Contribution Of NOx Research Articles

Synergistic effect evaluation method of atmospheric emission reduction based on deep learning fusion model

Currently, the absence of a nonlinear response between air quality and industrial emissions, which accurately captures the complex relationship between pollution levels and emission sources, poses a significant challenge in the formulation of effective control policies. For the purpose of effectively managing industrial emissions and mitigating severe pollution peaks, a new method for evaluating the synergistic effects of atmospheric emission reduction was proposed. The objective of this method is to simulate the impact of emissions on air quality. In particular, we have developed a deep learning fusion model, GR-BILSTM, which integrates a generative adversarial network for data enhancement and a ResNet-BILSTM model to effectively address the issue of gradient disappearance in deep networks and capture high-dimensional data features, thereby improving the model's prediction accuracy. This model is used to study the relationship between emissions and air pollution. Subsequently, a perturbation analysis method is employed to provide a quantitative assessment of the impact of varying types and scales of industrial park emissions on PM2.5 concentrations. By modifying the emission reduction ratio, the PM2.5 concentration in the subsequent moment is predicted, and the correlation between the predicted value and the measured value is examined. This provides a vital point of reference for the formulation of targeted emission policies in industrial parks. In comparison to the LSTM, BILSTM, and CNN-BILSTM models that are commonly employed in this field, the GR-BILSTM model has been demonstrated to exhibit superior performance in terms of fitting accuracy. Our research indicates that the greatest contributions of SO2, NOx, and TSP to PM2.5 pollution in industrial parks are 16 %, 15 %, and 18 %, respectively.

Nitrogen oxides emissions from coastal wetland sediments: Experimental assessment of the influence of vegetation and nitrogen input

Nitrogen oxides (NOx = NO + NO2) have essential impacts on global climate and the environment, making it essential to study the contribution of wetland-generated NOx to environmental problems. With exogenous nitrogen input from anthropogenic activities, wetland sediments become active emission hotspots for NOx. In this study, we conducted field experiments in a typical salt marsh wetland to measure nitric oxide (NO, the primary component of NOx from sediments) exchange fluxes in both mudflat and vegetated sediments. We found that NO fluxes in vegetated sediments (0.40 ± 0.15 × 10−12 kg N m−2 s−1) were relatively higher than in mudflat sediments (−1.31 ± 1.39 × 10−12 kg N m−2 s−1), with this difference occurring only during the vegetation-dying season (autumn). Correlations between sediment NO fluxes and environmental parameters revealed that NO flux variation during the observation period was primarily influenced by sediment respiration, temperature, water content, and substrate availability. However, the influence of these factors on NO fluxes differed between mudflat and vegetated sediments. In-situ data analysis also suggested that tidal horizontal migration, which affects sediment substrate and salinity, may regulate sediment NO emissions. Furthermore, in-situ incubations with nitrogen addition (ammonia, nitrite, and nitrate) were conducted to study the response of sediment NO emissions to exogenous nitrogen. We observed that nitrogen addition caused a 259.7 % increase in NO emissions from vegetated sediments compared to the control during the effective period of nitrogen addition (days 1–3). However, although nitrogen addition markedly stimulated sediment NO emissions, the overall NO production capacity constrained the extent of this increase.

Characteristics and Formation Mechanism of Ozone Pollution in Demonstration Zone of the Yangtze River Delta, China

Emerging research indicates that ground-level ozone (O3) has become a leading contributor to air quality concerns in many Chinese cities, with the Yangtze River Delta (YRD) region facing particular challenges. This study investigated the characterization of air pollutants in Wujiang, which is located within the YRD demonstration zone, during the warm season (April–September) of 2022. The contributions of emission and meteorology to O3 were identified, the O3-NOX-VOC sensitivities were discussed, and the VOC sources and their contributions to O3 formation were analyzed. A random forest model revealed that the high O3 concentration was mainly caused by a combination of increased emission intensity due to the resumption of work and production after the COVID-19 pandemic, along with adverse meteorological conditions. The results revealed more than 92% of the pollution days were related to O3 during the warm season, and the impact of O3 precursor emissions was slightly greater than that of the meteorological conditions. O3 formation was in the VOC-limited regime, and emission reduction strategies targeting VOCs, particularly aromatics such as toluene and xylene, have been identified as the most effective approach for mitigating O3 pollution. Changes in O3-NOX-VOC sensitivity were also observed from the VOC-limited regime to the transitional regime, which was primarily driven by variations in the NOX concentrations. The VOC source analysis results showed that the contributions of gasoline vehicle exhaust and diesel engine exhaust (mobile source emissions) were significantly greater than those of the other sources, accounting for 20.8% and 16.5% of the total VOC emissions, respectively. This study highlights the crucial role of mobile source emission control in mitigating O3 pollution. Furthermore, prioritizing the control of VOC emission sources with minimal NOX contributions is highly recommended within the VOC-limited regime.

