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Ambient volatile organic compounds (VOCs) were measured continuously from January 2018 to December 2020 at an urban site in Zhengzhou (China) to investigate their characteristics, sources, atmospheric oxidation capacity (AOC), and chemical reactivity. During the sampling period, the total concentration of observed VOCs was 94.3±53.1 µg m−3, and alkanes were the major VOC species, accounting for 58 % of the total. During the sampling period, the interannual variation in VOCs gradually reduced from 113.2±65.2 µg m−3 in 2018 to 90.7±52.5 µg m−3 in 2019 and 79.1±41.7 µg m−3 in 2020. Ethane and propane were the top two most abundant species during the 3-year observation period. Results showed that the total AOC, dominated by OH radical reactions, was 7.4×107 molec. cm−3 s−1. Total OH reactivity was 45.3 s−1, and it was mainly contributed by NOx. The AOC and ⚫OH reactivity both exhibited well-defined seasonal and interannual patterns. Therefore, control strategies should focus on the key species given their interannual and seasonal variations. Meanwhile, diagnostic ratios of VOC species indicated that VOCs in Zhengzhou were greatly affected by vehicle emissions and liquid petroleum gas/natural gas (LPG/NG). Positive matrix factorization analysis identified six sources: industrial sources, solvent use, vehicle emissions, LPG/NG, fuel burning, and biogenic sources. Vehicle emissions and industrial sources made the largest contributions to VOC emissions in each of the 3 years. The proportion of the contributions of vehicle emissions and LPG/NG increased with each passing year. However, the proportion of industrial and solvent sources presented a decreasing trend, which reflects the remarkable effect of control policies. The effect of VOCs on O3 formation suggests that vehicle emissions and solvent use remain key sources. Therefore, it is necessary to formulate effective strategies for reducing ground-level O3, and those sources mentioned above should be strictly controlled by the regulatory authorities.

The implementation of strict emission control during the 11th National Minority Games (NMG) in September 2019 provided a valuable opportunity to assess the impact of such emission controls on the characteristics of VOCs and other air pollutants. Here, we investigated the characteristics of VOCs and the O3 – NOx –VOC sensitivity comprehensively in Zhengzhou before, during, and after the NMG by delivering field measurements combined with WRF-CMAQ (Weather Research and Forecasting Community Multiscale Air Quality) model simulations. The average mixing ratios of VOCs during the control periods were 121 ± 55 µg m−3 and decreased by about 19 % and 11 % before and after emission reduction. The ozone precursors ( NOx ) also decreased significantly during the control period; however, the ozone pollution was severe during the entire observation period. Positive matrix factorization analysis indicated seven major sources of ambient VOCs, including coal combustion, biomass burning, vehicle exhausts, industrial processes, biogenic emissions, solvent utilization, and liquefied petroleum gas (LPG). The results show that the major source emissions, such as coal combustion and solvent utilization, were significantly reduced during the control period. As for ozone formation potential (OFP), the value during the control period was 183 ± 115 µg m−3 , which was 0.23 and 0.17 times lower than before and after the control period, respectively. Solvent utilization and combustion controls were the most important measures taken to reduce OFP during the NMG period. Control policies can effectively reduce carcinogenic risk. However, non-cancer risks of ambient VOC exposures were all exceeding the safe level (hazard quotient = 1) during the sampling periods, and emphasis on the reduction of acrolein emissions was needed. In addition, the WRF-CMAQ model simulation indicated that O3 formation was controlled by VOCs in Zhengzhou. The results of the Empirical Kinetic Modeling Approach showed that the NOx reduction in Zhengzhou might lead to higher ozone pollution. It is suggested that reduction ratios of the precursors (VOCs : NOx ) should be more than 2, which can effectively alleviate ozone pollution.

Heterojunction formation and morphology control have always been regarded as effective ways to improve the performance of visible-light-driven photocatalysts. In this study, a new facile strategy was applied to synthesize the Z-scheme GO/AgI/Bi2O3 heterojunction, where polyvinyl pyrrolidone (PVP) and γ-methacryloxypropyl trimethoxy silane (KH-570) were used to modulate the morphologies. Methyl orange and tetracycline hydrochloride were chosen as target contaminants to evaluate the photocatalytic properties of samples and the results revealed that 2% GO/AgI/Bi2O3 exhibited the best photocatalytic performance under visible-light irradiation. The enhanced photocatalytic activity can mainly attribute to Z-scheme heterojunction formed by the deposing of AgI and GO as well as the sufficient heterogeneous interfaces resulted from the improved morphology, which have effectively promoted the separation and transfer of electron-hole pairs. To deeply realize the enhanced performance of GO/AgI/Bi2O3 photocatalysts, the reaction kinetics, trapping experiments and photocatalytic mechanism were deduced.

