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The effectiveness of national policies for air pollution control has been demonstrated, but the relative effectiveness of short-term emission reduction measures in comparison with national policies has not. Here we show that short-term abatement measures during important international events substantially reduced PM2.5 concentrations, but air quality rebounded to pre-event levels after the measures ceased. Long-term adherence to strict emission reduction policies led to successful decreases of 54% in PM2.5 concentrations in Beijing, and 23% in atmospheric nitrogen deposition in China from 2012 to 2020. Incentivized by "blue skies" type campaigns, economic development and reactive nitrogen pollution are quickly decoupled, showing that a combination of inspiring but aggressive short-term measures and effective but durable long-term policies delivers sustainable air quality improvement. However, increased ammonia concentrations, transboundary pollutant flows, and the complexity to achieving reduction targets under climate change scenarios, underscore the need for the synergistic control of multiple pollutants and inter-regional action. In response to the rebound of air pollution during large events in China, the authors propose that a combination of ambitious short-term measures and enduring long-term pollution control policies is a sustainable solution for improving air quality. [ABSTRACT FROM AUTHOR]

While intensive peach production has expanded rapidly in recent years, few studies have explored the environmental impacts associated with specific regional systems or the optimal management strategies to minimize associated environmental risks. Here, data from a survey of 290 native farmers were used to conduct a life cycle assessment to quantify the acidification potential (AP), global warming potential (GWP), eutrophication potential (EP), and reactive nitrogen (Nr) losses in peach production in Pinggu District, Beijing. Total annual Nr losses, and GWP, AP, and EP values for peach production in Pinggu District were respectively 10.7 kg N t−1, 857 kg CO2-eq t−1, 12.9 kg SO2-eq t−1, and 4.1 kg PO4-eq t−1. The principal driving factors were fertilizer production, transportation, and application, which together accounted for 94%, 67%, 75%, and 94% of Nr losses, GWP, AP, and EP, respectively. In the high yield, high nitrogen-use efficiency (HH) group, relative values of Nr losses, GWP, AP, and EP were respectively 33%, 25%, 39%, and 32% lower than the overall averages for 290 orchards. Further analyses indicate that improved farming practices such as decreasing application rates of fertilizers, increasing proportion of base fertilization rate, and proper fertilization frequency in the HH group were the main reasons for these orchards' better performance in peach yields and partial factor productivity of nitrogen fertilizer, and their reduced environmental impacts. These results highlight the need to optimize nutrient management in peach production in order simultaneously to realize both environmental sustainability and high productivity in the peach production system. [ABSTRACT FROM AUTHOR]

Stringent emission controls during the Asia Pacific Economic Cooperation Summit (APEC; November 5–11, 2014) provide a valuable opportunity to examine the impact of such measures on the chemical properties of PM 2.5 and other air pollutants. Here, we measured the water-soluble inorganic ions (WSII) and carbonaceous species in PM 2.5 , NH 3 and NO 2 at multiple sites in Beijing between September and November 2014. Relative to the pre-APEC period (September and October 2014), significant reductions in the average concentrations of WSII (69% for NO 3 −, 68% for SO 4 2−, 78% for NH 4 +, and 29–71% for other species), elemental carbon (EC, 43%) and organic carbon (OC, 45%) in PM 2.5 were found during the APEC period. The contributions of secondary inorganic ions (SIA, including SO 4 2−, NO 3 −, and NH 4 +) to PM 2.5 were significantly lower during the APEC period (9–44%), indicating a combination of lower gaseous precursor emissions and a relative weak secondary aerosol formation. Ion-balance calculations indicated that the PM 2.5 sample in the pre-APEC period was alkaline but was acidic during the APEC period. Relatively lower mean concentrations of EC (1.5 μg m−3), OC (10.5 μg m−3), secondary organic carbon (SOC, 3.3 μg m−3), secondary organic aerosol (SOA, 5.9 μg m−3) and primary organic aerosol (POA, 10.0 μg m−3) appeared during the APEC period. The average concentrations of NH 3 and NO 2 at all road sites were significantly reduced by 48 and 60% during the APEC period, which is consistent with clear reductions in satellite NH 3 columns over Beijing city in the same period. This finding suggests that reducing traffic emissions could be a feasible method to control urban NH 3 pollution. During the APEC period, concentrations of PM 2. 5 , PM 10 , NO 2 , SO 2 and CO from the Beijing city monitoring network showed significant reductions at urban (20–60%) and rural (18–57%) sites, whereas O 3 concentrations increased significantly (by 93% and 53%, respectively). The control measures taken in the APEC period substantially decreased PM 2.5 pollution but can increase ground O 3 , which also merits attention. • Concentrations of PM 2.5 and components reduced significantly during the APEC period. • Major components in PM 2.5 and other pollutants were comparable with other cities. • Vehicle restrictions could lower atmospheric NH 3 concentration over Beijing. • Emission control measures significantly increased ground-level O 3 concentrations. [ABSTRACT FROM AUTHOR]

