Total NOx Research Articles

The impact on passenger car emissions associated with the promotion and demise of diesel fuel

The promotion and growth in the use of diesel fuel in passenger cars in the UK and Europe over the past two decades led to considerable adverse air quality impacts in urban areas and more widely. In this work, we construct a multi-decade analysis of passenger car emissions in the UK based on real driving emissions data. An important part of the study is the use of extensive vehicle emission remote sensing data covering multiple measurement locations, time periods, environmental conditions and consisting of over 600,000 measurements. These data are used to consider two scenarios: first, that diesel fuel use was not promoted in the early 2000s for climate mitigation reasons, and second, that there was not a dramatic decline in diesel fuel use following the Dieselgate scandal. The strong growth of diesel fuel use coincided with a time when diesel NOx emissions were high and, conversely, the strong decrease of diesel fuel use coincided with a time when diesel vehicle after-treatment systems for NOx control were effective. We estimate that the growth in diesel car use in the UK results in excess NOx emissions of 721 kt over a three decade period; equivalent to over 7 times total annual passenger car NOx emissions and greater than total UK NOx emissions of 681.8 kt in 2021 and with an associated damage cost of £5.875 billion. However, the sharp move away from diesel fuel post-Dieselgate only reduced NOx emissions by 41 kt owing to the effectiveness of modern diesel aftertreatment systems.

The impact of the variation in driving conditions on the NOx emissions characteristics in PEMS test for heavy-duty vehicle

The real driving emission test using a portable emission measurement system is the advanced solution to assess NOx emissions from heavy-duty vehicles in recent years. To reflect the NOx emissions of heavy-duty vehicles more realistically, the restrictions on driving conditions will likely be relaxed in the next emission standard for heavy-duty vehicles. In this study, several tests with different payloads were conducted on a China VI heavy-duty vehicle under two different driving conditions. The test results show that some NOx emissions “spikes” may occur in any driving type during the tests of heavy-duty vehicles, and they are mainly related to the NOx conversion efficiency of the SCR system. In general, there is no obvious relevance between the NOx emission rate and the driving type, but the increase of the vehicle speed is beneficial to maintain the temperature of the SCR system in the high-efficiency zone, thus reducing the NOx emission rate. The variation of driving conditions will cause a change in the valid windows of the test, which will lead to a change in the evaluation results of NOx emission compliance. Adding motorway driving to the test route significantly increases the power threshold of the valid windows and reduces specific NOx emissions of the valid windows, with a minimum reduction of more than 30% and a maximum reduction of nearly 50% for “SENOx-90” in this study. The variation in driving conditions can severely affect the true NOx emissions assessment, especially for low-payload tests. In this study, the difference in NOx emissions assessed due to variation in driving conditions reached 1/3 of the total NOx emissions and the difference will gradually decrease as the vehicle load increases.

Sediment nitrates reduction processes affected by non-native Sonneratia apetala plantation in South China

Numerous studies have highlighted the importance of nitrates (NOx−) reduction processes in estuarine and coastal ecosystems over the past decades. However, the biotic and abiotic factors sediment NOx− reduction processes in mangrove of varying ages are still not fully understood. Here, we investigated the dynamics of sediment NOx− reduction processes and associated gene abundances in mangroves of different ages (including 0-year unvegetated mudflats, 10 and 20-years Sonneratia apetala, as well as >40 years of mature native Kandelia obovate) on the Qi'ao Island using 15N stable-isotope pairing techniques and quantitative PCR. The denitrification (2.64–11.30 nmol g−1 h−1), anammox (0.06–0.83 nmol g−1 h−1), and dissimilatory nitrate reduction to ammonium (DNRA, 0.58–16.34 nmol g−1 h−1) rates varied spatially and seasonally, but their contributions to the total NOx− reduction (DEN%, ANA%, and DNRA%), associated gene abundance (nirS, anammox 16S rRNA, and nrfA), and organic matter only varied spatially. Organic matter and microbial abundances are the dominating factors controlling N loss and retention. Without considering confounding factors, mangroves conservation and restoration significantly increased DNRA rates, NIRI (DNRA/(denitrification + anammox)), organic matter content, and microbial abundances (p < 0.05 for all), but reduced N loss rates. Mangroves conservation and restoration are estimated to have increased sediment N retention (~931.81 t N yr−1) and reduced N loss (~481.32 t N yr−1) in coastal wetlands of China over the past 40 years (1980–2020). Overall, our results indicate that mangrove restoration and conservation can significantly increase sediment N retention due to the rapid biomass accumulation, and it can provide more nutrients for mangrove and microorganism growth, thus creating a virtuous cycle in these N-limited ecosystems.

