Nitrogen Oxides Emission Factors Research Articles

Research on the kinetics characteristics and in-cylinder combustion of opposed rotary piston engine for different power output modes

As a new type of internal combustion engine, opposed rotary piston (ORP) engine has the advantages of simple structure and high working frequency, and can achieve high power density. Consequently, it stands as an ideal power source for hybrid power systems and unmanned aerial vehicles. The ORP engine has different power output modes, corresponding to different piston rotation and volume evolutions of combustion chamber. However, the effect of power output modes on kinetics characteristics and in-cylinder combustion of ORP engines are still uncovered. In this paper, the kinematic model of an ORP engine is established for scenarios involving power output by different shafts (Shaft 1 and Shaft 3). Meanwhile, the piston rotation patterns and cylinder volume variations are investigated correspondingly. Further, three-dimensional numerical model of the ORP engine is established, enabling analysis of in-cylinder combustion characteristics, engine performance, as well as nitrogen oxides (NOx) emissions. The results indicate that the volume variations of all cylinders follow a consistent pattern under the power output by Shaft 3. A pair of opposed cylinders features longer durations of intake and expansion strokes, and shorter durations of compression and exhaust strokes, the other pair of combustion chambers is the opposite under the power output by Shaft 1. The engine demonstrates a charging efficiency of 95.36 %, with corresponding indicated thermal efficiency and indicated power output of 38.08 % and 40.9 kW, respectively. The two adjacent cylinders present significantly different operation processes in the case of the power output by Shaft 1, achieving charging efficiencies of 94.29 % and 89.11 %, respectively, with the indicated thermal efficiency of 34.49 % and 31.60 %. The corresponding minimum indicated specific fuel consumption under the two power output modes are 211.7 g/kW∙h and 243.7 g/kW∙h, respectively, accompanied by NOx emission factors of 25.3 g/kW∙h and 17.6 g/kW∙h. With the given range of ignition timing, a trade-off relationship exists between the engine performance and NOx emissions. The power density of the case of power output by Shaft 3 is superior to that of Shaft 1.

In Situ Sampling of NOx Emissions from United States Natural Gas Flares Reveals Heavy-Tail Emission Characteristic.

Natural gas flaring is a common practice employed in many United States (U.S.) oil and gas regions to dispose of gas associated with oil production. Combustion of predominantly hydrocarbon gas results in the production of nitrogen oxides (NOx). Here, we present a large field data set of in situ sampling of real world flares, quantifying flaring NOx production in major U.S. oil production regions: the Bakken, Eagle Ford, and Permian. We find that a single emission factor does not capture the range of the observed NOx emission factors within these regions. For all three regions, the median emission factors fall within the range of four emission factors used by the Texas Commission for Environmental Quality. In the Bakken and Permian, the distribution of emission factors exhibits a heavy tail such that basin-average emission factors are 2-3 times larger than the value employed by the U.S. Environmental Protection Agency. Extrapolation to basin scale emissions using auxiliary satellite assessments of flare volumes indicates that NOx emissions from flares are skewed, with 20%-30% of the flares responsible for 80% of basin-wide flaring NOx emissions. Efforts to reduce flaring volume through alternative gas capture methods would have a larger impact on the NOx oil and gas budget than current inventories indicate.

Real-Time Monitoring of Nitrogen Oxides Emission Factors Using Sensors in the Exhaust Pipes of Heavy Vehicles in the Metropolitan Region of Rio de Janeiro

The Metropolitan Region of Rio de Janeiro is one of the most populous in Brazil, besides being one of the most important routes for marketing goods through heavy vehicles. This type of vehicle is the main source of nitrogen oxides (NOx) emission into the atmosphere. To assess NOx emission factors, this pilot study used sensors to monitor in real-time the exhaust of 9 trucks from July to September 2022. To the best of our knowledge, this is the first study carried out in the city using low-cost sensors. Although there is legislation to reduce the emission of pollutants from the vehicle fleet, the results showed that 7 out of 9 trucks, exceeded the stipulated limits, reaching 6 g kWh-1. Furthermore, carrying out the maintenance of the engine of one of the vehicles decreased 60% of the NOx emission, even being an old vehicle. Thus, with this data, it was verified that the sensor performed excellently in monitoring NOx, demonstrating robust performance. This pilot study is part of a project that aims to make a long-term study of NOx emissions factors from heavy-duty diesel vehicles using sensors and other parameters.

