Proportion Of NO3 Research Articles

Physico-chemical Characteristics and Evolution of NR-PM1 in the Suburban Environment of Seoul

In South Korea, particulate matter (PM) is generated from various emission sources, including domestic air pollutants and long-range transport. Effective air quality policies require an understanding of the chemical characteristics of PM and differences between urban and non-urban areas (suburban and background areas). We analyzed the chemical characteristics of non-refractory submicron aerosols (NR-PM1) in Yongin City, a suburban area southeast of Seoul, using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) in spring/summer. In spring/summer, photochemical reactions resulted in the highest proportion of Organic Aerosol (OA) among NR-PM1. Positive matrix factorization (PMF) revealed four OA sources: Primary OA and Secondary OA (Oxidized Primary OA (OPOA), Less Oxidized Oxygenated OA (LO-OOA), and More Oxidized Oxygenated OA (MO-OOA)). OPOA was formed from the oxidation of emissions from biomass burning and coal combustion; LO-OOA and MO-OOA were correlated with inorganic compounds and influenced by long-range transport. The majority of OA was SOA (82%). High temperatures and humidity accelerated the conversion of SO2 to SO42−, resulting in the proportion of SO42−, second only to OA. Despite favorable conditions for nitrate formation in ammonium-rich conditions, the proportion of NO3− was relatively low due to the decomposition of NH4NO3 into gaseous NH3 and HNO3 at high temperatures. This indicated that while ammonium-rich conditions are conducive to NH4NO3 production, elevated temperatures lead to its decomposition, resulting in lower NO3− concentrations in spring/summer. In the case study, for the case associated with long-range transport, the PM concentration increased due to inorganic compounds such as NO3− and SO42−. Conversely, in cases of domestic air stagnation, the concentration of PM increased primarily due to the presence of OA. These findings provide crucial insights for air quality management in suburban areas and can guide policies to reduce PM levels in spring and summer.

Spatial distribution, sources, and human health risk assessment of elevated nitrate levels in groundwater of an agriculture-dominant coastal area in Hainan Island, China

In order to comprehend the groundwater nitrate contamination in Hainan Island, which is recognized as China's sole “tropical agricultural production base,” the distribution characteristics of nitrate in different aquifers and land-use types were elucidated through hydrochemical and geostatistical analysis methods. Principal component analysis (PCA), hierarchical cluster analysis (HCA), and absolute principal component score-multiple linear regression (APCS-MLR) were employed for qualitative and quantitative analysis of the nitrate source. The results showed that NO3−-high (>88.57 mg/L) groundwater accounted for about 10 % of the total distribution area of the western coastal area in Hainan Island. Moreover, the proportions of NO3−-high groundwater in pore water and fissure water were 10 % and 7 %, respectively. The order of groundwater nitrate concentration in different land-use types was as follows: bare land, cultivated land, construction land, grassland, and woodland. The main sources of elevated nitrate concentrations in pore water were animal feces and nitrogen/potassium fertilizers, accounting for 45.4 % of the overall contribution. These substances infiltrated through the vadose zone, leaching out and mobilizing selenium within this zone, ultimately leading to the characteristic enrichment patterns observed in pore water, including nitrate, arsenic, potassium, and selenium. Furthermore, the occurrence of high nitrate in fissure water was mainly attributed to the leaching of cultured manure, septic tank leakage, and infiltration of domestic sewage, accounting for a contribution rate of 32.9 %. Simultaneously, under oxidizing conditions, selenium became activated and entered groundwater through water flow, thereby exhibiting common enrichment characteristics with nitrate and potassium in fissure water. In addition, the assessment of human health risks revealed that 16 % and 40 % of groundwater samples posed unacceptable non-carcinogenic risks to adults and children respectively, with a higher risk for local children. The study recommends the reasonable application of chemical fertilizers, as well as the strengthening of sewage treatment capacity and standardized disposal of manure and feces, to reduce nitrate contamination of groundwater at source and ensure the safety of drinking water.

