Sulfur Oxidation Rate Research Articles

Spatiotemporal Characterization and Driving Factors of Fine Particulate Matter and Its Chemical Components in the Huaihe River Basin

According to the data sets of fine particulate matter （PM2.5） and its components in 35 cities in the Huaihe River Basin from 2015 to 2021, the temporal and spatial distribution patterns of pollutants were analyzed. The influence of meteorological factors on PM2.5 concentrations was examined using a random forest model. The original series of PM2.5, sulfate （SO42-）, nitrate （NO3-）, ammonium salt （NH4+）, organic matter （OM）, and black carbon （BC） were rebuilt using KZ （Kolmogorov-Zurbenko） filtering and multiple linear regression （MLR） to quantify the effects of meteorological conditions. The results demonstrated that from 2015 to 2021, the declining rates of PM2.5, SO42-, NO3-, NH4+, OM, and BC in the Huaihe River Basin were 4.71, 0.99, 1.05, 0.77, 1.01, and 0.19 μg·（m3·a）-1, respectively. The high mass concentrations of PM2.5 and its components were concentrated in the central and western regions of the HRB, whereas those in coastal and southern cities were lower. The variance contributions of the short-term, seasonal, and long-term components of PM2.5 to the original PM2.5 sequences in 35 cities were 51.6%, 35.9%, and 7.0%, respectively. The PM2.5 in coastal cities were more affected by the short-term components. The meteorological conditions were unfavorable for PM2.5 reduction in the HRB from 2015 to 2018, whereas the meteorological conditions supported the PM2.5 decrease from 2019 to 2021. From 2015 to 2021, the contribution rates of meteorological conditions to the long-term component reductions of PM2.5, SO42-, NO3-, NH4+, OM, and BC were 28.3%, 29.1%, 31.0%, 29.3%, 27.8%, and 28.6%, respectively. The contribution rates of meteorological conditions to the long-term PM2.5 reduction were 43.4%, 25.6%, 25.5%, and 20.6% in the HRB cities in Anhui, Shandong, Jiangsu, and Henan Provinces, respectively. With the decrease in PM2.5 concentration in the HRB, the sulfur oxidation rate （SOR） increased significantly, while the nitrogen oxide oxidation rate （NOR） changed little.

Heterologous expression of sulfur: quinone oxidoreductase (Sqr) to improve Thioalkalivibrio versutus D301 desulfurization performance.

Heterologous expression of sulfur: quinone oxidoreductase (Sqr) from Halomonas mongoliensis JS01, which is responsible for oxidizing sulfide to elemental sulfur, in Thioalkalivibrio versutus (T. versutus) D301 improves desulfurization. We expressed sqr in T. versutus D301 by conjugative transfer and then assayed its desulfurization capacity in an airlift reactor and analyzed its transcriptome at -380mV ORP. Our findings demonstrate that the D301-sqr+ strain, utilizing sodium sulfide as a sulfur source under optimal ORP conditions (-380mV), achieved an elemental sulfur yield of 95%. This represents an 8% increase over the T. versutus D301. Moreover, the sodium sulfide utilization rate for D301-sqr+showed a marked improvement [0.741vs. 0.651mmol∙(l·h)-1], with a concurrent increase in the rate of elemental sulfur production when compared to the T. versutus D301 (0.716vs. 0.518mmol ∙(l·h)-1). Transcriptome analysis revealed that the flavocytochrome c (fcc) and the sox system were differentially transcriptionally down-regulated in D301-sqr+ compared with the T. versutus D301. Heterologous expression of the gene sqr altered the transcription of related genes in T. versutus D301 sulfur oxidation pathway, increasing the yield of elemental sulfur and the rate of sulfur oxidation, and making D301-sqr+ more potential for industrial applications.

Yearly variations of water-soluble ions over Xi'an, China: Insight into the importance contribution of nitrate to PM2.5

Water-soluble inorganic ions (WSIIs) in PM2.5 play an important role in the formation of air pollution, which in turn affects climate change and human health. The formation pathways and factors influencing WSIIs have received extensive attention. Here, we analyzed the contents of nine WSIIs in PM2.5, collected from 2015 to 2021 in Xi'an City, China, with the aim of investigating long-term atmospheric pollution changes. Sulfate (SO42−), nitrate (NO3−), and ammonium (NH4+) together contributed to 66.8%–88.1% and Ca2+ accounted for 5.1%–13.1% of total WSIIs. The relative content of SO42− exhibited a gradually decreasing trend (from 49.80% in 2015 to 29.98% in 2021), whereas NO3− was increased in the same time period (from 13.96% in 2015 to 29.92% in 2021). In addition, the nitrogen oxidation rate showed an annual increase in this period, whereas the sulfur oxidation rate decreased, and their fitted curves intersected in 2019. The key finding of this study is that the air pollution pattern in Xi'an has changed from sulfate-dominated to nitrate-dominated particles, as evidenced by the feature importance results of the random forest model. We propose that more attention should be paid to vehicle emissions and road dust as pollution sources. Overall, the findings of this study serve as a useful reference to aid relevant authorities in devising more effective policies for controlling PM2.5 pollution at its source.