The Effects of Varying Altitudes on the Rates of Emissions from Diesel and Gasoline Vehicles Using a Portable Emission Measurement System

The high altitude in mountainous regions results in lower atmospheric pressure, oxygen concentration and temperature, leading to lower combustion efficiency in motor vehicles. Therefore, there may be differences in carbon dioxide (CO2), carbon monoxide (CO), and nitrogen oxides (NOx) emissions characteristics at different altitudes. In this study, a portable emission measurement system was used to investigate the effects of varying elevations on the emission factors of CO2, CO, and NOx on diesel and gasoline-powered vehicles at altitudes ranging from 2270 to 4540 m in the Qinghai–Tibet Plateau of China. Additionally, the influencing factors of CO2, CO, and NOx emissions were studied. Results showed that the CO2, CO, and NOx emission factors for diesel vehicles varied in the range of 161.83–195.54, 0.59–0.77, and 4.61–6.58 g/km; the population means with 90% confidence intervals were 178.54, 0.68, and 5.60 g/km, respectively. For gasoline vehicles, the CO2, CO, and NOx emission factors varied in the range of 161.66–181.98, 0.95–1.06, and 0.12–0.25 g/km; the population means with 90% confidence intervals were 171.82, 1.01, and 0.19 g/km, respectively. Overall, the emission factors of diesel vehicles were higher than those of gasoline vehicles, and the emissions increased with increasing altitude. Atmospheric pressure was identified as the primary environmental factor affecting CO2, CO, and NOx emissions. As the speed of motor vehicles increased, the emission of CO2 also increased, while there was a quadratic relationship with acceleration. This study provides a reference and guidance for vehicle pollution control in high-altitude regions.

Assessing light flex-fuel vehicle emissions with ethanol/gasoline blends along an urban corridor: A case of Fortaleza/Brazil

Brazil is the 9th largest producer of vehicles in the world, with 62.7% of the global fleet of Flex-Fuel Vehicles (FFVs). These vehicles used in Brazil operate with E27 (anhydrous ethanol used for gasohol blending) or E100 hydrous ethanol or any blend between these two. In recent years, Fortaleza city/Brazil has implemented Bus Rapid Transit (BRT) systems in two of the city’s most important avenues. Fortaleza BRT has two-way busways on the central verge of the roadway separated by two lanes from mixed traffic used by passenger cars, light commercial trucks, motorcycles, and heavy-duty vehicles. These systems have been regarded as a potential solution to improve some traffic factors, for only Buses, such as the average driving speed, thus benefiting both transportation and the environment. Thus, this research proposes a comprehensive impact evaluation of an FFV when traveling on BRT corridors, specifically on lanes from mixed traffic, and evaluate the emission factors, specifically on lanes from mixed traffic, composed of a wide variety of vehicle types. All tests in this study were performed at lanes from mixed traffic. Carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons (HCt) emissions were experimentally measured using a Portable Emission Measurement System (PEMS) under real-world traffic conditions in Fortaleza. FFV tailpipe emissions from E27, E85, and E100 fuels were highly sensitive to the power demand and traffic flow. Additionally, the VSP (Vehicle Specific Power) methodology was applied to characterize the driving modes. Overall, results showed the following: CO2 was, by far, the most highly emitted gas; the highest CO release occurred with E85 blend; NOx emission factors were similar for both E27 and E85, but much greater for E100; and HCt did not show a pattern, presenting both the highest and lowest emission levels with E100.

