Changes In NOx Emissions Research Articles

The effect of different climate and air quality policies in China on in situ ozone production in Beijing

Abstract. In recent years, clean air policies have led to reductions in air pollution across China. Alongside this, emerging carbon neutrality (CN) policies that aim to address the impacts of climate change may also deliver air quality (AQ) co-benefits or climate penalties. Different CN policies will lead to different changes in volatile organic compound (VOC), NOx and particulate matter (PM) emissions, which will in turn impact the photochemical production of secondary pollutants such as ozone (O3). It is currently unclear how different combinations of AQ and CN policies may impact in situ O3 production across China in the future. A detailed chemical box model incorporating the Master Chemical Mechanism was developed to investigate the impact of combined AQ and CN policies on O3 formation in Beijing. The Multi-resolution Emission Inventory model for Climate and air pollution research (MEIC) and the Dynamic Projection model for Emissions in China (DPEC) were used to estimate future pollutant mixing ratios, relative to ambient observations of 35 VOCs, NOx, CO and aerosol surface area (ASA) during the APHH-Beijing 2017 summer campaign. The most ambitious policy scenario, “Ambitious Pollution 1.5D Goals”, led to the largest reduction in O3 production by 2060 but was not the most impactful scenario for reducing O3 production between 2030–2045. Larger reductions were observed under the “Ambitious Pollution Neutral Goals” policy, which focuses on achieving net zero by 2060. O3 production was found to be most sensitive to changes in the OLE2 group of VOCs (alkenes where kOH>7×104 ppm−1 min−1; a 5 % increase in OLE2 increased simulated O3 production by 1.12 %). However, reducing less reactive but higher concentration species in Beijing (such as short-chain alkanes) led to larger reductions in O3 production under all scenarios. O3 production was not sensitive to changes in ASA, with a 69 % decrease in ASA leading to a change of <1 % in O3. However, doubling biogenic VOCs in the model further increased O3 production in 2060 under all future scenarios by up to 18 %, indicating that the influence of future climate-induced changes in biogenic emissions may have a significant impact on in situ O3 formation in Beijing. This study highlights that the emission trajectories of certain specific VOCs are highly influential in determining possible future O3 air quality effects that may arise from increasing ambient temperatures and decarbonisation in Beijing.

Research on the Ignition Strategy of Diesel Direct Injection Combined with Jet Flame on the Combustion Character of Natural Gas in a Dual-Fuel Marine Engine

In large-bore two-stroke diesel/nature gas dual-fuel marine engines, a certain quantity of diesel is injected into the cylinder to satisfy the full-power output engine rated power of the gas mixture. However, the ignition and flame propagation process based on the injection strategy of diesel direct injection combined with diesel jet flame on the ignition and combustion of natural gas is unclear, which directly affects the power and the thermal efficiency of engine and emissions. Therefore, this work numerically investigates the flame propagation characteristic under the strategy of the main and pilot diesel modes. The influence of the injection timing and proportion of diesel on combustion and emission performance are further analyzed. The results show that the influence of the injection timing of main diesel (MDIT) on the combustion process and emission performance is more obvious than that of the injection timing of pilot diesel (PDIT). The results indicate that the MDIT increased from −2°CA to −8°CA, the power increased by 316 kW, and the thermal efficiency improved by 1.5%. However, the CO2 emissions increased by 10.5 g/kWh, and the NOx emissions increased by 0.7 g/kWh. Additionally, an early PDIT is not conducive to the rapid organization of combustion, resulting in decreased engine power and thermal efficiency. Furthermore, it was found that the power improved by 50 kW and the thermal efficiency improved by 0.6%, with a decrease in the main diesel ratio (MDR) from 100% to 90%. Meanwhile, the CO2 emissions decreased by 4 g/kWh, although there was no obvious change in NOx emissions with the advance of MDR.