Characteristics of Secondary Inorganic Ions in PM2.5 and Its Influencing Factors in Summer in Zhengzhou

Nitrate (NO3-), sulfate (SO42-), and ammonium (NH4+) are important components of PM2.5, and studying their characteristics and influencing factors is essential for the continuous improvement of air quality. A series of online instruments were used to analyze the chemical components of PM2.5 in Zhengzhou in the summer of 2020. The results showed that the average ρ(PM2.5) was (28 ±13) μg·m-3, showing a daily variation characteristic of high at night and low during the day. The main concentrations of NO3-, SO42-, and NH4+ were (7.8 ±6.7), (7.2 ±3.7), and (5.5 ±3.1) μg·m-3, accounting for 22%, 21%, and 16% in PM2.5, respectively. The proportions of NO3- (27%) and SO42- (23%) in PM2.5, respectively, increased with the increase in PM2.5 and O3 concentration. In addition, the proportions of NO3- and NH4+ increased under low wind speed, high humidity, low temperature, and rainfall conditions. Moreover, the proportion of NO3- showed a daily variation characteristic of high at night and low during the day, whereas the opposite was true for SO42-. The gas-particle partitioning process of NH4NO3 was the main factor affecting the concentrations of NO3- and NH4+ in PM2.5. Low temperature, high humidity, and high aerosol water content concentrations favored the partitioning of HNO3 and NH3 to the particulate phase. High pH also favored the partitioning of gas-phase HNO3 to NO3-; however, it was not conducive to the partition of NH3 to NH4+. These trends partially explained the increase in the concentration and proportion of NO3- in PM2.5 under different scenarios.

Economic and Industrial Development SignificantlyContribute to Acidity and Ionic Compositions of Rainwaterin China

To achieve a holistic understanding of the intricate interactions among human activities, atmospheric chemistry, and acid rain in China, a rigorous analysis of rainwater chemistry was made using a dataset comprising 2656 data points from 24 sites. The main cation and anion in the chemical composition of precipitation were Ca2+ and SO42− in China, with an average concentration of 169.9 μeq/L and 135.4 μeq/L, respectively. Acid rain generally occurs in southern cities such as Shenzhen, Guangzhou, Zhuhai, Xiamen, and Chongqing. There were evident regional disparities in acidity and ion concentrations in rainwater, with an increase in acidity and a decrease in ion concentrations from north to south across China. Utilizing positive matrix factorization, the study found that NH4+, SO42−, and NO3− mainly originated from anthropogenic sources such as fossil fuel combustion, vehicle exhaust emissions, agricultural fertilization, and industrial emissions (as reflected by F3 and F4). Ca2+ mainly stems from crustal factors, including industrial dust and natural crust (as represented by F1 and F4). Na+ and Cl− were traceable from marine sources (as reflected by F5), while Mg2+ originated from crust origin (as presented by F1). K+ was mainly derived from a mixed source of crust, marine, and biomass burning (as indicated by F2 and F3). The correlation analyses showed that SO42− and NO3− showed significant correlations with GDP and population. F− was associated with wastewater, which may be linked to the production of brick and tiles from clay with high fluoride contents. The pH was negatively related to industrial wastewater. Long-term analysis of precipitation chemistry in four cities suggested a clear decrease in the proportion of SO42− but a considerable increase in the proportion of NO3− in anions in metropolitans of Shanghai and Chongqing due to the environmental measures that targeted reducing sulfur dioxide (SO2) emissions and increase of vehicles. This showed that pollution control strategies had an impact on precipitation ion concentrations. These results can conclude that economic and industrial growth, which will increase energy consumption, utilization of coal combustion, and a subsequent rise in pollutant emissions, can contribute to the change in the chemical compositions of rainwater and the exacerbation of acid rain.

Seasonal dynamics of soil nitrogen mineralization and their influencing factors during shrub anthropogenic introduction in desert steppe.

We selected enclosed grassland, grazed grassland and shrublands with different planting years (3, 12, 22 years)/densities (intervals of 2, 6, 40 m) to investigate soil N mineralization dynamics in the growing season (April-October) and its influencing factors during the process of desert steppe-degradation-shrub introduction. The results showed that soil moisture at 0-200 cm layer was decreased with increases of shrub age and density, and that the variations of soil moisture at 0-10 cm layer coincided with seasonal change. Compared with grazed grassland and enclosed grassland, the positive effect of shrubs on soil carbon, nitrogen and phosphorus contents first increased and then decreased with the increases of age and density. Moreover, soil N mineralization significantly varied across months and sites. Soil NO3- content and microbial biomass carbon and nitrogen were significantly higher from June to August. The proportion of NO3- to inorganic nitrogen significantly increased from 30.5% in enclosed grassland to 69.5% in shrublands. NH4+ content was mainly affected by months compared with sites. In the process of steppe-degradation-shrub introduction, the increases of shrub age and density significantly enhanced seasonal differences of soil nitrification and ammonification, but not on the seasonal mineralization of microbial biomass carbon and nitrogen. Soil NH4+ and NO3- contents were significantly and positively correlated with total nitrogen, organic carbon and N/P. Soil stoichiometric ratios (C/N and N/P) directly regulated N mineralization process.

