Bias in ammonia emission inventory and implications on emission control of nitrogen oxides over North China Plain

This study examined seasonal bias of ammonia (NH3) emission inventory over North China Plain (NCP) using the GEOS-Chem chemical transport model (NH3-standard simulation, SG1), and found that the MIX NH3 inventory overestimates winter NH3 by 31% and underestimates summer NH3 by 50%. NH3 emission from NCP is thus cut by 24% in winter and doubled in summer (NH3-corrected simulation, SG2) to match up with the observations. The corrected NH3 emission changes the surface PM2.5 and nitrate concentrations and is expected to impact the nitrogen oxides (NOx) emission control efficiency (relative changes of PM2.5 and nitrate concentration in response to 1% NOx emission change, beta(PM) and beta(NO3)). We then conducted sensitivity studies (SG3) by reducing 20% (S31) and 40% (S32) NOx emission based on NH3-standard and NH3-corrected simulation, respectively. Through comparing the NO emission control efficiency under the two NH3 emission conditions (NH3-standard and NH3-corrected), we find that NH3 emission bias under the NH3-standard condition causes similar to 30% overprediction of winter beta(PM) and similar to 35% underprediction of summer PPM. In addition, for the NH3-corrected simulation, beta(PM) increases by 43% in winter and 7.7% in summer from S31 to S32. Taken together, these findings highlighted the importance of stringent NOx emission control throughout the year and NH3 emission control in summer as well. Moreover, it is critical to obtain a more accurate seasonal pattern of NH3 emission inventory in assessing emission control efficiency of PM2.5 precursors.