# Quantification and evaluation of atmospheric ammonia emissions with different methods: a case study for the Yangtze River Delta region, China

To explore the effects of data and method on emission estimation, two inventories of inline-formulaNH3 emissions of the Yangtze River Delta (YRD) region in eastern China were developed for 2014 based on constant emission factors (E1) and those characterizing agricultural processes (E2). The latter derived the monthly emission factors and activity data integrating the local information of soil, meteorology, and agricultural processes. The total emissions were calculated to be 1765 and 1067 Gg with E1 and E2, respectively, and clear differences existed in seasonal and spatial distributions. Elevated emissions were found in March and September in E2, attributed largely to the increased top dressing fertilization and to the enhanced inline-formulaNH3 volatilization under high temperature, respectively. A relatively large discrepancy between the inventories existed in the northern YRD with abundant croplands. With the estimated emissions 38 % smaller in E2, the average of simulated inline-formulaNH3 concentrations with an air quality model using E2 was 27 % smaller than that using E1 at two ground sites in the YRD. At the suburban site in Pudong, Shanghai (SHPD), the simulated inline-formulaNH3 concentrations with E1 were generally larger than observations, and the modeling performance was improved, indicated by the smaller normalized mean errors (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 transportation and residential activities. Compared to inline-formulaNH3, 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 inline-formula $M6inlinescrollmathmlchem{\mathrm{normal NH}}_{normal 4}^{+}$ 24pt15ptsvg-formulamathimg6ca56caa63735c5009fe6b299c1a126b acp-20-4275-2020-ie00001.svg24pt15ptacp-20-4275-2020-ie00001.png , inline-formula $M7inlinescrollmathmlchem{\mathrm{normal SO}}_{normal 4}^{normal 2-}$ 29pt17ptsvg-formulamathimg70c2dca1cdebf0791ac6d03f5c421763 acp-20-4275-2020-ie00002.svg29pt17ptacp-20-4275-2020-ie00002.png , and inline-formula $M8inlinescrollmathmlchem{\mathrm{normal NO}}_{normal 3}^{-}$ 25pt16ptsvg-formulamathimg8a872e45f44a0fc3c08e466e371cfb3a acp-20-4275-2020-ie00003.svg25pt16ptacp-20-4275-2020-ie00003.png , respectively. Compared to the satellite-derived inline-formulaNH3 column, application of E2 significantly corrected the overestimation in vertical column density for January and October with E1, but it did not improve the model performance for July. The inline-formulaNH3 emissions might be underestimated with the assumption of linear correlation between inline-formulaNH3 volatilization and soil pH for acidic soil, particularly in warm seasons. Three additional cases, i.e., 40 % abatement of inline-formulaSO2, 40 % abatement of inline-formulaNOx, and 40 % abatement of both species, were applied to test the sensitivity of inline-formulaNH3 and inorganic aerosol concentrations to precursor emissions. Under an inline-formulaNH3-rich condition, estimation of inline-formulaSO2 emissions was detected to be more effective on simulation of secondary inorganic aerosols compared to inline-formulaNH3. Reduced inline-formulaSO2 would restrain the formation of (inline-formulaNH4)inline-formula2inline-formulaSO4 and thereby enhance the inline-formulaNH3 concentrations. To improve the air quality more effectively and efficiently, inline-formulaNH3 emissions should be substantially controlled along with inline-formulaSO2 and inline-formulaNOx in the future.

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Zhao, Yu / Yuan, Mengchen / Huang, Xin / et al: Quantification and evaluation of atmospheric ammonia emissions with different methods: a case study for the Yangtze River Delta region, China. 2020. Copernicus Publications.

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