No abstract

Excess reactive nitrogen (Nr), including nitrogen oxides (NOx) and ammonia (NH3), contributes strongly to fine particulate matter (PM2.5) air pollution in Europe, posing challenges to public health. Designing cost-effective Nr control roadmaps for PM2.5 mitigation requires considering both mitigation efficiencies and implementation costs. Here we identify optimal Nr control pathways for Europe by integrating emission estimations, air quality modeling, exposure-mortality modeling, Nr control experiments and cost data. We find that phasing out Nr emissions would reduce PM2.5 by 2.3 ± 1.2 μg·m−3 in Europe, helping many locations achieve the World Health Organization (WHO) guidelines and reducing PM2.5-related premature deaths by almost 100 thousand in 2015. Low-ambition NH3 controls have similar PM2.5 mitigation efficiencies as NOx in Eastern Europe, but are less effective in Western Europe until reductions exceed 40%. The efficiency for NH3 controls increases at high-ambition reductions while NOx slightly decreases. When costs are considered, strategies for both regions uniformly shift in favor of NH3 controls, as NH3 controls up to 50% remain 5-11 times more cost-effective than NOx per unit PM2.5 reduction, emphasizing the priority of NH3 control policies for Europe.

Atmospheric ammonia (NH3) has multiple impacts on the environment, climate change and human health. China is the largest emitter of NH3 globally, with the dynamic inventory of NH3 emission remaining uncertain. Here, we use the high-resolution secondary national pollution survey, integrated satellite data, 15N isotope source apportionment and multiple models to better understand those key features of NH3 emissions and its impacts in China. Our results show that the total NH3 emissions were estimated to be 12.3 Tg yr-1 in 2017 with three emission peaks in April, June and October. NH3 emissions have contributed approximately 23% to secondary PM2.5 formation, a 19.7% increase in nitrogen loading of surface waters, while ammonium deposition led to a decrease in soil pH by 0.0035 units and an increase in the terrestrial carbon sink by 83.4 Tg C yr-1. Reducing NH3 emissions in China would contribute to the mitigation of air and water pollution challenges, saving damage costs estimated at around 22 billion US dollars due to avoided human and ecosystem health impacts.