Effects of " Air Pollution Prevention and Control Action Plan " on PM2.5 and Chemical Compositions in Zhengzhou in Polluted Winters

The Air Pollution Prevention and Control Action Plan （APPCAP） was promulgated in China in 2013. To explore the effectiveness of APPCAP on PM2.5 in winter in Zhengzhou, PM2.5 samples were collected in Zhengzhou Monitoring Center during December 2013 and December 2018. The chemical composition of PM2.5 was analyzed, including EC, OC, water soluble ions, and metal elements. Pollution episodes under different stages were selected to investigate the changes in PM2.5 concentration and composition. The results showed that： ① The average concentration of PM2.5 in winter in Zhengzhou decreased from （215.38 ±107.28） μg·m-3 in 2013 to （77.45 ±49.81） μg·m-3 in 2018, with a decrease rate of 64%. ② The concentrations of EC, K+, SO42-, and Cl- decreased by 85%, 80%, 78%, and 72%, respectively, and the decrease rate in OC, NH4+, and NO3- was 50%, 41%, and 32%, respectively. ③ Compared with those in winter of 2013, the ratios of OC/EC in winter of 2018 increased by 2.6 times, and the proportion of secondary organic carbon in OC increased to 57%； meanwhile, values of sulfur oxidation rate and nitrogen oxidation rate increased by 1.5 and 1.0 times, respectively, indicating heavy secondary pollution in Zhengzhou. ④ The mass ratios of NO3-/SO42-increased from 0.8 ±0.2 in 2013 to 2.5 ±1.0 in 2018, indicating that the contribution of mobile sources increased and surpassed fixed sources as the main source in Zhengzhou. ⑤The comparison results of different stages of the heavy pollution process showed that ρ（PM2.5） decreased significantly in 2018 compared with that in 2013, with the peak concentration decreasing by 61%. The main chemical composition changed from OC, NO3-, SO42-, and NH4+ to OC, NO3-, and NH4+. The results indicated that the primary emission source control in Zhengzhou had achieved remarkable effects, but the contribution of secondary generation to PM2.5 showed an elevated trend； thus, the influence of secondary generation requires further attention in the future.

Characteristics and Cause of PM2.5 During Haze Pollution in Winter 2022 in Zhoukou, China

The characteristics and main factors of causes of haze in Zhoukou in January 2022 were analyzed. Six air pollutants, water-soluble ions, elements, OC, EC, and other parameters in fine particulate matter were monitored and analyzed using a set of online high-time-resolution instruments in an urban area. The results showed that the secondary inorganic aerosols(SNA), carbonaceous aerosols(CA, including organic carbon OC and inorganic carbon EC), and reconstructed crustal materials(CM, such as Al2O3, SiO2, CaO, and Fe2O3, etc.) were the three main components, accounting for 61.3%, 24.3%, and 9.72% in PM2.5, respectively. The concentrations of SNA, CA, CM, and SOA were increased, accompanied with higher AQI. The sulfur oxidation rate(SOR) and nitrogen oxidation rate(NOR) in January were 0.53 and 0.46, respectively. The growth rates[μg·(m3·h)] of sulfate and nitrate were 0.027(-5.89-9.47, range) and 0.051(-23.1-12.4), respectively. During the haze period, the growth rates of sulfate and nitrate were 0.13 μg·(m3·h)-1and 0.24 μg·(m3·h)-1, which were 4.8 and 4.7 times higher than the average value of January, respectively. Although the sulfur oxidation rate was greater than the nitrogen oxidation rate, the growth rate of nitrate was approximately 1.8 times that of sulfate owing to the difference in the concentration of gaseous precursors and the influence of relative humidity. The growth rates of nitrate in SNA were significantly higher than those of sulfate on heavily polluted days. The values of SOR, NOR, and concentrations of SNA and SOA during higher AQI and humidity periods were higher than those in lower AQI and humidity periods. The Ox(NO2+O3) decreased with the increase in relative humidity. The SOA was higher at nighttime, increasing faster with the humidity than that in daytime. Under the situation of lower temperature, higher humidity, and lower wind speed, the emission of gaseous precursors of SNA requires further attention in Zhoukou in winter. Advanced control strategies of emissions of SO2 and NO2, such as mobile sources and coal-burning sources, could reduce the peak of haze in winter efficiently.