Direct and indirect air pollutant reductions as co-benefits of the energy transition toward carbon-neutrality in India's residential sector

With increasing air pollution, exposure to air pollutants is becoming a critical health and environmental issue all over the world. In case of India, due to significant differences in the economic status and energy consumption characteristics, substantial variation in the air pollutant emissions is observed across Indian states in urban and rural areas. This study aims at developing a residential sector model to project CO2 emissions up to 2070, leading India's progress towards carbon-neutrality, and evaluating the dual benefits of reducing the aforesaid emissions. A bottom-up optimization model is used to analyze these emission projections for greenhouse gases (GHGs) and air pollutants across Indian states in rural and urban areas. Further, to evaluate the effects of Indian government policy, various mitigation scenarios are analyzed, which capture the energy transition and direct and indirect emissions in India's slow, medium, and fast-developing states. Rapid energy transition in India doubles the total energy consumption in the business-as-usual (BAU) scenario from 2010 to 2070. Consumption of traditional biomass and coal energy sources dramatically falls, and advanced energy sources such as liquefied petroleum gas (LPG) and electricity are adopted. Energy transitions help decrease the vulnerability to harmful direct air pollutants such as black carbon (BC), organic carbon (OC) and particulate matter (PM) among rural households. There are serious tradeoffs, however, as increased usage of LPG and electricity may raise total CO2, SO2, and NOX emissions. Higher LPG consumption leads to a more than two-fold increase in CO2 emissions by 2070, compared to 2020 in residential sector. By pursuing carbon-neutrality through a renewable electricity transition, the most ambitious scenario in this study, India could reduce CO2, SO2, NOX, and BC emissions by 67%, 87%, 89%, and 99%, respectively, from the 2070 BAU levels.

An improved hourly-resolved atmospheric NOx emission inventory of industrial sources based on Continuous Emission Monitoring System data: Case of Jiangsu Province, China

Current emission inventories with low spatial and temporal resolutions, slow updates, and great uncertainty can no longer meet the new demands for the precise prevention and control of air pollution. This study considered industrial sources of Jiangsu province in 2018 as the research object and divided key industrial sources into 16 processes. Based on the continuous emission monitoring system (CEMS) data of key enterprises, millions of hourly scale monitoring data from 17842-point source enterprises at 169289 emission outlets were collected. An hourly scale high-resolution industrial source NOx emission inventory was constructed and compared with existing inventories. The total NOx emissions of power plants, industrial boilers, ferrous metal manufacturing, non-metallic mineral manufacturing, and chemical manufacturing industries in Jiangsu Province in 2018 were 55, 27, 64, 28, and 3 Gg, respectively. The total emissions from industrial sources were high in summer, reaching a peak of 17 Gg in July, and low in winter, reaching 11 Gg in February. The emission factors of the power plants, coking, and cement industries decreased by 15.95%, 29.03%, and 51.61%, respectively. Hourly scales showed that the power plants had the most considerable fluctuation in 24 h emissions at 5.94%, with high emissions occurring in the afternoon and at night. However, the 24 h emissions of ferrous metal manufacturing fluctuated slightly, at only 3.22%, and the high emissions mostly occurred at night. The WRF-Chem model was used for simulation validation. The NO2 simulation results based on this study's inventory were significantly better than those based on the Multi-resolution Emission Inventory for China (MEIC), with normalized mean biases (NMBs) of −7.1% and −10.7% for January and July, respectively, as opposed to 30.8% and 14.4% in the MEIC. The hourly scale high-precision emission inventory established in this study is significant for formulating real-time differentiated precise prevention and control policies and improving the accuracy of air quality models.