The Clean Air Action implemented by the Chinese government in 2013 has greatly improved air quality in the North China Plain (NCP). In this work, we report changes in the chemical components of atmospheric fine particulate matter (PM 2.5) at four NCP sampling sites from 2012/2013 to 2017 to investigate the impacts and drivers of the Clean Air Action on aerosol chemistry, especially for secondary inorganic aerosols (SIA). During the observation period, the concentrations of PM 2.5 and its chemical components (especially SIA, organic carbon (OC), and elemental carbon (EC)) and the frequency of polluted days (daily PM 2.5 concentration ≥ 75 μg m−3) in the NCP, declined significantly at all four sites. Asynchronized reduction in SIA components (large decreases in SO 4 2− with stable or even increased NO 3 − and NH 4 +) was observed in urban Beijing, revealing a shift of the primary form of SIA, which suggested the fractions of NO 3 − increased more rapidly than SO 4 2− during PM 2.5 pollution episodes, especially in 2016 and 2017. In addition, unexpected increases in the sulfur oxidation ratio (SOR) and the nitrogen oxidation ratio (NOR) were observed among sites and across years in the substantially decreased PM 2.5 levels. They were largely determined by secondary aerosol precursors (i.e. decreased SO 2 and NO 2), photochemical oxidants (e.g. increased O 3), temperature, and relative humidity via gas-phase and heterogeneous reactions. Our results not only highlight the effectiveness of the Action Plan for improving air quality in the NCP, but also suggest an increasing importance of SIA in determining PM 2.5 concentration and composition. [Display omitted] • PM 2.5 and its chemical components were reduced in North China Plain during 2012–2017. • Reduced air pollutant emissions contributed more to PM 2.5 decline than meteorology. • NO 3 − became increasingly important in the formation of secondary inorganic aerosols. • Both sulfur oxidation ratio and nitrogen oxidation ratio increased unexpectedly. [ABSTRACT FROM AUTHOR]

Airborne bacteria are important components of fine particulate matter (PM 2.5), and have received increasing attention because of their impacts on public health and ecological systems. However, the relationships between the bacterial community and PM 2.5 pollution are poorly understood. The properties of bacterial communities in Beijing at low, medium and high PM 2.5 levels were analyzed during winter (December 2015–January 2016; January 2017) and spring (March 2016–May 2016; April 2017–May 2017). Variations in bacterial concentrations, Shannon and Simpson indices and relative abundance were significantly related to the seasons. In winter, there were no significant differences in bacterial communities among three PM 2.5 pollution levels. In contrast, significant correlations between bacterial abundance and PM 2.5 levels were observed in spring, and the bacterial concentrations, community richness and diversity indices were significantly higher on heavily polluted days compared to other pollution levels. Correlation results showed that relative humidity (RH), wind speed (WS), and O 3 were most closely associated with microbial community structure in winter (P < 0.05), but temperature (T), NO 2 , SO 2 , and CO in spring, while CO, NO 2 , O 3 , RH, and WS had significant relationships (|r| = 0.360–0.553, P < 0.05) with bacterial concentrations in winter, but PM 2.5 , O 3 , T, and RH (|r| = 0.281–0.527, P < 0.05) in spring. Chemical composition, especially that of secondary aerosol particles, which were mainly produced from anthropogenic sources (e.g. fossil fuel combustion, road traffic and industrial emissions), exerted the most control of bacterial community structure of PM 2.5. The effects of PM 2.5 levels on the bacterial community were modified by environmental conditions, heavy metal and nutrient contents of the PM 2.5. The relationships described provide a foundation for further research into the environmental and PM 2.5 chemical composition controls on the bacterial community and related health risk from air pollution. [Display omitted] • Conditional responses of bacterial communities to PM 2.5 pollution. • Stable bacterial communities across different PM 2.5 levels in winter. • Significant changes of bacterial communities to PM 2.5 levels in spring. • Secondary aerosol particles exerted the most control of bacterial community structure. [ABSTRACT FROM AUTHOR]

