Evaluation of the ammonia emission sensitivity of secondary inorganic aerosol concentrations measured by the national reference method

초록

A national reference method for fine particulate matter mass measurement usually specifies Teflon-membrane filter for the collection of ambient particles. Ammonium nitrate, one of the major components of fine particulate matter, is semi-volatile and susceptible to evaporation loss during and after field sampling by Teflon membrane filter. The goal of this study is to evaluate the ammonia emission sensitivity of secondary inorganic aerosol (SIA) concentrations measured by the national reference method. The evaporation loss of particulate ammonium nitrate during and after field sampling was included in the analysis to cover a wide range of emission scenarios and meteorological conditions. The global to mesoscale air quality forecast and analysis system was used to predict the PM2.5 concentrations and chemical compositions. The predicted relative humidity and temperature were used to calculate the amount of ammonium nitrate evaporation loss from the thermodynamic equilibrium model. Except for the cool months, the particulate ammonium nitrate evaporation loss significantly decreases the ammonium nitrate contents in the SIA and subsequently degraded the effectiveness of ammonia emission control over the SIA. The SIA concentration decrease achieved by a 30% reduction of ammonia emission is lessened by 27-33% in the spring, 49-79% in the summer, 21-41% in the fall when the ammonium nitrate evaporation loss is included. We also proposed the normalized ammonia emission sensitivity of ammonium nitrate concentrations (gamma(NH4NO3)) as a measure of the effectiveness of ammonia control and derived a mathematical relationship between gamma(NH4NO3) and ammonia reduction rates in ammonia-rich conditions.

키워드