Concentrations Of Nitrogen Oxides Research Articles

Impact of Thunderstorm Activities on Tropospheric NOx Over Koshi Province of Nepal and Their Possible Role in Climate Change

Lightning, a natural atmospheric phenomenon, plays a significant role in altering atmospheric chemistry and air quality by generating nitrogen oxides (NOX). This research aims to explore the correlation between lightning stroke density and atmospheric NOX over Koshi Province of Nepal by using observational data. Over the course of three year (2018, 2019 and 2020), sessional (lightning pre-dominant; pre-monsoon and post-monsoon) measurements of lightning activity (lightning stroke density) were obtained from Global Lightning Dataset (GLD 360) and NOX data acquired from NASA’s Ozone Monitoring Instrument (OMI). The computation was conducted by using programming language PYTHON. Correlation analysis was performed to examine the relationship between lightning stroke density and NOX concentrations by considering lightning stroke density as independent variable and average NOX as dependent variable. Our analysis shows a notable positive correlation between lightning stroke density and average NOX over Koshi Province of Nepal. The values of correlation coefficient (R) was found 0.625, 0.630 and 0.511 in pre-monsoon of years 2018, 2019 and 20120 respectively and 0.654, 0.605 and 0.370 respectively in post-monsoon. Increased lightning activity corresponded to heightened NOX concentrations, especially during pre-monsoon and post-monsoon. These results indicate that lightning significantly contributes to NOX emissions in Koshi Province. Understanding the relationship between lightning and NOX is essential for study atmospheric chemistry and assessing the impact of lightning on atmosphere.

Dielectric Properties of Materials Used for Microwave-Based NOx Gas Dosimeters.

Nitrogen oxides (NOx), primarily generated from combustion processes, pose significant health and environmental risks. To improve the coordination of measures against excessive NOx emissions, it is necessary to effectively monitor ambient NOx concentrations, which requires the development of precise and cost-efficient detection methods. This study focuses on developing a microwave- or radio frequency (RF)-based gas dosimeter for NOx detection and addresses the optimization of the dosimeter design by examining the dielectric properties of LTCC-based (Low-Temperature Co-fired Ceramics) sensor substrates and barium-based NOx storage materials. The measurements taken utilizing the Microwave Cavity Perturbation (MCP) method revealed that these materials exhibit more pronounced changes in dielectric losses when storing NOx at elevated temperatures. Consequently, operating such a dosimeter at high temperatures (above 300 °C) is recommended to maximize the sensor signal. To evaluate their high-temperature applicability, LTCC substrates were analyzed by measuring their dielectric losses at temperatures up to 600 °C. In terms of NOx storage materials, coating barium on high-surface-area alumina resolved issues related to limited NOx adsorption in pure barium carbonate powders. Additionally, the adsorption of both NO and NO2 was enabled by the application of a platinum catalyst. The change in dielectric losses, which provides the main signal for an RF-based gas dosimeter, only depends on the stored amount of NOx and not on the specific type of nitrogen oxide. Although the change in dielectric losses increases with the temperature, the maximum storage capacity of the material decreases significantly. In addition, at temperatures above 350 °C, NOx is mostly weakly bound, so it will desorb in the absence of NOx. Therefore, in the future development of a reliable RF-based NOx dosimeter, the trade-off between the sensor signal strength and adsorption behavior must be addressed.

Air quality on UK diesel and hybrid trains

Concentrations of particulate matter (PM10, PM2.5), ultrafine (UFP), particle number (PNC), black carbon (BC), nitrogen dioxide (NO2) and nitrogen oxides (NOX) were measured in train carriages on diesel and bi-mode trains on inter-city and long-distance journeys in the United Kingdom (UK) using a high-quality mobile measurement system. Air quality on 15 different routes was measured using highly-time resolved data on a total of 119 journeys during three campaigns in winter 2020 and summer 2021; this included 13 different train classes. Each journey was sampled 4–10 times with approximatively 11,000 min of in-train concentrations in total. Mean-journey concentrations were 7.552 µg m−3 (PM10); 3.936 µg m−3 (PM2.5); 333–11,300 # cm−3 (PNC); 225–9,131 # cm−3 (UFP); 0.6–11 µg m−3 (BC); 28–201 µg m−3 (NO2); and 130–3,456 µg m−3 (NOX). The impact of different factors on in-train concentrations was evaluated. The presence of tunnels was the factor with the largest impact on the in-train particle concentrations with enhancements by a factor of 40 greater than baseline for BC, and a factor 6 to 7 for PM and PNC. The engine fuel mode was the factor with the largest impact on NO2 with enhancements of up to 14-times larger when the train run on diesel compared to the times running on electric on hybrid trains. Train classes with an age < 10 years observed the lowest in-train PM, BC and NOX concentrations reflecting improvements in aspects of rail technology in recent years. Air quality on UK diesel trains is higher than ambient concentrations but has lower PM2.5 and PNC than most other transport modes, including subway systems, diesel and petrol cars. This paper adds significantly to the evidence on exposure to poor air quality in transport micro-environments and provides the industry and regulatory bodies with reference-grade measurements on which to establish in-train air quality guidelines.