In order to cope with heavy haze pollution in Beijing, the Air Pollution Prevention and Control Action Plan was issued in 2013. In this study, we took January observations from 2014 to 2018 as a case study to assess wintertime air quality improvement in Beijing after five years of continuous emission control measures and to investigate the causes of haze formation. SO 2 and NO 2 concentrations in January 2018 decreased by 84% and 41% from January 2014, while NH 3 concentrations remained relatively stable during these years with an average of 7.28 μg m−3. The mean concentrations of PM 2.5 and water-soluble inorganic ions declined over the study period, while compared with 2014, decreased SO 4 2− ratio and increased NO 3 − contribution in PM 2.5 were observed, highlighting the importance of reactive nitrogen (Nr) pollution control. High concentrations of NH 3 , NO 2 , as well as NH 4 + and NO 3 − in PM 2.5 at roadside monitoring sites, indicated that vehicle sources played a vital role in local urban Nr emissions. Finally, we found most NH 3 existed in the gas phase in the Beijing atmosphere, even on polluted winter days, suggesting a considerable risk for additional secondary aerosol formation. Our findings demonstrate the effectiveness of the emissions control in alleviating Beijing's air pollution. Significant reductions of precursor emissions are needed to achieve the goals set by air quality standards in the future, especially for NH 3. It is especially crucial to jointly consider and control multiple pollution sources to effectively reduce the high levels of air pollution that remain in Beijing. • Significant improvements in Beijing air quality were observed during January 2014 to 2018. • The concentrations of SO 2 , NO 2 in air and SO 4 2−, NO 3 −, NH 4 + in PM 2.5 significantly decreased. • NH 3 concentrations remained stable during these 5 years. • Vehicle sources are vital contributors to NH 3 and NO 2 emissions. • The Beijing atmosphere is NH 3 -rich. [ABSTRACT FROM AUTHOR]