Differences in PM2.5 Components Between Urban and Rural Sites During Heavy Haze Event in Northern Henan Province

In recent years, the Beijing-Tianjin-Hebei region and its surrounding areas have experienced multiple haze pollution processes. Owing to the limitation of observational instruments, there has not been a comparative study of haze pollution between urban and rural areas in northern Henan province. A series of high-time-resolution instruments were used during a regional heavy pollution process (January 12-25, 2018) at two urban sites and three rural sites. The results showed that SO42-, NO-3, and NH+4 (SNA) were the components with the highest proportion in PM2.5 at the five sites during the haze event with a range of 53%-63%, of which nitrate was the most important, accounting for 24%-32%, followed by sulfate, ranging from 13%-17%. Compared with urban sites, rural sites were more affected by organic matter, especially at night. With the aggravation of pollution, the proportion of SNA increased, reaching 67% during periods of heavy pollution. When the area was affected by the air mass transported from the south, the proportion of NO-3 in PM2.5 increased, and when the area was affected by the air transport in the north, the proportions of SO42- and organic matter increased. Ammonium nitrate was the most important component that led to the decrease in atmospheric visibility during the haze process. Moreover, the contributions of ammonium nitrate and ammonium sulfate at the urban sites were higher than those at the rural sites. To summarize, there were significant differences in PM2.5 components between the urban and rural sites. Urban areas need to continue to strengthen the reduction in gaseous precursors, and rural areas need to pay attention to the sources of carbonaceous aerosol.

Characteristics of chemical composition and source apportionment of PM2.5 during a regional haze episode in the yangtze river delta, china

The source of PM2.5 varies at different stages of urban haze pollution. In addition, there is obvious regional transport of pollutants between urban agglomerations. PM2.5 and its major chemical compositions in a regional haze episode were measured continuously from 16 to 27 November 2018 in Nanjing, China. The types of primary sources resolved by principal component analysis (PCA) and positive matrix factorization (PMF) were similar, and the result of PMF was more refined. The average contribution of each source by PMF was: secondary nitrate (64.01%), secondary sulfate (11.62%), incomplete combustion (4.49%), sea salt (8.61%), biomass burning (6.90%), and crustal dust (4.37%). In different haze stages, the distribution characteristics of air pollutants differed. The concentrations of SO42-, NO3−, NH4+, and black carbon were the highest in the haze developing stage, which was 2.0, 3.1, 3.0, and 2.4 times, respectively, higher than that under clean conditions. The increment of NO3− dominated the development of haze, and the proportion of NO3− from haze generation to development increased by 4.05%. The concentration contributions of secondary nitrate, sea salt, and biomass burning were highest in haze development, secondary sulfate was highest in haze generation, and incomplete combustion was highest in haze dissipation, which was 3.5, 1.8, 3.3, 1.7, and 9.5 times higher than the clean stage, respectively. In the haze episode, the contribution of crustal dust was lower than in the clean stage. Potential source contribution function (PSCF) and concentration weighted trajectory (CWT) revealed that the major source area of air pollutants in Nanjing came from the southeast, and the northwest was the major impact area.

Sources and migration similarly determine nitrate concentrations: Integrating isotopic, landscape, and biological approaches

Rapid land use change has significantly increased nitrate (NO3−) loading to rivers, leading to eutrophication, and posing water security problems. Determining the sources of NO3− to waters and the underlying influential factors is critical for effectively reducing pollution and better managing water resources. Here, we identified the sources and influencing mechanisms of NO3− in a mixed land-use watershed by integrating stable isotopes (δ15N-NO3− and δ18O-NO3−), molecular biology, water chemistry, and landscape metrics measurements. Weak transformation processes of NO3− were identified in the river, as evinced by water chemistry, isotopes, species compositions, and predicted microbial genes related to nitrogen metabolism. NO3− concentrations were primarily influenced by exogenous inputs (i.e., from soil nitrogen (NS), nitrogen fertilizer (NF), and manure & sewage (MS)). The proportions of NO3− sources seasonally varied. In the wet season, the source contributions followed the order of NS (38.6 %) > NF (31.4 %) > atmospheric deposition (ND, 16.2 %) > MS (13.8 %). In the dry season, the contributions were in the order of MS (39.2 %) > NS (29.2 %) > NF (29 %) > ND (2.6 %). Farmland and construction land were the original factors influencing the spatial distribution of NO3− in the wet and dry seasons, respectively, while slope, basin relief (HD), hypsometric integral (HI), and COHESION, HD were the primary indicators associated with NO3− transport in the wet and dry seasons, respectively. Additionally, spatial scale differences were observed for the effects of landscape structure on NO3− concentrations, with the greatest effect at the 1000-m buffer zone scale in the wet season and at the sub-basin scale in the dry season. This study overcomes the limitation of isotopes in identifying nitrate sources by combining multiple approaches and provides new research perspectives for the determination of nitrate sources and migration in other watersheds.