Using PMF model and Bayesian model to quantify NOx sources in non-typhoons and Super Typhoon Lekima (2019) in Hangzhou

Quantifying and comparing nitrate (NO3−) sources in typhoons and non-typhoons is important for controlling and reducing their emissions. In this study, the chemical compositions and stable isotopes (δ15N–NO3- and δ18O–NO3-) of non-typhoon and Typhoon Lekima precipitation in Hangzhou (from May–August during 2019 and 2020) were determined. The results revealed that severe acid rain occurred in Hangzhou, except during Typhoon Lekima. According to the positive matrix factorization (PMF) model results, the ion contributions of sources in non-typhoons were as follows: secondary inorganic aerosols + biomass burning > sea salt aerosols > agricultural sources > terrestrial sources, whereas sea salt aerosols + biomass burning were the primary contributors of ions in Typhoon Lekima. The δ15N–NO3- values of non-typhoon and Typhoon Lekima ranged from −4.0 to −1.3‰ and −2.7 to 5.8‰, respectively. The δ18O–NO3- values of non-typhoon and Typhoon Lekima ranged from 56.3‰ to 74.7‰ and 32.2–55.3‰, respectively. The calculated contribution of N2O5 pathway in NOx oxidation to NO3− during non-typhoon precipitation was 64.7 ± 12.2%. If the contribution of OH· pathway during Typhoon Lekima precipitation was 87%, the Monte Carlo simulation results demonstrated that the estimated oxidation proportions of NO via O3 and RO2 (or HO2) ranged from 48.8 to 100% and 0–51.2%, respectively. Based on the improved Bayesian model combined with nitrogen isotope fractionation, the NOx contributions from four sources (biomass burning > coal combustion > mobile sources > microbial N cycle) in non-typhoon precipitation ranged from 21 to 30% (Ԑ = 3.6). In Typhoon Lekima (Ԑ = 5.2), lightning (23.6 ± 11.2%) was one of the primary NOx contributors and a lower contribution from microbial N cycle (17.9 ± 5.4%) compared with the PMF model (22.8%). Moreover, for Typhoon Lekima, the sum of biomass burning, coal combustion, and mobile sources in the improved Bayesian model (58.5%) was slightly lower than that of secondary inorganic aerosols in the PMF model (62.4%). Therefore, the coupled PMF–improved Bayesian model is a feasible and reliable method for source identification and apportionment of NO3− in precipitation.

Observations of ozone, acyl peroxy nitrates, and their precursors during summer 2019 at Carlsbad Caverns National Park, New Mexico

ABSTRACT Carlsbad Caverns National Park (CAVE) is located in southeastern New Mexico and is adjacent to the Permian Basin, one of the most productive oil and natural gas (O&G) production regions in the United States. Since 2018, ozone (O3) at CAVE has frequently exceeded the 70 ppbv 8-hour National Ambient Air Quality Standard. We examine the influence of regional emissions on O3 formation using observations of O3, nitrogen oxides (NOx = NO + NO2), a suite of volatile organic compounds (VOCs), peroxyacetyl nitrate (PAN), and peroxypropionyl nitrate (PPN). Elevated O3 and its precursors are observed when the wind is from the southeast, the direction of the Permian Basin. We identify 13 days during the July 25 to September 5, 2019 study period when the maximum daily 8-hour average (MDA8) O3 exceeded 65 ppbv; MDA8 O3 exceeded 70 ppbv on 5 of these days. The results of a positive matrix factorization (PMF) analysis are used to identify and attribute source contributions of VOCs and NOx. On days when the winds are from the southeast, there are larger contributions from factors associated with primary O&G emissions; and, on high O3 days, there is more contribution from factors associated with secondary photochemical processing of O&G emissions. The observed ratio of VOCs to NOx is consistently high throughout the study period, consistent with NOx-limited O3 production. Finally, all high O3 days coincide with elevated acyl peroxy nitrate abundances with PPN to PAN ratios > 0.15 ppbv ppbv−1 indicating that anthropogenic VOC precursors, and often alkanes specifically, dominate the photochemistry. Implications: The results above strongly indicate NOx-sensitive photochemistry at Carlsbad Caverns National Park indicating that reductions in NOx emissions should drive reductions in O3. However, the NOx-sensitivity is largely driven by emissions of NOx into a VOC-rich environment, and a high PPN:PAN ratio and its relationship to O3 indicate substantial influence from alkanes in the regional photochemistry. Thus, simultaneous reductions in emissions of NOx and non-methane VOCs from the oil and gas sector should be considered for reducing O3 at Carlsbad Caverns National Park. Reductions in non-methane VOCs will have the added benefit of reducing formation of other secondary pollutants and air toxics.

