Development of a net ozone production rate detection system based on dual-channel cavity ring-down spectroscopy.

A novel system for measuring net photochemical ozone production rates in the atmosphere based on cavity ring-down spectroscopy (OPR-CRDS) was developed. The system consists of two chambers (a reaction chamber and a reference chamber) and a dual-channel Ox-CRDS detector. To minimize the wall loss of Ox in the chambers, the inner surfaces of both chambers are coated with Teflon film. The performance of the OPR-CRDS system was characterized. It was found that even though the photolysis frequency (J value) decreased by 10%, the decrease in the P(O3) caused by the ultraviolet-blocking film coating was less than 3%. The two chambers had a good consistency in the mean residence time and the measurement of NO2 and Ox under the condition of no sunlight. The detection limit of the OPR-CRDS was determined to be 0.20 ppbv/hr. To further verify the accuracy of the system, the direct measurement values of the OPR-CRDS system were compared with the calculation results based on radical (OH, HO2, and RO2) reactions, and a good correlation was obtained between the measured and calculated values. Finally, the developed instrument was applied to obtain the comprehensive field observations at an urban site in the Yangtze River Delta (China) for 40 days, the time series and change characteristics of the P(O3) were obtained directly, and the good environmental adaptability and stability of the OPR-CRDS system were demonstrated. It is expected that the new instrument will be beneficial to investigations of the relationship between P(O3) and its precursors.

A convolutional neural networks method for tropospheric ozone vertical distribution retrieval from Multi-AXis Differential Optical Absorption Spectroscopy measurements.

The vertical distribution of tropospheric ozone (O3) is crucial for understanding atmospheric physicochemical processes. A Convolutional Neural Networks (CNN) method for the retrieval of tropospheric O3 vertical distribution from ground-based Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements to tackle the issue of stratospheric O3 absorption interference faced by MAX-DOAS in obtaining tropospheric O3 profiles. Firstly, a hybrid model, named PCA-F_Regression-SVR, is developed to screen features sensitive to O3 inversion based on the MAX-DOAS spectra and EAC4 reanalysis O3 profiles, which incorporates Principal Component Analysis (PCA), F_Regression function, and Support Vector Regression (SVR) algorithm. Thus, these screened features for ancillary inversion include the profiles of temperature, specific humidity, fraction of cloud coverage, eastward and northward wind, the profiles of SO2, NO2, and HCHO, as well as season and time features to serve as sensitive factors. Secondly, the preprocessed MAX-DOAS spectra dataset and the sensitive factor dataset are utilized as input, while the O3 profiles of the EAC4 reanalysis dataset incorporating the surface O3 concentrations are employed as output for constructing the CNN model. The Mean Absolute Percentage Error (MAPE) decreases from 26 % to approximately 19 %. Finally, the CNN model is applied for inversion and comparison of tropospheric O3 profiles using independent input data. The CNN model effectively reproduces the O3 profiles of the EAC4 dataset, showing a Gaussian-like spatial distribution with peaks primarily around 950 hPa (550 m). Since the reanalysis data used for model training has been smoothed, the CNN model is insensitive to extreme values. This behavior can be attributed to the MAPE loss function, which evaluates Absolute Percentage Errors (APEs) of O3 concentration at all altitudes, resulting in varying retrieval accuracy across different altitudes while maintaining overall MAPE control. Temporally, the CNN model tends to overestimate surface O3 in summer by around 20 µg/m3, primarily due to the influence of the temperature feature in the sensitivity factor dataset. In conclusion, leveraging MAX-DOAS spectra enables the retrieval of tropospheric O3 vertical distribution through the established CNN model.

Vertically resolved meteorological adjustments of aerosols and trace gases in Beijing, Taiyuan, and Hefei by using RF model.