Carbonaceous fractions throughout the normal period and lockdown period (LP) before and during COVID-19 outbreak were analyzed in a polluted city, Zhengzhou, China. During LP, fine particulate matters, elemental carbon (EC), and secondary organic aerosol (SOC) concentrations fell significantly (29%, 32% and 21%), whereas organic carbon (OC) only decreased by 4%. Furthermore, the mean OC/EC ratio increased (from 3.8 to 5.4) and the EC fractions declined dramatically, indicating a reduction in vehicle emission contribution. The fact that OC1-3, EC, and EC1 had good correlations suggested that OC1-3 emanated from primary emissions. OC4 was partly from secondary generation, and increased correlations of OC4 with OC1-3 during LP indicated a decrease in the share of SOC. SOC was more impacted by NO

Particle acidity is a fundamental property that affects atmospheric particulate chemistry. Synchronous online monitoring was performed at two urban sites, Zhengzhou (U-ZZ) and Anyang (U-AY), and three rural sites, Anyang (R-AY), Xinxiang (R-XX), and Puyang (R-PY) in Henan Province, during a haze episode to investigate the pH value and its driving factors in the agricultural regions of China. The pH values of particles calculated by ISORROPIA-II model at rural sites were slightly higher than those at urban sites, with the median (min–max) values of 5.2 (4.8–6.9, R-PY), 5.1 (4.7–6.5, R-AY), 4.9 (4.1–6.8, R-XX), 4.8 (3.9–5.9, U-AY), and 4.5 (3.8–5.2, U-ZZ). Sensitivity tests show that TNHx (total ammonium, gas + aerosol) followed by total sulfate were the most important factors that influenced the predicted pH. Generally, particle pH increased with a cation increase and decreases in anions, temperature, and relative humidity. Similar pH values (∼3.0) at the required NHx concentrations for the five sites indicated that the presence of excess NHx was likely important for the lower acidity of PM2.5 during the severe haze episodes in this region. Moreover, the concentrations of excess NHx may drive the higher pH values at rural sites, because of the higher excess NHx concentrations at rural sites than those at urban sites. The underlying influence of regional transport on local particle pH cannot be neglected, as it differs the chemical components of PM2.5 and meteorological conditions. Air masses transported from rural and agricultural regions may enhance the particle pH value in urban aerosols given the high pH of particles and high ammonia levels. These results suggest that ammonia is urgently needed to be involved in the regional strategy for the improvement of air quality in China.

Mineral dust particles play an important role in the formation of secondary inorganic aerosols, which largely contribute to haze pollution in China. During this study, a haze episode (haze days) and a typical haze process mixed with sandstorm (sandy haze days) were observed in Zhengzhou with a series of high-time-resolution monitoring instruments from November 22 to December 8, 2018. Concentrations of PM10 and crustal elements clearly increased in the sandy haze days. Concentrations of gaseous pollutants, metallic elements emitted from anthropogenic sources, nitrate, and ammonium during sandy haze days were slightly lower than those during the haze days but still obviously higher than those during the non-haze days. The sulfate concentrations, the sulfate fractions in PM2.5, and the sulfur oxidation ratios significantly increased in the sandy haze days. Heterogeneous reactions dominated the conversion of SO2 during the haze and sandy haze days. Enhanced SO2 conversion during the sandy haze days may be attributed to the high concentrations of transition metal ions from the sandstorm when the values of relative humidity (RH) were in 30%-70%, and high O3 at certain time points. Gas-phase NO2 oxidation reactions were the main pathways for nitrate formation. In the sandy haze days, higher nitrogen oxidation ratio (NOR) at daytime may be associated with higher RH and lower temperature than those in the haze days, which facilitate the gas-to-particle partitioning of nitrate; higher NOR values at night may be attributed to the higher O3 concentrations, which promoted the formation of N2O5.