The impact of emission reduction policies on the results of PM2.5 emission sources during the 2016 G20 summit: Insights from carbon and nitrogen isotopic signatures

Intensive field observations were conducted on the PM2.5, gaseous pollutants, δ13C, and δ15N values to evaluate the efficacy of much stricter air quality measures and emergency response strategies implemented in Hangzhou and Ningbo during the 2016 G20 Summit. Our data showed that δ13C values of PM2.5 samples collected in two cities varied from −30.8‰ to −24.2‰, with an average of −25.8‰ ± 1.1‰ during sampling periods. Similar δ13C values observed in the two cities indicated that there is no pronounced differences of carbon sources between the Hangzhou and Ningbo. Based on the Bayesian model, results indicated that C3 plant combustion contributed 47.8% and 47.2% to carbon sources of PM2.5 in Hangzhou and Ningbo, respectively. δ15N values of PM2.5 ranged from 2.0‰ to 13.7‰, with a mean value of 8.5‰ ± 2.5‰ during the whole campaign. Notably, more effective results were observed in reducing NH3 compared to NOx in Hangzhou and Ningbo. Additionally, a more reliable source apportionment approach using isotope fractionation effects and a Bayesian model was applied (improved Bayesian model), which reduced the uncertainty in the apportionment of nitrogen sources. The estimated fractionation effects from NH3 to NH4+ averaged at 16.19‰ ± 3.49‰, and from NOx to NO3− averaged at 12.94‰ ± 2.60‰, respectively. Compared to the results of the Bayesian model, the contributions of NOx from coal combustion (13.8%) and vehicle exhausts (11.6%), and NH3 from coal combustion (12.1%) and vehicle exhausts (12.5%) by improved Bayesian model were more consistent with the emission inventory. Collective evidence of multiple isotopes indicated that pollution emissions were sensitive in response to strict control measures. Our results also revealed that fossil fuel combustion reduction and regional control policies should be synergistically implemented for better air quality.

Comparison of ozone formation attribution techniques in the northeastern United States

Abstract. The Integrated Source Apportionment Method (ISAM) has been revised in the Community Multiscale Air Quality (CMAQ) model. This work updates ISAM to maximize its flexibility, particularly for ozone (O3) modeling, by providing multiple attribution options, including products inheriting attribution fully from nitrogen oxide reactants, fully from volatile organic compound (VOC) reactants, equally from all reactants, or dynamically from NOx or VOC reactants based on the indicator gross production ratio of hydrogen peroxide (H2O2) to nitric acid (HNO3). The updated ISAM has been incorporated into the most recent publicly accessible versions of CMAQ (v5.3.2 and beyond). This study's primary objective is to document these ISAM updates and demonstrate their impacts on source apportionment results for O3 and its precursors. Additionally, the ISAM results are compared with the Ozone Source Apportionment Technology (OSAT) in the Comprehensive Air-quality Model with Extensions (CAMx) and the brute-force method (BF). All comparisons are performed for a 4 km horizontal grid resolution application over the northeastern US for a selected 2 d summer case study (9 and 10 August 2018). General similarities among ISAM, OSAT, and BF results add credibility to the new ISAM algorithms. However, some discrepancies in magnitude or relative proportions among tracked sources illustrate the distinct features of each approach, while others may be related to differences in model formulation of chemical and physical processes. Despite these differences, OSAT and ISAM still provide useful apportionment data by identifying the geographical and temporal contributions of O3 and its precursors. Both OSAT and ISAM attribute the majority of O3 and NOx contributions to boundary, mobile, and biogenic sources, whereas the top three contributors to VOCs are found to be biogenic, boundary, and area sources.