Characteristics and Generation Mechanism of Secondary Inorganic Ions in PM2.5 in Changsha-Zhuzhou-Xiangtan City Group

Secondary inorganic ions, the main components of atmospheric PM2.5, are a dominant contributor to haze formation. The detailed characteristics and main generation mechanism of secondary inorganic ions in PM2.5 are still unclear in the Changsha-Zhuzhou-Xiangtan City Group, which is suffering from severe haze pollution, particularly in the autumn and winter seasons. For our study, we collected PM2.5 samples in November 2020 and January 2021 from four urban sites in the Changsha-Zhuzhou-Xiangtan City Group. Secondary inorganic components such as SO42-, NO3-, and NH4+ in PM2.5 were quantified. The average values(μg·m-3) of ρ(SO42-), ρ(NO3-), and ρ(NH4+) in autumn and winter were(5.2±2.5) and(7.9±4.8),(4.1±2.2) and(7.2±4.2), and(17.1±10.5) and(7.8±5.2), respectively. During the heavy haze pollution events in winter, the sum of ρ(SO42-), ρ(NO3-), and ρ(NH4+)(SNA) contributed 72.7% to the growth of PM2.5 mass concentration, and ρ(NO3-) accounted for 41.2%. This result suggested that the generation of NO3- was the key factor leading to the formation of winter haze pollution. In the polluted stage, high aerosol water content(AWC) promoted the rapid secondary generation of SNA, whereas adverse meteorological conditions also led to the accumulation of pollutants. The values of sulfur oxidation rate(SOR) and nitrogen oxidation rate(NOR) were still high in the dissipation stage. It indicated that the PM2.5 concentration fell due to the reduction in primary emissions and favorable weather conditions in dissipation, instead of the weakening of secondary generation of SNA. Compared to that in autumn, the higher AWC concentration, pH value, and lower temperature in winter were the main factors for the higher ρ(NO3-)/ρ(PM2.5) and NOR values in the Changsha-Zhuzhou-Xiangtan City Group. At the same time, the heterogeneous reaction was the main generation pathway of NO3-, when the AWC concentration was high in winter. Affected by aerosol pH value and generation rate, the liquid-phase oxidation reactions of H2O2 and SO2 were the main generation pathways of SO42- in autumn and winter in the Changsha-Zhuzhou-Xiangtan City Group. Compared to that in autumn, the higher AWC was more conducive to forming SO42-, which led to higher SOR in winter.

Temporal Variation and Potential Sources of Water-Soluble Inorganic Ions in PM2.5 in Two Sites of Mexico City

This study presents the characterization and source apportionment of water-soluble inorganic ions (WSII), contained in particulate matter with an aerodynamic diameter equal to or less than 2.5 μm (PM2.5), performed using the positive matrix factorization model (PMF). PM2.5 were collected in Mexico City from two sites: at Merced (MER), which is a residential location with commercial activities, and at Metropolitan Autonomous University (UAM), which is located in an industrial area. The monitoring campaign was carried out across three seasons named Hot Dry (HD) (March–June), Rain (RA) (July–October), and Cold Dry (CD) (November-February). PM2.5 concentration behavior in both sites was similar, following the order: CD > HD > RA. The UAM site exhibited higher concentrations of PM2.5, of the five cations (Na+, Mg2+, Ca2+, K+ and NH4+), and of the four anions (Cl−, SO42−, NO3− and PO43−) than MER, since the UAM site is surrounded by several industrial zones. PM2.5 average concentrations for UAM and MER were 28.4 ± 11.2 and 20.7 ± 8.4 μg m−3, respectively. The ratio of cation equivalent to anion equivalent (CE/AC) showed that aerosol pH is acidic, which was confirmed by direct pH measurements. The sulfur oxidation rate (SOR) was 20 times larger than the nitrogen oxidation rate (NOR). Additionally, SO42− was the most abundant ion during the whole year, especially during the CD season with 5.13 ± 2.5 μg m−3 and 4.9 ± 3.6 μg m−3 for UAM and MER, respectively, when solar radiation displayed a high intensity. On the opposite side, the conversion of NO2 to NO3−, respectively, was low. The air mass backward trajectories were modeled using the National Oceanic and Atmospheric Administration (NOAA-HYSPLIT), which allowed us to know that differences in the mass trajectories during the days with higher concentrations were due to an effect of air recirculation, which favored PM2.5 accumulation and resuspension. On the other hand, on the days with less PM2.5, good air dispersion was observed. The main sources identified with the PMF model were secondary aerosol, vehicular, industrial crustal, and biomass burning for UAM, while for MER they were vehicular, secondary aerosol, and crustal.

