The Effects of NH3 Emission Reduction on Secondary Inorganic Aerosols Evaluated by CMAQ

초록

The secondary inorganic aerosols and their corresponding gaseous species were modeled by CMAQ (Community Multi-scale Air Quality Model) and validated by using monitoring data obtained from the dry deposition monitoring network for the year of 2015. And the effects of NH3 emission reduction on secondary inorganic aerosols were also modeled and evaluated. The dry deposition monitoring network consists of 27 urban stations, 13 rural stations, and 1 background station and monitors NH3, HNO3, sulfate, nitrate, ammonium, and miscellaneous sea salt and mineral species. The CMAQ simulation results compare fairly well with total NH3, which is sum of NH3 and ammonium, and total HNO3, which is sum of HNO3 and nitrate, gaseous NH3 measured by the dry deposition monitoring network. However, the CMAQ and near real-time monitoring method severely overestimate the nitrate during the summer because of not sufficiently reflecting evaporative losses typically occurring in filter based sampling methods. As the NH3 emission in Korea was reduced by 30%, the calculated ambient NH3 concentrations in Seoul, Busan, Daegu, Gwangju were lowered in a similar rate in the winter. The calculated averages of ammonium and nitrate concentrations in these four cities were also lowered by 7.1% and 7.4%, respectively. This low response of ammonium and nitrate concentrations to the NH3 emission reduction implied that the NH3 existed in excess to HNO3. And the adjusted Gas Ratio exceeded one, confirming the excess of NH3. In addition, the calculated average of sulfate was lowered by 3.6% as the decreased pH and increased hydrogen ion concentrations slowed the in-cloud sulfate production.

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