ocean, respectively. The research was published in National Science Review . Explore further.