Characteristics of Seasonal PM1 Chemical Components in the urban area of Ansan

In this study, chemical properties of particulate matter (PM<sub>1</sub>) present in the urban area of Ansan in 2021 were analyzed using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Intensive observation was conducted during the measurement periods of spring (22 days), summer (29 days), autumn (60 days), and winter (29 days). High concentrations of PM<sub>1</sub> were observed when a wind speed was low (< 0.81 m/s) and a direction of air flow was the east. PM<sub>1</sub> concentration was the highest in spring (March), followed by summer (June and August), winter (December), and autumn (September and October). The main components of PM<sub>1</sub> were organic, followed by nitrate, ammonium, and sulfate. The ratio of organic oxygen to organic carbon (O/C) was high in summer (0.64) and low in winter (0.51); conversely, the ratio of organic hydrogen to organic carbon (H/C) was higher in winter (1.66) than in summer (1.58). As for the oxidation rates of inorganic components, the nitrogen oxidation rate and sulfur oxidation rate were the highest in spring (NOR, 0.12; SOR, 0.64), which directly affected the rise in PM<sub>1</sub> mass concentration in spring. Highly soluble nitrate was the largest component among the inorganic components of PM<sub>1</sub>, and the PM<sub>1</sub> was found to be rich in ammonium in all seasons. PM<sub>1</sub> mass concentration and chemical composition increased with an increase of relative humidity (RH): the concentration of PM<sub>1</sub> in wet conditions (RH > 60%) was found to be more than twice of that in dry conditions (RH < 40%). The largest component of PM<sub>1</sub> in Ansan consisted of organic compounds; however, a high proportion of inorganic components, including nitrate, was also recorded.

Classification and sources of extremely severe sandstorms mixed with haze pollution in Beijing

Air quality has significantly improved in China; however, new challenges emerge when dust weather is combined with haze pollution during spring in northern China. On March 15, 2021, an extremely severe sandstorm occurred in Beijing, with hourly maximum PM10 and PM2.5 concentrations reaching 5267.7 μg m−3 and 963.9 μg m−3, respectively. Continuous sandstorm events usually lead to complicated pollution status in spring. Three pollution types were identified disregarding the time sequence throughout March. The secondary formation type was dominant, with high ratios of PM2.5/PM10 (mean 74%) and PM1/PM2.5 (mean 52%). This suggests that secondary transformations are the primary cause of heavy pollution, even during the dry seasons. Sandstorm type resulted in dramatic PM10 levels, with a noticeable decrease in PM2.5/PM10 levels (27%), although PM2.5 levels remain high. The transitional pollution type was distinguished by an independent increase in PM10 levels, although PM2.5 and PM1 levels differed from the PM10 levels. Throughout March, the sulfur oxidation rate varied considerably, with high levels during most periods (mean 0.52). A strong correlation indicated that relative humidity was the primary variable promoting the formation of secondary sulfate. Sandstorms promote heterogeneous reactions by providing abundant reaction surfaces from mineral particles, therefore aggravating secondary pollution. The sandstorm air mass from the northwest passing through the sand sources of Mongolia carried not only crustal matter but also organic components, such as bioaerosols, resulting in a sharp increase in the organic carbon in PM2.5.

An integrated biohydrometallurgical approach for the extraction of base metals from printed circuit boards

