Increasing Ammonia Concentrations Reduce the Effectiveness of Particle Pollution Control Achieved via SO2 and NOX Emissions Reduction in East China

Atmospheric ammonia (NH3) plays a crucial role in the formation of secondary inorganic aerosols (SIAs). Although China produces a large amount of NH3 emissions, it has not yet taken any measures to control NH3 emissions. Satellite retrievals show that NH3 vertical column densities (VCDs) have obviously increased in recent years, by approximately 20% from 2011 to 2014, in contrast to the decreases seen for SO2 and NOX VCDs. Evidence of the ground-based observations and satellite retrievals indicates that the increases in NH3 concentrations have weakened the benefits of the reduction in SIA concentrations (especially for nitrate) from SO2 and NOX emissions control. Results from model simulations suggest that the simultaneous control of NH3 emissions in conjunction with SO2 and NOX emissions is more effective in reducing particulate matter (PM) pollution than the process without NH3 emissions control is. Our findings indicate that the continual increases in free NH3 concentrations can result in a lower sensitivity of PM reduction to NH3 emissions control in the future, and reducing NH3 emissions is urgently required for the effective control of PM pollution in China.