Spatial-Temporal Distribution, Morphological Transformation, and Potential Risk of Dissolved Inorganic Nitrogen in the Contaminated Unconfined Aquifer from a Retired Nitrogenous Fertilizer Plant.

The accumulation of nitrogen in groundwater in the industrial plots, especially the high ammonium, can result in a serious threat to the groundwater system in the urban area. This study monitored the dissolved inorganic nitrogen (DIN) of the polluted groundwater four times in one year in a retired nitrogenous fertilizer plant site with a production history of nearly 40 years, to analyze the spatial-temporal characteristics of DIN species (NH4+-N, NO3−-N, and NO2−-N) and the effects of groundwater environment on their transfer and transformation. The results showed that NH4+-N (<0.025 to 1310 mg/L) was the main DIN species (61.38–76.80%) with low mobility, whereas the concentration of NO3−-N and NO2−-N was 0.15–146 mg/L and <0.001–12.4 mg/L, accounting for 22.34–36.07% and 0.53–2.83% of total DIN, respectively. The concentration and proportion of NO3−-N and NO2−-N showed an upward trend with time, posing a threat to the safety of surrounding groundwater, and their high spatial-temporal variation was related to the morphological transformation and the transport. In the wet season, the pH and redox condition benefited the nitrification, and NO3−-N easily migrated from the deep soil solution to groundwater, hence the NO3−-N can be accumulated. Therefore, the analysis of species and behaviors of DIN in shallow groundwater is indispensable for environmental risk assessment.

Simulating nitrate formation mechanisms during PM2.5 events in Taiwan and their implications for the controlling direction

The long-term downward trend of NOX concentrations does not reflect the reduction of nitrate (NO3−) in Taiwan. Instead, the proportion of NO3− in PM2.5 increased in recent years. To probe the increasing importance of NO3− in PM2.5, this study applied the WRF/CMAQ modeling system to implement a simulation from 16 March 2017 to 30 April 2017, in which 5 p.m.2.5 events with daily average concentrations ≥35 μg m−3 and their corresponding correlation coefficients (R) of simulated and observed PM2.5 above 0.6 were selected for analysis. During the daytime, the reaction of NO2 and OH contributed more than 90% of the total HNO3. After sunset, the high concentrations of NO3 and N2O5 peaked, followed soon by the simultaneous rise of NO3−, aerosol water content, and HNO3 concentrations around midnight, which indicated that the heterogeneous reaction was the main formation mechanism of NO3−, accounting for approximately 30%–90% of total HNO3. At nighttime, the daytime-formed gaseous phase NO3− condensed, and low wind and low boundary layer height favored accumulation; therefore, PM2.5 peaked around the midnight period to the early morning. The sensitivity test showed that doubling and halving the NOX and NH3 emissions could directly lead to the highest production and reduction of NO3−, respectively, followed by doubling and halving NMHC emissions, which caused the highest and lowest O3 concentrations. The correlation analysis of the simulation results showed that the daytime maximum O3 and HNO3 were highly correlated. The relationships between daytime maximum O3, nighttime maximum NO3, N2O5, and HNO3 in pairs were also moderately to highly correlated. This study implies that in addition to direct reduction of NOX or NH3 emissions, controlling O3 is possibly another useful strategy to reduce NO3−. Because NOX emission reduction could conflict with controlling O3, this study suggests to re-examine the determination of NOX-limited and VOCS-limited regions in order to develop strategies for reducing NOX emission and O3 simultaneously.