This study evaluated a novel two-step process for biological lixiviant generation to facilitate base metals leaching from waste printed circuit boards (PCBs). In the first step, crushed waste sulfur pastilles, a by-product of the petroleum industry, were biologically oxidised to produce biogenic H2SO4. The acidified effluent containing biogenic H2SO4 was then supplemented with ferrous iron (20 g L−1) in the second step, where it was biologically oxidised to produce ferric iron. The recovered biolixiviant was then used for base metal leaching from PCBs. The biological sulfur oxidation rate was 0.43 g L−1 d−1 with oxidation efficiency 43%, and the biological iron oxidation rate was 5.93 g L−1 d−1 with oxidation efficiency 96.5%. Acidithiobacillus caldus was primarily responsible for the oxidation of waste sulfur, whereas the iron oxidation was achieved by a microbial consortium dominated by Acidithiobacillus ferrooxidans. The leaching of base metals from PCBs using the biogenic lixiviant was investigated at various experimental conditions to determine leaching efficiency. Leaching parameters tested in this study included temperature (25-45 °C), aeration, PCB pulp density (PD, 1 and 5%), pH control, leaching reactor configuration, and pre-treatment of PCBs by ashing. The results showed that increasing temperature significantly increased (p < 0.05) metal extraction from PCBs using biogenic lixiviants. Aeration did not improve leaching efficiency when compared to vigorous mixing. High leaching efficiencies for Cu (97.9%), Ni (80.1%), Al (91.0%) and Zn (99.7%) were obtained at 45 °C without aeration at a 1% PD and a pH range of 1.25 to 1.64. Controlling pH to a set point of pH 1.4 with feedback-dosing of 2 M H2SO4 significantly increased (p < 0.05) the leaching efficiencies (78.8% Cu, 71.3% Ni, 85.3% Al and 90.6% Zn) at 35 °C as compared to leaching without pH control. Changing the leaching process from batch to sequential leaching (5% PD) also enabled higher extraction for Cu (92.4%), Ni (92.6%), Al (82.2%) and Zn (99.8%) when two cycles of lixiviant replacement were undertaken over 96 h. Pre-treatment of PCBs by ashing at 500 °C for 1 h resulted in high leaching efficiencies for Cu (93.7%), Ni (76.1%), Al (85.4%) and Zn (95.8%) using biogenic H2SO4 at 1% PD. This study showed that by separating the unit processes for biogenic lixiviant generation from the leaching process, the optimisation of biogenic lixiviant production and PCB leaching parameters could be effectively achieved without compromising the growth and activity of the microorganisms.

A novel rapid and selective microbially thiosulfate bioleaching of precious metals from discarded telecommunication printed circuited boards (TPCBs)

In this study for the first time, microbe-produced thiosulfate is considered as a new lixiviant in bioleaching of precious metals from discarded TPCBs. The effects of significant parameters for the selective over bio-production of thiosulfate (S2O32−) and sulfate (SO42−) were investigated. The cultivation of Acidithiobacillus thiooxidans in the 9K medium with inhibitor (3.2 mg/L KCN) by pH adjustment, led to the overproduction of thiosulfate up to 350 mg/L and significantly decreased sulfur oxidation rate to sulfate to 6%. In contrast, without inhibitor and pH adjustment considerably increased amounts of sulfate to 26000 mg/L by 83% of sulfur oxidation rate to sulfate. A 100% copper dissolution was obtained at optimum condition (Sulfate: 26000 mg/L; pH 0.5;H2O2: 5% (v/v); 20 g/L TPCBs; 24 h) prior thiosulfate bioleaching. In the next stage, at 10 g/L TPCBs, 31% (0.11 mg/gTPCB) gold and 40% (1.23 mg/gTPCB) silver after 48 h were successfully recovered by thiosulfate bioleaching.

The role of source emissions in sulfate formation pathways based on chemical thermodynamics and kinetics model

Sulfate is a major PM2.5 constituent and poses a significant threat to ecosystems and human health, which has attracted lots of attention to the sulfate formation mechanism. In recent years, there has been great scientific interest in the multiphase oxidation of SO2 in aqueous aerosol particles. Many factors are involved in the reaction process, including precursor SO2, oxidants/catalysts, and aerosol acidity, which are three channels closely related to the source emission. The conjoint analysis of source emissions and sulfate aqueous formation can provide a scientific basis for designing effective strategies, though the related research is extremely limited. Here, we applied an improved solute strength-dependent chemical Thermodynamics & Kinetics model (for aqueous pathway contribution) and the Partial Target Transformation-Positive matrix factor model (for source apportionment) to explore the role of source emission in sulfate aqueous formation. The results indicated H2O2 aqueous oxidation was the dominant pathway (65.9 %), and secondary nitrate source may grow together with sulfate formation from H2O2 pathway. H2O2 and TMI pathways were related to higher SOR (sulfur oxidation rate). TMI pathway was significant in summer (54.6 %) and increased with secondary sources and vehicle exhaust. NO2 pathway was more significant at low secondary source and high coal combustion (higher contribution of NO2 pathway appeared in winter, 24.7 %). While high formation rate of the O3 pathway always occurred at low source levels. Coal combustion and vehicle exhaust showed obvious effects on sulfate aqueous formation. Notably, aerosol acidity is a significant factor related to sources and plays a key role in sulfate formation. The result also suggested aerosol pH may be more important than the amounts of substances involved in the oxidation reaction. The findings in this work can provide useful information for better understanding sulfate aqueous formation and offer a scientific basis for designing strategies for air pollution control and sulfate mitigation.