Improving photocatalytic oxidation of semiconductor (TiO2, SnO2, ZnO)/CNTs for NOx removal

Traditional semiconductors, i.e., SnO2, ZnO, and TiO2 have a good photocatalytic activity but still many disadvantages to applying in industry. In this study, these semiconductors are combined by commercial CNTs to form heterojunctions by a ball-milling route. The physical–chemical analyses include X-ray diffraction pattern (XRD), diffused reflectance spectra (UV–Vis DRS), Fourier transform infrared spectrum (FTIR), Mott-Schottky analysis, high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) are run to characterize the as-prepared materials. The total photocatalytic NOx efficiency of SnO2/CNTs, ZnO/CNTs, and TiO2/CNTs composites generate green products, i.e., NO3–, HNO3, etc. with 10%, 10.1%, and 41.25% after 30 min under visible light illumination, respectively. We also found that ZnO/CNTs easily inactivated the photocatalytic ability and converted NO gas to a more toxic product. Meanwhile, the highest selectivity of green products conversion belongs to SnO2/CNTs nanocomposite. Our findings will design and select an excellent photocatalytic oxidation system for NOx removal towards a flue gas treatment established.

Anti-Poisoning Mechanisms of Sb on Vanadia-Based Catalysts for NOx and Chlorobenzene Multi-Pollutant Control.

Modulating vanadia-based metal oxides is one of the effective methods for designing difunctional catalysts for simultaneous control of NOx and chlorobenzene (CB) from the emissions of industrial sources. Excessive NH3 adsorption and polychlorinated species accumulation on the surface are the primary issues poisoning catalysts and reducing their lifetime. Herein, Sb is selected as an NH3 adsorption alleviator and polychlorinated species preventor dopant on V2O5-WO3/TiO2. The catalyst exhibits an excellent performance for total NOx and 90% CB conversions at 300-400 °C under a gas hourly space velocity (GHSV) of 60,000 mL g-1 h-1. The HCl and N2 selectivities are maintained at 90 and 98%, respectively. The anti-poisoning ability could be attributed to the generated V-O-Sb chains on the surface: the band gap of vanadium is narrowed and the electron capability is strengthened. The above variation weakens the Lewis acid sites and blocks the electrophilic chlorination reactions of the catalyst surface (formation of polychlorinated species). In addition, oxygen vacancies on Sb-O-Ti also increase: the ring opening of benzoates is accelerated and NH3 adsorption energy is weakened. The above variation lowers the energy barriers of C-Cl cleavage even under NH3 pre-adsorption models and enhances NOx reduction thermodynamically and kinetically.

NOx and N2O emissions from Ca-rich fuel conversion in oxyfuel circulating fluidized bed combustion

A part of Estonia’s power generation is based on oil shale combustion in thermal power plants, resulting in high CO2 and pollutant emissions. The presented paper is a part of long-term experimental work to investigate the combustion of Ca-rich oil shale for air and oxyfuel combustion environments. The experiments were performed in a 60 kWth circulating fluidized bed (CFB) test facility under air, O2/CO2, and O2 with the recycled flue gas (RFG) modes of inlet O2 as vol.% ranging from 21% to 52%, and with RFG of 50% and 87%. The influence of different combustion atmospheres, excess oxygen volumetric ratios in the primary oxidizer (λPr), and dense bed temperatures (TDB), on the total NOx and N2O formations, have been studied in detail.The results show that specific concentrations of NOx (per MJ) were reduced by 14% in O2/CO2 mode, and 22% in O2/RFG compared to air combustion. N2O emissions were increased in OXY21 mode and reduced significantly from 20 mg/MJ to 4 mg/MJ with increasing inlet O2% to 52% under O2/CO2. NOx and N2O emissions were the lowest of all combustion experiments at high inlet O2% with RFG application (OXY87 + RFG). Under all tested atmospheres, NOx emissions were increasing with increasing excess oxygen in the primary oxidizer. N2O enhanced with excess oxygen, accounted for the homogenous gas-phase reaction of volatile-N and the heterogenous reaction of char-N. NOx emissions at low operating TDB were decreasing with increasing bed temperatures and increased at higher TDB > 770 °C in air combustion and TDB > 850 °C in OXY30. N2O emissions were slightly decreased at higher bed temperatures under air and O2/CO2 modes. Combustion efficiency enhanced at higher inlet O2% resulting in lower CO concentrations with reduced fuel burnout, and increased NOx and N2O emissions.Overall, NOx and N2O formations were more affected by the condition of operating parameters under both air and oxyfuel combustion experiments, and the obtained results are giving confidence that oxyfuel technology does not influence the release of nitrogen emissions from oil shale combustion. To lower the cost of CO2 impurities removal, the optimal operating conditions during oil shale CFB combustion can be confirmed after considering the discussed parameters. However, further CO2 purification resulting from oil shale oxyfuel flue gas stream is possibly required.