Quantifying the Coupling Relationship of Road Grade Impacting Heavy-Duty Diesel Truck Operation Emissions in a Mountainous City in China

To reveal the complex impact of the road grade on heavy-duty diesel truck (HDDT) emissions, the dynamic coupling relationships among the road grade, vehicle operation, and emissions were quantified based on portable emission measurement system data from 24 HDDTs in Chongqing, China. The results showed that the average emission factors of nitrogen oxides (NO x) and carbon dioxide (CO2) of China IV HDDTs were the highest among all tested HDDTs, and NO x emissions often exceeded their corresponding standard limit values. Next, the coupling relationships of road grade, speed, and emissions were studied. Graded roads caused a 4%–44% decrease in the average vehicle speed, resulting in a coupling effect on emissions. For all pollutants and vehicle emission standards, the HDDT emissions on uphill roads were much higher, while those on downhill roads did not deteriorate significantly owing to the increased acceleration operation. Overall, ignoring the road grade led to estimation errors of between −99.14% and 291.30% for CO2 and between −99.21% and 247.73% for NO x. Speed was less correlated with emissions on downhill roads (≤−3%). For uphill roads (>0%), the joint effect of road grade and speed caused a significant increase in CO2 and NO x emissions up to 21.26 and 17.29 times compared to idling emissions. A Sigmoid function successfully modeled the coupling relationship (average R2 = 0.95), and grouped S-shaped mapping curves were revealed for between −8% and 7% road grade and emissions. The model can estimate the influence of road grades on emissions at different speeds, thus providing support for emission reduction control.

Investigation of real-world emissions of China III and China IV buses in a high-altitude city: A case study of Lhasa

Limitations still remain among vehicle emissions standards and regulations about high-altitude areas at altitude over 2400 m. In view of high vehicle-use intensity for buses, on-road measurements were performed on four heavy-duty diesel vehicles by employing a portable emissions measurement system (PEMS) in Lhasa, with an average elevation of approximately 3650 m. The result indicated that under real-world driving conditions of Lhasa, compared with China III buses, China IV buses did not show excellent emission performance consistently. For example, carbon monoxide (CO) emission factor of China III-5.2L buses is 2.4 times of China IV-5.2L buses, while the nitrogen oxides (NOx) is only 36% of China IV-5.2L. Furthermore, an operating mode binning and a micro-trips method are used to link real-world emissions of each vehicle to driving conditions. For China III-5.2L and China IV-5.2L buses, we found strong correlations between relative emission factors of carbon dioxide (CO2) and NOx and average speed. However, these correlations for China IV-7.8L bus were less strong. This phenomenon proves that the role of traffic conditions in affecting road driving emissions would be mitigated when selective catalytic reduction (SCR) functioning properly. This study have potential implications for policymakers concerning vehicle emissions management and control strategies, such as promotion of alternative fuel with in-used buses, aimed at emissions reduction.

Real-world emission for in-use non-road construction machinery in Wuhan, China.

Non-road construction machinery (NRCM) emissions pollutants significantly impact air quality. Six typical NRCM (2 excavators, 3 loaders, and 1 forklift) are analyzed based on a portable emission measurement system (PEMS) in Wuhan to estimate the real-world emission characteristics and chemical composition of PM2.5 of NRCM. The results show that the fuel-based average emission factors (EFs) of carbon monoxide (CO), hydrocarbon (HC), nitrogen oxides (NOx), and particulate matter (PM) are 19.4 ~ 35.7gkg-1 fuel, 2.9 ~ 7.9gkg-1 fuel, 57.5 ~ 95.3gkg-1 fuel, and 1.8 ~ 2.6gkg-1 fuel for the tested NRCM. The high NOx EF implies that the regulation of NOx emission in Wuhan should be strengthened. In addition, the PM2.5 chemical composition profiles for NRCM show that the PM2.5 emitted from NRCM is dominated by organic carbon and elemental carbon (56.11 ~ 73.85%), followed by water-soluble ions (WSIs, 1.47 ~ 3.46%), and elements (0.16 ~ 0.41%). The major WSIs species are Cl-, Na+ andNO3-, and the major elements are Ca, Na, and K, which are important markers for PM2.5 source analysis. The results of EFs and chemical composition emission characteristics of NRCM tailpipe pollutants obtained in the real-world can provide essential data support for accurately establish of emission inventory of non-road mobile sources in Wuhan.