Variations in Sulfur and Nitrogen Oxidation Rates in Summer Aerosols from 2014 to 2020 in Wuhan, China

To date, research regarding the changes of the sulfur and nitrogen rates in Wuhan during the summer is limited. In this study, we analyzed the air quality in Wuhan, China, using water-soluble ion, gaseous precursor, and weather data. A Spearman correlation analysis was then performed to investigate the temporal changes in air quality characteristics and their driving factors to provide a reference for air pollution control in Wuhan. The results indicate that SO2 in the atmosphere at Wuhan undergoes secondary conversion and photo-oxidation, and the conversion degree of SO2 is higher than that of NO2. During the summers of 2016 and 2017, secondary inorganic atmospheric pollution was more severe than during other years. The fewest oxidation days occurred in summer 2020 (11 days), followed by the summers of 2017 and 2014 (25 and 27 days, respectively). During the study period, ion neutralization was the strongest in summer 2015 and the weakest in August 2020. The aerosols in Wuhan were mostly acidic and NH4+ was an important neutralizing component. The neutralization factors of all cations showed little change in 2015. K+, Mg2+, and Ca2+ level changes were the highest in 2017 and 2020. At low temperature, high humidity, and low wind speed conditions, SO2 and NO2 were more easily converted into SO42− and NO3−.

Chemical characterization, source apportionment, and health risk assessment of PM2.5 in a typical industrial region in North China.

To clarify the chemical characteristics, source contributions, and health risks of pollution events associated with high PM2.5 in typical industrial areas of North China, manual sampling and analysis of PM2.5 were conducted in the spring, summer, autumn, and winter of 2019 in Pingyin County, Jinan City, Shandong Province. The results showed that the total concentration of 29 components in PM2.5 was 53.4 ± 43.9μg·m-3, including OC/EC, water-soluble ions, inorganic elements, and metal elements. The largest contribution was from the NO3- ion, at 14.6 ± 14.2μg·m-3, followed by organic carbon (OC), SO42-, and NH4+, with concentrations of 9.3 ± 5.5, 9.1 ± 6.4, and 8.1 ± 6.8μg·m-3, respectively. The concentrations of OC, NO3-, and SO42- were highest in winter and lowest in summer, whereas the NH4+ concentration was highest in winter and lowest in spring. Typical heavy metals had higher concentrations in autumn and winter, and lower concentrations in spring and summer. The annual average sulfur oxidation rate (SOR) and nitrogen oxidation rate (NOR) were 0.30 ± 0.14 and 0.21 ± 0.12, respectively, with the highest SO2 emission and conversion rates in winter, resulting in the SO42- concentration being highest in winter. The average concentration of secondary organic carbon in 2019 was 2.8 ± 1.9μg·m-3, and it comprised approximately 30% of total OC. The concentrations of 18 elements including Na, Mg, and Al were between 2.3 ± 1.6 and 888.1 ± 415.2ng·m-3, with Ni having the lowest concentration and K the highest. The health risk assessment for typical heavy metals showed that Pb poses a potential carcinogenic risk for adults, whereas As may pose a carcinogenic risk for adults, children, and adolescents. The non-carcinogenic risk coefficients for all heavy metals were lower than 1.0, indicating that the non-carcinogenic risk was negligible. Positive matrix factorization analysis indicated that coal-burning emissions contributed the largest fraction of PM2.5, accounting for 35.9% of the total. The contribution of automotive emissions is similar to that of coal, at 32.1%. The third-largest contributor was industrial sources, which accounted for 17.2%. The contributions of dust and other emissions sources to PM2.5 were 8.4% and 6.4%, respectively. This study provides reference data for policymakers to improve the air quality in the NCP.

