Combined short-term and long-term emission controls improve air quality sustainably in China

China's rapid economic growth over the past four decades has been accompanied by severe environmental challenges, including widespread air pollution. Public demand for improved air quality is strong. Initial efforts focused on sulfur dioxide (SO2) and acid rain, but after 2010, attention shifted to reactive nitrogen (Nr) pollution and fine particulate matter (PM2.5). The implementation of short-term emission control measures during major international events aimed to ensure "blue skies," involving temporary industrial suspensions and traffic restrictions. However, these measures were unsustainable, leading to a rebound effect once they ceased. In contrast, the government has also implemented long-term policies, like the Air Pollution Prevention and Control Action Plan (2013) and the Three-Year Action Plan for Winning the Blue-Sky Defense Battle (2018). These policies targeted major emission sources, such as coal-fired power plants and the transportation sector, aiming for more permanent emission reductions. This research seeks to compare the effectiveness of these short-term and long-term approaches, analyzing their impact on PM2.5 and nitrogen deposition, and identifying remaining challenges in achieving sustainable air quality improvements in China. The study utilizes data from the Nationwide Nitrogen Deposition Monitoring Network (NNDMN) and integrated observations from four major international events, assessing both short-term event-driven interventions and long-term policy impacts on air quality.

Existing literature demonstrates the effectiveness of national policies in controlling air pollution in China. Studies show a significant increase in PM2.5 and nitrogen deposition followed by a gradual stabilization with the implementation of long-term emission control policies. However, the relative effectiveness of short-term emission reduction measures compared to national policies has not been thoroughly investigated. Previous research has highlighted the role of specific policy interventions, such as the Atmospheric Ten Actions and the Three-Year Defense Battle, in reducing air pollution. The impact of meteorological conditions on air quality is well-documented, influencing the dispersion of pollutants. However, the interaction between short-term abatement measures and long-term policies and the role of climate change remain areas that need further investigation. Studies also point to challenges in controlling ammonia emissions and addressing transboundary pollutant flows. This study builds upon previous work by providing a comprehensive comparison of short-term and long-term strategies and their combined impact on air quality improvement in China.

The study utilizes a multi-faceted approach combining observational data and model simulations. For short-term impacts, an integrated observation dataset of PM2.5 and its precursors was collected during four international mega-events: the Olympic Games (2008), Asia-Pacific Economic Cooperation Summit (APEC, 2014), Military Parades (2015), and the Belt and Road Summit (BRS, 2017). Daily average PM2.5 concentrations, ionic components, and gaseous precursors (SO2, NO2, NH3) were obtained from various sources, including published literature and the China National Environmental Monitoring Centre (CNEMC). Monthly NH3 concentrations were measured using ALPHA passive samplers. For long-term impacts, the study leveraged data from the Nationwide Nitrogen Deposition Monitoring Network (NNDMN), spanning ten years (2011-2020) with data from nearly 60 monitoring sites. The NNDMN provided data on gaseous and particulate Nr, and precipitation. Dry and bulk N deposition were calculated using deposition velocity simulated by the GEOS-Chem chemical transport model. The study used both arithmetic averaging and area-weighted averaging to analyze spatial patterns of dry and bulk deposition. To evaluate the influence of multiple factors on N deposition, random forest (RF) analysis was employed, considering Nr emissions, meteorological parameters, soil parameters, and NDVI. Future trends of PM2.5 concentrations and N deposition were simulated using the WRF-EMEP model, considering different scenarios, including emission reduction policies and climate change effects (RCP4.5). Statistical analyses (ANOVA, nonparametric t-tests, Mann-Kendall test, Sen’s slope, linear/nonlinear regressions) were performed using SPSS and R software. GIS software was used for spatial data analysis.

Short-term measures during international events produced substantial decreases in PM2.5 and gaseous pollutants (SO2, NO2), with reductions of 30-60%. However, these improvements were temporary, with pollutant concentrations rebounding to pre-event levels after the measures ended. In contrast, long-term emission reduction policies resulted in sustained improvements. In Beijing, PM2.5 concentrations decreased by 68% from August 2005 to August 2020, with SO2 reductions reaching 90%. Nationwide, atmospheric nitrogen deposition decreased by 23% (2012-2020). The analysis revealed that short-term measures did not significantly alter the long-term downward trend in pollution. However, ammonia (NH3) concentrations increased over the study period. Spatial analysis showed regional variations in N deposition, with North China experiencing a more dramatic decline than other regions. The study found evidence of transboundary pollutant flows, highlighting the need for inter-regional collaboration. Simulations using the WRF-EMEP model projected significant decreases in PM2.5 and N deposition under stricter emission control policies (2030 and 2060 scenarios), but climate change effects might partially offset these gains. The study also showed that dry deposition of oxidized N (NOy) decreased while NH3 dry deposition increased. These findings suggest a trade-off between reducing oxidized and reduced N deposition and underscore the importance of synergistic multi-pollutant controls. The impact of the COVID-19 lockdown also showed that while SO2 and NO2 significantly decreased, NH3 concentrations only saw a small decrease due to its agricultural sources, emphasizing the challenges in rapidly reducing NH3 emissions.

This research directly addresses the effectiveness of various air pollution control strategies in China. The results demonstrate a clear contrast between the short-lived impact of event-based emission controls and the sustained benefits of long-term policy implementation. While short-term measures provide immediate improvements and serve as crucial public awareness campaigns, their temporary nature necessitates a greater reliance on long-term policies for sustainable change. The observed increase in NH3 concentrations highlights the need for comprehensive multi-pollutant control strategies. The regional differences in N deposition and transboundary pollution underscore the significance of inter-regional cooperation. The model simulations project future air quality improvements but also indicate the potential for climate change to offset some of the gains from emission reductions. These findings have significant implications for policymakers, emphasizing the need for a balanced approach combining targeted short-term measures with robust long-term policies.

This study demonstrates the effectiveness of a combined approach of short-term and long-term emission controls in improving air quality sustainably in China. While short-term measures provide immediate, visible improvements and raise public awareness, long-term policies are essential for sustained progress. The increase in NH3 concentrations highlights the necessity of synergistic multi-pollutant controls. Transboundary pollution underscores the importance of regional cooperation. Future research should focus on optimizing the balance between short-term and long-term strategies, further investigating the impact of climate change, and developing effective strategies for NH3 emission reduction.

The study relies on data from specific monitoring networks, which may not fully capture the spatial heterogeneity of air pollution across China. The model simulations rely on certain assumptions about future emissions and climate change, which introduce uncertainties. While the study provides a comprehensive analysis, the complexity of atmospheric processes and interactions between various pollutants may lead to some simplifications.