Ambient volatile organic compounds (VOCs) were measured continuously to investigate their characteristics, sources, atmospheric oxidation capacity (AOC) and chemical reactivity from January 2018 to December 2020 at an urban site in Zhengzhou, China. In this study, the total concentration of observed VOCs was 38.2 ± 15.6 ppbv during the sampling period, with the characteristics that alkanes were the major VOC species, accounting for 60 % of total VOCs. During the sampling period, the inter-annual variation of VOCs gradually reduced from 45.0 ± 25.2 ppbv in 2018 to 36.7 ± 22.0 ppbv in 2019, and to 30.5 ± 15.4 ppbv in 2020. Ethane, ethene, and propane were the top three abundant species during the three-year observation period. The results showed that total AOC, dominated by OH radical reactions, was 7.4 × 107 molecules cm−3 s−1. The total OH reactivity was 45.3 s−1, and mainly contributed by NOx. The AOC and •OH reactivity exhibited well-defined seasonal and inter-annual patterns. Therefore, the control strategy should focus on key species among inter-annual and seasonal variations. Meanwhile, diagnostic ratios of VOC species indicated VOCs in Zhengzhou were greatly affected by vehicle emissions and liquefied petroleum gas/natural gas (LPG/NG). Positive matrix factorization analysis showed six sources were identified, consisting of industrial sources, solvent use, vehicle exhaust, LPG/NG, coal+biomass burning and biogenic sources. Vehicle emissions, solvent use and LPG/NG made the largest contributions to VOC emission in all three years. The proportion of the contribution of vehicle emissions and LPG/NG has increased with each passing year. However, the proportion of industrial and solvent sources presented a decreasing trend, which is speculated that the policy control effect is remarkable. The effect of VOCs on ozone formation suggests that vehicle emission and solvent utilization were still key sources. Therefore, it is necessary to formulate effective strategies for reducing ground-level O3, and those sources mentioned above should be strictly controlled by the regulatory authorities.

Secondary inorganic aerosol, including sulfate, nitrate, and ammonium (SNA), is a significant source of PM

The significant reduction in PM2.5 mass concentration after the outbreak of COVID-19 provided a unique opportunity further to study the formation mechanism of secondary inorganic aerosols. Hourly data of chemical components in PM2.5, gaseous pollutants, and meteorological data were obtained from January 1 to 23, 2020 (pre-lockdown) and January 24 to February 17, 2020 (COVID-lockdown) in Zhengzhou, China. Sulfate, nitrate, and ammonium were the main components of PM2.5 during both the pre-lockdown and COVID-lockdown periods. Compared with the pre-lockdown period, even though the concentration and proportion of nitrate decreased, nitrate was the dominant component in PM2.5 during the COVID-lockdown period. Moreover, nitrate production was enhanced by the elevated O3 concentration, which was favorable for the homogeneous and hydrolysis nitrate formation despite the drastic decrease of NO2. The proportion of sulfate during the COVID-lockdown period was higher than that before. Aqueous-phase reactions of H2O2 and transition metal (TMI) catalyzed oxidations were the major pathways for sulfate formation. During the COVID-lockdown period, TMI-catalyzed oxidation became the dominant pathway for aqueous-phase sulfate formation because the elevated acidity favored the dissolution of TMI. Therefore, the enhanced TMI-catalyzed oxidation affected by the elevated particle acidity dominated the sulfate formation, resulting in the slight increase of sulfate concentration during the COVID-lockdown period in Zhengzhou., Graphical abstract Image 1

The series Ag-AgI/BiOI-Bi2O3 visible-light-driven photocataslyts were successfully synthesized by solvothermal method. The as-synthesized samples were systematically characterized by XRD, SEM, TEM, EDS, BET, XPS, FR-IR, UV–vis DRS, photoelectrochemical measurements and EPR. The formation mechanism of the new composite photocataslyts was investigated and the simulate formation process had been illustrated. The photocatalytic properties of the samples were evaluated by degradation of methyl orange under visible-light irradiation. The results shown that the 30% Ag-AgI/BiOI-Bi2O3 photocataslyts possessed the best photocatalytic activity and the kinetics reaction models were followed pseudo-first-order kinetics. The enhanced photocatalytic performance could be attributed to the effective separation and transfer of electron–hole pairs resulting by the deposing of Ag-AgI nanoparticles and Bi2O3. The photocatalytic mechanism was deduced by trapping experiments and EPR, and the results demonstrated that h+, OH, O2− radicals played different roles in the degradation. Furthermore, a new Z-scheme multi-heterojunction mechanism was proposed basing on the results of trapping experiments and EPR.