PM2.5 wintertime sensitivity to changes in NOx, SO2, and NH3 emissions in Lombardy Region

PM2.5 wintertime sensitivity to changes in NOx, SO2, and NH3 emissions in Lombardy Region

Development of a Hydrogen Micro Gas Turbine Combustor: Atmospheric Pressure Testing

Abstract The vision of a carbon-neutral world implies the shift from fossil to clean fuels for combustion-driven processes and machines like gas turbines. Green hydrogen is a promising alternative to substitute natural gas and other fossil fuels. In the H2mGT project, funded by the German BMWK, a microgas turbine (mGT) burner with 100% hydrogen firing is developed and validated. The project is collaboration between Technische Universität Berlin (TUB) and the manufacturer Euro-K GmbH. The project consists of three phases: (1). Atmospheric pressure tests with a fused silica combustion chamber; (2). Atmospheric pressure tests with counterflow-cooled steel combustion chamber and secondary air injection; (3). Validation of the burner in the micro gas turbine at elevated pressure levels. This paper will present the results of Phase 1. The hydrogen burner is based on a swirl-stabilized burner of TUB and was scaled to match the requirements of the mGT with its 130 kW thermal power. The burner design features multiple geometrical parameters to enable the optimization of the flame towards low NOx emissions. Therefore, a variable swirl intensity, additional axial momentum of air in the mixing tube, a movable center-body and different fuel injection locations are implemented. Phase 1 investigates the parameter space in terms of flame stability, operational range, and parameter impact on flame shape and emissions. Therefore, temperature, pressure, and emission measurements as well as OH* imaging are carried out. It is found that the flame can be operated over a large range of equivalence ratios and preheating temperatures up to 500 ∘C for many parameter settings. However, at some configurations, flashback into the mixing tube is triggered. As expected, the NOx emissions are mainly influenced by the equivalence ratio, the fuel distribution, and the swirl intensity. Single-digit emissions are reached up to an equivalence ratio of 0.4 at atmospheric pressure conditions. Furthermore, at low air mass flow, the burner can be operated at 100% natural gas or 100% hydrogen without any geometry changes. The fuel switch, thereby, does not change the NOx emissions significantly if reasonable normalization is used.

Analyzing and Optimizing the Emission Impact of Intersection Signal Control in Mixed Traffic

Signalized intersections are one of the typical bottlenecks in urban transport systems that have reduced speeds and which have substantial vehicle emissions. This study aims to analyze and optimize the impacts of signal control on the emissions of mixed traffic flow (CO, HC, and NOx) containing both heavy- and light-duty vehicles at urban intersections, leveraging high-resolution field emission data. An OBEAS-3000 (Manufacturer: Xiamen Tongchuang Inspection Technology Co., Ltd., Xiamen, China.) vehicle emission testing device was used to collect microscopic operating characteristics and instantaneous emission data of different vehicle types (light- and heavy-duty vehicles) under different operating conditions. Based on the collected data, the VSP (Vehicle Specific Power) model combined with the VISSIM traffic simulation platform was used to quantitatively analyze the impact of signal control on traffic emissions. Heavy-duty vehicles contribute to most of the emissions regardless of the low proportion in the traffic flows. Afterward, a model is proposed for determining the optimal signal control at an intersection for a specific percentage of heavy-duty vehicles based on the conversion of emission factors of different types of vehicles. Signal control is also optimized based on conventional signal timing, and vehicle emissions are calculated. In the empirical analysis, the changes in CO, HC, and NOx emissions of light- and heavy-duty vehicles before and after conventional signal control optimization are quantified and compared. After the signal control optimization, the CO, HC, and NOx emissions of heavy-duty vehicles were reduced. The CO and HC emissions of light-duty vehicles were reduced, but the NOx emissions of light-duty vehicles remained unchanged. The emissions of vehicles after optimized signal control based on vehicle conversion factors are reduced more significantly than those after conventional optimized signal control. This study provides a scientific basis for developing traffic management measures for energy saving and emission reduction in transport systems with mixed traffic.