Air pollution represents a complex phenomenon defined by the presence of various gases and particulate matter, leading to intricate spatio-temporal fluctuations. This study aims to enhance our understanding of how meteorological factors influence trace gases and aerosols, exacerbating air pollution in various geographical locations, specifically in Beijing's Fengtai (BJFT), Taiyuan City (SXTY), and Hefei's Science Island (HFDP). The study employs 2D-MAX-DOAS observations and utilizes the Random Forest (RF) model to decouple the influence of meteorological conditions from pollutant data. The vertical profile of nitrogen dioxide (NO2), sulfur dioxide (SO2), formaldehyde (HCHO), and aerosols at each study site was classified into four distinct layers, followed by conducting a meteorological decoupling analysis on each layer. This decoupling analysis demonstrates that meteorology significantly influences aerosols across all sites, with reductions ranging from 75 % to 95 % after de-weathering. SO2 shows minimal susceptibility, with the changes ranging from ±20 % to ±60 % after de-weathering. Among all sites, BJFT's pollutants exhibit less susceptibility overall, while pollutants at HFDP are more susceptible. The findings further reveal significant meteorological interventions in pollutants in surface layers (0.05 km and 0.2-0.4 km) at BJFT, with some exceptions at SXTY. However, pollutants, particularly NO2 and aerosols in higher layers (0.6-0.8 km and 1.0-1.2 km) at HFDP, also experience significant meteorological interferences. The findings at HFDP and SXTY reveal that removing meteorological influence also adjusts the profile shape of pollutants. For instance, the NO2 profile at HFDP during the winter season shifted from a bimodal to an exponential shape after de-weathering. Overall, this study sheds light on the complex interplay between meteorological factors and trace gases at various altitudes across different geographic locations, offering insights crucial for holistic and effective pollution mitigation strategies.

The impact of evolving synoptic weather patterns on multi-scale transport and sources of persistent high-concentration ozone pollution event in the Yangtze River Delta, China.

High-concentration ozone pollution pose threats to ecosystems and human health. However, there is limited research on the impact of the alternating evolution of synoptic weather patterns (SWPs) on the multi-scale transport processes and sources of ozone. From June 14 to 18, 2018, a rare consecutive ozone pollution plagued in Hefei and broader Yangtze River Delta region (YRD). This study investigates the meteorological factors and sources using in-situ observational data and WRF-Chem model simulations. Analysis reveals a northeastern low-pressure system moving from north to south generated a cold front. This moving cold front facilitated the vertical transport of warm air masses carrying high-concentration ozone originating from North China. Subsequently, Ozone-rich air masses (ORMs) were transported over the YRD, influenced by the eastward movement of the Mongolian high-pressure system. Based on WRF-Chem model with NOx tagging mechanisms and WRF-FLEXPART backward simulations, it is confirmed that a notable atmospheric transport originated from North China region (NCR) to Hefei, especially on June 15. As the Mongolian high-pressure weakens and shifts east-southward, it carried ORMs generated by NOx emissions from the YRD, accumulating over the sea within the range of 120°E to 126°E and 25°N to 30°N. Both WRF-chem model results and TRopospheric Ozone and Precursors from Earth System Sounding (TROPESS) Chemistry Reanalysis dataset Version 2 (TCR-2) revealed the existence of ORMs in this geographic range. Subsequently, the ORMs carried out to sea by the weakened high-pressure system were reintroduced inland, influenced by southeast winds brought about by the peripheral circulation of typhoon "Gaemi". In summary, the alternating evolution of SWPs significantly influences multi-scale ozone transport from both the NCR and the YRD regions, making substantial contributions to this prolonged episode. These findings offer valuable insights for improving regional ozone pollution prevention and control mechanisms.

Evaluating the multi-variable influence on O3, NO2, and HCHO using BRTs and RF model.

