Emission fluxes of nitrous acid (HONO) from livestock and poultry wastes

Abstract

Gaseous nitrous acid (HONO) is a critical contributor to daytime hydroxyl radical in the troposphere. Livestock farming has been recognized as an overlooked HONO source, but the lack of detailed flux measurements from livestock and poultry wastes would cause uncertainties in modeling its environmental impacts. Here, based on field flux measurements and laboratory experiments, we observed substantial HONO emissions from the composting of swine feces and chicken manure in the warm season, which might be mainly attributed to nitrification process in livestock and poultry wastes. The HONO emission from chicken manure was found to be much higher than that from swine feces, and the higher NH₃ emission but lower N₂O and NO emissions from chicken manure were also observed. Considering that the interaction among these nitrogen species during nitrification process, the obviously lower HONO emission from swine feces was likely to be explained by the lack of the total ammonia nitrogen and H⁺ donors in swine feces. Temperature is also a key factor that influences the HONO emission from livestock wastes. In addition, the total HONO emission from swine feces in China was estimated to be approximately 107.7 Gg-N/yr according to the national swine amounts, which is comparable to the national soil HONO emissions, underscoring its non-negligible contribution to regional air quality. Therefore, effective emission control of HONO from livestock and poultry wastes should be carried out to further improve air quality in China.