Prediction of nitrogen excretion from data on dairy cows fed a wide range of diets compiled in an intercontinental database: A meta-analysis

Manure nitrogen (N) from cattle contributes to nitrous oxide and ammonia emissions and nitrate leaching. Measurement of manure N outputs on dairy farms is laborious, expensive, and impractical at large scales; therefore, models are needed to predict N excreted in urine and feces. Building robust prediction models requires extensive data from animals under different management systems worldwide. Thus, the study objectives were (1) to collate an international database of N excretion in feces and urine based on individual lactating dairy cow data from different continents; (2) to determine the suitability of key variables for predicting fecal, urinary, and total manure N excretion; and (3) to develop robust and reliable N excretion prediction models based on individual data from lactating dairy cows consuming various diets. A raw data set was created based on 5,483 individual cow observations, with 5,420 fecal N excretion and 3,621 urine N excretion measurements collected from 162 in vivo experiments conducted by 22 research institutes mostly located in Europe (n = 14) and North America (n = 5). A sequential approach was taken in developing models with increasing complexity by incrementally adding variables that had a significant individual effect on fecal, urinary, or total 2manure N excretion. Nitrogen excretion was predicted by fitting linear mixed models including experiment as a random effect. Simple models requiring dry matter intake (DMI) or N intake performed better for predicting fecal N excretion than simple models using diet nutrient composition or milk performance parameters. Simple models based on N intake performed better for urinary and total manure N excretion than those based on DMI, but simple models using milk urea N (MUN) and N intake performed even better for urinary N excretion. The full model predicting fecal N excretion had similar performance to simple models based on DMI but included several independent variables (DMI, diet crude protein content, diet neutral detergent fiber content, milk protein), depending on the location, and had root mean square prediction errors as a fraction of the observed mean values of 19.1% for intercontinental, 19.8% for European, and 17.7% for North American data sets. Complex total manure N excretion models based on N intake and MUN led to prediction errors of about 13.0% to 14.0%, which were comparable to models based on N intake alone. Intercepts and slopes of variables in optimal prediction equations developed on intercontinental, European, and North American bases differed from each other, and therefore region-specific models are preferred to predict N excretion. In conclusion, region-specific models that include information on DMI or N intake and MUN are required for good prediction of fecal, urinary, and total manure N excretion. In absence of intake data, region-specific complex equations using easily and routinely measured variables to predict fecal, urinary, or total manure N excretion may be used, but these equations have lower performance than equations based on intake

Effects of Precursor Concentration and Acidic Sulfate in Aqueous Glyoxal−OH Radical Oxidation and Implications for Secondary Organic Aerosol

Previous experiments demonstrated that aqueous OH radical oxidation of glyoxal yields low-volatility compounds. When this chemistry takes place in clouds and fogs, followed by droplet evaporation (or if it occurs in aerosol water), the products are expected to remain partially in the particle phase, forming secondary organic aerosol (SOA). Acidic sulfate exists ubiquitously in atmospheric water and has been shown to enhance SOA formation through aerosol phase reactions. In this work, we investigate how starting concentrations of glyoxal (30−3000 μM) and the presence of acidic sulfate (0−840 μM) affect product formation in the aqueous reaction between glyoxal and OH radical. The oxalic acid yield decreased with increasing precursor concentrations, and the presence of sulfuric acid did not alter oxalic acid concentrations significantly. A dilute aqueous chemistry model successfully reproduced oxalic acid concentrations, when the experiment was performed at cloud-relevant concentrations (glyoxal <300 μM), but predictions deviated from measurements at increasing concentrations. Results elucidate similarities and differences in aqueous glyoxal chemistry in clouds and in wet aerosols. They validate for the first time the accuracy of model predictions at cloud-relevant concentrations. These results suggest that cloud processing of glyoxal could be an important source of SOA

Towards a complete picture of the atmospheric radical cycles

SSCI-VIDE+ATARI+BNOInternational audienceThe understanding of the atmospheric radical cycles and of atmosphere’s oxidative capacity is mostly limited today by technical challenges: the inability of current techniques to monitor specific organic radicals in the atmosphere (“speciated detection”), especially organic peroxy radicals (“RO2”, where R is an organic group) that are intermediates in the atmospheric oxidation of most organic gases. Past and current techniques employed to monitor these radicals in the atmosphere (PERCA, ROxMax, PerCIMS, ROXLIF…) convert them into a single species (NO2, H2SO4 or HO2/OH) and provide thus overall concentrations or, at best, semi-speciated ones, distinguishing between saturated and unsaturated radicals. While valuable, this information is not sufficient for a full picture of the radical cycles.Over the last decades, mass spectrometry using chemical ionization has been explored for its ability to detect different organic radical separately (fully speciated detection). Some first examples of applications of this technique will be presented, as well as the many groundbreaking possibilities it offers for the understanding of the radical cycles

CLOUDS. Don't forget the surface

SSCI-VIDE+ATARI+BNOInternational audienc

Towards a complete picture of the atmospheric radical cycles

SSCI-VIDE+ATARI+BNOInternational audienceThe understanding of the atmospheric radical cycles and of atmosphere’s oxidative capacity is mostly limited today by technical challenges: the inability of current techniques to monitor specific organic radicals in the atmosphere (“speciated detection”), especially organic peroxy radicals (“RO2”, where R is an organic group) that are intermediates in the atmospheric oxidation of most organic gases. Past and current techniques employed to monitor these radicals in the atmosphere (PERCA, ROxMax, PerCIMS, ROXLIF…) convert them into a single species (NO2, H2SO4 or HO2/OH) and provide thus overall concentrations or, at best, semi-speciated ones, distinguishing between saturated and unsaturated radicals. While valuable, this information is not sufficient for a full picture of the radical cycles.Over the last decades, mass spectrometry using chemical ionization has been explored for its ability to detect different organic radical separately (fully speciated detection). Some first examples of applications of this technique will be presented, as well as the many groundbreaking possibilities it offers for the understanding of the radical cycles

Speciated monitoring of organic peroxy radicals: first laboratory applications

SSCI-VIDE+ATARI+BNOInternational audienceOrganic peroxy radicals (“RO2”, with R organic) are key intermediates in the oxidation of organic compounds in many chemical systems, such as the Earth atmosphere and combustion engines. For decades, the lack of detection technique distinguishing different RO2 (“speciated” detection) has been a major limit to the understanding of their reaction mechanisms, as many different RO2 with very different reactivity are often present simultaneously in these systems. A mass spectrometric technique based on proton transfer ionization has thus been developed for the speciated detection of oxygenated organic radicals. Its first applications to the investigation of RO2 reactions in laboratory will be presented, such as:- an investigation of the cross-reactions between different radicals (CH3O2, CH3C(O)O2, c-C6H11O2, and (CH3)3CO2) where, for the first time, each radical was monitored individually and in real-time, and their consumption by the cross-reaction was observed directly (Nozière and Hanson, J. Phys. Chem. A, 212, 8453-8464, 2017),- an investigation of the autoxidation of n-hexylO2 in the oxidation of n-hexane at room temperature, where the initial radicals and those produced by autoxidation (O2QOOH and O2QOH) were observed directly and allowed to determine the autoxidation rates.These examples will show how this new technique can improve the understanding of RO2 reactions

The detection of organic radicals and intemediate ions in the atmosphere

International @ AIR+BNOInternational audienceNon