Quantification and evaluation of atmospheric ammonia emissions with different methods: A case study for the Yangtze River Delta region, China
Authors: Zhao Yu , Yuan Mengchen , Huang Xin , Chen Feng , Zhang Jie 
Published: November 2019

Abstract. To explore the effects of data and method on emission estimation, two inventories of NH3 emissions of the Yangtze River Delta (YRD) region in eastern China were developed for 2014 based on the constant emission factors (E1) and those characterizing the agricultural processes (E2), respectively. The latter integrated the detailed information of soil, meteorology and agricultural processes, and derived the monthly information of emission factors and activity data. The total emissions were calculated at 1765 and 1067 Gg, respectively, and agricultural activities (livestock farming and fertilizer use) were estimated to contribute 74–84 % to total emissions in the two inventories. Clear differences existed in seasonal and spatial distributions of NH3 emissions. Elevated emissions were found in March and September in E2, attributed largely to the increased top dressing fertilization and to the enhanced NH3 volatilization under high temperature, respectively. Relatively large discrepancy between the methods existed in northern Yangtze River Delta areas with abundant croplands. The two inventories were evaluated through air quality modeling and available ground and satellite observation. With the estimated emissions 38 % smaller in E2, the average of simulated NH3 concentrations using E2 was 27 % smaller than that using E1 at two ground observation sites in the YRD region. At the suburban SHPD site, the simulated NH3 concentrations with E1 were generally larger than observation, and the modeling performance was largely improved indicated by the smaller NMEs when E2 was applied. In contrast, very limited improvement was found at the urban site JSPAES, as E2 failed to improve the emission estimation of local sources including transportation and residential activities. Compared to NH3, the modeling performance for inorganic aerosols was better for most cases, and the differences between the simulated concentrations with E1 and E2 were clearly smaller, at 7 %, 3 % and 12 % (relative to E1) for NH4+, SO42−, and NO3−, respectively. Regarding the satellite-derived NH3 column, application of E2 significantly corrected the overestimation in vertical column density simulation for January and October with E1, but did not improve the model performance for July. The NH3 emissions might be underestimated with the assumption of linear correlation between NH3 volatilization and soil pH for acidic soil, particularly in warm seasons. Three additional cases, i.e., 40 % abatement of SO2, 40 % abatement of NOX, and 40 % abatement of both species were applied to test the sensitivity of NH3 and inorganic aerosol concentrations to precursor emissions. Under an NH3-rich condition for most of YRD, estimation of SO2 emissions was detected to be more effective on simulation of secondary inorganic aerosols compared to NH3. Reduced SO2 would restrain the formation of (NH4)2SO4, and thereby enhance the NH3 concentrations. Besides the emissions, uncertainties existed as well in the limitations of ground and satellite observation and incomplete mechanism of gas to particle conversion applied in the model. To improve the air quality more effectively and efficiently, NH3 emissions should be substantially controlled along with SO2 and NOX in the future.