Deciphering isoprene variability across dozen of Chinese and overseas cities using deep transfer learning

The short-term reduction of air pollutant emissions is an important emergency control measure for avoiding air pollution exceedances in Chinese cities. However, the impacts of short-term emission reductions on the air qualities in southern Chinese cities in spring has not been fully explored. We analyzed the changes in air quality in Shenzhen, Guangdong before, during, and after a city-wide lockdown associated with COVID-19 control during March 14 to 20, 2022. Stable weather conditions prevailed before and during the lockdown, such that local air pollution was strongly affected by local emissions. In-situ measurements and WRF-GC simulations over the Pearl River Delta (PRD) both showed that, due to reductions in traffic emissions during the lockdown, the concentrations of nitrogen dioxide (NO2), respirable particulate matter (PM10), and fine particulate matters (PM2.5) in Shenzhen decreased by (-26±9.5)%, (-28±6.4)%, and (-20±8.2)%, respectively. However, surface ozone (O3) concentration did not change significantly[(-1.0±6.5)%]. TROPOMI satellite observations of formaldehyde and nitrogen dioxide column concentrations indicated that the ozone photochemistry in the PRD in spring 2022 was mainly controlled by the volatile organic compound (VOCs) concentrations and was not sensitive to the reduction in nitrogen oxide (NOx) concentrations. Reduction in NOx may even have increased O3, because the titration of O3 by NOx was weakened. Due to the small spatial-temporal extent of emission reductions, the air quality effects caused by this short-term urban-scale lockdown were weaker than the air quality effects across China during the widespread COVID-19 lockdown in 2020. Future air quality management in South China cities should consider the impacts of NOx emission reduction on ozone and focus on the co-reduction scenarios of NOx and VOCs.

Mechanism of heterogeneous reduction of NO over graphite-supported single-atom Fe catalyst: DFT study

Switching to electric vehicles can lead to significant reductions of PM2.5 and NO2 across China

Tropospheric ozone (O3) is a typical secondary pollutant and produced by a series of chemical reactions of precursors such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) under light conditions. The emission of precursors in industrial cities is large and complex, and the relationship between O3 and its precursors is not clear, making it is challenged to identify the key factors and source influencing O3 formation. This study used observation-based-model (OBM), based on the precursors’ observation data and chemical mechanism, to analyze O3 sensitivities to VOCs and NOx during summer in a typical industrial city in China. In our research, higher concentrations of O3 precursors were observed during O3 polluted periods in summertime indicating that precursor accumulation contributed to the higher max net (O3) (16.6 ppbv∙h-1) and HOx· concentrations. The important reactions in ROx· recycling was mainly dominated by the precursors of NO, NO2 and alkene, which were mainly discharged from sources caused by the developed industry. Analyses of relative incremental reactivity (RIR) indicated that O3 production during polluted period is in a chemical transition regime and was sensitive to both VOCs (RIR=0.39) and NOx (RIR=0.56), particularly emphasizing the crucial of phased control of O3 precursors. Results from PMF analysis indicated that gasoline vehicle emissions were the major contributor to VOCs (27.0%), followed by coal combustion (20.3%), diesel vehicle emissions (15.9%), industrial processes (15.1%). For NOx, coal combustion (44.0%) and diesel vehicle emissions (35.2%) had the largest contribution, followed by industrial processes (12.5%) and gasoline vehicle emissions (8.3%). Based on PMF results and OBM, O3 source was analyzed used RIR method in this study, and industrial process (36.7%) and biogenic source (24.6%) were the major sources of O3. The sensitivities of O3 formation to these sources depend on if both VOC and NOx sensitivities are considered. Previous studies only considered the influence of VOCs on O3 formation when analyzing the source of O3, but this study indicated that the influence of NOx in industrial cities on O3 formation should not be ignored. Meanwhile, considering only VOCs but not NOx in the analysis of O3 sources will underestimate the emission proportion of anthropogenic sources and overestimate the proportion of biogenic sources, resulting in inaccurate results. Industrial cities are typical cities in transition areas, and the sensitivity of O3 to both VOCs and NOx should also be taken into account when analyzing the source of O3 in transition areas, which can ensure the accuracy of source analysis results. In addition, emission reduction of VOCs and NOx simultaneously should be considered in the control of O3 in transition areas. This study provides an improved direction for the source analysis of O3 in industrial cities and even cities in transition areas.