Assessment of the Effect of International Maritime Regulations on Air Quality in the Southern North Sea

Air pollution is a leading cause of death worldwide, and it has a profound impact on the planet’s climate and ecosystems. A substantial portion of air pollution is attributable to Ocean Going Vessels (OGVs). In light of this, international regulations have been put in place to mitigate air pollutant emissions from OGVs. While studies have indicated that these regulations can create significant health, environmental, and economic benefits, there remains a research gap regarding their specific impact on enhancing air quality. The aim of this study is to investigate how the implemented regulations have affected air quality in the Southern North Sea. The study found that the international regulations on ship emissions have successfully led to a decline in SO2 emissions from OGVs in the Southern North Sea, which resulted in a reduction of ambient SO2 concentrations inland, leading to positive effects on public health and the environment. However, the proportion of shipping’s contribution to SO2 emissions is projected to increase in the future. Moreover, the study revealed that the use of Exhaust Gas Cleaning Systems (EGCS) presents significant concerns. They were more frequently found to be non-compliant, and, more alarmingly, they emit higher mean levels of SO2. It also emerged that international regulations in the southern North Sea have less of an impact on the reduction of NOx emissions from OGVs than expected, which is all the more important given that NOx emissions from OGVs are expected to account for 40% of the total domestic NOx emissions for the northern region of Belgium by 2030.

Air Quality Improvement in Urban Street Canyons: An Assessment of the Effects of Selected Traffic Management Strategies Using OSPM Model

Constantly changing vehicle stock, modification of road infrastructure, and other conditions result in a need to update the knowledge on the effectiveness of individual traffic management strategies, which could form the basis for actions taken by local authorities to improve air quality in crowded city centers, especially in street canyons. The article presents research results that evaluate the theoretical effects of introducing select traffic reorganization scenarios in the example of four street canyons located in Krakow (Poland) that are different in terms of vehicle traffic volume and canyon geometry. These scenarios were based on a reduction in the average traffic speed, road capacity or the admission of cars meeting certain exhaust emission standards. The authors estimated changes in emissions of nitrogen oxides (NO, NO2 and total NOx) and particulate matter (PM10 and PM2.5) as well as investigated the effect of these changes on air quality in the canyons using the Operational Street Pollution Model (OSPM). Significant effects in terms of improving air quality were identified only in scenarios based on a significant reduction in traffic volume and the elimination of passenger cars and light commercial vehicles with internal combustion engines that did not meet the requirements of the Euro 4, Euro 5 or Euro 6 emission standards. For these scenarios, depending on the variant and canyon analyzed, the emission reduction was achieved at a level of approximately 36–66% for NO, 28–77% for NO2, 35–67% for NOx and 44–78% for both PM10 and PM2.5. The expected effect of improving air quality in individual street canyons for these substances was 15–44%, 5–14%, 11–36% and 3–14%, respectively. The differences obtained in the percentage reduction of emissions and pollutant concentrations in the air were the result of a relatively high background of pollutants that suppress the achieved effect of improving air quality to a large extent.