To investigate the formation of haze during the cold season, continuous ambient air measurements were taken at an urban site in Zhengzhou from October 10, 2016 through December 31, 2016 using a single particle aerosol mass spectrometer. In total, 4,099,800 particles were analyzed and classified into eight major particle types: elemental carbon (EC, 36.7%), organic carbon (OC, 30.0%), ECOC (8.6%), K-rich (13.0%), levoglucosan (1.2%), metal (2.2%), NH4-K (2.1%), and dust (6.2%). By combining these measurements with correlation analysis and wind data, particle sources were determined to be vehicles, industrial emissions, coal combustion, biomass burning, secondary aerosols, agriculture, and dust. Additionally, analysis of mixing states indicated that particles underwent substantial aging and secondary OC particles were dominant OC species. Temporal profiles of meteorological parameters, mixing states, and particle types during a typical haze episode revealed that EC and OC particles were dominant components during haze formation, and a northeastern transport route (Anyang-Zhengzhou and Puyang-Xuchang) for OC particles was identified by potential source contribution function and concentration weighted trajectory analysis. Relatively higher humidity and lower temperature favored the formation of secondary inorganic aerosol. Wind direction and speed determined the transport, formation, and elimination of stagnant weather conditions. In sum, heavy haze during the cold season in Zhengzhou was observed due to extensive aerosol aging under adverse weather conditions (i.e., northeastern wind direction, wind speed 60%, temperature inversion, and uniform pressure field).

Size-resolved samples were collected using a 14-stage impactor during four seasons in Zhengzhou and analyzed for 26 elements to calculate the health risks from atmospheric particle-bound metals. High concentrations of heavy metals were observed in ultrafine (10.2 (Ni)–66.9 (Cd) ng m−3) or submicrometer (11.4 (Ni)–134 (Pb) ng m−3) mode in winter. Two size-dependent models were used to estimate the deposition of inhaled toxic metals in various regions of the human respiratory system. Results show that heavy metals deposited in the alveolar region ranged from 7.6 (As)–375 (Al) ng m−3 and were almost concentrated in ultrafine and fine modes. Cd (2.2–8.6) may cause accumulative non-carcinogenic health effects on children, and Cr (1.0 × 10−4–2.2 × 10−4) may lead to carcinogenic health risks for nearby residents around the sampling site. The major sources by principal component analysis that contributed to Cr and Cd in ultrafine and fine particles were coal combustion, vehicular and industrial emissions. The atmospheric dry deposition fluxes of Cr and Cd were between 0.7 and 1.9 μg m−2 day−1 calculated by a multi-step method. From the environmental and public health perspective, environmental agencies must control the emission of heavy metals in the atmosphere.

A total of 588 daily PM filters were collected at five sites in Zhengzhou, and the mass concentrations and sources of the elements were analyzed. The health risks and source regions of the particles and toxic elements were also estimated. The results indicated severe PM2.5 and PM10 pollution, especially at traffic sites. Additionally, the PM10-bound As far exceeded the Chinese standards. Although the total elemental levels were relatively low at the rural site, they were high at the GY site. High levels of crustal elements were also observed at the SSQ and HKG sites. Seasonal-variation analysis revealed that the crustal elements, more abundant in the PM10, occurred at high levels in spring; the combustion-source elements, more abundant in the PM2.5, caused significant pollution in winter; and the elemental concentrations were low in summer. The coefficients of divergence for the PM2.5 were slightly higher than those for the PM10. Vehicles, industry, coal combustion, oil fuel, dust, and biomass burning were important sources of the PM-bound elements. Although the ZM site was characterized by low traffic and high contributions from biomass burning and dust emission, the HKG site featured a high proportion of emissions from traffic sources, and the SSQ site was also highly affected by vehicular pollution. Whereas elements in the PM2.5 largely originated in combustion sources, those in the PM10 received greater contributions from dust sources. The levels of As and Ni posed intolerable carcinogenic risks (CR) and, along with that of Pb, also demonstrated significant non-CR risks. Children were more sensitive than adults to these risks, and the daily intake pathway demonstrated the highest CR and hazard index (HI) values. Obvious differences in the CR and HI values were detected between the various sites, suggesting the necessity of multiple-site studies for health risk assessment. Jiyuan, Jiaozuo, Xuchang, and Zhoukou; Pingdingshan and Nanyang; and Jiyuan, Jiaozuo, Xinxiang, Anyang, and Kaifeng were the main potential sources of PM2.5, PM10, and As, respectively.

