Using hybrid methodologies to characterize temporal behavior and source of ambient ammonia

For the areas with much less agricultural activities, it is hotly debatable whether the atmospheric ammonia (NH3) mainly comes from agricultural or non-agriculture sources. This paper chooses the city of Taichung, the second most populated city in Taiwan, to resolve this debate by analyzing the data of NH3, PM2.5-bound water-soluble ions, SO2 and NOx monitored from 2016 to 2018 through online measurement instruments. We conclude that a significant amount of NH3 came from agricultural sources in light of (1) the strong correlations between NH3 concentrations and temperature, (2) the weak correlations between NH3 concentrations and the traffic related pollutants (NOx) and industrial pollutants (SO2)), (3) the high conversion ratio of ammonium (NHR), and (4) high background source contribution to NH3 in multiple linear regression models. As to other sources of NH3, while less impactful than the agriculture sources, the coal combustion, iron ore and steel industry, and oil combustion are three majors local NH3 emissions to form PM2.5. The results of this study can help control and regulate PM2.5 in NH3-rich regions such as Taichung. •Temporal variations of NH3 were comprehensively investigated.•Source contributions of local NH3 were quantified by PMF and regression analysis.•Agriculture emissions were the major source of NH3 using two-year online data.•Two identified sources contributed major local non-agriculture emission of NH3.