Enhancement of La0.8Sr0.2MnO3-based amperometric total NOX sensor via modification with Pt nanoparticles

Pt nanoparticle (PtNP)-modified La0.8Sr0.2MnO3 (LSM)-sensing electrodes (SE) were developed successfully by the impregnation method for amperometric total NOX (NO and NO2) sensors. The structure, morphology, and surface valence state of SE were characterized by thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results showed that all SEs of the sensors were uniformly modified with PtNPs; interestingly, the size of the PtNPs increased with an increase in the modified content. Compared with pure LSM, the sensor based on 0.50 vol% Pt/LSM exhibited enhanced gas-sensing properties toward total NOX. The sensitivity improved from − 9.04 to − 18.7 μA/decade in the NOX, ranging from 50 ppm to 800 ppm. Moreover, the sensor maintained a 94% response signal after a long-term stability test, showing a stable response during the long-term thermal cycling test towards total NOX. Meanwhile, the sensor exhibited markable selectivity and consistency. The catalytic effect of Pt nanoparticles was believed to be the main reason for the enhancement of gas-sensing characteristics.

Long-Term Air Pollution Characteristics and Multi-scale Meteorological Factor Variability Analysis of Mega-mountain Cities in the Chengdu-Chongqing Economic Circle.

The online version contains supplementary material available at 10.1007/s11270-023-06279-8.

Potential of TROPOMI for understanding spatio-temporal variations in surface NO2 and their dependencies upon land use over the Iberian Peninsula

Abstract. In orbit since late 2017, the Tropospheric Monitoring Instrument (TROPOMI) is offering new outstanding opportunities for better understanding the emission and fate of nitrogen dioxide (NO2) pollution in the troposphere. In this study, we provide a comprehensive analysis of the spatio-temporal variability of TROPOMI NO2 tropospheric columns (TrC-NO2) over the Iberian Peninsula during 2018–2021, considering the recently developed Product Algorithm Laboratory (PAL) product. We complement our analysis with estimates of NOx anthropogenic and natural soil emissions. Closely related to cloud cover, the data availability of TROPOMI observations ranges from 30 %–45 % during April and November to 70 %–80 % during summertime, with strong variations between northern and southern Spain. Strongest TrC-NO2 hotspots are located over Madrid and Barcelona, while TrC-NO2 enhancements are also observed along international maritime routes close the strait of Gibraltar, and to a lesser extent along specific major highways. TROPOMI TrC-NO2 appear reasonably well correlated with collocated surface NO2 mixing ratios, with correlations around 0.7–0.8 depending on the averaging time. We investigate the changes of weekly and monthly variability of TROPOMI TrC-NO2 depending on the urban cover fraction. Weekly profiles show a reduction of TrC-NO2 during the weekend ranging from −10 % to −40 % from least to most urbanized areas, in reasonable agreement with surface NO2. In the largest agglomerations like Madrid or Barcelona, this weekend effect peaks not in the city center but in specific suburban areas/cities, suggesting a larger relative contribution of commuting to total NOx anthropogenic emissions. The TROPOMI TrC-NO2 monthly variability also strongly varies with the level of urbanization, with monthly differences relative to annual mean ranging from −40 % in summer to +60 % in winter in the most urbanized areas, and from −10 % to +20 % in the least urbanized areas. When focusing on agricultural areas, TROPOMI observations depict an enhancement in June–July that could come from natural soil NO emissions. Some specific analysis of surface NO2 observations in Madrid show that the relatively sharp NO2 minimum used to occur in August (drop of road transport during holidays) has now evolved into a much broader minimum partly de-coupled from the observed local road traffic counting; this change started in 2018, thus before the COVID-19 outbreak. Over 2019–2021, a reasonable consistency of the inter-annual variability of NO2 is also found between both datasets. Our study illustrates the strong potential of TROPOMI TrC-NO2 observations for complementing the existing surface NO2 monitoring stations, especially in the poorly covered rural and maritime areas where NOx can play a key role, notably for the production of tropospheric O3.

