Chemical characterization of volatile organic compounds emitted by animal manure

Animal manure is considered a valuable organic fertilizer due to its important nutrient content enhancing soil fertility and plant growth in agriculture. Besides its beneficial role as fertilizer, animal manure represents a significant source of volatile organic compounds (VOCs), playing a significant role in atmospheric chemistry. Understanding the composition of VOCs Understanding VOCs from animal manure is crucial for assessing their environmental impact, as they can cause air pollution, odors, and harm to human health and ecosystems. Laboratory studies enhance field measurements by providing a precise inventory of manure emissions, addressing gaps in existing literature. Both approaches complement each other in advancing our understanding of manure emissions. In this context, we conducted an experimental study involving various animal manures (cow, horse, sheep, and goat) taken from a farm in Grignon (near Paris, France). We employed atmospheric simulation chambers within a controlled laboratory environment. The analysis of VOCs involved the combination of Proton Transfer Reaction-Quadrupole ion guide-Time-of-Flight Mass Spectrometry (PTR-QiTOF-MS) and Thermal Desorption-Gas Chromatography-Mass Spectrometry (TD-GC-MS). Using PTR-QiTOF-MS, 368 compounds were detected and quantified within the manure samples. The complementary analysis by TD-GC-MS enhanced our identification of VOCs. Our findings revealed various chemical groups of VOCs, including oxygenated compounds (e.g., ethanol, cresol, acetaldehyde, etc.), nitrogenated compounds (ammonia, trimethylamine, etc.), sulfur compounds (methanethiol, dimethyl sulfide, etc.), aromatic compounds (phenols and indoles), terpenes (isoprene, D-limonene, etc.) and halogenated compounds. Cow manure exhibited the highest VOC emission fluxes, followed by goat, sheep, and horse manures. Notably, oxygenated VOCs were dominant contributors to total VOC emission fluxes in all samples. Statistical analysis highlighted the distinct nature of cow manure emissions, characterized by oxygenated compounds and nitrogenated compounds. In addition, goat manure was isolated from the other samples with high emissions of compounds having both oxygen and nitrogen atoms in their molecular formulas (e.g., CH₃NO₂). The experimental dataset obtained in this study provides an inventory reference for both VOCs and their emission fluxes in animal manures. Furthermore, it highlights odorant compounds and VOCs that serve as atmospheric aerosol precursor. Future studies can explore the effectiveness of various manure treatment methods to promote sustainable agriculture practices.