Identifying the sources of increased ammonia (NH 3) in the atmosphere has important implications for air quality, ecosystems, and climate. While analysis of the nitrogen isotopic composition (δ15N) can aid in the apportionment of NH 3 emission sources, the widely-used passive collection methods have not been verified for their ability to accurately characterize δ15N-NH 3. In this study, three types of passive samplers (ALPHA, Analyst, and Radiello) were employed and collocated with a denuder based active sampler (DELTA, serves as a reference method) to compare and contrast their ability in collecting atmospheric NH 3 for subsequent concentration and δ15N-NH 3 analysis in urban Beijing during the summer of 2018. The results showed that NH 3 concentrations determined using passive collection samplers that included ALPHA (n = 11), Analyst (n = 12), and Radiello (n = 7) samplers were 13.4%, 14.4%, and 27.5% lower than that of the active sampler (n = 12), respectively. The low NH 3 concentration bias in the passive collection samplers was suggested to be the result of inaccurate effective sampling rates due to incorrect mass transfer correction factors for the environmental conditions of this study. The δ15N-NH 3 values did not show significant differences between passive samplers, with weekly means of −31.0 ± 1.0‰ (n = 4), −28.4 ± 5.5‰ (n = 4), and −29.1 ± 0.9‰ (n = 4) for the ALPHA, Analyst, and Radiello, respectively. Notably, the overall mean δ15N-NH 3 values collected by these passive samplers (−29.5 ± 3.2‰, n = 12) was significantly lower than that of the active sampler (−14.1 ± 1.6‰, n = 4), with a difference of 15.4 ± 3.5‰. The large underestimation of δ15N-NH 3 values by passive samplers can be explained by the diffusive isotope fractionation of NH 3 isotopologues, which is driven by relative mass differences of 14NH 3 and 15NH 3. Overall, these findings highlight a potential low bias in NH 3 concentrations and a substantial uncertainty in previous source interpretation using δ15N-NH 3 as previous studies have almost exclusively characterized δ15N-NH 3 using passive samplers. We suggest that the denuder-based active sampler should be used in the future for characterizing δ15N-NH 3 whether at the source or in an atmospheric environment with mixed sources. This work also has important implications for characterizing δ15N of other gaseous nitrogen compounds. Unlabelled Image • Nitrogen isotopic composition of ammonia (δ15N-NH 3) aids in source apportionment. • Conventional collection methods for δ15N-NH 3 were almost based on passive samplers. • δ15N-NH 3 obtained by passive and active samplers were respective −29.5‰ and −14.1‰. • The low bias of 15.4‰ by passive δ15N-NH 3 was due to diffusive isotope fractionation. • Source apportionment based on passive δ15N-NH 3 might mislead mitigation strategy. [ABSTRACT FROM AUTHOR]

Precipitation chemistry and atmospheric nitrogen (N) deposition are of great concern worldwide due to their close relationships with air quality and impacts on ecosystems. However, evaluation of the chemical composition of precipitation and N deposition flux in rural areas of Beijing has received little attention to date. This paper presents the chemical constituents, possible sources and wet deposition fluxes of water-soluble ions (NH 4 +, NO 3 −, SO 4 2−, Cl−, Na+, K+, Ca2+, Mg2+) in precipitation samples collected during 2017–2018 at a rural site located at northwest of Beijing city; meanwhile, dry deposition of reactive N species (gaseous ammonia, nitrogen dioxide, nitric acid, and particulate (p) NH 4 + and NO 3 −) were also quantified. During this 2-year period, the volume-weighted mean (VWM) pH of precipitation was 6.73, and all samples had pH values above 6.0. The VWM electric conductivity of precipitation and the mean sum of all measured ions was 43.8 μS cm−1 and 591.9 μeq L−1, respectively, indicating a significant impact of atmospheric pollution. Ca2+ and NH 4 + were the dominant neutralizing species for precipitation acidity. Positive matrix factorization analysis further confirmed five sources for water-soluble ions, including sea salt aging, secondary formation, agriculture, crust, and biomass burning. The annual mean wet N deposition was 4.6, 3.4 and 8.0 kg N ha−1 yr−1 for NH 4 +, NO 3 − and total inorganic N, respectively. The total dry N deposition was dominated by gaseous ammonia (11.5 kg N ha−1 yr−1). The total N deposition (wet plus dry) was 27.7 kg N ha−1 yr−1, where dry deposition contributed to 75% and wet deposition 25% of the total. The simulations from the GEOS-Chem model indicate that agricultural (fertilizer use and livestock) and nonagricultural sources (industry, power plant, and transportation) are both important contributors to total N deposition. These results could be useful in evaluating/developing emission control policies to protect the eco-environment in Beijing. • Precipitation chemistry and nitrogen (N) deposition were investigated in Beijing. • The pH values of precipitation samples were all above 6.0 and averaged 6.7. • Ion source was sea salt, secondary source, agriculture, crust, and biomass burning. • Total N deposition was 27.7 kg N ha−1 yr−1, of which 75% was from dry deposition. • Agricultural and nonagricultural sources contributed equally to total N deposition. [ABSTRACT FROM AUTHOR]