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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.

In the Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) trace gases profile retrieval, it needs to obtain the vertical profile of aerosols as the a priori, and depends on the atmospheric radiative transfer model (RTM). Therefore, a data mining method named CNN-SVR was adopted to achieve the prediction of NO2 profile, which combines the advantages of convolutional neural network (CNN), support vector regression (SVR) and MAX-DOAS. The optimization core of the hybrid model is embodied in three aspects. (1) CNN extracting the effective features of MAX-DOAS spectral data. The input data are MAX-DOAS spectrum, wind direction, wind speed, season, temperature, relative humidity, aerosol optical depth (AOD), cloud cover. Feature variables of MAX-DOAS spectra were extracted by CNN. The output data set is the NO2 profile retrieved by MAX-DOAS profile inversion algorithm PriAM. The data set is processed by normalization to unify the dimensions to ensure the accelerated convergence of the program. (2) The mean impact value (MIV) method selecting the input variables sensitive to NO2 profile forecasting. The MAX-DOAS spectral data, temperature, AOD and low cloud cover are finally determined as the best input parameters of the prediction model. (3) The hybrid forecasting method. Combined with the advantages that CNN can reduce the amount of data processing and retain useful information, and SVR does not depend on the dimension of input space, a CNN-SVR hybrid prediction model is proposed. The average percentage error (MAPE) of the CNN-SVR model is 9.14%. Compared with the separately constructed CNN, SVR and backpropagation models, the MAPE of CNN-SVR is reduced by 8.22%, 6.00% and 32.28% respectively. Therefore, CNN-SVR can effectively predict tropospheric NO2 profiles by using MAX-DOAS observation.

Correspondence: Min Qin(mqin@aiofm.ac.cn)Abstract: A measurement campaign using long-path differential optical absorption spectroscopy (LP-DOAS) instrument at Hefei Xinqiao International Airport to investigate the regional concentrations of various trace gases in the airport’s northern area and the variation characteristics of the gas concentrations during an aircraft’s taxiing and take-off phases. The total light path of the LP-DOAS system was about 964 meters and the time resolution of the LP-DOAS instrument was approximately 10 seconds. The measured light path of the LP-DOAS passed through an aircraft taxiway and take-off runway concurrently without affecting aircraft operations. The results of NO2 and SO2 pollution peaks were clearly visible, and their timing was well matched to the time the aircraft crossed the light path. While the aircraft take-offs increased the regional average NO2 concentrations by 10-20 ppbV and flight take-offs increased the regional average SO2 concentrations by 1-5 ppbV, the overall pollution levels in the airport area were low due to the airport's openness and rapid dispersion of pollutants, and the maximum hourly average NO2 and SO2 concentrations during the observation period were better than the Class 1 ambient air quality standards in China. Additionally, we discovered that the NO2 and SO2 emissions from the Boeing 737-800 aircraft used in this experiment were positively related to the age of the aircraft.Acknowledgements: This work was supported by the Plan for Anhui Major Provincial Science & Technology Project (Grant No. 202203a07020003), the Anhui Provincial Key R&D Program (No.202104i07020010) and the HFIPS Director’s Fund (Grant No. YZJJQY202205).

Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) has been widely used in the three-dimensional monitoring of air pollutants. It is of great significance for MAX-DOAS to reconstruct the state of air pollutants by establishing an accurate vertical profile retrieval algorithm. At present, the profile retrieval algorithm of MAX-DOAS mainly adopts the iterative method based on a priori profile, which leads to strong dependence on priori profiles. We try to reduce the dependence on priori profiles by first calculating the vertical column density and then calculating the vertical distribution from observation. Therefore, we propose a new MAX-DOAS trace gas profile inversion algorithm - McPrA (Monte Carlo profile inversion algorithm by Anhui Institute of Optics and Fine Mechanics (AIOFM)). The algorithm uses Monte Carlo method to solve the optimal estimation problem of the gas profile. Firstly, the gas vertical column density is obtained through the air mass factor calculated by the radiative transfer model SCIATRAN. Secondly, the vertical distribution of trace gas is retrieved by combining the weight function with the a priori profile. Besides, we introduce the normalization process in the vertical distribution solution to make the prior profile better match the weight function. McPrA can set the vertical resolution of profile by modifying the grid, and we increase the vertical resolution of gas profile to 50m. By conducting sensitivity experiments on parameters such as Monte Carlo sampling, covariance matrix and the priori profiles, the optimal configuration of retrieval parameter is obtained. At the same time, the degree of freedom is more than 3.0. Finally, comparative verification experiments were carried out to compare with in situ data from LP-DOAS and National Air Quality Monitoring Station. The correlation coefficient for NO2 VMR at the first layer retrieved by McPrA in 50 m grid reached above 0.89. The comparison of NO2 profiles retrieval by McPrA with that from WRF-Chem and simulation of synthetic data also shows that McPrA algorithm can retrieve trace gas profiles accurately.

A newly constructed thermal dissociation cavity ring-down spectrometer (TD-CRDS) for simultaneous measuring NO2, total peroxy nitrates (ΣPNs) and total alkyl nitrates (ΣANs) was presented. NO2 is detected directly at around 405.46 nm, ΣPNs and ΣANs are detected as NO2 after thermal decomposition at 180℃ and 360℃. The influences of the recombination reaction of RO2 radicals in two different types of heated inlets were discussed and compared, and the thermal decomposition efficiency of PNs was found to be higher with the value of 96% at the heated inlet filled with glass beads than the other (72%). Possible interferences, mainly O3 (including reactions of O3 via NO and O3 via NO2) and NOx (such as the recombination reactions of NOx and peroxy radicals at different thermal temperatures), were quantitatively characterised. The effects were found to be much weaker in the heated inlet filled with glass beads. Thus, a calibration method for measuring ΣPNs and ΣANs was established, especially to solve the accurate measurement of ΣPNs and ΣANs under high amounts of ambient NOx and O3 in China. At the time resolution of 20 s, the detection limits of the TD-CRDS instrument for NO2, ΣPNs and ΣANs are 6 pptv (1σ), 15 pptv (1σ) and 15 pptv (1σ), respectively. Finally, we applied the instrument to the Hefei field campaign, obtaining the concentration distribution and variation characteristics of ΣPNs and ΣANs.

Nitrogen dioxide (NO2) is a major air pollutant. Tropospheric NO2 vertical column densities (VCDs) retrieved from sun-synchronous satellite instruments have provided abundant NO2 data for environmental studies, but such data are limited by insufficient temporal sampling (e.g., once a day). The Geostationary Environment Monitoring Spectrometer (GEMS) launched in February 2020 monitors NO2 at an unprecedented high temporal resolution. Here we present a research product for tropospheric NO2 VCDs, referred to as POMINO-GEMS. We develop a hybrid retrieval method combining GEMS and TROPOMI observations as well as GEOS-Chem simulations to generate hourly tropospheric NO2 slant column densities (SCDs). We then derive tropospheric NO2 air mass factors (AMFs) with explicit corrections for the anisotropy of surface reflectance and aerosol optical effects, through pixel-by-pixel radiative transfer calculations. Prerequisite cloud parameters are retrieved with the O2-O2 algorithm by using ancillary parameters consistent with those used in NO2 AMF calculations. Initial retrieval of POMINO-GEMS tropospheric NO2 VCDs for June–August 2021 reveals strong hotspot signals over megacities and distinctive diurnal variations over polluted and clean areas. POMINO-GEMS NO2 VCDs agree well with our POMINO-TROPOMI v1.2.2 product (R = 0.97, and NMB = 3.6 %) over Asia. Comparison with ground-based MAX-DOAS VCD data at nine sites shows a small bias of POMINO-GEMS (NMB = –15.7 %); however, the correlation for diurnal variation varies from -0.66 to 0.90, suggesting location-dependent performance. Surface NO2 concentrations estimated from POMINO-GEMS VCDs are consistent with measurements from the Ministry of Ecology and Environment of China at 855 sites (NMB = –24.1 %, and R = 0.95 for diurnal correlation averaged over all sites). POMINO-GEMS data will be made freely available for users to study the spatiotemporal variations, sources and impacts of NO2.

