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 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 NH3 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 NH3 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 NH3 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 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. Compared to the satellite-derived NH3
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 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, 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. To improve the air quality more effectively and efficiently,
NH3 emissions should be substantially controlled along with SO2
and NOx in the future.
Impact of COVID-19 on air quality in the Yangtze River Delta, China
