Ammonia emission control in China would mitigate haze pollution and nitrogen deposition, but worsen acid rain

Abstract

China has been experiencing fine particle (i.e., aerodynamic diameters ≤ 2.5 µm; PM2.5) pollution and acid rain in recent decades, which exert adverse impacts on human health and the ecosystem. Recently, ammonia (i.e., NH3) emission reduction has been proposed as a strategic option to mitigate haze pollution. However, atmospheric NH3 is also closely bound to nitrogen deposition and acid rain, and comprehensive impacts of NH3 emission control are still poorly understood in China. In this study, by integrating a chemical transport model with a high-resolution NH3 emission inventory, we find that NH3 emission abatement can mitigate PM2.5 pollution and nitrogen deposition but would worsen acid rain in China. Quantitatively, a 50% reduction in NH3 emissions achievable by improving agricultural management, along with a targeted emission reduction (15%) for sulfur dioxide and nitrogen oxides, can alleviate PM2.5 pollution by 11−17% primarily by suppressing ammonium nitrate formation. Meanwhile, nitrogen deposition is estimated to decrease by 34%, with the area exceeding the critical load shrinking from 17% to 9% of China’s terrestrial land. Nevertheless, this NH3 reduction would significantly aggravate precipitation acidification, with a decrease of as much as 1.0 unit in rainfall pH and a corresponding substantial increase in areas with heavy acid rain. An economic evaluation demonstrates that the worsened acid rain would partly offset the total economic benefit from improved air quality and less nitrogen deposition. After considering the costs of abatement options, we propose a region-specific strategy for multipollutant controls that will benefit human and ecosystem health.

Initial Cost Barrier of Ammonia Control in Central China

“…However, large NH x reductions beyond the CTAC will effectively decrease particulate mass but increase particulate acidity, the latter of which has negative consequences on the environment (e.g., Guo et al, 2018;Liu et al, 2019). At an NH x reduction of 80%, concurrent reduction of TNO 3 up to 50% has little effect on ΔWSI concentrations, while the effect of concurrent SO 4 2reduction of 50% is half of no concurrent SO 4 2reduction.…”

“…Among the various measures, controlling ammonia emissions in fertilizer applications is most cost effective Pinder et al, 2007). As in Liu et al (2019), we used an estimate of $1,700 per ton of ammonia emission reduction through improving fertilizer applications based on the work by Klimont and Winiwarter (2011) and obtained a total of $140-320 million for Hubei Province. As in Liu et al (2019), we used an estimate of $1,700 per ton of ammonia emission reduction through improving fertilizer applications based on the work by Klimont and Winiwarter (2011) and obtained a total of $140-320 million for Hubei Province.…”

“…Recently, An et al (2019) indicated a 50% reduction in ammonia yielded a 10% reduction in PM 2.5 in a haze event in North China. Liu et al (2019) also implied that a 50% reduction in ammonia emissions with a 15% reduction in sulfur dioxide and nitrogen oxides can reduce PM 2.5 by 11% − 17%. On the other hand, Guo et al (2018) suggested that the effect of NH x control on reducing ionic masses of PM 2.5 is not as good as controlling TNO 3 and SO 4 2unless NH x is reduced by more than 60% in Beijing.…”

“…Wang et al (2011) speculated that a 90% increase in ammonia emissions during 1990 -2005 contributed to about a 50% -60% increase in sulfate and nitrate aerosol concentrations. Liu et al (2019) also implied that a 50% reduction in ammonia emissions with a 15% reduction in sulfur dioxide and nitrogen oxides can reduce PM 2.5 by 11% − 17%. Recently, An et al (2019) indicated a 50% reduction in ammonia yielded a 10% reduction in PM 2.5 in a haze event in North China.…”

Trends of Precipitation Acidification and Determining Factors in China During 2006–2015

“…To enable the simulation of precipitation acidity, we developed a diagnosis program offline coupled with the WRF‐Chem wet deposition module to calculate precipitation pH. This program has been demonstrated to produce reasonable simulation of precipitation acidity over China (Liu et al, 2019). First, in the wet deposition module of WRF‐Chem, the simulated wet deposition of gases and aerosol compounds (like sulfate, nitrate, ammonium, and mineral particles) onto surface through scavenging processes (i.e., in‐cloud rainout and below‐cloud washout) were accumulated within each grid during precipitation events.…”