Ozone responses to reduced precursor emissions: A modeling analysis on how attainable goals can improve air quality in the Mexico City Metropolitan Area

Few studies have assessed the impact of regulatory actions on air quality improvement through a comprehensive monitoring effort. In this study, we designed saturation sampling of nitrogen oxides (NOX) for the counties of Los Angeles and Alameda (San Francisco Bay) before (2003-2007) and after (2008-2013) implementation of goods movement actions in California. We further separated the research regions into three location categories, including goods movement corridors (GMCs), nongoods movement corridors (NGMCs), and control areas (CTRLs). Linear mixed models were developed to identify whether reductions in NOX were greater in GMCs than in other areas, after controlling for potential confounding, including weather conditions (e.g., wind speed and temperature) and season of sampling. We also considered factors that might confound the relationship, including traffic and cargo volumes that may have changed due to economic downturn impacts. Compared to the pre-policy period, we found reductions of average pollutant concentrations for nitrogen dioxide (NO2) and NOX in GMCs of 6.4 and 21.7 ppb. The reductions were smaller in NGMCs (5.9 and 16.3 ppb, respectively) and in CTRLs (4.6 and 12.1 ppb, respectively). After controlling for potential confounding from weather conditions, season of sampling, and the economic downturn in 2008, the linear mixed models demonstrated that reductions in NO2 and NOX were significantly greater in GMCs compared to reductions observed in CTRLs; there were no statistically significant differences between NGMCs and CTRLs. These results indicate that policies regulating goods movement are achieving the desired outcome of improving air quality for the state, particularly in goods movement corridors where most disadvantaged communities live.

The use of diesel engines is becoming more widespread because their fuel economy is superior to and their emission levels of carbon monoxide and carbon dioxide are considerably lower than those of gasoline engines. However, the high-temperature combustion in diesel engines generates significant amounts of nitrogen oxides (NOx), which have harmful effects on the environment and human beings, and are limited by increasingly stringent government regulations worldwide. The O2-rich environment of diesel engine exhaust will deactivate the traditional three-way catalysts that work effectively in gasoline engine exhaust. Therefore, there is a great demand for new technology to control NOx emissions in diesel engine exhaust. The most extensively researched technologies in this area are currently selective catalytic reduction with ammonia (NH3-SCR) and NOx storage and reduction catalysts (NSR), both of which require a reducing agent, either from a secondary supply system or by switching the operation state of the engine between lean and rich conditions. One attractive alternative to these approaches is electrochemical NOx reduction using a solid state cell. Using this approach, NOxis reduced to nitrogen at the polarized cathode, thereby eliminating the need for the addition of reducing agents or changes in the operational state of the engine. At present, the main obstacle to the practical application of this technology is the achievement of high selectivity for NOx reduction in the presence of excess O2. Because competitive O2 reduction consumes substantial amount of current, the current efficiency or selectivity of the cell towards NOxreduction is genetally a few percent relative to the total current supplied to the cell. Extensive research effort has been put on finding suitable cathode materials or optimizing the cell structure to increase its selectivity. However, the highest current efficiency reported in the literature was below 20% in an oxidizing atmosphere using a multilayered electrochemical cell with Pt cathode [1]. In this study, we proposed a novel concept for the electochemical NOx reduction, which significantly improve the selectivity towards NOx reduction. According to our previous research, it is found that the electrochemical reduction of NOx is probably limited by the formation of intermediate NO2. Besides, NO2 is also reported to be an necessary precursor for the NOx trapping process over the NOx aborbents added in the electrochemical cell. NO is usually the dominant species of NOx (90-95%) in exhaust gases, but can be converted to NO2 efficiently by the catalysis of DOC. As the high efficiency of DOC for NO converstion to NO2 has already been well demonstrated, in this study, we focus on the reduction of NO2 on the electrochemical cell. We developed and characterised two typed of cells: one is a modify mulilayered cells with Pt and Ni/YSZ cathode with a K-Pt-Al2O3 adsorption layer, the other is a LSM/CGO symmetric cell infiltrated with BaO. We compare the NOx removal properties of the cells in the atmosphere of mainly NO2 with O2 with that in mainly NO with O2 and investigated the effect of temperature, voltage, and polarization method on the performance of cells. Under O2-rich conditions, a current efficiency as high as 50-65% is achieved with a NOx converstion of 50-70% on a modified multilayer cell with Pt and a 10% current efficiency with more than 30% NOx converstion is realized on a fully ceramic cell free of noble metal. The contribution will briefly outline, how the concept can be further implemented in automotive exhaust cleaning systems. [1] K. Hamamoto, Y. Fujishiro, M. Awano, J. Electrochem. Soc., 155 E109 (2008)