Contrasting changes in ozone during 2019–2021 between eastern and the other regions of China attributed to anthropogenic emissions and meteorological conditions

Ozone pollution is one of the most severe air quality issues in China that poses a serious threat to human health and ecosystems. During 2019–2021, the maximum daily 8-h average ozone concentrations in eastern China (110–122.5°E, 26–42°N) and the rest of China (ROC) show different decreasing patterns, with ozone concentrations in eastern China decreasing by 14.9 μg/m3, which is much larger than 4.8 μg/m3 in ROC. Here, based on two independent methods, the atmospheric chemical transport model (GEOS-Chem) simulations and the machine learning (ML) model (LightGBM) predictions, the reasons for the differences in ozone changes between eastern China and ROC during the warm season (April to September) are investigated. According to the GEOS-Chem (LightGBM) results, changes in the meteorological conditions contributed to an ozone decrease by 7.3 (6.8) μg/m3 in eastern China due to decreased chemical production and an ozone decrease by 6.8 (7.0) μg/m3 in ROC attributed to the weakened horizontal and vertical advection. With the influence of meteorological factors excluded, the observations show that changes in anthropogenic emissions resulted in an ozone decrease by 7.6 (8.1) μg/m3 in eastern China and an ozone increase by 2.0 (2.2) μg/m3 in ROC, which is primarily induced by the changes in NOx emissions. The surface measurements and satellite retrievals also indicate that the reduction in NOx emissions in ROC is less efficient than that in the more developed eastern China, leading to contrasting changes in ozone concentrations between eastern China and ROC during 2019–2021. Our results highlight the critical need to reduce ozone precursor emissions in the rest regions of China apart from eastern China.

Long-term historical trends in air pollutant emissions in South Korea (2000–2018)

This study aims to understand the impact of previous air quality improvement policies on historical emission changes by examining long-term emission trends in Korea. Annual emissions from 2000 to 2018 were estimated using Korea’s official emissions inventory, the Clean Air Policy Support System (CAPSS). To ensure a consistent comparison, standardization of the method for calculating emissions and unification of the reported emission sectors were conducted each year. Furthermore, Korea’s emissions history was compared with that of neighboring countries, such as China and Japan. The annual emissions of these countries were acquired from the HTAPv3 emissions inventory, an international long-term emission trend study. For comparison, the emission source classification of Korea was matched with that of HTAPv3. As a result of the analysis, NOx and SOx emissions in Korea have shown decreasing trends, whereas VOCs (volatile organic compounds) have indicated a gradual increasing trend since 2000. Compared to the previous period of implementing South Korea’s air quality improvement policy, changes in NOx and SOx emissions, which are combustion-related pollutants, showed a relationship with the policy’s timeline. However, non-combustion-related pollutants such as VOCs did not exhibit such a relationship. It was concluded that the related policies were not as effective in reducing VOCs as planned in the policy. By comparing the emission trends of Japan, Korea, and China, it was confirmed that Japan was the first country to experience a decrease in combustion-related pollutants emissions, followed by Korea and China. Additionally, combustion-related pollutants decreased in all three countries, whereas VOCs decreased only in Japan. VOC is a precursor material generating secondary PM2.5 and Ozone; considering that, if relevant policies are additionally implemented to control future PM2.5 concentrations, and to reduce emissions efficiently and effectively, Japan’s VOC reduction policies can be applied to Korea’s emission reduction policies. These results are expected to serve as important references when establishing future air quality improvement policies in Korea.

STUDY OF INFLUENCE DEGREE OF GAS PUMPING UNIT OUTPUT PARAMETERS ON POLLUTANT EMISSION

Gas turbine plants, as well as all types of gas-using equipment, have a long service life, during which, along with the operational performance deterioration, pollutant emissions are expected to change.
 To take this factor into account, when developing algorithms for determining pollutant emissions from gas pumping units based on operational parameters, an analysis of changes in NOx and COx emissions (nitrogen oxides and carbon oxides) when the output parameters of the gas pumping unit deviates from the nominal ones has been carried out.
 The impact of operating time, repairs of the drive motor, flushing of the AL-31ST flow section was investigated.
 Additional tests to simulate the reduction in the available power of the unit due to a decrease in the efficiency of the axial compressor, which made it possible to quantify the impact of the deterioration in the technical condition of the gas turbine plant on NOx and COx emission were carried out.