Mentha spicata L. grown with nitrate: Ammonium proportions in different light environments

Mentha spicata L. is an aromatic and medicinal plant, known as mint and used in the pharmaceutical and cosmetic industry and in phytotherapy. Although the cultivation of medicinal plants is traditional, there are several questions about which practices are most appropriate in the management of these plants, especially regarding nutrition and availability of light. The objective of this work was to evaluate the growth, phytomass production and physiological aspects of M. spicata cultivated in proportions of nitrate (NO3-) and ammonium (NH4+) and light environments. The research was carried out in a greenhouse at the Universidade Federal do Recôncavo da Bahia, Cruz das Almas, BA, Brazil. The experimental design used was completely randomized, in a 5 x 3 factorial scheme, with five proportions of NO3-:NH4+ (0: 100; 25:75; 50:50; 75:25; 100: 0) and three light environments (ChromatiNet® meshes red, black and in full sun), with seven repetitions. There was a significant interaction between the proportions of ammonium and nitrate with the light environments for most of the evaluated parameters. It is concluded that M. spicata plants grown under balanced proportions of nitrate and ammonium in a light environment favorably favored the initial growth and physiological indications of this species.

Preliminary Evaluation of the Possible Occurrence of Pesticides in Groundwater Contaminated with Nitrates—A Case Study from Southern Poland

This paper addresses groundwater pollution and the potential presence of pesticides within the catchment areas of two reservoirs that are sources of drinking water. The two reservoirs are Goczałkowice and Kozłowa Góra, both in Southern Poland. Agricultural and rural areas dominate both catchments. Archival data showed local groundwater contamination with nitrates. This indicated the possible presence of pesticides in shallow groundwater. In total, 13 groundwater samples from shallow sandy aquifers were collected. All the samples were tested for the presence of 35 organophosphate pesticides and 28 organochlorine pesticides. Additionally, in order to determine the current groundwater conditions, physicochemical parameters were measured in the field, and water samples were subjected to analysis of their chemical composition (incl. the determination of nitrates). The research outcomes showed that pesticides were not detected above the detection limits in any of the samples. Due to variations in the persistence and degradation rates of pesticides, the occurrence of these substances in the groundwater environment and the possibility of their migration to aquifers should not be completely excluded. Natural processes and factors (e.g., sorption, biodegradation, hydrolysis and redox conditions) may gradually reduce the pesticide concentrations in groundwater. The chemical analyses revealed high concentrations of nitrates in the groundwater. This suggests the possible influence of agriculture and fertilizer application on groundwater quality; however, a proportion of NO3- ions may be connected with improper sewage management within the two catchments. The absence of pesticides in groundwater impacted by agriculture may result from processes occurring in the aquifer and the rapid degradation of these compounds due to photolysis and prevailing weather conditions. In the vicinity of dwellings, nitrates also originate from domestic wastewater. Thus, the occurrence of pesticides in groundwater contaminated with NO3 cannot always be expected.

Characteristics, sources and health risk assessment of PM2.5 in China's coal and coking heartland: Insights gained from the regional observations during the heating season

High emissions of particulate pollutants in a regional scale adversely affect global air quality, health welfare and climate change. The Fen-Wei Plain (FWP) of China is among the most polluted regions of China and worldwide due to its thriving coal and coking industry. However, the joint regional observations are scarce in the FWP of China. In this study, comprehensive measurements were performed in 11 FWP cities from November 15, 2019, to March 15, 2020 (the heating period). The results showed that the FWP experienced the severest PM2.5 (particulate matter with an aerodynamic diameter of 2.5 μm or less) pollution with an average concentration of 95.0 ± 52.4 μg/m3 despite the Chinese government's rolling out of a three-year action plan for clean air. Benefitted from desulfurization technologies, organic matter (OM) and nitrate became the most dominant contributors, accounting for averages of 28.3% and 22.2% of PM2.5, respectively. In addition to chemical conversion, as determined by the potential source contribution function analysis, atmospheric circulation within the FWP resulted in high concentrations of OM and NO3−. The major water-soluble ionic concentrations in PM2.5 were found in the order NO3− > SO42− > NH4+ > Cl− in the FWP. The observed elements accounted in total for 3.4% of the PM2.5 mass. For the spatial distribution of PM2.5-associated chemical species, OM ranged from 17.9 to 40.3 μg/m3, with the highest OM observed in Yuncheng. The proportions of NO3−/PM2.5 in the cities of Henan and Shaanxi Provinces were higher than those in Shanxi Province. Five or six kinds of PM2.5 sources were identified in the 11 FWP cities during the heating period including secondary sulfate and nitrate, vehicular exhaust, biomass burning and coal combustion or their mixing sources, industry and dust. The contribution of the secondary sulfate and nitrate comprised the largest source of PM2.5 (approximately 25.5%), while that of dust was the lowest (6.7%) in the FWP. The lifetime cancer risks in the 11 cities of the FWP from exposure to ambient PM2.5-bound elements ranged from 1.2 E−4 to 8.7 E−4, which were higher than the United States Environmental Protection Agency (U.S. EPA) acceptable level of 1 E−4; while the hazard quotients from exposure to ambient PM2.5-bound elements was more than 18, much higher than the U.S. EPA acceptable level of 1. This study provides insights on the heavy particulate pollution problem in highly polluted regions of China and up-to-date dataset to study climatic effect and health risk assessment caused by high PM loading.