Differences between VOCs and NOx transport contributions, their impacts on O3, and implications for O3 pollution mitigation based on CMAQ simulation over the Yangtze River Delta, China

The relationship between O3 and its precursors during urban polluted episodes remains unclear. In this study, the simultaneous source apportionment of VOCs, NOx, and O3 over the Yangtze River Delta (YRD) region during the O3 polluted episode on July 24–30, 2018, was performed based on the Integrated Source Apportionment Method (ISAM) embedded in the Community Multiscale Air Quality Modeling System (CMAQ). The results of the ISAM were compared with those of the Brute Force Method (BFM) and Positive Matrix Factorization (PMF). Furthermore, the differences between the transport contributions of VOCs and NOx, and their impacts on O3 were analyzed. The results indicate that observations of VOCs species can be well captured by simulated VOCs, and the ISAM has a significant advantage in the source apportionment of VOCs, especially for sources emitting highly reactive species. In the clean and polluted periods, the local contribution percentages of VOCs in urban sites ranged from 60 % to 77 %, much higher than those of NOx (31 %–43 %) and O3 (16 %–33 %). NOx and O3 have strong transport abilities with high and close contribution percentages, which are highly correlated, mainly because oxygen atoms produced by the photolysis of NO2 in the aged air mass combined rapidly with O2 to form O3 during transport. The VOCs chemical loss caused by the oxidation of OH radicals during transport makes the ability of VOCs for long-distance transport much weaker than that of NOx. Furthermore, owing to the sufficient aging of VOCs, those contributed by long-distance transport have little effect on O3. To a certain extent, controlling one's NOx emissions can help other cities more, while controlling one's VOCs emissions can help itself more. Therefore, it is recommended to attach enough importance to joint prevention and control of NOx among cities and even long-distance areas to alleviate regional O3 pollution.

Dissimilatory nitrate reduction processes in surface sediments of shrimp ponds during the culture period

Intensive aquaculture in estuaries and coasts has resulted in several ecological and environmental problems. Among various nitrogen transformation pathway, dissimilatory nitrate (NO3-) reduction is considered to be highly important in regulating reactive nitrogen. However, there are relatively few studies on the processes and contribution of NOx- reduction in sediment during the shrimp pond culture period. Three sediment NO3- reduction processes, denitrification (DNF), anaerobic ammonium oxidation (ANA), and dissimilatory NO3- reduction to ammonium (DNRA), were surveyed in eight shrimp ponds across three subtropical estuaries using 15N isotope tracing experiments. The rates of DNF, ANA and DNRA ranged from 2.87–18.11, 0.10–1.92, and 0.21–1.25 nmol N g -1 h -1, respectively. DNF was responsible for 64.2–91.6% of the total NO3- reduction. Regarding environmental factors, C and N substrates, as well as salinity, significantly affected NO3- reduction. In general, the N losses were approximately 32.43–131.64 g N m-2 yr-1 for DNF and 2.38–15.85 g N m-2 yr-1 for ANA in this study, indicating that coastal reclamation is a nonnegligible way to remove nitrogen. Our results provide a scientific foundation for understanding the mechanism of nitrogen cycling in the artificial aquatic environment of shrimp ponds.

Analysis of the Spatial and Temporal Patterns of Ground-Level Ozone Concentrations in the Guangdong–Hong Kong–Macao Greater Bay Area and the Contribution of Influencing Factors

Ozone (O3) pollution has negative impacts on human health and property. The Guangdong–Hong Kong–Macao Greater Bay Area (GBA) is facing severe O3 pollution problems due to rapid economic development. In this paper, we used sensitivity experiments and GeoDetector to analyze the effects of meteorological factors, anthropogenic emissions, and landscape patterns on O3 concentrations as well as the contributions of NOx and NMVOC (non-methane volatile organic compounds) to the variation of O3 concentrations and the causes of sectoral emissions in the GBA in 2017. The results revealed that, in GBA, the contribution of meteorology to the variation of O3 concentration was dominant both in terms of region and extent, and the contribution of emissions was relatively weak. The contribution of meteorology and emissions to O3 production was mainly contributory. Meteorology contributed significantly to O3, and its non-linear interaction with anthropogenic emissions and surface landscape affected O3 concentration changes. The degree of contribution of NOx and NMVOC varied widely among seasons, and the variation of their relative contribution areas was related to residential sector emissions and agricultural sector emissions. This article enriches the exploration of the O3 formation mechanism in the GBA and provides theoretical support for the implementation of differentiated regional and seasonal mitigation strategies for O3 concentration.