Abstract: The implementation of strict emission control during the 11th National Minority Games (NMG) in September 2019 provided a valuable opportunity to assess the impact of such emission controls on the characteristics of VOCs and other air pollutants. Here, we investigated the characteristics of VOCs and the O3-NOx-VOCs sensitivity comprehensively in Zhengzhou before, during, and after the NMG by delivering field measurements combined with the WRF (Weather Research and Forecasting)-CMAQ (Community Multi-scale Air Quality) model simulations. The average mixing ratios of VOCs during the control periods were 34 ppbv, and cut down by about 16% before and after emission reduction. The ozone precursors (NOx) also decreased significantly during the control period; however, the ozone pollution was severe during the entire observation period. Positive Matrix Factorization analysis indicated seven major sources of ambient VOCs, including coal combustion, biomass burning, vehicle exhausts, industrial processes, biogenic emissions, solvent utilization and liquefied petroleum gas (LPG). The results show that the major source emissions, such as coal combustion and solvent utilization, were significantly reduced during the control period. As for ozone formation potential (OFP), the value during the control period was 183 μg/m3, which was 0.23 and 0.17 times lower than those before and after control period, respectively. Solvent utilization and combustion controls were the most important measures taken to reduce OFP during NMG period. Through control policies, it can effectively reduce carcinogenic risk. However, non-cancer risks of ambient VOC exposures were all exceeding the safe level (hazard quotient = 1) during the sampling periods, and emphasis on the reduction of acrolein emissions was needed. In addition, the WRF/CMAQ model simulation indicated that O3 formation was controlled by VOCs in Zhengzhou. The results of the Empirical Kinetic Modelling Approach showed that the NOx reduction in Zhengzhou might led to higher ozone pollution. It is suggested that reduction ratios of the precursors (VOCs : NOx) is more than 2, which can effectively alleviate ozone pollution.

The size distribution and formation of secondary inorganic aerosol play a key role in the increasing PM

Heterojunction formation and morphology control have always been regarded as effective ways to improve the performance of visible-light-driven photocatalysts. In this study, a new facile strategy was applied to synthesize the Z-scheme GO/AgI/Bi

To investigate the characteristics of elements in size-segregated atmospheric particulates, samples were collected using a 14-stage electrical low-pressure impactor (ELPI+) at an urban site in Zhengzhou from October 1 till 25, 2016, and analyzed for 25 elements. Results show that crustal elements were concentrated in coarse particles and toxic elements were concentrated in ultra-fine particles. The size distributions of Na, Mg, Al, Si, Ca, Fe, Ti, S and Cl were uni-modal with dominant peaks in the size range of 1.43–2.14 µm or 0.295–0.487 µm. K, P, Mn and Ba exhibited bimodal distributions, and the remaining elements showed multimodal distributions. Enrichment factor, correlation and principal component analyses indicated that vehicles were the dominant source of particles. Biomass burning, coal combustion and dust also contributed to the accumulation of particles. The elemental concentrations affected by different air masses are discussed to investigate the effects of regional transport. An increase in elemental concentrations related to vehicle and coal sources was observed when air masses came from eastern areas. Furthermore, air masses from the southeast could be a major factor in air pollution for Zhengzhou during special times, such as periods of biomass burning or naked cropland. When air masses came from the northwest, the majority of elements from dust and coal combustion were lower in concentration compared with clean days, while elements originating from vehicle emissions increased.