Atmospheric aerosols have effects on atmospheric radiation assessments, global climate change, local air quality and visibility. In particular, aerosols are more likely transformed and accumulated in winter. In this paper, we used the Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument to study the characteristics of aerosol type and contributions of PM2.5 chemical components to aerosol extinction (AE), vertical distribution of aerosols, and source. From December 30, 2018 to January 27, 2019, we conducted MAX-DOAS observations on Sanmenxia. The proportion of PM2.5 to PM10 was 69.48%–95.39%, indicating that the aerosol particles were mainly fine particles. By analyzing the ion data and modifying Interagency Monitoring of Protected Visual Environments (IMPROVE) method, we found that nitrate was the largest contributor to AE, accounting for 31.51%, 28.98%, and 27.95% of AE on heavily polluted, polluted, and clean days, respectively. NH4+, OC, and SO42− were also major contributors to AE. The near-surface aerosol extinction retrieved from MAX-DOAS measurement the PM2.5 and PM10 concentrations measured by an Unmanned Aerial Vehicle (UAV) have the same trend in vertical distribution. AE increased about 3 times from surface to 500 m. With the backward trajectory of the air mass during the haze, we also found that the continuous heavy pollution was mainly caused by transport of polluted air from the northeast, then followed by local industrial emissions and other sources of emissions under continuous and steady weather conditions.

We report car-borne measurements of atmospheric NO2 close to the ground by incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS). A compact IBBCEAS spectrometer with a blue light emitting diode (LED) having a central wavelength of 458 nm, a full width at half maximum of 25 nm, and a 50-cm-long cavity was developed for mobile measurements. The NO2 detection limit of the spectrometer was calculated as 1.9 parts per billion by volume (ppbv) for a 30 s acquisition time by stabilizing the LED emitting spectrum, optimizing the NO2 reference cross sections, and by calibrating the reflectivity of the cavity mirrors. The accuracy of the spectrometer was verified by measuring NO2 samples with various mixing ratios between 1–200 ppbv, which were produced by a gas dilution system in the laboratory. Three distinct journeys in Nanjing and the surrounding areas were selected as observation routes. The atmospheric NO2 close to the ground was measured by the spectrometer from August 4 to 7, 2013. The mixing ratios of NO2 ranged from 3 to 144 ppbv. These results were compared with the column density of NO2 measured by a passive differential optical absorption spectroscopy (DOAS) instrument on the same car. Hence, we demonstrate the feasibility of using the spectrometer for car-borne measurements of atmospheric NO2.

An instrument to detect atmospheric HO2 radicals using fluorescence assay by gas expansion (FAGE) technique has been developed. HO2 is measured by reaction with NO to form OH and subsequent detection of OH by laser-induced fluorescence at low pressure. The system performance has been improved by optimizing the expansion distance and pressure, the influence factors of HO2 conversion efficiency are also studied. The interferences of RO2 radicals were investigated by determining the conversion efficiency of RO2 to OH during the measurement of HO2. The dependence of the conversion of HO2 on NO concentration was investigated, and low HO2 conversion efficiency was selected to realize the ambient HO2 measurement, where the conversion efficiency of RO2 derived by propane, ethene, isoprene and methanol to OH has been reduced to less than 6% in the atmosphere. Furthermore, no significant interferences from PM2.5 and NO were found in the ambient HO2 measurement. The detection limits for HO2 (S/N = 2) are estimated to 4.8 × 105 cm−3 and 1.1 × 106 cm−3 ( ρ H O 2 = 20%) under night and noon conditions, with 60 sec signal integration time. The instrument was successfully deployed during STORM-2018 field campaign at Shenzhen graduate school of Peking University. The concentration of atmospheric HOx radical and the good correlation of OH with j(O1D) was obtained here. The diurnal variation of HOx concentration shows that the OH maximum concentration of those days is about 5.3 × 106 cm−3 appearing around 12:00, while the HO2 maximum concentration is about 4.2 × 108 cm−3 appearing around 13:30.