Evaluation of the Relationship between Meteorological Variables and NOx Emission Factors Based on Plume-Chasing Measurements

A relationship that links the accuracy of nitrogen oxide emission factors (NOx EFs) calculated from chasing measurements (EFchasing) to meteorological variables was developed. To quantitatively evaluate this relationship, we postulated an “effective ratio” concept based on the momentum wake theory. The effective ratio is considered a function of meteorological variables in the vehicle wake. A mobile platform was used to characterize NOx EFs by following tested vehicles that were installed with a portable emission measuring system (PEMS) on a restricted driving track. The relationship was evaluated based on 172 plume-chasing measurements that were conducted under various operating scenarios such as different tested vehicle speeds and vehicle types. Two calculation approaches (i.e., baseline vs rolling minimum) were used to calculate EFchasing and benchmark against NOx EF from PEMS (EFPEMS). A consistent positive linear relationship (slope ∼28, p < 0.01) is found between the effective ratio and the relative error of EFchasing under all operating scenarios and is independent of calculation approaches. This is evidence that the effective ratio could be a good parameter that quantifies the relative deviation of EFchasing and is independent of calculation approaches. Based on this relationship, the effective ratio can be further used to identify erroneous chasing measurements and improve the accuracy of EFchasing.

Improved estimation of pollutant emissions from agricultural machinery and projection of its reduction potential in the Beijing-Tianjin-Hebei region, China

As an important non-road mobile source, agricultural machinery has gradually become an important source of air pollution in China. However, research on the emission factors and mitigation potential of agricultural machinery is still in its infancy. In this study, the emission characteristics of ten common agricultural machinery in the Beijing-Tianjin-Hebei (BTH) region were measured using a portable emission measurement system (PEMS). The results show that the instantaneous emission of pollutants from agricultural machinery increased with an increase in engine power. Nitrogen oxide (NOX) emissions were 2.2 and 3.9 times higher in moving and working modes, respectively, than that in idling. The measured hydrocarbon (HC), carbon monoxide (CO), NOX, and particulate matter (PM2.5) emission factors were 0.99, 0.94, 1.12, and 0.95 times, respectively, higher than the recommended values. The CO, HC, NOX, and PM2.5 emissions from agricultural machinery in the BTH region in 2020 were 134.83, 28.54, 182.51, and 15.40 Kt, respectively. Based on the newly established inventory, four scenarios were set up to analyse the emission reduction potential. Under the integrated scenario (IS), the emission reduction potential of pollutants reaches the maximum, and the emission reduction in HC, CO, NOX, and PM2.5 in 2030 was 62.33%, 64.41%, 49.19%, and 70.94%. For single control measures, the update emission standards scenario (UES) has the best emission reduction effect of the four pollutants, the controls on in-use vehicles scenario (CIV) has the best emission reduction effect on NOX and PM2.5. These results can provide fundamental information for the development of agricultural machinery emission control policies.

Air pollutant emissions from sludge-bituminous briquettes as a potential household energy source

To promote the sustainable and clean use of sewage sludge (SS) and bituminous coal (BC), BC was mixed with SS at 2%, 4% and 16% as sludge-coal briquettes (named by SBC1, SBC2 and SBC3) which were characterized in this study to evaluate combustion performance and emissions of hazardous air pollutants in an advanced residential stove. Fuel burning rate and modified combustion efficiency (MCE) were similar among the three fuels, while the emission factors of carbon monoxide (CO) and mercury (Hg) were significantly different ( p < 0.05), with the highest emissions from the biomass-coal briquette with the sludge content of 4%. Ash content is a key factor affecting the emission factors (EFs) of CO and Hg. EFs of particulate matter with aerodynamic equivalent diameter ≤2.5 μm (PM 2.5 ) was significantly correlated with the EFs of nitrogen oxides (NO x ), cadmium (Cd) and total polycyclic aromatic hydrocarbons (tPAHs). It appears that by mixing sludge with briquettes at 16%, there were insignificant changes in emissions of most hazardous pollutants including Hg and PAHs compared with mixing sludge at 2%. This study suggested possibilities in support of high-efficient co-utilization of sludge and briquette coals especially in the residential sector.