Application of bi-directional long short-term memory in separating NO and SO2 ultraviolet differential absorption spectrum signals

To safeguard the environment, it is crucial to monitor the emissions of nitrogen oxide (NO) and sulfur dioxide (SO2), harmful pollutants generated during fossil fuel combustion in industries. However, accurately measuring ultra-low concentrations of SO2 and NO remains a challenge. In this study, we developed an optical measurement system based on ultraviolet differential optical absorption spectroscopy (UV-DOAS) to address this issue. The 200–230 nm cross-sensitivity band was chosen for SO2 and NO. Experimental data with a mixed gas concentration range of 1–25 ppm for SO2 and NO was utilized. We proposed a fast algorithm based on Bi-directional Long Short-Term Memory (Bi-LSTM) to extract the differential optical density, overcoming the mutual interference between SO2 and NO. A nonlinear calibration model was employed to invert the separated differential absorption spectra and determine the gas concentrations. The results demonstrated a detection limit (DL) of 0.27 ppm and a full-scale error of 3.15 % for SO2, while for NO, the DL was 0.32 ppm and the full-scale error was 2.81 %. The uncertainties in SO2 and NO detection were calculated as 1.73 % and 1.96 %, respectively.

A Comparative Study of SOx, NOx, PM2.5 and PM10 in the UK and Poland from 1970 to 2020

Presently, there is growing discourse surrounding climate change, global warming, and the possibility of urban smog. Daily, we encounter air pollutants unwittingly, often oblivious to the substantial adverse impacts they may impart on our health. This manuscript furnishes a thorough examination of the shifts in the concentrations of distinct air pollutants, namely, sulphur oxides (SOx), nitrogen oxides (NOx), and particulate matter PM2.5 and PM10, within the contexts of the United Kingdom (a country progressively transitioning to alternative energy sources) and Poland (a country in the EU with the second lowest climate policy evaluation in the climate change performance index or CCPI) from 1970 to 2020. This comparative study between the two countries clearly showed the importance of the transition to clean energy sources. The UK’s efforts towards cleaner energy sources have led to reduced emissions of sulphur oxides (SOx) and particulate matter. In contrast, Poland’s heavy dependence on energy primarily from coal over the years has resulted in elevated pollution levels, notably in the concentration of pollutants such as particulate matter. This study also revealed that changes in emissions predominantly stem from technological advancements and economic activities. Additionally, political regulations and the gradual phase-out of specific fuels or energy-rich substances and their substitution with alternative energy sources have also imparted considerable influence.

Dissecting Drivers of Ozone Pollution during the 2022 Multicity Lockdowns in China Sheds Light on Future Control Direction.

In 2022, many Chinese cities experienced lockdowns and heatwaves. We analyzed ground and satellite data using machine learning to elucidate chemical and meteorological drivers of changes in O3 pollution in 27 major Chinese cities during lockdowns. We found that there was an increase in O3 concentrations in 23 out of 27 cities compared with the corresponding period in 2021. Random forest modeling indicates that emission reductions in transportation and other sectors, as well as the changes in meteorology, increased the level of O3 in most cities. In cities with over 80% transportation reductions and temperature fluctuations within -2 to 2 °C, the increases in O3 concentrations were mainly attributable to reductions in nitrogen oxide (NOx) emissions. In cities that experienced heatwaves and droughts, increases in the O3 concentrations were primarily driven by increases in temperature and volatile organic compound (VOC) emissions, and reductions in NOx concentrations from ground transport were offset by increases in emissions from coal-fired power generation. Despite 3-99% reduction in passenger volume, most cities remained VOC-limited during lockdowns. These findings demonstrate that to alleviate urban O3 pollution, it will be necessary to further reduce industrial emissions along with transportation sources and to take into account the climate penalty and the impact of heatwaves on O3 pollution.