A hybrid selective noncatalytic reduction/selective catalytic reduction (SNCR/SCR) system that uses two types of technology, low-temperature SCR process and SNCR process, was designed to develop nitrogen oxide (NOx) reduction technology. SCR was conducted with space velocity (SV) = 2400 hr−1 and hybrid SNCR/SCR with SV = 6000 hr−1, since the study focused on reducing the amount of catalyst and both achieved 98% NOx reduction efficiency. Characteristics of NOx reduction by NH3 were studied for low-temperature SCR system at 150 °C using Mn-V2O5/TiO2 catalyst. Mn-added V2O5/TiO2 catalyst was produced, and selective catalyst reduction of NOx by NH3 was experimented. NOx reduction rate according to added Mn content in Mn-V2O5/TiO2 catalyst was studied with varying conditions of reaction temperature, normalized stoichiometric ratio (NSR), SV, and O2 concentration. In the catalyst experiment according to V2O5 concentration, 1 wt.% V2O5 catalyst showed the highest NOx reduction rate: 98% reduction at temperature window of 200~250 °C. As a promoter of the V2O5 catalyst, 5 wt.% Mn was added, and the catalyst showed 47~90% higher efficiency even with low temperatures, 100~200 °C. Mn-V2O5/TiO2 catalyst, prepared by adding 5 wt.% Mn in V2O5/TiO2 catalyst, showed increments of catalyst activation at 150 °C as well as NOx reduction. Mn-V2O5/TiO2 catalyst showed 8% higher rate for NOx reduction compared with V2O5/TiO2 catalyst in 150 °C SCR. Thus, (5 wt.%)Mn-(1 wt.%)V2O5/TiO2 catalyst was applied in SCR of hybrid SNCR/SCR system of low temperature at 150 °C. Low-temperature SCR hybrid SNCR/SCR (150 °C) system and hybrid SNCR/SCR (350 °C) showed 91~95% total reduction rate with conditions of SV = 2400~6000 hr−1 SCR and 850~1050 °C SNCR, NSR = 1.5~2.0, and 5% O2. Hybrid SNCR/SCR (150 °C) system proved to be more effective than the hybrid SNCR/SCR (350 °C) system at low temperature.Implications: NOx control is very important, since they are the part of greenhouse gases as well as the cause of acid rain and ozone hole. A technology, so-called hybrid SNCR/SCR process, was tested using Mn-V2O5/TiO2 monolithic catalyst for NOx reduction, and the method is promising. The results of this study would provide some ideas to parties such as policy makers, environmental engineers, and so on.

Gaseous and particulate pollutants in Lhasa, Tibet during 2013–2017: Spatial variability, temporal variations and implications

ABSTRACTTo study the effect of NH3 on nitrogen oxides (NOx) formation and reduction in a fuel-rich zone during pulverized coal combustion, the reaction properties of urea solution with NOx have been investigated using a drop-tube furnace system. The results indicate that NOx could be reduced by urea solution effectively in a fuel-rich zone, when the temperatures are in the range of 1200–1400 ºC. The lower stoichiometric ratio (SR) in the combustion zone makes NOx reduction more effective by the injection of urea solution. High normalized stoichiometric ratio (NSR) results in a high percentage of NOx reduction under strong reducing atmosphere conditions. The maximum NOx reduction efficiency can reach up to 94.1%, of which 13.4% is achieved by injecting urea solution in the fuel-rich zone. The concentration of NOx emission decreased with the increase of quantity of water. However, the extent of decrease was inconspicuous.