On the Issues of NOx as Greenhouse Gases: An Ongoing Discussion…

Nitrogen oxides (NOx = NO + NO2) emitted from a stationary combustion chamber (including waste to energy plants) or engines cause numerous undesirable environmental effects. These include negative influences on human and animal health, detrimental effects on plants and vegetation, acid rain, and smog. These negative influences are commonly accepted by the scientific community. However, the impact of NOx on the greenhouse effect (GHE) is not generally accepted by the scientific community. In this paper, the issue of the impact of NOx on the GHE is discussed, and it was analyzed and explained that NOx are an indirect greenhouse gas (GHG). However, the impact of NOx on the GHE is a complex process affected by different parameters (cooling and warming nature is possible). It has been estimated that NOx emitted from stationary, ground-placed sources (such as boilers and furnaces) have little impact on the GHE compared to CO2 and other direct GHGs. The contribution of NOx in the GHE compared to the emission of all GHGs is less than 3%. NOx sources from waste incineration and co-incineration plants were especially considered and analyzed. The co-incineration in smaller plants (capacity range of 1 ÷ 5 MW) gives more benefits to the environment due to a decrease in the NOx emission standards when the share of the waste increases.

Separately resolving NOx and VOC contributions to ozone formation

Ozone (O3) is widely recognized as a significant air pollutant that affects public health across the globe. O3 is formed from precursor emissions of oxides of nitrogen (NOx) and volatile organic compounds (VOCs) that react in the atmosphere, making it complex to identify the major source contributions to O3 concentrations. O3 source apportionment calculations within chemical transport models (CTMs) provide a specialized approach to resolve source contributions. Traditional O3 apportionment techniques track source contributions based on the chemical formation regime, but they do not separately distinguish between NOx and VOC source contributions. In this study, a new O3 source apportionment technique was developed to explicitly resolve the contributions from both NOx and VOC sources in order to provide a more detailed view on O3 source origins so that policy makers can design more effective emission control strategies. The new technique is flexible and can be configured to identify the original source of precursors that contribute to O3 formation or the most recent source depending on the choice of the tagging method. The detailed features of the new technique are demonstrated during a peak O3 event in September 2010 in Los Angeles, while trends in O3 source contributions over time are evaluated during two additional simulations in July 2005 and August 2015. Quality control checks show that the new source apportionment methodology does not alter predicted total O3 concentrations, and the detailed source apportionment information can be averaged to yield results that are consistent with traditional O3 source apportionment calculations. The detailed O3 source apportionment results during Sept 2010 show that, among NOx sources, on-road gasoline, on-road diesel, off-road diesel, and soil NOx account for over 60% of the ground level O3 concentrations. Among VOC sources, upwind boundary conditions and biogenic sources account for approximately 90% of the ground-level O3 formed. The formaldehyde to NO2 ratio suggests that the chemical regime in the year 2015 was VOC-limited, but given the uncontrollable nature of the VOC emissions, the results suggest that NOx emission controls would have been the preferred emission control strategy to reduce O3 concentration in Los Angeles at that time, with the understanding that some period of O3 disbenefits would need to be tolerated until the emissions control program shifts the atmospheric chemistry back into the NOx-limited regime. The NOx source apportionment results for O3 identify the largest NOx sources that could be reduced in an effort to reach NOx-limited conditions. The chemical regime in the Los Angeles atmosphere is continuously evolving, and so these calculations would need to be repeated under current conditions to determine if we have arrived at this NOx limited regime. Future studies will undertake this analysis.

Effect of H2, H2O, and CO2 on the deNOx characteristics of a combined passive NOx adsorber and NOx reduction catalyst

AbstractThe effect of H2, H2O, and CO2 on the NOx removal characteristics of a non‐PGM material (Ag/MgO/γ‐Al2O3) is investigated, which is shown to be active for both NOx adsorption and reduction. H2O facilitates NOx adsorption at early times but inhibits it at longer times. The inhibiting effect of CO2 is observed at low temperatures and is proposed to be due to bicarbonates. However, the inhibiting effect of both H2O and CO2 decreases at higher temperatures. The formation of NO2 at low temperatures is attributed to NO oxidation, and the contribution of stored NOx to NO2 formation increases with temperature. H2O inhibits NH3 oxidation at high temperatures as well as NOx reduction by NH3‐SCR at low temperatures. However, the NOx reduction activity is not affected by CO2. H2 significantly promotes the NH3‐SCR reactions, which is attributed to the facilitation of NOx spillover from the reduced Ag sites to the support.