This study addresses significant knowledge gaps in understanding the complex interplay between atmospheric chemistry and synoptic conditions. Using emerging machine learning techniques-Boosted Regression Trees (BRTs) and Random Forest (RF) models-we investigate the influence of synoptic conditions on pollutant levels. Several BRTs and RF models are developed to estimate surface concentrations of ozone (O3), nitrogen dioxide (NO2), and formaldehyde (HCHO). By considering a range of algorithmic structures and explanatory variables for each pollutant, the research aims to identify the most skillful predictive approaches and influential factors governing pollutant levels. The design seeks to highlight key determinants of concentration patterns without constraining the investigation to pre-defined model structures or explanatory variable sets. Introducing a novel methodology, Correlation Coefficient Differential Evaluation (C2DE), we quantitatively assess the influence of explanatory variables. C2DE reveals significant contributions from spatial variables (i.e., trajectory clusters at varying altitudes), formaldehyde to nitrogen dioxide ratio (FNR), and meteorological parameters. Specifically, spatial variables contribute approximately 28 % to O3 concentrations, while the FNR accounts for around 5.2-9.8 % of the overall influence. For NO2 and HCHO, spatial variables contribute around 26.5 % and 32.1 %, respectively. Moreover, when considering the combined influence of meteorological parameters, these collectively explain about 45.34 %, 35.31 %, and 45.41 % of the variations in O3, NO2, and HCHO concentrations, respectively. Thus, C2DE provides valuable insights into the relative contributions of these factors, aiding in the comprehensive evaluation of air quality dynamics. This underscores the need for a multifaceted approach to comprehending and effectively addressing air pollution before devising its control strategies.

A CNN-SVR model for NO2 profile prediction based on MAX-DOAS observations: The influence of Chinese New Year overlapping the 2020 COVID-19 lockdown on vertical distributions of tropospheric NO2 in Nanjing, China.

In this study, a hybrid model, the convolutional neural network-support vector regression model, was adopted to achieve prediction of the NO2 profile in Nanjing from January 2019 to March 2021. Given the sudden decline in NO2 in February 2020, the contribution of the Coronavirus Disease-19 (COVID-19) lockdown, Chinese New Year (CNY), and meteorological conditions to the reduction of NO2 was evaluated. NO2 vertical column densities (VCDs) from January to March 2020 decreased by 59.05% and 32.81%, relative to the same period in 2019 and 2021, respectively. During the period of 2020 COVID-19, the average NO2 VCDs were 50.50% and 29.96% lower than those during the pre-lockdown and post-lockdown periods, respectively. The NO2 volume mixing ratios (VMRs) during the 2020 COVID-19 lockdown significantly decreased below 400 m. The NO2 VMRs under the different wind fields were significantly lower during the lockdown period than during the pre-lockdown period. This phenomenon could be attributed to the 2020 COVID-19 lockdown. The NO2 VMRs before and after the CNY were significantly lower in 2020 than in 2019 and 2021 in the same period, which further proves that the decrease in NO2 in February 2020 was attributed to the COVID-19 lockdown. Pollution source analysis of an NO2 pollution episode during the lockdown period showed that the polluted air mass in the Beijing-Tianjin-Hebei was transported southwards under the action of the north wind, and the subsequent unfavorable meteorological conditions (local wind speed of < 2.0 m/sec) resulted in the accumulation of pollutants.

A three-channel thermal dissociation cavity ring-down spectrometer for simultaneous measurement of ambient total peroxy nitrates, total alkyl nitrates, and NO2.

A newly constructed thermal dissociation cavity ring-down spectrometer (TD-CRDS) for the simultaneous measurement of ambient total peroxy nitrates (ΣPNs, RO2NO2), total alkyl nitrates (ΣANs, RONO2), and NO2 was presented in this work. ΣPNs and ΣANs were detected as NO2 with the CRDS instrument after thermal dissociation. PNs and ANs completely dissociated at 180 °C and 360 °C, with conversion efficiencies of 96 % and 99 %, respectively. The effects of NO2 and NO on measurement in different temperatures and two types of thermal dissociation inlet (TDI) were further explored. The influence of ambient NO2 and NO on PNs and ANs in the improved TDI (TDI-2) was significantly improved. To further enhance the measurement accuracy, the consistency of the observed NO2 in the three channels was tested, which achieved good agreement. The detection limits of the TD-CRDS instrument for NO2, ΣPNs, and ΣANs were determined as 6.5, 6.8, and 8.6 pptv (10 s, 1σ), respectively. Observations of PNs and ANs were conducted in a suburban site in Hefei, China, from September 2-30, 2021, using the TD-CRDS instrument, and the consecutive time series of PNs and ANs were derived, verifying the capability of the TD-CRDS instrument for continuous field observations of ΣPNs and ΣANs.

McPrA - A new gas profile inversion algorithm for MAX-DOAS and apply to 50 m vertical resolution.