Nitrogen oxides emissions from selected cities in North America, Europe, and East Asia observed by the TROPOspheric Monitoring Instrument (TROPOMI) before and after the COVID-19 pandemic

Abstract. Nitrogen oxides (NOx=NO+NO2) emissions are estimated in three regions in the Northern Hemisphere, generally located in North America, Europe, and East Asia, by calculating the directional derivatives of NO2 column amounts observed by the TROPOspheric Monitoring Instrument (TROPOMI) with respect to the horizontal wind vectors. We present monthly averaged emissions from 1 May 2018 to 31 January 2023 to capture variations before and after the COVID-19 pandemic. We focus on a diverse collection of 54 cities, 18 in each region. A spatial resolution of 0.04∘ resolves intracity emission variations and reveals NOx emission hotspots at city cores, industrial areas, and sea ports. For each selected city, post-COVID-19 changes in NOx emissions are estimated by comparing monthly and annually averaged values to the pre-COVID-19 year of 2019. While emission reductions are initially found during the first outbreak of COVID-19 in early 2020 in most cities, the cities' paths diverge afterwards. We group the selected cities into four clusters according to their normalized annual NOx emissions in 2019–2022 using an unsupervised learning algorithm. All but one of the selected North American cities fall into cluster 1 characterized by weak emission reduction in 2020 (−7 % relative to 2019) and an increase in 2022 by +5 %. Cluster 2 contains mostly European cities and is characterized by the largest reduction in 2020 (−31 %), whereas the selected East Asian cities generally fall into clusters 3 and 4, with the largest impacts in 2022 (−25 % and −37 %). This directional derivative approach has been implemented in object-oriented, open-source Python and is available publicly for high-resolution and low-latency emission estimation for different regions, atmospheric species, and satellite instruments.

Changes in Ozone Pollution Trend Characteristics and Sensitivity in Jinan from 2015 to 2020

The surface ozone (O3) spatiotemporal distribution, variations, and its causes in Ji'nan from 2015 to 2020 were revealed based on the air quality monitoring network data and satellite retrievals from the Ozone Monitoring Instrument (OMI). The results showed that the ozone concentration in Ji'nan gradually increased from 2015 to 2020. The annual 90th percentile of the daily maximum 8-h average (MDA8) O3(namely the annual evaluation value) and the MDA8 O3(April-September) increased by 4.8 μg·(m3·a)-1 and 3.8 μg·(m3·a)-1, respectively. The trend of the ozone levels in the high-concentration range increased faster than that in the low-concentration range. The MDA8 in June increased by 7.4 μg·(m3·a)-1, and the rate range of increases was 2.6-3.9 μg·(m3·a)-1 in the cool seasons (December-February); thus, the O3 control in winter cannot be ignored. It is apparent from the diurnal variations in ozone from 2015 to 2020 in April-September that the average ozone levels have risen in recent years. The growth rate in the daytime was higher than that at night. The capacity of photochemical production has been increasing, especially in recent years. Additionally, it is noteworthy that the peak time for ozone levels occurred approximately 1-2 h earlier. The disparity of ozone concentrations among different stations gradually decreased in recent years. Compared with that in 2015, the range of areas with high O3 concentrations in 2019-2020 was further expanded. The significant positive trends in MDA8-90th and MDA8 (April-September) were observed in 16.1% and 22.6% of the monitoring sites in Ji'nan (P<0.05), most of which were located in urban areas and the suburbs close to urban areas. The temporal and spatial changes in ozone in Jinan had been affected by the changes in VOCs and NOx emissions since 2015. Satellite remote sensing data from 2015 to 2020 revealed that the NO2 tropospheric columns (April-September) showed reductions of 20.6%, with a decreasing rate of 0.3×1015 mole·(cm2·a)-1, especially in the urban areas and suburbs. The detected variation trends of tropospheric HCHO were weak and insignificant, which suggested that the decrease in NOx emissions was much greater than the decrease in VOCs emissions, and the gap had become more obvious in the urban areas. With responses to precursor emissions, the chemical sensitivity of O3 formation had been changing. The VOCs-limited regimes continuously decreased, and the mixed NOx/VOCs-sensitive regimes and NOx-limited regimes increased. In general, such an extremely inappropriate control ratio of ozone precursor NOx/VOCs led to an overall trend of slow increasing fluctuations of O3 in Ji'nan. The findings clearly indicate that the reduction of VOCs in Ji'nan was far from sufficient, and strengthening the current control of VOCs emissions is an effective measure to control the growth trend of O3 pollution in Ji'nan in the near future, especially in urban and surrounding suburban areas.