Numerical Investigation of a Hydrogen–Air Flame for NOx Prediction

Abstract Sustainable aviation fuels are a major candidate to reduce pollutant emissions in future aeronautical engines. Recently, the use of hydrogen as a fuel has gained a high interest partly because its combustion is free from carbon dioxide, a greenhouse gas, and produces few pollutants, mainly nitrogen oxides (NOx). Over the last decades, efforts on numerical methods for combustion simulation in aero-engines have largely been focused on kerosene-air combustion. However, the current transition may have a significant impact on the computational methodologies for combustor design. Hydrogen defines novel modeling issues and challenges the current state of art on numerical methodologies. The current study presents a numerical investigation of a hydrogen–air burner using large-eddy simulations (LES) with a focus on NOx prediction. The considered configuration is a two-staged combustor, similar to the well-known RQL (Rich-Quench-Lean) technology, supplied by a single coaxial injector characterized experimentally. Two combustion models are investigated: (i) tabulated chemistry based on premixed flamelets (ii) transported chemistry description by using a 21-species chemical scheme. Numerical results are compared with experimental data (NOx concentrations, temperature distributions, pressure losses). A focus on model predictions is carried out. Results show a good agreement to predict the main flow characteristics and the premixed flame position over different operating points and geometries for both frameworks. In contrast, NOx emissions are more sensitive: while the overall trend is well captured, the quantification is more scattered. Finally, an in-depth analysis is proposed to link NOx production with the nonpremixed flame size.

Experimental investigations of plasma-assisted ammonia combustion using rod-electrode-type microwave plasma source

Ammonia have been attractive as one of the alternative fuels for reducing greenhouse gas (GHG) emissions. However, ammonia combustion has lower combustion performance than common hydrocarbon fuels. Furthermore, it may emit nitrous oxide (N2O), which is one of the GHGs. This paper presents the experimental investigations of plasma-assisted ammonia combustion (PAAC) using a rod-electrode-type microwave plasma source (MPS) at atmospheric pressure. The equivalence ratios of premixed ammonia/dry air (NH3/Air) gas are set below the stoichiometric combustion of NH3 to reduce toxic NH3 in the combustion gas. Under the condition of the equivalence ratios, the experiments are focused on reducing the unburned NH3 and produced N2O concentrations in the combustion gas. In the experiments, the unburned NH3, nitrogen oxide (NOx) (the sum of nitric oxide (NO) and nitrogen dioxide (NO2)), and N2O concentrations in the combustion gas are investigated in terms of the flow velocity of premixed NH3/Air gas inside the rod-electrode-type MPS and the transmission power to the rod-electrode-type MPS. In conclusion, the rod-electrode-type MPS is identified to be useful for PAAC. The NH3 and N2O concentrations in the combustion gas reach approximately 25 and 4 parts per million (ppm), respectively, under the conditions of the equivalence ratio of 1.0, flow velocity of approximately 0.167 m/s, and transmission power of about 84 W. At that time, the NOx concentration is approximately 4300 ppm, and the power transmission efficiency is approximately 68 %.

Comparison of Air Pollutants during the Two COVID-19 Lockdown Periods in Winter 2019 and Spring 2022 in Shanghai, China