The nano-scale Ag3PO4 was successfully synthesized by the silver ammonia complexing precipitation method at room temperature. And the Graphene oxide (GO)/Ag3PO4 nanocomposites with different contents of GO were successfully synthesized using the electrostatic driving method. The as-prepared GO/Ag3PO4 nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–visible diffuse reflectance spectroscopy (UV–Vis DRS), confirming that Ag3PO4 were highly dispersed to GO sheet. The photocatalytic properties of GO/Ag3PO4 were evaluated by the degradation of Methyl Orange (MO) under visible light irradiation and solar irradiation respectively. The results showed that the photocatalytic efficiencies of GO/Ag3PO4 nanocomposites had enhanced largely and the kinetics reaction models were followed first-order. Furthermore, 5% GO/Ag3PO4 exhibited the highest photocatalytic activity on degradation of MO under visible-light irradiation. The improved photocatalytic performances of the GO/Ag3PO4 nanocomposites mainly attributed to the introducing of GO, which benefit for electron transfer and inhibit the recombination of electron–hole pairs, promoting the practical application of Ag3PO4 in water purification.

Particle acidity is a fundamental property that affects atmospheric particulate chemistry. Synchronous online monitoring was performed in two urban sites (e.g., Zhengzhou (U-ZZ) and Anyang (U-AY)) and three rural sites (e.g., Anyang (R-AY), Xinxiang (R-XX), and Puyang (R-PY)) in Henan Province during a haze episode to investigate the pH value and its driving factors in the agricultural regions of China. The pH values of particles calculated by ISORROPIA-II model at rural sites were slightly higher than those urban sites, with the median values in the order of 5.2 (4.8–6.9, R-PY) > 5.1 (4.7–6.5, R-AY) > 4.9 (4.1–6.8, R-XX) > 4.8 (3.9–5.9, U-AY) > 4.5 (3.8–5.2, U-ZZ). Sensitivity tests showed that excess ammonia mainly affected the pH value of PM2.5. Moreover, low ammonia determined the high sensitivities of particle pH to sulfate and nitrate at urban sites. Elevated sulfate and nitrate in aerosol caused high pH sensitivity to ammonia. Regional transport may enhance the particle pH value in urban aerosols given the high pH of particles and high ammonia levels in rural and agricultural regions. These results suggest that ammonia is urgently needed to be involved in the regional strategy for the improvement of air quality in China.

Mineral dust particles play an important role in the formation of secondary inorganic aerosols, which largely contribute to haze pollution in China. During this study, a haze episode (haze days) and a typical haze process mixed with sandstorm (sandy haze days) were observed in Zhengzhou with a series of high-time-resolution monitoring instruments from November 22 to December 8, 2018. Concentrations of PM

The series Ag-AgI/BiOI-Bi

The size distribution and formation of secondary inorganic aerosol play a key role in the increasing PM2.5 concentration. Size-segregated data including mass, number, and chemical component concentrations were obtained during a haze episode from January 12 to 23 in Zhengzhou to gain insight into the dominant factors for the growth of PM2.5. PM2.5 levels during two local processes (LP1 and LP2) were mainly affected by the accumulation and secondary formation of local pollutants. The transport process (TP) was affected by the air mass transported from the northern area of Zhengzhou. Results show that the growth of particle mass concentration in LP1 mainly occurred in the size range of 400–640 nm and 640–1000 nm. With the aggravated particles increases (LP2), 640–1000 nm and 1–1.6 μm particles dominated the increasing PM2.5 concentration. The particles carried by northern air mass (TP) were concentrated in the size range of 1–1.6 μm. Variation trends of hourly PM2.5 chemical components and size distribution of water-soluble inorganic ions suggested that the formation and growth of droplet-mode nitrate, sulfate, and ammonium dominated the increase of PM2.5, and the particle sizes of these components increased with the increasing PM2.5. High concentrations of aerosol water content and large surface area in droplet-mode were beneficial for the heterogeneous reactions for droplet-mode nitrate formation. Moreover, large particle surface area in droplet-mode particles also provided adequate carriers for the adsorption and condensation of gaseous HNO3 onto these particles. Elevated aerosol water, surface area, and particle acidity enhanced the H2O2 and transition metal (TMI) oxidation for aqueous-phase droplet-mode sulfate formation. The contribution of TMI-catalyzed oxidation significantly increased in LP2 because of the high TMI concentration and particle acidity. Relatively low aqueous-phase sulfate production rates in TP suggest that the observed high concentration of droplet-mode sulfate was mainly originated from the completely transformed SO42− carried by air masses. Moreover, droplet-mode particles exhibited moderate acidity, which enhanced the gas-particle partitioning of NH3(g)/NH4+(a).