We present an improved incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) system based on an iterative retrieval algorithm for the simultaneous detection of atmospheric nitrous acid (HONO) and nitrogen dioxide (NO2). The conventional IBBCEAS retrieval algorithm depends on the absolute change in the light intensity, which requires high light source stability and the stable transmission of the light intensity of all optical components. The new algorithm has an iterative module to obtain the effective absorption optical path length, and the concentrations of HONO and NO2 are then determined by differential optical absorption spectroscopy (DOAS) retrieval; thus, the method is insensitive to the fluctuation in the absolute light intensity. The robustness of the system is verified by simulating the influence of the relative change in the light intensity on the spectral retrieval results. The effect of nitrogen purging in front of the cavity mirrors on shortening the actual cavity length was measured and corrected using NO2 gas samples. Allan deviation analysis was conducted to determine the system stability, and it indicated that the detection limits (2σ) of HONO and NO2 are 0.08 and 0.14 ppbv at an integration time of 60 s respectively. Furthermore, Kalman filtering was used to improve the measurement precision of the system. The measurement precision at an integration time of 3 s can be improved 4.5-fold by applying Kalman filtering, which is equivalent to the measurement precision at an integration time of 60 s without applying Kalman filtering. The atmospheric HONO and NO2 concentrations were observed by the IBBCEAS system based on an iterative algorithm and were compared with values measured by conventional IBBCEAS.

Mobile differential optical absorption spectroscopy (mobile DOAS) has become an important tool for the quantification of emission sources, including point sources (e.g., individual power plants) and area emitters (e.g., entire cities). In this study, we focused on the error budget of mobile DOAS measurements from point sources, and we also offered recommendations for the optimum settings of such measurements via a simulation with a modified Gaussian plume model. Following the analysis, we conclude that (1) the proper sampling resolution should be between 5 and 50 m. (2) When measuring far from the source, undetectable flux (measured slant column densities (SCDs) are under the detection limit) resulting from wind dispersion is the main error source. The threshold for the undetectable flux can be lowered by larger integration time. When measuring close to the source, low sampling frequency results in large errors, and wind field uncertainty becomes the main error source of SO2 flux (for NOx this error also increases, but other error sources dominate). More measurement times can lower the flux error that results from wind field uncertainty. The proper wind speed for mobile DOAS measurements is between 1 and 4 m s−1. (3) The remaining errors by [NOx] ∕ [NO2] ratio correction can be significant when measuring very close. To minimize the [NOx] ∕ [NO2] ratio correction error, we recommend minimum distances from the source, at which 5 % of the NO2 maximum reaction rate is reached and thus NOx steady state can be assumed. (4) Our study suggests that emission rates

The nitrate radical (NO3) and dinitrogen pentoxide (N2O5) play an important role in the nocturnal atmosphere chemistry. Observations of NO3 radicals and N2O5 were performed in a semirural ground site at Tai'Zhou in polluted southern China using cavity ring down spectroscopy (CRDS) from 23 May to 15 June 2018. The observed NO3 and N2O5 concentrations were relatively low, with 1 min average value of 4.4 ± 2.2 and 26.0 ± 35.7 pptV, respectively. The N2O5 uptake coefficient was determined to be from 0.027 to 0.107 based on steady state lifetime method. Fast N2O5 hydrolysis was the largest contributor to the loss of NO3 and contributed to substantial nitrate formation, with an average value of 14.83 ± 6.01 µg/m3. Further analysis shows that the N2O5 heterogeneous reactions dominated the nocturnal NOx loss and the nocturnal NOx loss rate is 0.14 ± 0.02 over this region.