During the winter of 2019, the global outbreak of COVID-19 prompted extensive research on urban air pollution under lockdown measures. However, these studies predominantly focused on winter conditions, thereby limiting investigations into changes in urban air pollutants during other seasons that were also subject to lockdown restrictions. Shanghai, China, has undergone two COVID-19 lockdown periods in two seasons: winter 2019 and spring 2022. The seasonal variations and human activities were represented by meteorological factors and nighttime light brightness in this paper, respectively. The reduction in human-related emissions during the two lockdown periods was estimated based on the targets outlined in China’s Air Pollution Prevention and Control Action Plan. The results showed significant reductions in NO2 and PM particles during the two lockdown periods, both accompanied by a notable increase in O3 concentration. In comparison to the winter lockdown, there was an approximate 40% decrease in the NO2 and PM2.5 concentrations in the spring, while the O3 concentration exhibited an increase of 48.81%. Furthermore, due to shifting wind patterns during the two lockdowns from winter to spring, the high-pollution core areas shifted 20–25 km southeastward in the spring. The PM particles and NO2 concentrations exhibited a considerable impact from human activities, whereas the O3 concentration was affected mostly by seasonal change and interactions among air pollutants. Compared to the corresponding non-lockdown condition, the concentration of CO decreased during the winter lockdown; however, it increased during the spring lockdown. The different change in CO concentration during the two lockdown periods was found to have a lower effect on the O3 concentration than that caused by changes in meteorological factors and nitrogen oxide (NO, NO2) concentrations. In summary, the impact of COVID-19 lockdown periods on urban air pollutants was more pronounced in spring compared to winter, and the interactions among air pollutants also underwent alterations.

Rapid CO detection using MWCNTs/SnO2 hierarchical structure: synthesis, characterization, and RT gas sensing features

Industrialization, modernization, and heavy car populations cause an extensive release of hazardous gases which impact the environment and human health. In this respect, employing gas sensors for detecting different concentrations of carbon oxides, nitrogen oxides, and other harmful gases is being advanced with much interest and necessity. In our current work, we have feasibly synthesized MWCNTs/SnO2 hierarchical structure through a hydrothermal process. The attained XRD diffraction pattern reflects the crystallinity with a crystallite size <10 nm. The FTIR results signify the presence of the functional group which verifies the successful interaction and connection for the composite network. Morphological features using SEM, HRTEM depict the hierarchical structure persistence. The adsorption/desorption curves are investigated using BET analysis acquiring a surface area of 189 cc/g. Numerous gases were included in the gas sensing study such as ethanol, methanol, acetone, ammonia, CO, and CO2. The sensing performance displays a remarkable result for carbon monoxide (CO) detection. The response time for CO detection was 5 s, while the recovery was 7s for 300 ppm at RT. The improved selectivity of CO amongst ethanol, CO2 and other gases is demonstrated. The proposed CO sensing structure combines feasible approach, low-cost, room temperature operation, and fast response/recovery times. The structure is promising for CO gas detection for versatile industrial applications.

Comparative Analysis of Exhaust Emission of Retrofitted SI Engine Runs by Different Fuels

The purpose of this study was to experimentally inspect the pollutant emission of a retrofitted SI engine using octane, compressed natural gas, and liquefied petroleum gas fuels operated at different speeds. The study was conducted using a retrofitted SI engine. The engine was coupled with an exhaust gas analyzer to measure the composition of the exhaust emission gas. The results showed that the carbon dioxide (CO2) and carbon monoxide (CO) content is lower when CNG is used compared to octane. The CO2 emission was even lower for LPG than CNG, as LPG has a lower carbon-energy ratio and higher octane quality than LPG and burns faster as a lean mixture. The O2 emission supports that octane and CNG burn as a lean mixture whereas LPG burns as rich. Again, the HC emissions are more prominent and CO emissions are higher for LPG than CNG. Because, it showed incomplete combustion with LPG as fuel due to inappropriate air-fuel mixture in the gas-air mixing chamber, which was specifically designed for CNG. Nitrogen oxide (NOx) emission was minimal when the engine was operated with LPG due to incomplete combustion, and it was found maximum for octane, where medium NOx content was found in the case of CNG. Moreover, the relative air fuel ratio or excess air factor, λ increased as the engine operating speed was raised. Because at high speed, there is some turbulence effect and increased combustion duration.