Modeling and CFD Analysis of Combustion Chamber of Jet Engine to Reduce the Emissions using Biofuels

The biodiesel can be extracted from different sources and then it is blend with engine fuels to counter factors like fuel scarcity, pollution, cost and increasing of consumers. The use of algal oil diesel-biodiesel blend is one of the methods to reduce the emissions and in increasing performance of jet engine. To emphasize on the reduction of NOx in the combustion chamber of the jet engine. Combustion chamber is the main part of the jet engine where many important chemical reactions take place and generates heat. In this paper, the main focus is on the percentage of NOx in the output and how we can reduce that by changing some parameters into input. The challenges in fuel high performance combustion engines haven’t had any major changes over the years. However, more sophisticated analysis process has been deployed to overcome these challenges. The biofuels i.e., algal oil diesel-biodiesel is taken first to blend, then standard boundary conditions were applied and then observed the results carefully. By looking at the results then decided to make some changes in the diesel i.e., the bio diesel (B10, B15 and B20) where it found drastic changes in NOx emission and got some more positive changes.

Integrating ambient carbonyl compounds provides insight into the constrained ozone formation chemistry in Zibo city of the North China Plain

Quantifying the impact of carbonyl compounds (carbonyls) on ozone (O3) photochemical formation is crucial to formulating targeted O3 mitigation strategies. To investigate the emission source of ambient carbonyls and their integrated observational constraint on the impact of O3 formation chemistry, a field campaign was conducted in an industrial city (Zibo) of the North China Plain from August to September 2020. The site-to-site variations of OH reactivity for carbonyls were in accordance with the sequence of Beijiao (BJ, urban, 4.4 s−1) > Xindian (XD, suburban, 4.2 s−1) > Tianzhen (TZ, suburban, 1.6 s−1). A 0-D box model (MCMv3.3.1) was applied to assess the O3-precursor relationship influenced by measured carbonyls. It was found that without carbonyls constraint, the O3 photochemical production of the three sites was underestimated to varying degrees, and the biases of overestimating the VOC-limited degree were also identified through a sensitivity test to NOx emission changes, which may be associated with the reactivity of carbonyls. In addition, the results of the positive matrix factorization (PMF) model indicated that the main source of aldehydes and ketones was secondary formation and background (81.6% for aldehydes, 76.8% for ketones), followed by traffic emission (11.0% for aldehydes, 14.0% for ketones). Incorporated with the box model, we found that biogenic emission contributed the most to the O3 production at the three sites, followed by traffic emission as well as industry and solvent usage. Meanwhile, the relative incremental reactivity (RIR) values of O3 precursor groups from diverse VOC emission sources featured consistencies and differences at the three sites, which further highlights the importance of the synergetic mitigation of target O3 precursors at regional and local scales. This study will help to provide targeted policy-guiding O3 control strategies for other regions.