Attenuated sensitivity of ozone to precursors in Beijing–Tianjin–Hebei region with the continuous NOx reduction within 2014–2018

Facing the elevated surface summer O3 over North China in recent years with the continuous NOx reduction, we conducted the ozone-precursor sensitivity study in summer (July) in Beijing–Tianjin–Hebei region (BTH) under the 2018 and 2014 emissions, based on WRF-Chem model. On 2018 emission condition, 30% precursor reduction simulations presented the positive contribution of VOCs and the negative contribution of NOx to daytime O3. The occurrence probabilities of VOCs-sensitive, NOx-titration, mixed sensitive, NOx-sensitive, and non-sensitive regimes respectively reached 3–49%, 2–82%, 0–7%, 0–6% and 14–82% in the urban grids, and 2–32%,1–19%, 1–6%, 0–5% and 54–86% in the rural grids. For several widely used photochemical indicators, their values in VOCs-sensitive regime were well separated from those in NOx-sensitive regime, but the NOx-sensitive values were very similar to the non-sensitive values, which implied the inefficiency of these indicators in indicating NOx-sensitive regime. Finally, VOCs-sensitive regime was discerned based on the indicator HCHO/NO2, occupying about a third of areas in morning and dusk but shrinking to about a tenth of areas in 11:00–16:00 in BTH. And these areas apparently decreased from 2014 emission to 2018 emission. However, the rest areas of this region were under non-sensitive regime but not NOx-sensitive regime, for the noticeable O3 drop never happened in NOx reduction scenario. Meanwhile, the modeled O3/PAN in the areas under non-sensitive regime exceeded 60, which also implied the minor impact of local photochemistry on O3 there. Additionally, the responses of daytime O3 to precursor emissions in the urban grids were calculated, declining by 20.8% for NOx and 6.9% for VOCs from 2014 to 2018. Therefore, to solve the ozone pollution problem of BTH, the cross-region strategy coupled with the VOCs and NOx co-control will be essential.

Exhaust emission characteristics study of light and heavy-duty diesel vehicles in India

A study has been conducted using a portable emission tester (PET) for the city of Imphal, India using twelve (12) key business locations for determining the combustion by-products (exhaust emissions) & their characteristics from both light and heavy-duty diesel vehicles. The ambient temperature varied from 23.5 to 28 °C and humidity to be 65 ± 15% during the course of the study. Higher values of CxHy and CO, compared to the standard permissible values, have been observed from light duty diesel (LDD) vehicles, with average values of 430 ppm and 465.4 ppm respectively, while NOx has an average value of 99.2 ppm. Similar characteristics are also witnessed from the heavy-duty diesel (HDD) vehicles with CO and CxHy having alarming values of 1585 ppm and 2968 ppm respectively, while NOx have an average value of 140.06 ppm. Using total emission approach, the CO2 emissions have been estimated to be about 38.02*105 tons and 1135*105 tons from LDD and HDD respectively till 2018. With respect to the present study, HDD have the maximum contribution of CxHy, NOx and CO in the atmosphere with values of 76.9%, 69.3% and 58.5% respectively. The authors believed that such alarming emissions from the vehicles would have been controlled if the authorities had performed regular checks and imposed strict laws against heavy emissions from vehicles.

Analysis of the National Air Pollutant Emissions Inventory (CAPSS 2017) Data and Assessment of Emissions based on Air Quality Modeling in the Republic of Korea