We present a new product with explicit aerosol corrections, POMINO-TROPOMI, for tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) over East Asia, based on the newly launched TROPOspheric Monitoring Instrument with an unprecedented high horizontal resolution. Compared to the official TM5-MP-DOMINO (OFFLINE) product, POMINO-TROPOMI shows stronger concentration gradients near emission source locations and better agrees with MAX-DOAS measurements (R2=0.75; NMB=0.8 % versus R2=0.68, NMB=-41.9 %). Sensitivity tests suggest that implicit aerosol corrections, as in TM5-MP-DOMINO, lead to underestimations of NO2 columns by about 25 % over the polluted northern East China region. Reducing the horizontal resolution of a priori NO2 profiles would underestimate the retrieved NO2 columns over isolated city clusters in western China by 35 % but with overestimates of more than 50 % over many offshore coastal areas. The effect of a priori NO2 profiles is more important under calm conditions.

Nitrous acid (HONO), an important precursor of the hydroxyl radical (OH), plays a key role in atmospheric chemistry, but its sources are still debated. The production of HONO on aerosol surfaces or on ground surfaces in nocturnal atmospheres remains controversial. The vertical profile provides vertical information on HONO and NO2 to understand the nocturnal HONO production and loss. In this study, we report the first high-resolution (

A simultaneous in-situ detection technique to obtain multi-optical parameters was proposed. The same 403.56 nm, low power, blue diode laser was used to conduct the cavity ring-down spectroscopy and photoacoustic spectroscopy, which were coupled. Four photoacoustic spectra were applied to the simultaneous in-situ detection of the cavity ring-down spectrum, which were systematically compared and analyzed for the first time. And the main performance of the systems varied with the arrangement of the photoacoustic pool. The results reveal that the photoacoustic response was optimized by the high reflectivity mirror with the pool constant of 1450.64 (Pα·cm)/W and the signal sensitivity of 0.2562 μv/ppb. The intensity value of the photoacoustic pool inside the cavity ring down was superimposed to 48.45% of the initial intensity. The corresponding experimental results were consistent with the theoretical analysis and shown the coupled cavity could suitable for simultaneous in-situ measurement of high concentration. The coupled two detection techniques detected different optical parameters and thus provided a new method for the simultaneous in-situ detection of the multi-optical parameters of specific atmospheric components.

Satellite retrievals of columnar nitrogen dioxide (NO 2 ) are essential for the characterization of nitrogen oxides (NO x ) processes and impacts. The requirements of modeled a priori profiles present an outstanding bottleneck in operational satellite NO 2 retrievals. In this work, we instead use neural network (NN) models trained from over 360,000 radiative transfer (RT) simulations to translate satellite radiances across 390-495 nm to total NO 2 vertical column (NO 2 C). Despite the wide variability of the many input parameters in the RT simulations, only a small number of key variables were found essential to the accurate prediction of NO 2 C, including observing angles, surface reflectivity and altitude, and several key principal component scores of the radiances. In addition to the NO 2 C, the NN training and cross-validation experiments show that the wider retrieval window allows some information about the vertical distribution to be retrieved (e.g., extending the rightmost wavelength from 465 to 495 nm decreases the root-mean-square-error by 0.75%) under high-NO 2 C conditions. Applying to four months of TROPOMI data, the trained NN model shows strong ability to reproduce the NO 2 C observed by the ground-based Pandonia Global Network. The coefficient of determination ( R 2 , 0.75) and normalized mean bias (NMB, -33%) are competitive with the level 2 operational TROPOMI product ( R 2 = 0.77 , NMB = − 29 % ) over clear ( geometric cloud fraction < 0.2 ) and polluted ( N O 2 C ≥ 7.5 × 10 15 molecules/cm 2 ) regions. The NN retrieval approach is ~12 times faster than predictions using high spatial resolution (~3 km) a priori profiles from chemical transport modeling, which is especially attractive to the handling of large volume satellite data.

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.

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.

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

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 technicalproduction 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.

A continuous wintertime observation of ambient OH and HO

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 (NO

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.

Comprehensive observations of the nocturnal atmospheric oxidation of NO

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/(m