Analyzing the increasing importance of nitrate in Taiwan from long-term trend of measurements

In recent years, many sample analyses have revealed that the proportion of nitrate (NO3−) in PM2.5 frequently exceeds that of other major PM2.5 species, such as SO42−, NH4+, and OC. This phenomenon has attracted considerable attention because it could change the direction of PM2.5 control policies. The present study analyzed the long-term trends of gaseous pollutants, PM2.5 and PM2.5 species. PM2.5 and precursor gases, such as SO2, NOX, and NMVOCs, showed obvious downtrends from 2005 to 2020, while O3 and NH3 remained roughly the mean level. In addition, the two stages (sampling period I: 2003–2009; sampling period II: 2015–2019) of PM2.5 composition analysis showed that the SO42−, OC, and EC concentrations obviously decreased annually while the NO3− concentrations did not. The proportion of NO3− in PM2.5 increased from 2.4% to 12.6% during sampling period I to 12.6%–23.9% during sampling period II when PM2.5 concentrations was higher than 35 μg m−3. NO3− and NH4+ were both highly correlated with PM2.5 in sampling period II, suggesting that NH4NO3 is the major chemical in PM2.5. Because most cities are under NH3-rich conditions, the control of NO3− will become the key to controlling PM2.5. According to the trends of O3, NO3−, and NH3, the amount of NH3, and the formation mechanism of NO3−, this study suggests that O3 can be regulated to control NO3− and thus control PM2.5. Methods of controlling O3 are beyond the scope of the current study but will be studied in the near future.

Evaluation of continuous emission reduction effect on PM2.5 pollution improvement through 2013–2018 in Beijing

Beijing has achieved significant air quality improvement over the past decade. In this study, we applied a simulation technique on pollutant monitoring data to investigate the contribution of emission reduction (ERE) and meteorological effects (ME) to the improvement of air quality. We measured the daily PM2.5 concentrations during four months (representing the four seasons) in 2013 and 2018. We found that the concentrations of NH4+, NO3−, and SO42− decreased from 2013 to 2018, but the proportion of NO3− in PM2.5 showed an apparent increase. Multiple scenarios were simulated using the WRF-CAMx model to determine the impact of ERE and ME on air pollution. The results showed that both variables positively contributed to the annual air quality improvement, with ERE contributing more than 70% to the total PM2.5 reduction. However, their seasonal contributions showed notable differences. In winter, ME contributed more than 40 μg/m3 to the PM2.5 decrease, which was much higher than that in other seasons. This suggests that the positive effect of pollutant emission reduction on air quality may have been weakened under extremely adverse meteorological conditions. Hence, the monitoring and modeling results were coupled to evaluate the secondary conversion degree. We found that the emissions of precursors, including SO2 and NOx, notably decreased, but both the local and regional conversion degrees increased from 2013 to 2018. Therefore, for effective air pollution reduction, we suggest that future air pollution mitigation measures should focus on reducing secondary pollution in Beijing.

Characteristics and Sources of Water-soluble Ion Pollution in PM2.5 in Winter in Shenyang

In order to explore the characteristics of PM2.5 and water-soluble ions in Shenyang in winter, the URG-9000D online monitoring system was used to continuously sample PM2.5 and gas components during 2018. The results indicated that the average concentration of PM2.5 in Shenyang during the sampling period was 80.67 μg·m-3, and the total water-soluble ion concentration ranged from 2.68 to 132.79 μg·m-3. Compared with clean days, the proportion of NO3-, SO42-, and NH4+ (SNA) in polluted days increased significantly, reached 43.7% of PM2.5. The rapid accumulation of SO2 in a short period of time made atmospheric PM2.5 explosively increase in Shenyang in winter. A Pearson correlation analysis showed that the correlation coefficients of SNA, Cl-, and PM2.5 were all above 0.78, indicating that the main contribution components of winter PM2.5 in Shenyang were SNA and Cl-. The apportionment of PMF sources indicated that the sources of pollutants in winter in Shenyang mainly included secondary reaction sources, coal and biomass combustion sources, and dust sources.