Impact of Active Diesel Particulate Filter Regeneration on Carbon Dioxide, Nitrogen Oxides and Particle Number Emissions from Euro 5 and 6 Vehicles under Laboratory Testing and Real-World Driving

Particulate mass concentration is a crucial parameter for characterising air quality. The diesel particulate filter (DPF) is the primary technology used to limit vehicle particle emissions, but it needs periodic cleaning, a process called regeneration. This study aims to assess the impact of active DPF regeneration on the performance and emissions of Euro 5 and 6 vehicles. The study examined both carbon dioxide (CO2) and pollutant (nitrogen oxides (NOx) and particle number (PN)) emissions for eight vehicles tested in the laboratory and on the road. Apart from the DPF, a wide range of emission control systems was covered in this experimental campaign, including exhaust gas recirculation (EGR), diesel oxidation catalyst (DOC), lean NOx trap (LNT) and selective catalytic reduction (SCR) catalyst, revealing the different impacts on NOx emissions. The regeneration frequency and duration were also determined and used to calculate the Ki factor, which accounts for the emissions with and without regeneration, weighted over the distance driven between two consecutive regeneration events. Based on these outcomes, representative emission factors (EF) were proposed for the regeneration phase only and the complete regeneration interval. In addition, the effect of regeneration on efficiency was estimated and compared with other energy consumers. The results indicated a significant impact of DPF regeneration on CO2, NOx and PN emissions, higher in the case of driving cycle testing in the laboratory. The relevant mechanisms behind the elevated emission levels were analysed, focusing on the regeneration period and the test phase following immediately after. The calculation of the Ki factor and the comparison with the official values revealed some weaknesses in its application in real-world conditions; to overcome these, new NOx EF values were calculated, depending on the emission control system. It was revealed that Euro 6 vehicles equipped with SCR could comply with the applicable limits when considering the complete regeneration interval. Finally, it was indicated that the DPF regeneration impact on vehicle efficiency is similar to that of driving with the air conditioning (A/C) system and headlights on.

Road Grade Estimation Based on Power Demand Difference of Heavy-Duty Diesel Trucks for Emission Estimation

Road grades have significant impacts on the emissions of heavy-duty diesel trucks (HDDTs), even in the same operating mode. Existing gradient identification methods are time-consuming and difficult to conduct for entire road networks; moreover, few previous studies have considered uncertainty of HDDT emissions caused by various road grades. In this study, an estimation method for road grade was developed based on second-by-second field operating data, with noise reduction performed using the Kalman filter. The consistency and symmetry of the road grade calculated by the proposed method were then analyzed. Finally, differences in emission rate and emission factor for carbon dioxide (CO2), carbon monoxide (CO), total hydrocarbon (THC), and nitrogen oxides (NOx) under various grades were compared. The results indicated that the grade recognition results of each truck were consistent, with an average grade difference of 0.153%. Based on symmetry analysis of the estimation results in opposite directions, the two opposite road grades were found to have a strong negative correlation, and the average error of the grade was 0.125%. Pollutant results showed the emission rate of CO was most affected by grade, followed by NOx, and THC was the least affected. The emission factors of CO2, CO, THC, and NOx were found to increase by 32.4% to 82.8%, 75.6% to 198.4%, 19.9% to 39.9%, and 73.1% to 186.3%, respectively at 1.0%, 2.0%, and 3.0% gradients compared with 0.0% gradient. This study can improve the estimation accuracy for HDDT emissions, especially in areas with undulating terrain such as mountains and hills.

Dynamic NOx emission factors for main engines of bulk carriers

Emission factors are essential for estimating ship emissions. To improve the accuracy of the nitrogen oxides (NOx) emissions, dynamic emission factors of NOx were implemented in this study. First of all, the influences of wind, waves and currents on the speed of the Automatic Identification System (AIS) were eliminated. Furthermore, with the adaption of modified speed, the accuracy of estimated main engine loads was increased, compared with the raw AIS speed. Moreover, the dynamic emission factors of NOx were further developed using modified speed for the estimation of main engine loads. In the numerical study, the dynamic emission factors of NOx model manifested an improvement of up to 86% for the estimation of the NOx emissions of two bulk carriers, compared with commonly used emission factors of NOx.