Meteorological and chemical causes of heavy pollution in winter in Hohhot, Inner Mongolia Plateau

In January 2020, severe and persistent haze events occurred in the plateau city of Hohhot, which was one of the regions with the worst air quality in China. The monthly average concentration of PM1, PM2.5 and PM10 came to 74 μg·m−3, 106 μg·m−3 and 130 μg·m−3, respectively. Coal burning for heating, pollutant transport, and stable atmosphere led to frequent haze events. Local temperature inversion and regional neutral atmospheric stability provided good meteorological conditions for the accumulation of particulate matter. The southerly and southeasterly winds carried in primary and secondary pollutants, as well as large amounts of water vapor, which was an important reason for the haze events this month. The large increase of fine particles was mainly caused by the massive generation of sulfate and nitrate aerosols, with monthly average concentrations of 26 μg·m−3 and 20 μg·m−3, respectively. During the day, SO2 was rapidly converted to SO42− through photochemical and heterogeneous reactions under the effect of sufficient NO2 and high humidity. Meanwhile, the conversion of NOx to NO3− was also enhanced. During the night, suspended fine particles generated during the day accumulated, and the increased humidity strengthened the oxidation of S(IV) to SO42− again and NO2 and N2O5 to NO3− under the effect of NO2 and HONO. The sulfur oxidation rate (SOR) and nitrogen oxidation rate (NOR) rose from ~0.20 and ~0.10 in the cleaning period to ~0.60 and ~0.30 in the pollution period, respectively. In addition, the setting off of fireworks, firecrackers and the traditional bonfires caused a steep rise in PM2.5 to ~1120 μg·m−3 at midnight on the Chinese Spring Festival. A strong dry north wind broke the static and neutral structure of the atmosphere and completely remove the pollutants from the region.

Characteristics of Water-soluble Ions in an Autumn Haze Process in the Southern Sichuan Urban Agglomeration After the Implementation of China's Air Pollution Prevention and Control Action Plan

To investigate the PM2.5 pollution in the southern Sichuan urban agglomeration after the implementation of China's Air Pollution Prevention and Control Action Plan (APPCAP), PM2.5 samples were simultaneously collected in four cities (Neijiang, Zigong, Yibin, and Luzhou) from November 7 to 19, 2018. The pollution characteristics of PM2.5 and main water-soluble ions were analyzed in combination with the synoptic situation, and the influence of regional transport on atmospheric pollution was also discussed in this study. The results showed that the mean ρ(PM2.5) in this region was (67.2±38.3) μg·m-3, being highest in Luzhou and lowest in Neijiang. The proportion of SNA (SO42-, NO3-, and NH4+) in PM2.5 was 33.3%, among which NO3- was dominant. From the intermediate stage (2015) to the end(2018) of the implementation of APPCAP, ρ(PM2.5) values were increased by 13.8%, 47.2%, and 69.1% in Neijiang, Yibin, and Luzhou, respectively, though unchanged in Zigong. Due to the significant reduction in ρ(SO2) but slight decrease or increase in ρ(NO2), as well as the lack of controlling NH3 emissions, from 2015 to 2018, ρ(NO3-) had increased by 36.7%-116.0%, whereas ρ(SO42-) decreased by 19.8%-40.2%, and ρ(NH4+) changed slightly in four cities. On haze days, the nitrogen oxidation rate (NOR) increased by 60.0%-118.2%, whereas the sulfur oxidation rate (SOR) increased slightly or decreased, leading to a significant increase in ρ(NO3-) (2.7-3.0 times that on clean days) and NO3-/SO42- mass ratios (1.7-1.9 on haze days). These values indicated that the secondary formation of nitrate was the dominant chemical mechanism in this haze process. On haze days, the PM2.5 pollution in this region was mainly affected by the regional transport within Sichuan Basin, particularly by the northeasterly air masses passing through Chongqing.

THE INFLUENCING FACTORS OF SO42- AND NO3- IN PM10 IN JINHUA, CHINA

Sulfate (SO42-) and nitrate (NO3-) are the main secondary inorganic components in atmospheric particulates. It is of great significance to understand the formation and evolution of air pollution in the process of air pollution. In this study, samples of PM10 were collected in Jinhua City in eastern China from December 2019 to January 2020 and from June 2020 to August 2020, and also analyzed the influence of different meteorological conditions and gaseous pollutants on the formation of SO42- and NO3- in PM10. The results show that high relative humidity has a significant effect on the increase of sulfur oxidation rate (SOR) in winter, indicating that the winter liquid phase reaction is more conducive to the formation of SO42-. SOR and nitrogen oxidation rate (NOR) decrease with increasing temperature in winter, and increase with increasing temperature in summer. The light intensity has an important promoting effect on both SOR and NOR, indicating that the photochemical reaction is beneficial to the formation of SO42- and NO3-. Both the gaseous precursors SO2 and NO2 have significant promoting effects on the formation of SO42- and NO3- in winter, and the promoting effect of O3 on NOR is higher than that on SOR, indicating that atmospheric oxidation capacity has a greater effect on the formation of NO3-, and the effect of CO on SOR is higher than that on NOR, and there is a negative correlation with SOR.

