Emissions of NMVOC from field application of manure measured by PTR-MS

Non-methane volatile organic compounds are important air pollutants that contribute to tropospheric ozone production in combination with nitrogen oxides (NO_x) and sunlight. Ozone is an important but often overlooked greenhouse gas with adverse effects on human health and crop yields as well as climate. Due to these indirect effects, there is a need for knowledge on emissions and potential mitigation strategies for NMVOC from key sources. Agricultural activities have recently been assessed to be a major source of non-methane volatile organic compounds (NMVOC) with particular importance in regions with intensive livestock production and manure management. In e.g. Denmark, recent assessments indicate that agriculture is the dominant source of NMVOC exceeding emissions from industry, transportation and residential heating. However, estimates of NMVOC emissions from agriculture are based on very limited realistic data and obtained by e.g. indirect calculations relative to ammonia. According to estimates for 2020 (EMEP Centre on Emission Inventories and Projections), around 25% of NMVOC in EU are from agriculture with livestock production and manure management being the dominant sources. These emission inventories are, however, quite uncertain and only based on measured data to a very low degree. Only very few studies have actually attempted to quantitatively measure NMVOC emissions from agricultural facilities and activities. In addition, little is known about the NMVOC composition and how composition varies with sources and conditions. Here, data on emissions from field application of manure based on a number of wind tunnel experiments are presented and used to estimate the contribution to national NMVOC emissions. NMVOC were quantified by proton-transfer-reaction mass spectrometry (PTR-MS) and simultaneous measurement of ammonia was used to achieve national emission estimates from field application of manure. Measurements were performed by placing a series of wind tunnels with realistic air flow rates in agricultural fields following application of liquid manure (slurry) and analyzing emissions over one week with a time resolution of typically 1 – 2 hours. The results demonstrate that emissions are significant and consist mainly of carboxylic acids with smaller contributions from phenols. Highly dynamic diurnal variations are identified. Impacts of different source types and manure treatments are discussed together with recommendations for future investigations.