Emission ratio determination from road vehicles using a range of remote emission sensing techniques

The development of remote emission sensing techniques such as plume chasing and point sampling has progressed significantly and is providing new insight into vehicle emissions behaviour. However, the analysis of remote emission sensing data can be highly challenging and there is currently no standardised method available. In this study we present a single data processing approach to quantify vehicle exhaust emissions measured using a range of remote emission sensing techniques. The method uses rolling regression calculated over short time intervals to derive the characteristics of diluting plumes. We apply the method to high time-resolution plume chasing and point sampling data to quantify gaseous exhaust emission ratios from individual vehicles. Data from a series of vehicle emission characterisation experiments conducted under controlled conditions is used to demonstrate the potential of this approach. First, the method is validated through comparison with on-board emission measurements. Second, the ability of this approach to detect changes in NOx / CO2 ratios associated with aftertreatment system tampering and different engine operating conditions is shown. Third, the flexibility of the approach is demonstrated by varying the pollutants used as regression variables and quantifying the NO2 / NOx ratios for different vehicle types. A higher proportion of total NOx is emitted as NO2 when the selective catalytic reduction system of the measured heavy duty truck is tampered. In addition, the applicability of this approach to urban environments is illustrated using mobile measurements conducted in Milan, Italy in 2021. Emissions from local combustion sources are distinguished from a complex urban background and the spatiotemporal variability in emissions is shown. The mean NOx / CO2 ratio of 1.61 ppb/ppm is considered representative of the local vehicle fleet. It is envisaged that this approach can be used to quantify emissions from a range of mobile and stationary fuel combustion sources, including non-road vehicles, ships, trains, boilers and incinerators.

Modelling for Cleaner Production & Optimization

The process of manufacturing nitric acid, the main building block in the manufacturing of explosives and fertilizer, is one of the main emitters of NOx gases. NOx is a key contributor to global warming, Typical approaches to operational improvement in the chemical manufacturing industry are cost intensive, with environmental implications. Majority of publications on optimization of chemical processes use expensive design and simulation software or a physical trial. The study adopts a process centric optimization approach for a nitric acid manufacturing process. Real time and historic process data is used to develop regression models for forecasting process impact in terms of energy use, environmental emissions and production outputs. Four regression models are developed: NO2 production, nitric acid production, total NOx emissions and the energy balance of the manufacturing process compressor train. The robustness of the four models is compared to the virtual process; overall, the average error of the combined models is 17.5% with the energy balance model proving to be the most robust. Applying the regression models allows the organization to optimize operations while adhering to environmental regulations and maintaining commercial competitiveness.

Protective Effects of L-Arginine on Mitochondria of Rat Epididymis in Hyperhomocysteinemia Induced by Prolonged Methionine Load

INTRODUCTION: The study of markers of oxidative stress, metabolites of nitric oxide (II) (NOx) and the balance of carnitine fractions in mitochondria of rat epididymis, permits to evaluate the protective role of L-arginine in experimental hyperhomocysteinemia.&#x0D; AIM: To study the influence of L-arginine on the parameters of energy metabolism, level of NO metabolites, oxidative modification of proteins and balance of carnitine fractions in mitochondria of the head and tail of rat epididymis in hyperhomocysteinemia.&#x0D; MATERIALS AND METHODS: In animals of group 1 (n = 8), severe hyperhomocysteinemia (HHcy) was modeled by administration of methionine suspension at a dose of 1.5 g/kg twice daily for 21 days with addition of 1% methionine in drinking water; group 2 rats (n = 8) received suspension base without methionine; animals of group 3 (n = 8) were daily administered L-arginine solution at a dose of 500 mg/kg intragastrically against the background methionine load from day 11 to day 21; group 4 animals (n = 8) were administered L-arginine solution of at a dose of 500 mg/kg for 10 days; group 5 (n = 8) served as a control for group 4 and received drinking water intragastrically. Concentrations of total homocysteine and NOx were determined in serum. In the mitochondrial fraction of the homogenate of epididymis tissues, the level of oxidatively modified proteins (OMP), the concentration of NOx, lactate and carnitine fractions, the activity of lactate dehydrogenase (LDH), superoxide dismutase (SOD), H+-ATPase, succinate dehydrogenase (SDH) were evaluated.&#x0D; RESULTS: HHcy was accompanied by reduction of the level of NOx in blood serum and mitochondria of epididymis head tissues. In mitochondria of tissues of head and tail of epididymis, a marked reduction of all fractions of carnitine, activity of LDH, H+-ATPase, SDH, increase in the activity of SOD and in the level of OMP were observed. With modeled HHcy, L-arginine reduced the extent of hyperhomocysteinemia, prevented reduction of NOx level in the blood serum and epididymis head and reduced the content of OMP of the epididymis mitochondria.&#x0D; CONCLUSION: L-arginine introduced in combination with methionine, reduces the extent of severity of hyperhomocysteinemia. The positive effect of L-arginine on increase in the concentration of NOx metabolites in blood serum and mitochondria of epididymis in conditions of methionine load was also confirmed. L-arginine exhibits antioxidant properties, reducing the severity of oxidative stress induced by hyperhomocysteinemia. Differences in the adaptive response to oxidative stress of the mitochondria of the head and tail of epididymis were demonstrated.