According to the 2017 National Air Pollutant Emissions Inventory (NEI), air pollutant emissions in the Republic of Korea comprised 817,420 metric tons (hereafter tons) of CO, 1,189,800 tons of NOx, 315,530 tons of SOx, 592,582 tons of TSP, 218,476 tons of PM10, 91,731 tons of PM2.5, 15,555 tons of black carbon (BC), 1,047,585 tons of VOCs, and 308,298 tons of NH3. Emissions of the 13 first-level emission source categories, which constitute the NEI, were estimated and, based on their characteristics, the emission source categories were grouped into five sectors (energy, industry, road, non-road, and everyday activities and others). In addition, the contributions of primary PM2.5 and its four precursors (NOx, SOx, VOCs, and NH3) to the 2017 NEI were assessed in this study. The emission contributions of NOx to the NEI were 36.5% for the road sector, which was the highest of those of all the air pollutants for this sector; NOx emissions for this sector were 4.2% lower than those in the previous year. The emission contributions of SOx and PM2.5 to the NEI were higher than those of the other air pollutants for the industry sector; SOx and PM2.5 emissions for this sector decreased by 9.8% and 19.7%, respectively, compared with those in the previous year. The emission contributions of VOCs and NH3 to the NEI were 65.3% and 83.9% for the everyday activities and others sector, respectively, higher than those of the other air pollutants for this sector; VOCs and NH3 emissions for this sector increased by 0.8% and 2.9%, respectively, compared with those in the previous year. A three-dimensional (3D) chemical transport modeling system was used to validate the emission estimates. These data suggest that simulated SOx emissions were overestimated in areas with dense large-scale industrial complexes, such as Jeollanam-do, Gyeongsangbuk-do, and Ulsan, and that simulated NOx emissions were overestimated in Seoul, Incheon, and Jeollanam-do.

Effects of marine produced organic matter on the potential estuarine capacity of NOx− removal

Dissolved inorganic nitrogen (DIN) is very high in the Pearl River Estuary (PRE) and nitrate (NOx−) removal processes such as denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) are important for determining export of DIN to coastal waters. However, fluxes of NOx− removal and influencing factors in the PRE are still unclear. We conducted 4 cruises at 11 sites in the PRE to investigate potential NOx− removal rates, their contributions, and corresponding gene abundances, and controlling factors in surface sediments (0–5 cm). The results showed that the potential rates of denitrification, anammox, and DNRA as well as their contributions varied spatially and seasonally. Denitrification (1.98 ± 1.7 μg N g−1 d−1) was the major NOx− removal processes (68.43 ± 14.61%) while DNRA (0.45 ± 0.28 μg N g−1 d−1) contributed 22.61 ± 14.89% in NOx− removal. The NOx− removal processes and corresponding gene abundances were correlated with the chlorophyll concentrations in both overlying water and sediment, indicating that marine-produced organic matter was the major driver for benthic NOx− removal processes. In addition, water column turbidity had important effects on primary production, which affects benthic N processes. Our study provides evidences for that the turbidity-regulated primary production in overlying water is the primary driver for benthic NOx− removal processes. The contribution of sediment NOx− removal fluxes to water column NOx− concentration was low in the upper estuary and increased in the lower estuary where marine produced chlorophyll a was higher. However, daily fluxes of NOx− removal were estimated to account for only 0.18–7.22% (mean 1.85 ± 1.62%) of NOx− in the whole overlying water column. This suggests that most riverine NOx− was exported out into the adjacent coastal waters.

Temporal variations, regional contribution, and cluster analyses of ozone and NOx in a middle eastern megacity during summertime over 2017-2019.

Particulate matter is usually regarded as the dominant pollutant in Tehran megacity in Iran. However, the number of ozone exceedance days significantly increased in recent years. This study analyzes simultaneous measurements of O3 and NOx (NO+NO2) concentrations to improve our understanding of ozone evolution during the summers of 2017 to 2019. The k-means clustering technique was used to select five representative air quality monitoring sites in Tehran to capture O3 and NOx concentrations' variability. The findings show that all of the investigated sites failed to meet the ozone non-attainment criterion. The ozone weekend effect is seen in the study of weekday/weekend differences in 2017 and 2018, but not in 2019, which can be due to the shift in the ozone production regime. The summer mean variation analysis can also be used to deduce this regime change. In 2017, the O3 and NO2 summer mean variations suggest a holdback in the NO2 upward trend and a reversal in the O3 downward trend that had been in place since 2012. Air mass back trajectory clustering reveals that east and north-east air mass clusters have the most significant impact on Tehran's O3 pollution and the highest regional contribution to OX. The study of OX against NOx shows that the regional contribution to OX increased from 2017 to 2018 and then decreased in 2019; however, the local contribution is the opposite. The diurnal analysis of the regional and local contributions to OX indicated that OX in Tehran might be primarily affected by pollutants from a short distance. The findings reveal critical changes in the behavior of O3 in recent years, indicating that decision-makers in Tehran should reconsider air pollution control measures.