Analysis of Pollutant Emission in Poland From Road Vehicles of the Generalised Category in Accordance With the Vehicle Application Criterion

Abstract This paper presents the results of analyses that were focused on pollutant emissions from road vehicles classified into the generalised categories with respect to vehicle use. The analyses were performed using the authorised results of Poland's pollutant emission inventory, carried out in 1990–2020 by the National Centre for Emissions Management (KOBiZE) at the Institute of Environmental Protection – National Research Institute (IOŚ-PIB) in order to meet requirements for the national emissions reporting under EU legislation and the UNECE Convention on Long-range Transboundary Air Pollution. The following road vehicle categories were analysed: passenger cars, light duty vehicles, heavy-duty trucks, buses (urban buses and coaches) and L category (motorcycles, mopeds, quads, microcars). The emissions of selected pollutants that are harmful to the health of living beings were studied, i.e. nitrogen oxides, non-methane volatile organic compounds, sulfur compounds, particulate matter size fractions, carbon monoxide and lead compounds. The shares of national annual pollutant emissions from each studied vehicle category of the total pollutant emissions from road transport were determined. With the aim to assess trends in improving environmental properties of road vehicles, there were determined changes of the energy emission factors for individual pollutants in all the vehicle categories under the study. The results obtained showed dynamic decreases in the energy emission factors for nitrogen oxides, non-methane volatile organic compounds and carbon monoxide. In the case of particulate matter emission, the improvement was not as pronounced. The evident reduction in the emissions of sulfur and lead compounds in the 21st century was confirmed to be a consequence of practical elimination of these compounds from road vehicle fuels.

In-Use Passenger Vessel Emission Rates of Black Carbon and Nitrogen Oxides.

This study quantified emission factors of black carbon (BC) and nitrogen oxides (NOx) from 21 engines on in-use excursion vessels and ferries operating in California's San Francisco Bay, including EPA uncertified and Tier 1-4 engines and across engine operating modes. On average, ∼60 fuel-based emission factors per engine were measured using a novel combination of exhaust plume capture combined with GPS location and speed data that can be more readily deployed than common portable emissions measurement systems. BC and NOx emission factors (g kg-1) were lowest and least variable during fast cruising and highest during maneuvering and docked operation. Selective catalytic reduction (SCR) reduced NOx emissions by ∼80% when functional. However, elevated NOx emissions that exceeded corresponding exhaust standards were measured on most Tier 3 and Tier 4 engines sampled, which can be attributed to inactive SCR during frequent low engine load operation. In contrast, BC emissions exceeded the PM emission standard for only one engine, and SCR systems employed as a NOx reduction technology also reduced emitted BC. Using these measured emission factors to compare commuting options, we show that the CO2-equivalent emissions per passenger-kilometer are comparable when commuting by car and ferry, but BC and NOx emissions can be several to more than ten times larger when commuting by ferry.

Pollutant emission performances of improved solid fuel heating stoves and future implications in rural China

Solid fuel combustion in traditional heating stoves leads to severe environmental pollution. Thus, improved solid fuel heating stoves have been introduced to replace traditional stoves, but their emission performances have rarely been evaluated. In this study, we measured the particulate matter with aerodynamic diameter ≤ 2.5 μm (PM2.5), carbon monoxide (CO), nitrogen oxides (NOx), and sulfur dioxide (SO2) emission performances of an anthracite coal briquette heating stove, a semi-coke heating stove, and a biomass pellet heating stove consuming wood, rice husk, and maize straw pellets during high and low firepower phases, and used a traditional bituminous coal chunk heating stove as comparison baseline. The results showed that these solid fuel heating stoves had lower PM2.5 and CO emissions and higher NOx and SO2 emissions during the high firepower phase than the low firepower phase. During the same phase, the biomass pellet heating stove consuming wood pellets had the lowest PM2.5, CO, and SO2 emission factors, and the semi-coke heating stove emitted the lowest NOx emission factors. After replacing the traditional stove, the improved coal heating stoves reduced PM2.5, CO, and NOx emission amounts by 18.0 %–73.9 %, 41.4 %–55.6 %, and 42.4 %–45.4 %, respectively, but increased SO2 emission amounts by 19.8 %–67.8 %, while the biomass pellet heating stove reduced PM2.5, CO, and SO2 emission amounts by 64.2 %–91.9 %, 72.8 %–87.0 %, and 58.0 %–100 %, respectively, but emitted more NOx emission amounts, except for this stove consuming wood pellets. Overall, the biomass pellet heating stove was more suitable for space heating. This study provides useful information regarding solid fuel heating stove selection for intervention projects in rural China.