Photocatalytic asphalt pavements are evaluated in this study as a possible air-pollution reduction strategy and to comprehend their behaviour in the real-world environment. Statistical models from real-world experiments or reaction kinetics are two approaches to understand the photocatalytic reduction in real-world environments. The objective of this study was to develop a statistical model for nitrogen oxide (NO) reduction using data from a field study and to evaluate the photocatalytic reaction kinetics of NO reduction, which could be used in future theoretical air-pollution model simulations. To achieve this objective, a photocatalytic water-based spray coating was applied on an existing asphalt pavement site for the field study statistical model and on laboratory samples for the kinetic study. Based on the field data, the NO reduction was modelled using statistical regression techniques by creating a model for a non-coated pavement and photocatalytic pavement. The coefficient of determination was 0.79 and 0.67, respectively. To improve prediction, other parameters may need to be included into the model and more sampling time is required. Based on the laboratory results, the NO reduction was reaction controlled following the Langmuir–Hinshelwood (L–H) model. The adsorption equilibrium constant calculated for photocatalytic asphalt pavements was similar to those of concrete pavements while the reaction rate constant was significantly lower. While humidity has a negative correlation on both L–H constants, intensity has a positive correlation. However, interaction between these two parameters exists.

ABSTRACTThe Beijing Municipal Environmental Protection Bureau (EPB) is considering strengthening the Emission Standard of Air Pollutants for Stationary Gas Turbines, originally published in 2011 (DB11/847–2011), with a focus on reducing nitrogen oxides (NOx) emissions. A feasibility study was conducted to evaluate the current operation of 12 existing combined-cycle gas turbine power plants and the design of two new plants in Beijing and their emission reduction potential, in comparison with a state-of-the-art power plant in California. The study found that best management practices (BMPs) could potentially improve the emission level of the power plants, and should be implemented to minimize emissions under current design characteristics. These BMPs include (1) more frequent tuning of turbine combustors; (2) onsite testing of natural gas characteristics in comparison to turbine manufacturer’s specifics and tuning of turbine to natural gas quality; (3) onsite testing of aqueous ammonia to ensure adequate ammonia concentration in the mixed solution, and the purity of the solution; (4) more careful inspection of the heat recovery steam generator (HRSG), and the selective catalytic reduction (SCR) during operation and maintenance; (5) annual testing of the catalyst coupon on the SCR to ensure catalyst effectiveness; and (6) annual ammonia injection grid (AIG) tuning. The study found that without major modification to the plants, improving the management of the Beijing gas turbine power plants may potentially reduce the current hourly average NOx emission level of 5–10 parts per million (ppm; ranges reflects plant variation) by up to 20%. The exact improvement associated with each BMP for each facility requires more detailed analysis, and requires engagement of turbine, HRSG, and SCR manufacturers. This potential improvement is an important factor to consider when strengthening the emission standard. However, note that with the continuous needs of improving air quality within the area, more expensive control measures, such as retrofitting the turbines or the HRSGs, may be considered.Implications: This study analyzed the potential emission reductions associated with implementing the best management practices (BMPs) on the combined cycle and cogeneration power plants in Beijing. It determined that implementing the BMPs could potentially achieve up to 580 metric tonnes, or 0.6%, reductions of all NOx emissions in Beijing. Many other cities in China and Asia battling air quality issues may find the information useful in order to evaluate the emission reduction potential of their own gas turbine power plants.