Assessing the contribution of open crop straw burning to ground-level ozone and associated health impacts in China and the effectiveness of straw burning bans

In recent years, ozone pollution in China has been shown to increase in frequency and persistence despite the concentrations of fine particulate matter (PM2.5) decreasing steadily. Open crop straw burning (OCSB) activities are extensive in China and emit large amounts of trace gases during a short period that could lead to elevated ozone concentrations. This study addresses the impacts of OCSB emissions on ground-level ozone concentration and the associated health impact in China. Total VOCs and NOx emissions from OCSB in 2018 were 798.8 Gg and 80.6 Gg, respectively, with high emissions in Northeast China (31.7%) and North China (23.7%). Based on simulations conducted for 2018, OCSB emissions are estimated to contribute up to 0.95 µg/m3 increase in annual averaged maximum daily 8-hour (MDA8) ozone and up to 1.35 µg/m3 for the ozone season average. The significant impact of OCSB emissions on ozone is mainly characterized by localized and episodic (e.g., daily) changes in ozone concentration, up to 20 µg/m3 in North China and Yangtze River Delta region and even more in Northeast China during the burning season. With the implementation of straw burning bans, VOCs and NOx emissions from OCSB dropped substantially by 46.9%, particularly over YRD (76%) and North China (60%). Consequently, reduced OCSB emissions result in an overall decrease in annual averaged MDA8 ozone, and reductions in monthly MDA8 ozone could be over 10 µg/m3 in North China. The number of avoided premature death due to reduced OCSB emissions (considering both PM2.5 and ozone) is estimated to be 6120 (95% Confidence Interval: 5320–6800), with most health benefits gained over east and central China. Our results illustrate the effectiveness of straw burning bans in reducing ozone concentrations at annual and national scales and the substantial ozone impacts from OCSB events at localized and episodic scales.

Patterns of embodied pollutant emissions along the global light industrial chain: A complex network perspective

With the upgrading of consumer goods and accelerating trade globalization, enormous amounts of pollution related to the light industry sector's production are transferred across borders along the global industrial chain, but their network patterns and evolution remain unclear. Here, we developed an analytical framework for trade-embodied pollutant emissions transfer (TPET) network by combining complex network theory and input– output theory to analyze the network of 16 light industries in 43 economies from 2000 to 2014. We revealed the critical economies, key industries, critical paths and their evolution trends. The light industry sector's total TPET was consistently large, but many factors (e.g., upgrading consumer goods, increasing trade volume, the 2008 financial crisis) caused large fluctuations. The network densities remained relatively high, with an obvious small-world property and significant centralization. Large economies (especially the world's top 10 economies with a total GDP exceeding US $1.86 trillion in 2014) were critical nodes due to their stable and dominant importance, but played opposite roles (i.e., net TPET importers vs. net exporters). Due to large differences in domestic demand, and environmental regulations, high-income economies (e.g., the U.S., and Germany) were the leading net TPET exporters, whereas low- or middle-income economies (e.g., China, Russia) were the dominate net importers; TPET therefore primarily flowed from high-income to low- or middle-income economies, with substantial growth over time. The electricity, gas, steam and air conditioning supply industry, the manufacture of other non-metallic mineral products, the manufacture of basic metals, and the fishing and aquaculture industry together accounted for 81.2 and 89.0% of total trade-embodied NOX and SOX emissions, respectively; they were thus key industries. To reduce emissions, critical economies should consume more environment-friendly products, strengthen technological innovation and pollution control in key industries, and expand environmental cooperation with other countries. Our results provide insights into the global light industry sector's TPET characteristics and reduction strategies. They also provide a reference for adjusting trade patterns and industrial structures.