Particles liquid water and acidity determine formation of secondary inorganic ions in Urumqi, NW China

Secondary atmospheric pollutants are an important component of the particles found in Urumqi city, China, Further, secondary inorganic aerosols, in particular, increase significantly during the winter heating period. In this study, samples collected from October 2017 to August 2018 from Urumqi were analyzed. Results showed that the average concentration of water-soluble inorganic ions (WSIs) in the heating period (86.9 ± 31.1 μg·m−3) was significantly higher than that in the non-heating period (14.1 ± 8.67 μg·m−3). SNA (SO42−, NO3−, NH4+) accounted for 90.7% of the total WSIs (TWSIs) in the heating period. Simulations revealed that the in situ pH (3.1) was higher in the heating period than that in non-heating period (0.66) when they were calculated by the aerosol thermodynamic model. The particles were found to be acidity during the entire period. The liquid water content of the particulates (LWC) was found to higher in the heating period (55.5 ± 51.8 μg·m−3) than the non-heating period (21.3 ± 40.3 μg·m−3). The average nitrogen oxidation rate (NOR) and sulfur oxidation rate (SOR) were 0.16 and 0.36, respectively, indicating a significant secondary formation of nitrate and sulfate in the atmosphere of Urumqi. Further analysis indicated that sulfate was significantly affected by the LWC and acidity of the particulates; nitrate was produced under ammonia-rich conditions in Urumqi, and the LWC facilitated the production of nitrate. This study provides information about the formation of secondary sulfate and nitrate aerosols during different periods in suburban Urumqi.

Effect of Liquid Water Content of Particles and Acidity of Particulate Matter on the Formation of Secondary Inorganic Components in Xinjiang Petrochemical Industrial Area

Secondary species are dominant components of PM2.5 in Dushanzi, Xinjiang. It is crucial to investigate the conversion process of secondary components in the atmosphere for regional air pollution control. The water-soluble components were analyzed for samples collected from Dushanzi District of Xinjiang from September 2015 to July 2016. The results showed that the total water-soluble ions (TWSIs) showed a seasonal variation consistent with PM2.5, and the seasonal variation of the ions was in the order-winter (67.86 μg·m-3) > autumn (13.77 μg·m-3) > spring (10.09 μg·m-3) > summer (4.85 μg·m-3); secondary ions (NH4+, SO42-, and NO3-)-accounting for 98% of TWSIs in winter. The results of the aerosol thermodynamic model (E-AIM) that explores the particle liquid water and acidity in Dushanzi District showed that the particles in Dushanzi are acidic with an annual in-situ pH of 0.81, and the pH value of the winter samples was the highest (2.93). The seasonal variation of particles in water was of the order: winter (331.32 μg·m-3) > autumn (5.91 μg·m-3) > spring (5.46 μg·m-3) > summer (1.62 μg·m-3). The annual average nitrogen oxidation rate and sulfur oxidation rate were 0.13 and 0.47, respectively, indicating a secondary conversion of regional pollutants. Further analysis showed that the concentration of sulfate in the particle phase was significantly affected by liquid water content of particles and in-situ pH. The formation of nitrate was mainly caused by heterogeneous reactions under high water content of particle.

Seasonal Variation of Water-soluble Ions in PM2.5 in Xi'an

To explore the seasonal variations and sources of water-soluble ions, PM2.5 samples were collected from 2017 to 2018. Water-soluble ions including SO42-, NO3-, Cl-, F-, Na+, Mg2+, NH4+, K+, and Ca2+ were determined via ion chromatography. Furthermore, the existing form of NH4+, nitrogen oxidation rate (NOR), sulfur oxidation rate (SOR), and [NO3-]/[SO42-] ratio were explored. The results showed that dust, coal combustion, biomass burning, and secondary aerosols were the dominant contributors to water-soluble ions. Ca2+, SO42-, NH4+, and NO3- were the main water-soluble ions in PM2.5 in Xi'an. Correlation analysis results showed that NH4+ could not completely neutralize SO42- in spring; unneutralized SO42- could be mainly combined with K+ and Ca2+. NH4+ mainly existed in the form of ① NH4HSO4 and (NH4)2SO4 in summer; ② NH4HSO4 and NH4NO3 in autumn; and ③ (NH4)2SO4 and NH4NO3 in winter. The yearly mean values of SOR and NOR were 0.35 and 0.16, respectively, indicating a high secondary aerosol transformation rate during the study period. The [NO3-]/[SO42-] ratio showed Xi'an was mainly affected by stationary sources in spring and summer, while the contribution of mobile sources in autumn and winter was greater than stationary sources.