Air pollutants represent an environmental and health risk, and the methods for their effective assessment are of the greatest importance. The MAX-DOAS method is a reliable retrieval algorithm, enabling a vertical gas profile analysis. However, the current MAX-DOAS retrieval algorithm heavily relies on the a priori profile, limiting its accuracy. To address this issue, we introduced a novel MAX-DOAS trace gas profile inversion algorithm called McPrA, which is less dependent on the a priori profile. It employs the Monte Carlo method to resolve the problem of optimal estimation of trace gases. The gas vertical column density is obtained from the air mass factor calculated by SCIATRAN. Afterward, the trace gas vertical distribution is retrieved by combining the weight function with the a priori profile. A normalization process is also included to improve the matching of the weight function and the a priori profile. The McPrA algorithm enables greater flexibility in grid modification to achieve a higher vertical resolution of up to 50 m, while sensitivity experiments contribute to determining the optimal configuration of retrieval parameters, with a degree of freedom of over 3.0. Comparative verification experiments indicate that the McPrA algorithm accurately retrieves gas profiles, with a correlation coefficient of over 0.89 for NO2 in the first layer compared to in situ data. Furthermore, comparisons with WRF-Chem and the simulation of synthetic data demonstrate the effectiveness of the McPrA algorithm in accurately retrieving gas profiles.

A Mid-Infrared Quantum Cascade Laser Ultra-Sensitive Trace Formaldehyde Detection System Based on Improved Dual-Incidence Multipass Gas Cell.

Formaldehyde (HCHO) is a tracer of volatile organic compounds (VOCs), and its concentration has gradually decreased with the reduction in VOC emissions in recent years, which puts forward higher requirements for the detection of trace HCHO. Therefore, a quantum cascade laser (QCL) with a central excitation wavelength of 5.68 µm was applied to detect the trace HCHO under an effective absorption optical pathlength of 67 m. An improved, dual-incidence multi-pass cell, with a simple structure and easy adjustment, was designed to further improve the absorption optical pathlength of the gas. The instrument detection sensitivity of 28 pptv (1σ) was achieved within a 40 s response time. The experimental results show that the developed HCHO detection system is almost unaffected by the cross interference of common atmospheric gases and the change of ambient humidity. Additionally, the instrument was successfully deployed in a field campaign, and it delivered results that correlated well with those of a commercial instrument based on continuous wave cavity ring-down spectroscopy (R2 = 0.967), which indicates that the instrument has a good ability to monitor ambient trace HCHO in unattended continuous operation for long periods of time.

Study of SO2 measurement based on a dual optical path Fabry-Perot correlation spectroscopy.

This paper investigates a method for measuring SO2 concentration using Fabry-Perot interferometer correlation spectroscopy. In this method, the experimental system is designed as a separated beam, with the beam entering the F-P cavity at two incidence angles simultaneously to match the peak and valley positions of the SO2 absorption cross-section. The system achieves a 2σ detection limit of 28.2 ppm·m(15 cm) at a sampling frequency of 10 Hz. An outfield comparison experiment with the differential optical absorption spectroscopy method shows good agreement for the simultaneous measurement of SO2 concentration from sulfur combustion, with a correlation coefficient of R2 = 0.93. This study introduces a non-dispersive, highly accurate, and fast gas detection technique.

Key emergency response technologies for abrupt air pollution accidents in China.

Abrupt air pollution accidents can endanger people's health and destroy the local ecological environment. The appropriate emergency response can minimize the harmful effects of accidents and protect people's lives and property. This paper provides an overview of the key emergency response technologies for abrupt air pollution accidents around the globe with emphasis on the major achievements that China has obtained in recent years. With decades of effort, China has made significant progress in emergency monitoring technologies and equipment, source estimation technologies, pollutant dispersion simulation technologies and others. Many effective domestic emergency monitoring instruments (e.g., portable DOAS/FT-IR systems, portable FID/PID systems, portable GC-MS systems, scanning imaging remote sensing systems, and emergency monitoring vehicles) had been developed which can meet the demands for routine emergency response activities. A monitoring layout technique combining air dispersion simulation, fuzzy comprehensive evaluation, and a post-optimality analysis was proposed to identify the optimal monitoring layout scheme under the constraints of limited monitoring resources. Multiple source estimation technologies, including the forward method and the inversion method, have been established and evaluated under various scenarios. Multi-scale dynamic pollution dispersion simulation systems with high temporal and spatial resolution were further developed. A comprehensive emergency response platform integrating database support, source estimation, monitoring schemes, fast monitoring of pollutants, pollution predictions and risk assessment was developed based on the technical idea of "source identification - model simulation - environmental monitoring" dynamic interactive feedback. It is expected that the emergency response capability for abrupt air pollution accidents will gradually improve in China.