Characteristics and Source Apportionment of PM2.5 and O3 during Winter of 2013 and 2018 in Beijing

Beijing, the capital city of China, has achieved remarkable progress in terms of an improvement in air quality under strict control policies in the past 10 years from various sources. In this paper, the characteristics of fine particulate matter (PM2.5) and O3 in January 2013 and 2018 in Beijing are discussed on the basis of daily sample analysis and hourly monitoring data. It was found that the PM2.5 pollution for the month of January in Beijing has been greatly curbed. The SO42− concentration and proportion of PM2.5 decreased, while the proportions of NO3− and NH4+ increased. Organic matter represented the major component during the two periods with the proportions of 31.7% ± 8.2% and 31.4% ± 9.8%. The results of the Hybrid Single Particle Lagrangian Integrated Trajectory (Hysplit) model and Potential Source Contribution Function (PSCF) method showed that air mass from southern nearby regions accounted for 34% and 10% in 2013 and 2018, respectively, which was closely related to the pollution period. Thus, the input direction of air mass in January 2018 was more conducive to the diffusion of pollutants. Modeling results of the Weather Research and Forecasting model (WRF) coupled with Comprehensive Air Quality Model Extensions (CAMx) indicated that the contribution of industry sources to PM2.5 and O3 decreased from 2013 to 2018, while mobile sources increased. This was mainly due to the different control policies on various emission sources. In terms of O3 sources, more control measurements should be taken on volatile organic compounds (VOCs) due to its prominent effect on O3 concentration in both periods. The reduction in emissions and the meteorological conditions both contributed effectively to the sharp decrease in PM2.5 concentration. However, the change in weather conditions had the greater impact on the decrease in PM2.5 concentration, while the reduction in emissions was weakened as a function of this change.

Characteristics and Formation Mechanism of Three Haze Pollution Processes in Chengdu in Winter

Based on the online monitoring data of gaseous pollutants and components in PM2.5 from Chengdu super observatory of atmospheric environment, the meteorological factors and component characteristics of three haze pollution process in Chengdu from 2019 to 2020 were analyzed. The CMB model was adopted to simulate the sources and variation trends of PM2.5 pollution during the study period, and the causes of each pollution process were analyzed. The results showed that all the three pollution processes occurred under adverse meteorological conditions, where the relative humidity and temperature continued to rise and the wind speed and boundary layer height continued to decrease. The average daily relative humidity was greater than 70%, average daily temperature was greater than 8℃, average daily wind speed was less than 0.8 m ·s-1, and average daily boundary layer height was less than 650 m. During the three events of pollution, the main components were NO3-, OC, NH4+, and SO42-. Among them, the mass concentration and proportion of NO3- increased by 1.47-2.09 and 0.22-0.35 times, respectively, during the pollution period as compared to those during the clean period. NO3- was a key component of PM2.5 pollution during winter in Chengdu. During the three pollution processes, the mean values of SOR and NOR were 0.40 and 0.27, respectively, and the secondary transformation degree of SO2 and NOx was high. The conversion of SO2 to SO42- was mainly dominated by heterogeneous oxidation at night, and the conversion of NOx to NO3- was dominated by heterogeneous hydrolysis. The characteristics of the three processes were slightly different. Process Ⅰ showed evident secondary nitrate-dominated characteristics. During the period of rising PM2.5 concentration in process Ⅱ, it was mainly affected by coal emissions, but during the periods of high PM2.5 concentration, it was mainly affected by NO3-. Process Ⅲ was also a nitrate-dominated process, but emissions of fossil fuel combustion had increased during certain polluted periods. Secondary nitrate, secondary sulfate, motor vehicles, and coal combustion were the main pollution sources during the study period. The PM2.5 concentration was positively correlated with the contribution of secondary nitrate and negatively correlated with the contribution of dust source.