Anthropogenic NOx Emission Estimations over East China for 2015 and 2019 Using OMI Satellite Observations and the New Inverse Modeling System CIF-CHIMERE

The Chinese government introduced regulations to control emissions and reduce the level of NOx pollutants for the first time with the 12th Five-Year Plan in 2011. Since then, the changes in NOx emissions have been assessed using various approaches to evaluate the impact of the regulations. Complementary to the previous studies, this study estimates anthropogenic NOx emissions in 2015 and 2019 over Eastern China using as a reference the Hemispheric Transport of Air Pollution (HTAP) v2.2 emission inventory for 2010 and the new variational inversion system the Community Inversion Framework (CIF) interfaced with the CHIMERE regional chemistry transport model and OMI satellite observations. We also compared the estimated NOx emissions with the independent Multi-resolution Emission Inventory for China (MEIC) v1.3, from 2015. The inversions show a slight global decrease in NOx emissions (in 2015 and 2019 compared to 2010), mainly limited to the most urbanized and industrialized locations. In the locations such as Baotou, Pearl River Delta, and Wuhan, the estimations in 2015 compared to 2010 are consistent with the target reduction (10%) of the 12th Five-Year Plan. Comparisons between our emission estimates and MEIC emissions in 2015 suggest that our estimates likely underestimate the emission reductions between 2010 and 2015 in the most polluted locations of Eastern China. However, our estimates suggest that the MEIC inventory overestimates emissions in regions where MEIC indicates an increase of the emissions compared to 2010.

Разработка математической модели газотурбинной установки с малоэмиссионной камерой сгорания и особенности ее интеграции в среду SimInTech

The results of the development of a mathematical model of a gas turbine plant (GTP) SGT5-4000F with an annular low-emission combustion chamber are presented. This plant has a low NOx emission and a high coefficient of performance (COP). The obtained results of mathematical modeling are integrated into the domestic environment of dynamic modeling of technical systems "SimInTech". The obtained results were verified by comparing the model values with the trends of the real technological parameters of the gas turbine unit taken from the archive of the automated process control system of the power plant. According to the results of the experimental studies carried out on the model with changes in the electrical load from 280 to 160 MW, it is shown that the model allows you to control the combustion process in the combustion chamber, depending on the composition of the fuel, evaluate the change in NOx emissions and provide an analysis of the stability of the gas turbine compressor according to surging in conditions of changing temperature and humidity of the incoming air.

Downward trend of NO2 in the urban areas of Beijing-Tianjin-Hebei region from 2014 to 2020: Comparison of satellite retrievals, ground observations, and emission inventories

Significant downward trend of NO2 over BTH region has been detected by both satellite and ground surface observations in recent years due to the continuous regulatory policies in China. Previous studies mostly focused on the scientific issue of analyzing the distribution characteristics of NO2 and the drivers of interannual NO2 variations. Whether the declines derived from independent data sets with different spatiotemporal representations are comparable? If they are, what is the significance of these observed quantitative interannual trends for evaluating the estimated NOx emission changes is poorly characterized. This issue is still need to be brought to more attention.This study first investigates the variations of the long-term trends derived from satellite and ground observations, and then uses these data to evaluate the updates of NOx emissions from MEIC (Multi-resolution Emission Inventory for China) inventory during 2014–2020 over the BTH (Beijing-Tianjin-Hebei) region. In the 12 cities examined here, both the OMI (Ozone Monitoring Instrument) and the AQS (Air Quality System) detected comparable and substantial downward trends, with the overall reduction ranging from 28.2% to 49.5% and from 27.4% to 54.8% in urban areas according to OMI and AQS, respectively. The NOx emission adopted from MEIC showed a similar downward trend, but with a much lower reduction ranging from 4.3% to 32.5% (from 2014 to 2019). Large discrepancies were also found in the annual trends between NOx emissions (MEIC) and NO2 observations (OMI and AQS) especially after 2016, suggesting that the magnitude of recent emission reductions over the BTH region doesn't seem to be well captured by the MEIC emission projection, and in urban areas, in particular, there are significant overestimations. Assuming a linear relationship between NOx emissions and NO2 columns, 45.2% overestimation errors of simulations using priori NOx emissions can be explained by using posteriori inventory optimized by OMI observation. Our findings demonstrate that the combination of satellite and ground observations is likely to provide more reliable estimates of NOx emission and its trend over the BTH region under continuous emission reductions.