Atmospheric environment monitoring technology and equipment in China: A review and outlook.

Accurate monitoring of the atmospheric environment and its evolution are important for understanding the sources, chemical mechanisms, and transport processes of air pollution and carbon emissions in China, and for regulatory and control purposes. This study gives an overview of atmospheric environment monitoring technology and equipment in China and summarizes the major achievements obtained in recent years. China has made great progress in the development of atmospheric environment monitoring technology and equipment with decades of effort. The manufacturing level of atmospheric environment monitoring equipment and the quality of products have steadily improved, and a technical & production system that can meet the requirements of routine monitoring activities has been initiated. It is expected that domestic atmospheric environment monitoring technology and equipment will be able to meet future demands for routine monitoring activities in China and provide scientific assistance for addressing air pollution problems.

The vertical distribution and potential sources of aerosols in the Yangtze River Delta region of China during open straw burning.

To explore the impact of open straw burning on air quality in the Yangtze River Delta (YRD) and surrounding areas, three key cities in the YRD, namely Hefei, Nanjing, and Shanghai, were selected to observe changes in aerosol characteristics. Based on Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations from May to June 2021, the spatial-temporal distribution and potential sources of aerosol were studied. During the observation period, aerosol optical depth (AOD) in Shanghai was 55.15 % and 29.50 % higher than that in Hefei and Nanjing, respectively. For Shanghai, aerosols accumulated at night, and the aerosol extinction could reach 1.3 km-1 in the morning. The aerosol variations in Hefei and Nanjing were consistent due to the relative conformity of the surrounding environmental conditions (R = 0.84). The vertical distribution of aerosol in all three cities had the same Gaussian shape. The aerosol lifted layers in Nanjing and Shanghai were higher than that in Hefei, with heights of 0.2-0.8 km and 0.2-0.6 km, respectively. The averaged aerosol extinctions for these two cities were 0.34 km-1 and 0.49 km-1, respectively. Pollution source analysis was conducted based on wind field trajectory, satellite observation, and model simulation, taking Hefei as the recipient. The results showed that western Shandong Province, northern Anhui Province, northern Jiangxi Province, central Jiangsu Province, and the central YRD were the most important aerosols sources for Hefei. The contributions of central and southern Jiangsu Province were significantly higher than those of other potential sources, with a WCWTAOD (Meteoinfo concentration weight trajectory) between 1.2 and 3.0. The influence of fine particles produced by open biomass burning inside the YRD was significantly higher than that outside the region (outside contribution: 36.6 %). Regarding the influence between YRD cities, more aerosols were transported from Shanghai to Hefei and Nanjing, with similar transport contributions between Nanjing and Hefei.

Intercomparison of OH radical measurement in a complex atmosphere in Chengdu, China.

