Advances in methods and instruments for determining concentration of gaseous air pollutants in large-scaled livestock farms

Abstract: With the development of Chinese large-scale and intensive livestock production, the animal stocking density increases, resulting in a lot of pollutant gas emissions. They are not only the important sources of greenhouse gas (GHG) emissions such as carbon dioxide (CO2), methane (CH4) , nitrous oxide (N2O), but also the sources of nitrogen or sulfur organic odors such as hydrogen sulfide (H2S), ammonia (NH3), mercaptan, phenol, paracresol, indole, skatole, which are produced by manure fermentation and decomposition. These gases contain large amounts of toxic and hazardous ingredients. If the concentration of pollution gas is small, the gas can be diluted by diffusion after emitting into the air. If the gas fails to be cleaned up or improperly handled, the odors will keep increasing and gather together. These gases will affect the growth of livestock and poultry, and they will cause environmental pollution, seriously affecting the air quality in urban and rural areas when these contaminated gases largely diffuse into the atmosphere. The environment could be deteriorating; the health of the feeders and residents also could be influenced. This paper reviewed the characteristics of several typical pollutant gases mainly including NH3, H2S, volatile organic compounds (VOCs) and other toxic and harmful gases. We also reviewed the research status of the pollution detection methods and analytical instruments at home and abroad for determining pollutant gas discharged from large-scale livestock and poultry breeding. Along with the development of computer technology, spectral analysis technology, sensor technology and wireless communication technology, there are more researchers applying the novel techniques on pollutant gas emissions from livestock farms in the domestic and foreign. This review synthesized the development of the methods and analyzers for the component and concentration detection of the gases emitted from livestock farms. According to the principal of the detection methods, the detection methods can be classified into optical methods and chemical methods. Optical methods can be divided into two types. One is the conventional optical method that determines the concentration of the pollution gas through measuring the light intensity change; the other is the spectral method that obtains the spectral information on the pollution gas using the spectrum analyzer. Chemical methods mainly include electrochemical method, chemiluminescence method, chromatography and mass spectrometry. In accordance with the measurement methods we summarized the type and origin of the instruments, the corresponding usage in the researches and the research findings using these instruments. In the end we compared the technical characteristics and application between internal and external situation. The goal of this review is for providing the basis to quick and accurate detection methods of the pollutant gases, which include the gases composition and concentration determination, and gives a reference for the development of pollution gas detection technology in livestock farming. To develop detection technology and integration system in situ, which can simultaneously detect all varieties of pollution gases emitted from livestock husbandry, will be the direction for the instrument and equipment development of livestock farm's gas emission detection in future.