Contributions of cleaner production and end-of-pipe treatment to NOx emissions and intensity reductions in China, 1997–2018

The Chinese experience of economic development and environmental protection provides an important reference for developing countries. Although changes in aggregate NOx emissions have been widely studied, there is a relative lack of studies analysing NOx intensity changes and their related development strategies in China. This study attempts to identify the socioeconomic drivers and change patterns for both NOx emissions and intensity considering the cleaner production and end-of-pipe treatments. Both structural decomposition analysis and structural path analysis were used to analyse the NOx emissions/intensity changes at different levels and transmission layers in China in the last two decades (1997–2018). The results indicate that construction contributes the most to NOx emissions/intensity, followed by transportation. The emission intensity effect is the primary driver of NOx emissions/intensity reduction, which mainly benefits from end-of-pipe treatment and energy efficiency improvement. Especially, during 2012–2018, they decreased 11,916 Kt-NOx and 8,103 Kt-NOx emissions and aggregate embodied intensity by 43.2% and 29.8%, respectively. The final demand effect is the primary deterrent, which is attributed to investment and consumption effects. The critical sectors for future NOx reduction are the construction and building materials industry, transportation and other services industry. The policy implications and recommendations for the future developments are discussed based on the study findings.

Responses of ozone concentrations to the synergistic control of NOx and VOCs emissions in the Chengdu metropolitan area

Simulations of 108 emission reduction scenarios for NOx and VOCs using Comprehensive Air Quality Model with Extensions (CAMx) were conducted for eight cities in the Chengdu metropolitan area (CMA). The isopleth diagrams were drawn to explore the responses and differences of ozone (O3) concentrations to NOx and VOCs emission changes under Chengdu, CMA and Sichuan Province emission reduction scenarios. The results show that the O3-sensitive regimes of eight cities may change under different emission reduction scenarios. Under Chengdu emission reduction scenario, the Chengdu city is in the transition regime and O3 formation will shift from transition to VOC-limited when the VOCs emissions decreased by 50%, and the decreases in O3 concentrations caused by VOCs emission reductions are small. For the CMA and Sichuan Province emission reduction scenarios, all cities are NOx-limited in the baseline cases and with at least a 66% and a 77% reduction in NOx emissions, respectively, the daily maximum 8-h average O3 (MDA8) can attain the O3 standard (160 μg m−3). Although reductions in VOCs emissions can also lessen the O3 concentration, the effectiveness is relatively small. The changes in O3 concentrations under different VOCs to NOx emission reduction ratios indicate that all cities achieve a relatively high O3 concentration decrement with low VOCs to NOx emission reduction ratios and that the decreasing O3 concentrations caused by non-local emission reductions are much higher than those achieved by local emission reductions. In addition, the decreases in O3 concentrations in Chengdu are quite close when the total NOx and VOCs emissions reduction percentages are less than 30% under the CMA and Sichuan emission reduction scenarios.

Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 period

Abstract. The South Coast Air Basin (SoCAB), which includes the city of Los Angeles and is home to more than 15 million people, frequently experiences ozone (O3) levels that exceed ambient air quality standards. While strict regulation of O3 precursors has dramatically improved air quality over the past 50 years, the region has seen limited improvement in O3 over the past decade despite continued reductions in precursor emissions. One contributing factor to the recent lack of improvement is a gradual transition of the underlying photochemical environment from a VOC-limited regime (where VOC denotes volatile organic compound) towards an NOx-limited one. The changes in human activity prompted by COVID-19-related precautions in spring and summer of 2020 exacerbated these existing changes in the O3 precursor environment. Analyses of sector-wide changes in activity indicate that emissions of NOx decreased by 15 %–20 % during spring (April–May) and by 5 %–10 % during summer (June–July) relative to expected emissions for 2020, largely due to changes in mobile-source activity. Historical trend analysis from two indicators of O3 sensitivity (the satellite HCHO/NO2 ratio and the O3 weekend/weekday ratio) revealed that spring of 2020 was the first year on record to be on average NOx-limited, while the “transitional” character of recent summers became NOx-limited due to COVID-19-related NOx reductions in 2020. Model simulations performed with baseline and COVID-19-adjusted emissions capture this change to an NOx-limited environment and suggest that COVID-19-related emission reductions were responsible for a 0–2 ppb decrease in O3 over the study period. Reaching NOx-limited territory is an important regulatory milestone, and this study suggests that deep reductions in NOx emissions (in excess of those observed in this study) would be an effective pathway toward long-term O3 reductions.

Cost–Benefit Analysis of Synergistic CO2 and NOx Energy-Efficient Technologies for the Road Transport Sector in China

The transportation sector is a major source of greenhouse gases and air pollutants, and it has a crucial effect on the synergistic reduction of NOx and carbon. In order to find the energy-efficient vehicle technologies with the highest net reduction potential and lowest net reduction cost over the life cycle, this study traced the CO2 and NOx emission streams of 33 energy-efficient technologies, hidden in the supply chain during the production phase, through structural path analysis, and measured the emission reductions during the use phase using the emission factor method. Moreover, we applied structural decomposition analysis to quantify the three main drivers, including emission intensity, industrial structure, and final demand, of changes in CO2 and NOx emissions from 11 transport subsectors during 2012–2018. Results indicate that CO2 emissions of the transport sector more than doubled from 2012 to 2018; however, the influence of NOx was less significant. The final demand of the road subsector was the most significant driver contributing to CO2 emission changes, with an increase of 109.27 Mt. The emission intensity of road transportation caused the greatest mitigation effect on NOx emission changes, with a decrease of 1902 Kt. The findings of the scenario analysis demonstrate that the most efficient action of the pure electric technology for passenger cars reduces 20.92 Mt NOx emissions, and the parallel hybrid technology for heavy trucks offers the greatest cost effectiveness with a net abatement of 2577 Mt CO2 over its life cycle. Consequently, the aggressive development of new energy technology has become a prerequisite strategy to synergistically reduce CO2 and NOx emissions.

Major Regional-Scale Production of O3 and Secondary Organic Aerosol in Remote Amazon Regions from the Dynamics and Photochemistry of Urban and Forest Emissions.

The Amazon rainforest suffers increasing pressure from anthropogenic activities. A key aspect not fully understood is how anthropogenic atmospheric emissions within the basin interact with biogenic emissions and impact the forest's atmosphere and biosphere. We combine a high-resolution atmospheric chemical transport model with an improved emissions inventory and in-situ measurements to investigate a surprisingly high concentration of ozone (O3) and secondary organic aerosol (SOA) 150-200 km downwind of Manaus city in an otherwise pristine forested region. We show that atmospheric dynamics and photochemistry determine a gross production of secondary pollutants seen in the simulation. After sunrise, the erosion of the nocturnal boundary layer mixes natural forest emissions, rich in biogenic volatile organic compounds, with a lofted pollution layer transported overnight, rich in nitrogen oxides and formaldehyde. As a result, O3 and SOA concentrations greater than ∼47 ppbv and 1.8 μg m-3, respectively, were found, with maximum concentrations occurring at 2 pm LT, 150-200 km downwind of Manaus city. These high concentrations affect a large primary forested area of about 11,250 km2. These oxidative areas are under a NOx-limited regime so that changes in NOx emissions from Manaus have a significant impact on O3 and SOA production.