Implementation of a dynamical NH₃ emissions parameterization in CMAQ for improving PM_2.5 simulation in Taiwan

Ammonia (NH₃) is an important precursor of inorganic fine particulate matter (PM_2.5). Without specific information on the temporal variation in NH₃ emissions, a simplified temporal variation in NH₃ emissions is often used in chemical transport models. To better characterize NH₃ emissions in an air quality model simulation for Taiwan, a dynamical NH₃ emissions parameterization was applied to improve the temporal profile of NH₃ emissions from livestock operations, synthetic nitrogen fertilizers, and standing crops. The Community Multiscale Air Quality (CMAQ) modeling simulation with a fixed NH₃ emissions rate (the CONST experiment) presents a large positive bias in simulated nitrate and NH₃, particularly during the nighttime and winter months. On the other hand, the CMAQ simulation with a dynamical NH₃ emissions approach (the DYN experiment) improves the diurnal and seasonal variations and reduces the simulated bias. Moreover, according to the Taiwan emissions inventory, NH₃ emissions from sewage accounts for a large portion (37%) of total NH₃ emissions in Taiwan. The CMAQ simulation with the dynamical NH₃ emissions approach and with a reduced level of NH₃ emissions from sewage (the DYN1 experiment) was conducted to assess the possibility that the existing Taiwan emissions inventory may overestimate sewage NH₃ emissions. The evaluations with observed NH₃, nitrate, and ammonium wet deposition concentrations indicate that the DYN1 experiment performs better than the CONST and DYN experiments.