2019–2020年西安城市PM2.5、气体污染物及气象数据集

Air pollution in China has improved in recent years, but Central Shaanxi region continues to face great pressure and challenges in pollution control due to its unique geographical location and climatic conditions. The regional and complex air pollution, characterized by ozone (O3) and fine particulate matter (PM2.5), is becoming increasingly serious. More meticulous observation data are needed to clarify the causes of air pollution and provide scientific support for control policies. This dataset comprises the data on the concentrations of nitrogen oxides, sulfur dioxide, ozone and carbon monoxide in the atmosphere obtained by gas analyzer in Gaoxinzi Observation Site of the National Observation and Research Station of Regional Ecological Environment Change and Comprehensive Management in Guanzhong Plain. Weather stations collected data on temperature, humidity, air pressure, solar radiation, wind speed, wind direction and other meteorological parameters around the station. Offline PM2.5 filter membranes were measured and the mass concentrations were analyzed. The observation site is located in the urban area of Xi 'an, Shaanxi Province. The data covers the period from January 2019 to December 2020 with a resolution of 5 minutes for pollution gas data, one minute for meteorological data, and PM2.5 collected every 24 hours. Online instruments are calibrated monthly to ensure data quality, while the offline PM2.5 sampler is calibrated and maintained weekly to ensure its data quality. This dataset can provide fundamental data records for the atmospheric environment in Central Shaanxi Province and offer data support for further pollution evaluation, control, and treatment. Moreover, it can give researchers scientific insights into the processes, casual mechanisms, as well as prevention and control of atmospheric pollution in Central Shaanxi Province.

Исследование новой микрофакельной горелки с помощью программы Ansys Fluent

A study of a new micro-flame burner device (MFBD) for the combustion chamber of a gas turbine unit (GTU) using the Ansys Fluent program is presented. Research objective: determination of the optimal operating modes of the investigated burner, initial air parameters for maximum combustion efficiency, examination of the uniformity of the temperature field, and the concentration of nitrogen oxides in the combustion chamber of the gas turbine unit with the MFBD. The features of the design and operation of the micro-flame burner device are described, as well as the stages of modeling combustion processes in the Ansys Fluent software. The calculations conducted using various simulation parameters in this program allowed the evaluation of the efficiency of the new MFBD, determination of the temperature field distribution, and the nitrogen oxide content in the combustion products. The nitrogen oxide emissions in the combustion products during different modes of operation did not exceed 9 ppm. This data will be useful for further optimization and development of GTUs taking into account the requirements of efficiency and environmental safety. The presented study demonstrates the application of Ansys Fluent in the development of new technologies in the field of combustion and energy

Działalność Międzyresortowej Komisji ds. Najwyższych Dopuszczalnych Stężeń i Natężeń Czynników Szkodliwych dla Zdrowia w Środowisku Pracy w 2023 r.

In the sixth phase of the national programme “Governmental Programme for Improvement of Safety and Working Conditions” in 2023, three meetings of the Interdepartmental Commission for Maximum Admissible Concentrations and Intensities for Agents Harmful to Health in the Working Environment were considered, during which: eight documentations of the occupational exposure limit values, a position regarding the extension of the transitional period for the OEL for nitrogen oxide by 3 years for the underground mining and tunnel construction sector, the position of the Cobalt Institute, the Group Expert of Chemical and Dust Agents regarding the proposal of the ECHA Risk Assessment Committee (RAC) for OEL values for cobalt and its inorganic compounds (as Co) and the position of the regarding the exemption for nickel and lead compounds included in the annex to the Regulation of MAC and MAI of 2018. The Interdepartmental Commission for MAC and MAI adopted and submitted to the minister responsible for labour three proposals to amend the list of MAC and MAI in the following scope: introduction of occupational concentration values for five new chemical substances, leaving the current MAC value for the inhalable fraction of glyphosate (herbicide), extension by 3 years of the transitional period for the permissible concentration of nitrogen oxide in the underground mining and tunnel construction sector, i.e. until August 21, 2026, removal of exclusions regarding nickel and lead compounds included in the annex to the regulation on NDS and NDN of 2018 (implementation of Directive 2022/431/EU). The results of the Commission’s activities in 2023 were presented in three notes, communication No. XVI, a popular science publication, at the 23rd PTHP Symposium, and in a brochure entitled “Harmful factors in the work environment - limit values for carcinogenic/mutagenic, reprotoxic substances” as well as regular occupational health and safety training and in postgraduate studies.

