A Long Term Trend of Gaseous and Particulate Acid/Base Species and Effects of Ammonia Reduction on Nitrate Contained in PM2.5, 2009 similar to 2018

Particulate sulfate, nitrate, ammonium, and gaseous nitric acid, ammonia concentrations monitored in Korean dry deposition monitoring network from the year 2009 to 2018 were analyzed to derive their nationwide distributions, long-term trends, seasonal variations. In addition, effects of ammonia reduction on particulate nitrate were assessed by considering gas-particulate partitioning in summer and excess ammonia in winter. The 10 year averaged concentrations from Korean dry deposition monitoring network showed that ammonia mass concentration was the highest and sulfate mass concentration was the second highest among particulate nitrate, ammonium, sulfate and gaseous ammonia and nitric acid. The monitored total nitrogen acid was high in winter and low in summer similarly to nitrogen dioxide. On the other hand, the monitored total ammonia was peaked in spring due to seasonal agricultural activity. Nitric acid is primarily partitioned into the particulate phase in winter and into the gas phase in summer. In summer, the reduction of ammonia may facilitate evaporation of nitrate but nitrate concentration is too small to affect PM2.5 concentrations. In winter, the adjusted gas ratios calculated from monitored nitrate, ammonia, nitric gas concentration mostly ranged from 2 to 4, which implies that the nitrate may decrease only 5 similar to 10% for 20% reduction of the total ammonia.