Preheating and premixing effects on NOx emissions in a high-pressure axially staged combustor

NOx emissions remain a primary concern for modern and future gas turbines, particularly as we progress towards a net-zero carbon future. It is critical to identify novel strategies to mitigate environmental pollutants for both modern turbines operated on natural gas and future turbines projected to use carbon-free fuels (such as hydrogen). In the current study, NOx emissions of a reacting methane-air jet in a vitiated crossflow are experimentally investigated in a model axially staged combustor at 5 atm. The combustion products from the main stage combustor flow into the axial stage at temperatures ranging from 1580 to 1650 °C. The axial stage contains a reacting jet in crossflow, which provides an overall temperature rise ranging from 50 to 220 °C to generate exit temperatures similar to gas turbine engines. The focus of this paper is to explore the effects of flame liftoff and ignition timescales on the NOx contribution of this secondary jet. This is done by varying the premixed level and preheat temperature of the axial jet. The effects are explored at different momentum flux ratios (J), jet equivalence ratios (φjet), exit temperatures (Texit), and main stage (headend) temperatures (THE). High-speed CH* chemiluminescence imaging is employed for each test case to determine the flame stabilization point. For a given temperature rise and combustor exit temperature, an increase in ignition delay was observed with a decrease in jet temperature. This provided a NOx benefit, particularly for jets that are injected at or close to an ignitable mixture fraction. Similarly, the coaxial injector caused a significant ignition delay compared to the fully premixed injector; this also led to a NOx benefit. Overall, the results show that a thermally driven delay in the axial stage provides a greater NOx reduction than a mixing delay.

Preliminary Data Monitoring In Vivo Sources of Reactive Oxygen Species Production in Human Obesity

Introduction Excessive reactive oxygen species (ROS) production is a prominent feature of obesity-related conditions including impairments in endothelial function. NADPH oxidases (Nox) and mitochondria are major sources of ROS production within the vasculature. However, studies involving direct measurement of in vivo ROS production are limited in humans. Thus, the relative contributions of Nox- and mitochondrial-derived ROS in human obesity remain to be fully characterized. The objective of this study was to determine the predominant sources of in vivo ROS production in the skeletal muscle microvasculature of individuals with obesity. We hypothesize that both Nox- and mitochondria-dependent ROS production are upregulated in human obesity. Methods Two sedentary men with Class II and above obesity (body mass index ≥ 35 kg/m2) and the Metabolic Syndrome were studied. Microdialysis was used for measurements of in vivo skeletal muscle ROS production. Microdialysis probes were perfused with saline containing Amplex Ultrared, horseradish peroxidase and superoxide dismutase to measure local hydrogen peroxide and superoxide concentrations. To assess ROS production from distinct sources, microdialysis probes were perfused with the following: apocynin (non-specific Nox inhibitor), MitoTEMPO (mitochondrial-ROS inhibitor), and GKT 137831 (specific Nox 4 inhibitor). Results The concentrations of hydrogen peroxide and superoxide decreased upon addition of apocynin to microdialysis probes (mean ± SEM; hydrogen peroxide: 1.18 ± 0.58 to 0.76 ± 0.01 μM; superoxide: 1.47 ± 0.46 to 1.10 ± 0.62 μM). MitoTEMPO perfusion elicited an increase in hydrogen peroxide (1.12 ± 0.76 to 1.51 ± 1.08 μM) and decrease in superoxide (1.47 ± 0.46 to 0.78 ± 0.10 μM). The combination of apocynin plus MitoTEMPO resulted in concentrations of hydrogen peroxide (0.22 ± 0.10 μM) and superoxide (0.23 ± 0.06 μM) that were 69.7% and 79.1% lower than apocynin alone. In addition, the hydrogen peroxide (0.56 ± 0.25 μM) and superoxide (0.43 ± 0.18 μM) concentrations with co-perfusion of apocynin and GKT were 26.3% and 60.9% lower than with apocynin alone. Conclusions Our preliminary data suggest that mitochondria and Nox together are significant sources of ROS production within the skeletal muscle microvasculature of obese individuals. The local inhibition of Nox- and mitochondrial-derived ROS resulted in marked decreases in extracellular ROS levels within the skeletal muscle microvasculature. Although the small sample size currently limits our interpretation of the results, this study is anticipated to become the first to report on distinct sources of in vivo ROS production in human obesity.