Direct estimates of biomass burning NO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; emissions and lifetimes using daily observations from TROPOMI

Abstract. Biomass burning emits an estimated 25 % of global annual nitrogen oxides (NOx), an important constituent that participates in the oxidative chemistry of the atmosphere. Estimates of NOx emission factors, representing the amount of NOx per mass burned, are primarily based on field or laboratory case studies, but the sporadic and transient nature of wildfires makes it challenging to verify whether these case studies represent the behavior of the global fires that occur on earth. Satellite remote sensing provides a unique view of the earth, allowing for the study of emissions and downwind evolution of NOx from a large number of fires. We describe direct estimates of NOx emissions and lifetimes for fires using an exponentially modified Gaussian analysis of daily TROPOspheric Monitoring Instrument (TROPOMI) retrievals of NO2 tropospheric columns. We update the a priori profile of NO2 with a fine-resolution (0.25∘) global model simulation from NASA's GEOS Composition Forecasting System (GEOS-CF), which largely enhances NO2 columns over fire plumes. We derive representative NOx emission factors for six fuel types globally by linking TROPOMI-derived NOx emissions with observations of fire radiative power from Moderate Resolution Imaging Spectroradiometer (MODIS). Satellite-derived NOx emission factors are largely consistent with those derived from in situ measurements. We observe decreasing NOx lifetime with fire emissions, which we infer is due to the increase in both NOx abundance and hydroxyl radical production. Our findings suggest promise for applying space-based observations to track the emissions and chemical evolution of reactive nitrogen from wildfires.

Comparison of NOx and PN emissions between Euro 6 petrol and diesel passenger cars under real-world driving conditions

With emission standards becoming stricter, nitrogen oxides (NOx) and particle number (PN) emissions are the main concerns of modern passenger cars, especially for the real-world driving. In this paper, two direct injection (DI) petrol passenger cars and a diesel passenger car are tested on the same routes, driven by the same driver. Instantaneous NOx and PN emissions are monitored by a portable emission measurement system (PEMS) in the tests. During the real-world driving, the exhaust temperatures of the two petrol cars are sufficiently high to ensure high efficiency of three-way catalysts (TWCs). On the other hand, the exhaust temperatures of the diesel car in some sections of the route are lower than the crucial light-off temperature of the selective catalytic reduction (SCR) below which its effectiveness in NOx reduction would be much affected. NOx and PN concentrations are low during motorway driving for the petrol passenger car equipped with a gasoline particulate filter (GPF); however, they are high and change frequently in the whole journey for the petrol passenger car without a GPF. NOx emission factors are quite low over most of the driving sections for the diesel car, but some significant high peaks are observed in the acceleration process. NOx emission distributions over speed and acceleration are similar for both petrol cars; and they differ significantly from the diesel counterpart. Particle size from the diesel car is the largest, followed by the petrol car with a GPF.

NOx Emission from Diesel Vehicle with SCR System Failure Characterized Using Portable Emissions Measurement Systems

Nitrogen oxides (NOx) emissions from diesel vehicles are major contributors to increasing fine particulate matter and ozone levels in China. The selective catalytic reduction (SCR) system can effectively reduce NOx emissions from diesel vehicles and is widely used in China IV and V heavy-duty diesel vehicles (HDDVs). In this study, two China IV HDDVs, one with SCR system failure and the other with a normal SCR system, were tested by using a portable emissions measurement system (PEMS). Results showed that the NOx emission factors of the test vehicle with SCR system failure were 8.42 g/kW∙h, 6.15 g/kW∙h, and 6.26 g/kW∙h at loads of 0%, 50%, and 75%, respectively, which were 2.14, 2.10, and 2.47 times higher than those of normal SCR vehicles. Emission factors, in terms of g/km and g/kW∙h, from two tested vehicles were higher on urban roads than those on suburban and motorways. The NOx emission factor of the vehicle with failed SCR system did not meet the China IV emission standard. The time-weighted results for normal SCR vehicle over the three road types show that, except for NOx emission factor 12.17% higher than the China IV limit at 0% load, the emission values are 16.21% and 27.54% below the China IV standard limit at 50% load and 75% load, respectively. In general, with higher load, NOx emissions (in terms of g/kW∙h) from the tested vehicle decreased. Furthermore, NO/NOx concentrations of both vehicles with normal and failed SCR systems showed a decreasing trend with the increase in load.