In situ continuous hourly observations of wintertime nitrate, sulfate and ammonium in a megacity in the North China plain from 2014 to 2019: Temporal variation, chemical formation and regional transport

Nitrate (NO3−), sulfate (SO42−) and ammonium (NH4+) in airborne fine particles (PM2.5) play a vital role in the formation of heavy air pollution in northern China. In particular, the increasing contribution of NO3− to PM2.5 has attracted worldwide attention. In this study, a highly time-resolved analyzer was used to measure water-soluble inorganic ions in PM2.5 in one of the fastest-developing megacities, Tianjin, China, from November 15 to March 15 (wintertime heating period) in 2014–2019. Severe PM2.5 pollution episodes markedly decreased during the heating period from 2014 to 2019. The highest concentrations of NO3− and SO42− were recorded in the heating period of 2015/2016. Afterwards, NO3− decreased from 2015/2016 (20.2 ± 23.8 μg/m3) to 2017/2018 (11.6 ± 14.8 μg/m3) but increased with increasing NOx concentrations during the heating period of 2018/2019. A continuous decrease in the SO2 concentration led to a decrease in SO42− from 2015/2016 (16.8 ± 21.8 μg/m3) to 2018/2019 (6.5 ± 8.9 μg/m3). The NO3− and SO42− concentrations increased as the air quality deteriorated. However, the proportion of NO3− and SO42− in PM2.5 slightly increased when the air quality deteriorated from moderate pollution (MP) to severe pollution (SP) levels. The average molar ratios of NH4+ to [NO3−+2 × (SO42−)] were 1.7, 0.9, 1.2, 1.2 and 1.5 for the heating periods of 2014/2015, 2015/2016, 2016/2017, 2017/2018 and 2018/2019, respectively, most of which were higher than 1.0, thus revealing an overall excess of NH4+ during the heating periods. However, the molar equivalent ratios of [NH4+] to [NO3−+2 × (SO42−)] were less than 1 under increasing PM2.5 pollution. The molar equivalent ratios of [NO3−]/[SO42−] were positively correlated with those of [NH4+]/[SO42−]. When the molar equivalent ratios of [NH4+]/[SO42−] were more than 1.5, those of [NO3−]/[SO42−] increased from close to 1 to higher values, indicating that the dominance of NO3− formation played an important role. The results of nonparametric wind regression exhibited distinct hot spots of NO3−, SO42− and NH4+ (higher concentrations) in the wind sectors between NE and SE at wind speeds of approximately 6–21 km/h. The southern areas in the North China Plain and parts of the western areas of China contributed more NO3−, SO42− and NH4+ than other areas to the study site. The abovementioned areas were also characterized by a higher contribution of NO3− than of SO42− to the study site and by NH4+-rich conditions. In summary, more efforts should be made to reduce NOx in the Beijing-Tianjin-Hebei region. This study provides observational evidence of the increasingly important role of nitrate as well as scientific support for formulating effective control strategies for regional haze in China.

Nitrogen wet deposition in the Three Gorges Reservoir area: Characteristics, fluxes, and contributions to the aquatic environment

Measurements of nitrate nitrogen (NO3−-N), ammonia nitrogen (NH4+-N), and dissolved organic nitrogen (DON) in precipitation were conducted at six different sites in the hinterland of the Three Gorges Reservoir (TGR) area from January 2016 to December 2017. The characteristics and the sources of nitrogen (N) species were identified. N flux of wet deposition in the hinterland of the TGR area were 13.56 ± 2.95 kg N ha−1 yr−1, of which the proportions of NO3−-N, NH4+-N and DON were 60.9%, 25.1% and 14.0%, respectively. N flux in urban area was significantly higher than those in suburban, agricultural, and wetland areas. Industrial activities, biomass burning, and secondary transformation were the main contributors of N in urban area. In agricultural area, biomass burning, crustal, and manure were main sources of N. In suburban area, mixed emissions from industry, agriculture, and crustal sources were primary contributors of N. For wetlands, the major contributions were from industrial sector and biomass burning. Additional, analysis of regional distribution of dissolved N deposition in the TGR area was conducted by combining current study data and previously published data between 2000 and 2017. N flux of wet deposition in the entire TGR area ranged from 12.17 to 51.93 kg N ha−1 yr−1, with an average of 26.81 kg N ha−1 yr−1. Regional N distribution was greatest in the tail region, followed by the head region, and then the hinterland in the TGR area. The amount of N entering the TGR directly through atmospheric wet deposition was 2906 t yr−1, accounting for 2.1% of the total N inputs. N load from wet deposition had exceeded the critical loads from that of the water, forest, and even some farmland ecosystems in the TGR area. Decreasing NH3 emissions from agricultural activities is the key to alleviate the regional N deposition.