Solar FTIR measurements of NOx vertical distributions – Part 1: First observational evidence of a seasonal variation in the diurnal increasing rates of stratospheric NO2 and NO

Abstract. Observations of nitrogen dioxide (NO2) and nitrogen oxide (NO) in the stratosphere are relevant to understand long-term changes and variabilities in stratospheric nitrogen oxide (NOx) and ozone (O3) concentrations. Due to the versatile role of NO2 and NO in stratospheric O3 photochemistry, they are important for recovery and build-up of O3 holes in the stratosphere and therefore can indirectly affect human life. Thus, we present in this work the evaluation of NO2 and NO stratospheric partial columns (&gt; 16 km altitude) retrieved from ground-based Fourier-transform infrared (FTIR) measurements of over 25 years at Zugspitze (47.42° N, 10.98° E; 2964 m a.s.l.) and 18 years at Garmisch (47.47° N, 11.06° E; 745 m a.s.l.), Germany. The obtained stratospheric columns are only weakly influenced by tropospheric pollution and show only a very small bias of 2.5 ± 0.2 % when comparing NO2 above Zugspitze and Garmisch. Stratospheric columns of both NO2 and NO show a diurnal increase that depends on local solar time (LST). We quantified this behavior by calculating diurnal increasing rates. Here, we find mean values for the NO2 diurnal increasing rate of (0.89 ± 0.14) × 1014 and (0.94 ± 0.14) × 1014 cm−2 h−1 at Zugspitze and Garmisch, respectively. The mean NO morning diurnal increasing rate above Zugspitze is found to be (1.42 ± 0.12) × 1014 cm−2 h−1. Regarding the seasonal dependency of these increasing rates, for the first time, we were able to experimentally detect a significant seasonal variation in both NO2 diurnal increasing rates and NO morning diurnal increasing rates with a maximum of (1.13 ± 0.04) × 1014 cm−1 h−1 for NO2 and (1.76 ± 0.25) × 1014 cm−1 h−1 for NO in September and a minimum of (0.71 ± 0.18) × 1014 cm−1 h−1 in December for NO2 and a minimum of (1.18 ± 0.41) × 1014 cm−1 h−1 in November for NO. This similar behavior may be explained by the interconnection of both species in stratospheric photochemistry. The outcome of this work is a retrieval and analysis strategy of FTIR data for NOx stratospheric columns, which can help to further validate photochemical models or improve satellite validations. The first use of this data set is shown in the companion paper (Nürnberg et al., 2023) wherein experiment-based NOx scaling factors describing the diurnal increase in the retrieved partial columns are extracted and recently published model-based scaling factors are validated.

Effect of the NO concentration on the ratio I₅₅₇.₇/I₄₂₇.₈ in auroras

We have examined the effect of the nitrogen oxide concentration on the ratio between λ557.7 nm and λ427.8 nm emission intensities in auroras caused by precipitating electron fluxes, using the numerical simulation method. The ratio I₅₅₇.₇/I₄₂₇.₈ has been shown to strongly depend on the NO concentration: the ratio decreases from 7 to 2 with increasing NO maximum concentration at the height profile from 10⁷ to 3·10⁹. This fact is in satisfactory agreement with experimental data.The effect of nitric oxide on the ratio has been demonstrated to occur through the excitation channel of the emission λ557.7 nm, namely, the dissociative recombination of the molecular oxygen ion O⁺₂+eₜₕ due to the ion deactivation by collision reaction with nitric oxide O⁺₂+NO.

Влияние концентрации NO на отношение I₅₅₇.₇/I₄₂₇.₈ в полярных сияниях

We have examined the effect of the nitrogen oxide concentration on the ratio between λ557.7 nm and λ427.8 nm emission intensities in auroras caused by precipitating electron fluxes, using the numerical simulation method. The ratio I₅₅₇.₇/I₄₂₇.₈ has been shown to strongly depend on the NO concentration: the ratio decreases from 7 to 2 with increasing NO maximum concentration at the height profile from 10⁷ to 3·10⁹. This fact is in satisfactory agreement with experimental data.The effect of nitric oxide on the ratio has been demonstrated to occur through the excitation channel of the emission λ557.7 nm, namely, the dissociative recombination of the molecular oxygen ion O⁺₂+eₜₕ due to the ion deactivation by collision reaction with nitric oxide O⁺₂+NO.