Fine particulate matter (PM2.5) pollution can harm the climate, the environment, and human health. With sustainability initiatives receiving increasing attention, whether compact urban development can yield green environmental benefits has become an essential research proposition among urban planners. The compact city theory advocates energy efficiency enhancement through the mutual superposition of urban functions. First, a theoretical analysis framework for the effect of urban compactness on environmental quality was constructed. Second, on the basis of panel data from 285 prefecture-level cities in China from 2010 to 2021, exploratory spatial data analysis (ESDA) was applied to reveal the spatiotemporal nonstationary distribution of urban PM2.5 pollution. Finally, the heterogeneous influence mechanisms of compact urban factors on PM2.5 pollution were empirically studied through the geographical and temporal weighted regression (GTWR) model. The main findings are as follows: (1) From 2010 to 2021, the proportion of cities in China with good air quality significantly increased. The cities with high–high pollution clustering are currently located mainly in Beijing–Tianjin–Hebei, Shandong, and Henan. (2) Economic and transportation compactness factors mitigated PM2.5 pollution in most cities, whereas the long-term combined effects of the population and land compactness factors may have exacerbated urban PM2.5 pollution. (3) There was significant spatial and temporal heterogeneity in the effects of urban compactness factors on air pollution. Cities where land-use compactness exerts a pollution mitigation effect were located east of the Hu line. Cities in Northeastern China had the strongest pollution mitigation effect from transportation compactness, followed by the cities in Southwestern China.

NOx emissions from the offshore installations in Norway have until now not been subject to regulations. As one of the main contributor of nitrogen oxides (NOx) emissions, regulations have been foreseen. Several studies have been initiated on behalf of The Norwegian Oil Industry Association (OLF) since 1990 to acquire knowledge about the industry's NOx emissions. A common set of emission factors and a detailed inventory for NOx have been established. NOx reduction measures have been studied and installation of Dry Low Emissions (DLE) combustion technology for gas fueled turbines on new installations appears to be the most realistic NOx reduction measure in the near future. A cost efficiency curve for implementation of this technology has been established. Contribution to the environmental impact from the Norwegian oil and gas industry as regards acidification, fertilization and ground level ozone concentrations have been calculated based on first results obtained by a newly developed dispersion modeling tool. An open dialogue with relevant regulatory bodies was promoted throughout the studies. As a result, a common approach for NOx reductions has been found and results achieved have been utilized by the authorities in their work to establish a national action plan for NOx. Introduction Norway has ratified the 1988 Sofia Protocol on NOx to the Convention on Long-Range Transboundary Air Pollution which entered into force 14.02.1991. The Protocol called for a stabilization of emissions by 1994 compared to the 1987 level. Norway also signed a declaration of intent to reduce the NOx emissions further by 30% within 1998 based on the 1986 level. Projection of the national emissions shows that the objective for 1998 will not be met unless new measures are implemented. As the oil and gas industry contributes with 14% of the emissions on a national level in 1992, there is a need for reductions. Fig. 1 show the major contributors of NOx emissions in Norway and Fig. 2 the prognosis for the oil and gas industry until the year 2000. Regulation of NOx emissions has been foreseen. The introduction of a NOx tax is not considered to be an economically nor an efficient alternative to reduce NOx emissions. More cost efficient reductions can be achieved by other means where the industry and authorities join their forces. This has been the basic approach for work with environmental matters for the Norwegian offshore oil and gas industry. As the authorities were working towards a national action plan for reductions of NOx, the industry needed to know more about its emissions, the possibilities for reduction and inherent cost in order to assess the potential future consequences for the industry. As this was an area of mutual interest within the different companies, work was conducted as a joint effort through OLF. Cooperation between OLF and the authorities was initiated in order to achieve a common understanding of the situation and to avoid double work. The purpose of this paper is to describe the approach to improve knowledge of the NOx emissions and to present results from three recently completed studies;Emission factors and inventory for the Norwegian Continental Shelf (NCS),evaluation of technologies for NOx reductions, including scenarios for implementation of Dry Low Emissions (DLE) combustion technology on gas fueled turbines with related cost efficiency calculations andenvironmental impact from the Norwegian oil and gas industry and contributions to acidification, fertilization and ground level ozone concentrations. A White Paper concerning Norwegian policy for handling NOx emissions was issued in June 1995. This opens up for negotiated agreements with the industry as a regulatory measure to facilitate reductions for e.g. NOx. In order to be prepared for possible negotiations on emission reductions, new studies were initiated in 1996. The scope is to establish cost efficiency figures for other NOx reduction technologies, including associated marine activities as well as further development of the dispersion modeling tool. P. 13^

Application of urea-based SNCR to a municipal incinerator: On-site test and CFD simulation