Intensive temporary air pollution control measures were implemented in Zhengzhou (ZZ), a megacity in central China, and six neighboring cities during the 2019 National Games of Ethnic Minorities. The Community Multiscale Air Quality (CMAQ) model and a high-resolution local emission inventory were applied to evaluate the control measures. Reductions of ~35–60% of primary PM (PPM), 45–65% of VOCs, ~5% of NH3, 35–45% of NOx, and 30–70% of SO2 emissions in the central area (i.e., ZZ) and collaborative cities (i.e., the six neighboring cities) lead to significant reductions of daily PM2.5 by 25–45% in ZZ. Hourly concentrations of PM2.5 are reduced by as much as 100 μg m−3. Most of the reduction in PM2.5 is due to primary PM, and NO3−, SO42−, and NH4+ ion concentrations only decrease by 5–6%. Emission reductions in the collaborative cities contribute to 10–30% of the decrease in PM2.5 and PM10 in ZZ. Concentrations of daily maximum 8-hr (DM8H) O3 increase by 2–5% on high O3 days. Isopleth analysis suggests that the local molar reductions ratio of NOx to VOC needs to be

This study aimed to investigate the characteristics of the water-soluble ions concentrations in atmospheric particulates. Highly time-resolved measurements of inorganic ions associated with PM2.5 were conducted from December 1, 2017 to February 28, 2018 in Zhengzhou. The hourly mean and standard deviation of PM2.5 concentration during the observation episodes were 108.2 ± 80.7 μg/m3. The hourly mass concentration of PM2.5 increased from 8 μg/m3 to 438 μg/m3 throughout the entire observation. The proportion of water-soluble inorganic ions in PM2.5 was 52.5% throughout the entire observation period. The ions existed mainly in the form of (NH4)2SO4 and NH4NO3. The average mass concentration ratio of NO3− to SO42− was 1.9 ± 0.8 throughout the entire observation period, which initially increased and then decreased with the increased pollution level. The average ratio of the molar equivalent concentration of [NH4+] to that of [NO3− + SO42−] was 1.14 ± 0.27, which decreased with the increased pollution level. Homogeneous reactions played an important role in the formation of nitrate, while, the heterogeneous reactions were important in the formation of sulfate. Both of the values of sulfur oxidation ratios (SOR) and nitrogen oxidation ratios increased with relative high humidity (RH) condition; especially, the SOR values sharply increased when the RH was above 50%. The results of potential source contribution function model demonstrated that the western and northeastern regions of Zhengzhou had a greater influence on PM2.5 pollution in Zhengzhou. All these results suggested that reducing the emission of precursors of secondary inorganic ions was highly important in controlling PM2.5 pollution in Zhengzhou.

Episodic haze is frequently observed in Zhengzhou, China. Such haze typically contains secondary inorganic aerosols. In this paper, we explore the formation mechanisms of sulfate, nitrate, and ammonium (SNA) in Zhengzhou from January 3 to 25, 2018 based on the results of a series of online instruments and a size-segregated filter sampler. Our results document the remarkable contributions of SNA to winter haze episodes in Zhengzhou, where they account for about 50% of PM2.5 mass concentration. SNA were mainly concentrated in droplet-mode particles, which increased remarkably with the aggravation of the haze episode. In addition, KNO3 and NaNO3 were formed in droplet-mode particles and coarse-mode particles respectively with increasing PM2.5 concentration. The atmosphere during the observation period was ammonia-rich, and the aerosol was acidic under high PM2.5 concentration. Homogeneous reactions dominated the formation of nitrate. HONO photolysis played a more important role in the origin of OH radicals when O3 decreased during haze episode. Under high relative humidity (RH), nitrate formation was influenced by heterogeneous hydrolysis reactions of N2O5. Sulfates were mainly formed through aqueous-phase reactions, especially when the RH was higher than 60%. Under these conditions, there were amounts of liquid water content existed in aerosols. Finally, we observed enhanced conversion of SO2 and NO2 during snowfall periods. This effect may be attributable to the higher RH and O3 levels despite the unfavorable effects of wet deposition and low concentrations of gaseous precursors.