A Study on the Temporal and Spatial Changes of Nitrogen Oxides in the Southwest Corner of Jingzhou City Wall

With the growth of people's consumption capacity, the production and consumption of energy are rapidly increasing every year, and the emissions of nitrogen oxides are also increasing. Nitrogen oxides include many types of compounds, such as nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (N2O), etc. Except for nitrogen dioxide, the properties of other nitrogen oxides are extremely unstable. Therefore, in the actual atmosphere, nitric oxide (NO) and nitrogen dioxide (NO2) are usually collectively referred to as nitrogen oxides (NOx). This article measured and compared the nitrogen oxide concentration and other meteorological indicators in the public, commercial, and civilian areas at the southwest corner of the city wall in Jingzhou City in March and April 2022. The following conclusions were drawn: the mass concentration of nitrogen oxide pollutants was highest around noon and evening, and the concentration was relatively small before and after sunrise and afternoon, with a "double peak and double valley" distribution. The nitrogen oxide concentration began to decrease at night and reached the first valley in the early morning, then it gradually rises, reaching its peak around 8:00 and then showing a downward trend. A second trough will appear around 13:00, followed by a continuous increase in concentration, and finally a small peak will appear at 18:00.

A quantitative analysis of causes for increasing ozone pollution in Shanghai during the 2022 lockdown and implications for control policy

Ground-level ozone (O3) pollution is a major air quality issue in densely populated urban areas. Despite a significant decline in human activities in the megacity Shanghai from March 28 to May 31, 2022, ground-level measurements indicate a rise in maximum daily average 8-h (MDA8) O3 concentrations in comparison to the corresponding period in 2021. There is a need for quantitative analysis to identify the reasons behind this increasing O3 concentration. We analyzed ground measurements of O3 and its precursors and meteorological parameters made in Shanghai, using random-forest (RF) model and chemical box model to elucidate the roles of meteorological and chemical factors in influencing O3 concentrations. Across urban, suburban, semi-rural, and coastal sites, the urban center of Shanghai experienced the largest decreases in the concentrations of nitrogen oxides (NOx; 53%) and volatile organic compounds (VOCs; 52%), with the most notable rise in MDA8 O3 concentrations (16%). RF modeling indicates that meteorological factors reduced MDA8 O3 concentrations by a marginal 3%, whereas a decline in anthropogenic emissions resulted in a 17% increase in MDA8 O3 concentrations. Chemical box modeling at the Pudong urban site indicates that while the decline in VOCs reduced O3 production by 42%, this was negated by a reduction in NOx from traffic emissions, which enhanced O3 production by 51%, resulting in an increase in O3 production overall. Despite a halving in precursor levels, Shanghai's urban centre remains predominately under VOC-limited conditions throughout the study period, with high NO2 levels from the petrochemical industry and traffic emissions. Joint control of anthropogenic VOCs (AVOCs) and NOx, with a ratio greater than 1.29, could help avoid exacerbation of O3 pollution and reduce NO2 pollution. Our findings emphasize the necessity of reducing industrial emissions along with ongoing green transportation strategies for alleviating O3 pollution in megacities like Shanghai.

Ozone Pollution in Suzhou During Early Summertime: Formation Mechanism and Interannual Variation

This study investigated the concentrations of atmospheric pollutants in the urban area of Suzhou from May to June, 2017-2021. The variation characteristics and annual changes of ozone (O3), nitrogen oxide (NOx), total oxidant (Ox), carbon monoxide (CO), and volatile organic compounds (VOCs) were analyzed. The O3 formation mechanism and its annual changes were studied using an Observation-Based Model (OBM), and VOCs source apportionments and their trends were discussed. The results indicated that ① The volume fractions of Ox and the concentrations of NOx and CO have decreased in the urban area of Suzhou in recent years, while the volume fractions of VOCs have increased, and sufficient photochemical conditions for O3 formation still existed during polluted days. ② The O3-NOx-VOCs sensitivity in Suzhou was in the VOCs-limited regime. The long-term reduction ratio between VOCs and NOx should not be less than 5:1, and aromatics and alkenes were the critical VOCs for mitigating O3 pollution. ③ The results of VOCs source apportionment revealed that industrial emissions, gasoline vehicle exhaust, and diesel engine exhaust were the major sources of VOC emissions in Suzhou. Industrial emissions and solvent usage declined from 2017 to 2021; however, gasoline vehicle exhaust and gasoline evaporation, which possess higher O3 formation potential(OFP), increased significantly. ④ The OFP source apportionments results indicated that controlling VOC emissions from solvent usage and gasoline vehicle exhaust is crucial for O3 pollution control in Suzhou.