Atmospheric oxidation is a driving force of complex air pollution, and accurate hydroxyl radical (OH) measurement is helpful in investigating the radical-cored photooxidation mechanism in the troposphere. A self-developed laser-induced fluorescence instrument by the Anhui Institute of Optics Fine Mechanics, Chinese Academy of Sciences (AIOFM-LIF), was able to measure OH concentration with high sensitivity and good time resolution, and a detection limit of 1.7 × 105 cm-3 (1σ, 30 s). A long-period, multi-level intercomparison of hydroxyl radical (OH) measurements between AIOFM-LIF and PKU-LIF (the Peking University laser-induced fluorescence system) was conducted in Chengdu, China. The measurement between two instruments was in excellent agreement in the 5-min time resolution. Linear regression analysis reported a linear slope of 0.96 with a 0.68 × 106 cm-3 offset, and the correlation coefficient R2 was 0.85. The overall linearity with only a slight offset indicated a negligible influence on OH measurement. No noticeable artifacts from ozonolysis were observed under the condition of high ozone and ozonolysis-related compound concentrations. In addition to the subtraction of background signal through wavelength modulation, the dynamic correction on ozone photolysis interference ensured high intercomparison quality in both relatively constant and rapidly varying periods. Based on the reliability of OHAIOFM and OHPKU, comparisons under different oxidation-related species (NOx, VOCs, O3, PM2.5) levels and typical scenarios (rich-BVOC and high-reactivity) were carried out to evaluate the performance under complex atmospheres. A slightly higher drift was observed in a certain scenario, but the general data variability due to environmental changes did not affect the measurement accuracy. The intercomparison demonstrated that both systems are able to achieve reliable OH data under typical conditions of complex atmospheric pollution in China. Additional improvements are necessary for future intercomparisons in order to enhance the confidence in OH detection accuracy.

Measurement of HONO flux using the aerodynamic gradient method over an agricultural field in the Huaihe River Basin, China.

To investigate nitrous acid (HONO) levels and potential HONO sources above crop rotation fields. The HONO fluxes were measured by the aerodynamic gradient (AG) method from 14 December 2019 to 2 January 2020 over an agricultural field in the Huaihe River Basin. The ambient HONO levels were measured at two different heights (0.15 and 1.5 m), showing a typical diurnal cycle with low daytime levels and high nighttime levels. The upward HONO fluxes were mostly observed during the day, whereas deposition dominated at night. The diurnal variation of HONO flux followed solar radiation, with a noontime maximum of 0.2 nmol/(m2∙sec). The average upward HONO flux of 0.06 ± 0.17 nmol/(m2∙sec) indicated that the agricultural field was a net source for atmospheric HONO. The higher HONO/NO2 ratio and NO2-to-HONO conversion rate close to the surface suggested that nocturnal HONO was formed and released near the ground. The unknown HONO source was derived from the daytime HONO budget analysis, with an average strength of 0.31 ppbV/hr at noontime. The surface HONO flux, which was highly correlated with the photolysis frequency J(NO2) (R2 = 0.925) and the product of J(NO2) × NO2 (R2 = 0.840), accounted for ∼23% of unknown daytime HONO source. The significant correlation between HONO fluxes and J(NO2) suggests a light-driven HONO formation mechanism responsible for the surface HONO flux during daytime.

Nocturnal atmospheric chemistry of NO3 and N2O5 over Changzhou in the Yangtze River Delta in China.

Comprehensive observations of the nocturnal atmospheric oxidation of NO3 and N2O5 were conducted at a suburban site in Changzhou in the YRD using cavity ring-down spectroscopy (CRDS) from 27 May to 24 June, 2019. High concentrations of NO3 precursors were observed, and the nocturnal production rate of NO3 was determined to be 1.7 ± 1.2 ppbv/hr. However, the nighttime NO3 and N2O5 concentrations were relatively low, with maximum values of 17.7 and 304.7 pptv, respectively, illustrating the rapid loss of NO3 and N2O5. It was found that NO3 dominated the nighttime atmospheric oxidation, accounting for 50.7%, while O3 and OH only contributed 34.1% and 15.2%, respectively. For the reactions of NO3 with volatile organic compounds (VOCs), styrene was found to account for 60.3%, highlighting its dominant role in the NO3 reactivity. In general, the contributions of the reactions between NO3 and VOCs and the N2O5 uptake to NO3 loss were found to be about 39.5% and 60.5%, respectively, indicating that N2O5 uptake also played an important role in the loss of NO3 and N2O5, especially under the high humidity conditions in China. The formation of nitrate at night mainly originated from N2O5 uptake, and the maximum production rate of NO3- reached 6.5 ppbv/hr. The average NOx consumption rate via NO3 and N2O5 chemistry was found to be 0.4 ppbv/h, accounting for 47.9% of the total NOx removal. The predominant roles of NO3 and N2O5 in nitrate formation and NOx removal in the YRD region was highlighted in this study.