Assessment of the NOх integral emission from the St.Petersburg megacity by means of mobile DOAS measurements combined with dispersion modelling

Megacities are strong sources of environmental pollution. Accurate estimates of the corresponding emissions are important to assess environmental impact and to ensure reliable operation of numerical atmospheric models. One of the most important factors of air pollution in large cities and industrial centers is anthropogenic emission of nitrogen oxides, NOx (= NO + NO2). St. Petersburg is the second largest industrial city in Russia and one of the largest northern megacities in the world. This study aims to experimentally derive the total NOx emission from the metropolitan area of St. Petersburg, based on data from mobile DOAS measurements of NO2 amount. We use data from a series of mobile experiments performed around the city in March and April 2019 and combine them with NO2 field calculations based on HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) simulations. As an initial approximation to a priori information on the spatial distribution of NOx emission sources in the St. Petersburg area, we consider ODIAC (Open-source Data Inventory for Anthropogenic CO2) data. Based on fitting the HYSPLIT simulation results to our mobile DOAS (Differential Optical Absorption Spectroscopy) measurements, and applying some assumptions about the daily, weekly and seasonal cycles of urban anthropogenic pollution, we obtained an experimental estimate of total NOx emissions of 77 ± 27 kilotons in 2019. Moreover, we managed to obtain an estimate of the contribution of urban thermal power plants to the total NOx emissions, which amounting to ∼28%.

Inverse modelling of Chinese NOx emissions using deep learning: integrating in situ observations with a satellite-based chemical reanalysis

Abstract. Nitrogen dioxide (NO2) column density measurements from satellites have been widely used in constraining emissions of nitrogen oxides (NOx = NO + NO2). However, the utility of these measurements is impacted by reduced observational coverage due to cloud cover and their reduced sensitivity toward the surface. Combining the information from satellites with surface observations of NO2 will provide greater constraints on emission estimates of NOx. We have developed a deep-learning (DL) model to integrate satellite data and in situ observations of surface NO2 to estimate NOx emissions in China. A priori information for the DL model was obtained from satellite-derived emissions from the Tropospheric Chemistry Reanalysis (TCR-2). A two-stage training strategy was used to integrate in situ measurements from the China Ministry of Ecology and Environment (MEE) observation network with the TCR-2 data. The DL model is trained from 2005 to 2018 and evaluated for 2019 and 2020. The DL model estimated a source of 19.4 Tg NO for total Chinese NOx emissions in 2019, which is consistent with the TCR-2 estimate of 18.5 ± 3.9 Tg NO and the 20.9 Tg NO suggested by the Multi-resolution Emission Inventory for China (MEIC). Combining the MEE data with TCR-2, the DL model suggested higher NOx emissions in some of the less-densely populated provinces, such as Shaanxi and Sichuan, where the MEE data indicated higher surface NO2 concentrations than TCR-2. The DL model also suggested a faster recovery of NOx emissions than TCR-2 after the Chinese New Year (CNY) holiday in 2019, with a recovery time scale that is consistent with Baidu “Qianxi” mobility data. In 2020, the DL-based analysis estimated about a 30 % reduction in NOx emissions in eastern China during the COVID-19 lockdown period, relative to pre-lockdown levels. In particular, the maximum emission reductions were 42 % and 30 % for the Jing-Jin-Ji (JJJ) and the Yangtze River Delta (YRD) mega-regions, respectively. Our results illustrate the potential utility of the DL model as a complementary tool for conventional data-assimilation approaches for air quality applications.