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

Atmospheric ammonia (NH 3 ) plays a crucial role in the formation of secondary inorganic aerosols (SIAs). Although China produces a large amount of NH 3 emissions, it has not yet taken any measures to control NH 3 emissions. Satellite retrievals show that NH 3 vertical column densities (VCDs) have obviously increased in recent years, by approximately 20% from 2011 to 2014, in contrast to the decreases seen for SO 2 and NO X VCDs. Evidence of the ground-based observations and satellite retrievals indicates that the increases in NH 3 concentrations have weakened the benefits of the reduction in SIA concentrations (especially for nitrate) from SO 2 and NO X emissions control. Results from model simulations suggest that the simultaneous control of NH 3 emissions in conjunction with SO 2 and NO X emissions is more effective in reducing particulate matter (PM) pollution than the process without NH 3 emissions control is. Our findings indicate that the continual increases in free NH 3 concentrations can result in a lower sensitivity of PM reduction to NH 3 emissions control in the future, and reducing NH 3 emissions is urgently required for the effective control of PM pollution in China.