Enhanced electrochemical sensing performance for trace Hg(II) by high activity of Co3+ on Co3O4-NP/N-RGO surface.

Constructing a highly sensitive and selective electrochemical interface is of great significance for the effective detection of Hg2+ in water and biological samples. Herein, Co3O4 nanopolyhedron (NP) anchored on nitrogen-doped reduced graphene oxide (N-RGO) is utilized as the electrode material for the detection of Hg2+ in the range of 0.1 µM-1.0 µM, with high sensitivity (1899.70 µA µM-1 cm-2) and low detection limits (0.03 µM) in natural water. Moreover, the Co3O4-NP/N-RGO modified electrode possesses reasonable anti-interference ability for Hg2+ in the presence of inorganic ions and glucose, which is the basis of its good response to trace Hg2+ in serum. Besides, combined with X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations, the electron transfer tendency is revealed. Additionally, combined with the electron state density of Co-p, it is speculated that Co3+ is an optimum active site for catalytic reaction. The above results elucidate an electrochemically sensitive interface is constructed to realize the efficient detection of Hg2+, which provides some theoretical guidance for the development of electrochemical sensors.

Generation and Release of OH Radicals from the Reaction of H2 O with O2 over Soot.

OH radicals in the air maintain the oxidizing power of the troposphere. A conventional view is that particulate matter (PM) in the atmosphere is a major sink of OH radicals, thereby lowering the oxidizing power of atmosphere in the event of high-level PM. By contrary, our joint experimental/theoretical study reveals a new mechanism for the generation of gaseous OH radicals by carbonaceous soot particles. We show that water and O2 react on carbonaceous surfaces and give rise to gaseous OH radicals under irradiation. With ample delocalized π electrons, carbonaceous surfaces enable the easy desorption of hydroxyl groups to produce gaseous OH radicals, evidenced by direct observation of the steady generation of OH radicals on a carbonaceous surface. Our results reveal a new chemical mechanism for the production of OH radicals.

Application of smog chambers in atmospheric process studies.

Smog chamber experimental systems, which have been widely used in laboratory simulation for studying atmospheric processes, are comprehensively reviewed in this paper. The components, development history, main research topics and main achievements of smog chambers are introduced. Typical smog chambers in the world, including their volumes, wall materials, light sources and features, are summarized and compared. Key factors of smog chambers and their influences on the simulation of the atmospheric environment are discussed, including wall loss, wall emission and background pollutants. The features of next-generation smog chambers and their application prospect in future studies of the atmospheric environment are also outlined in this paper.

Vertical characteristics of NO2 and HCHO, and the ozone formation regimes in Hefei, China.

The research on the mechanism of combined air pollution in the Yangtze-Huaihe region, which is characterized by unique meteorological and geographical conditions and pollution emission characteristics, is still insufficient. We performed an experiment on key pollutants and an ozone formation study in Hefei, which is a pivotal city in the Yangtze-Huaihe region, from September 1 to 20, 2020. The aerosols retrieved via two-dimensional Multi-axis Differential Optical Absorption Spectroscopy (2D-MAX-DOAS) with a Boltzmann-shaped a priori profile had the best agreement with the results of Light Detection and Ranging (LIDAR) and sun-photometer measurements among the three typical a priori profiles (Gaussian, Boltzmann, and exponential shapes). The correlation coefficients of the near-surface gas concentrations retrieved using both 2D-MAX-DOAS and in situ measurements were 0.86 (NO2) and 0.61 (HCHO). The high NO2 and HCHO concentrations were observed at azimuths of 180° and 315° at heights of 0.8-1.5 km, and they may have been emitted by aircrafts. Importantly, the ratio of HCHO to NO2 during a typical pollution episode revealed that the factors controlling the O3 formation changed with altitude: VOCs (surface) to NOx (0.4 km) to transition (1.0 km) to VOCs (1.6 km). Moreover, the effect of VOCs on the O3 generation was stronger than that of NOx, especially in the downtown area of Hefei. When the ratio of HCHO to NO2 was 3.55-7.46, the ozone concentration in Hefei could be controlled well, especially at the optimal value of 5.50.