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17 pages, 4664 KiB

Open AccessArticle

Using Neural Network NO₂-Predictions to Understand Air Quality Changes in Urban Areas—A Case Study in Hamburg

by Anne-Sophie Jesemann, Volker Matthias, Jürgen Böhner and Benjamin Bechtel

Atmosphere 2022, 13(11), 1929; https://doi.org/10.3390/atmos13111929 - 19 Nov 2022

Cited by 2 | Viewed by 1860

Abstract

Due to the link between air pollutants and human health, reliable model estimates of hourly pollutant concentrations are of particular interest. Artificial neural networks (ANNs) are powerful modeling tools capable of reproducing the observed variations in pollutants with high accuracy. We present a [...] Read more.

Due to the link between air pollutants and human health, reliable model estimates of hourly pollutant concentrations are of particular interest. Artificial neural networks (ANNs) are powerful modeling tools capable of reproducing the observed variations in pollutants with high accuracy. We present a simple ANN for the city of Hamburg that estimated the hourly NO₂ concentration. The model was trained with a ten-year dataset (2007–2016), tested for the year 2017, and then applied to assess the efficiency of countermeasures against air pollution implemented since 2018. Using both meteorological data and describing the weekday dependent traffic variabilities as predictors, the model performed accurately and showed high consistency over the test data. This proved to be very efficient in detecting anomalies in the time series. The further the prediction was from the time of the training data, the more the modeled data deviated from the measured data. Using the model, we could detect changes in the time series that did not follow previous trends in the training data. The largest deviation occurred during the COVID-19 lockdown in 2020, when traffic volumes decreased significantly. Concluding our case study, the ANN based approach proved suitable for modeling the NO₂ concentrations and allowed for the assessment of the efficiency of policy measures addressing air pollution. Full article

(This article belongs to the Special Issue Air Quality Impacts of Vehicle Emissions)

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12 pages, 3578 KiB

Open AccessArticle

Development of an Engine Power Binning Method for Characterizing PM_2.5 and NOx Emissions for Off-Road Construction Equipment with DPF and SCR

by Qi Yao, Seungju Yoon, Yi Tan, Liang Liu, Jorn Herner, George Scora, Robert Russell, Hanwei Zhu and Tom Durbin

Atmosphere 2022, 13(6), 975; https://doi.org/10.3390/atmos13060975 - 16 Jun 2022

Cited by 2 | Viewed by 1463

Abstract

Aftertreatment technologies in Tier 4 off-road engines have resulted in significant emission reductions compared to older tier engines without aftertreatments. The appropriate characterization of Tier 4 engine emissions in consideration of aftertreatment operation is important for projecting emissions and developing mitigation strategies. The [...] Read more.

Aftertreatment technologies in Tier 4 off-road engines have resulted in significant emission reductions compared to older tier engines without aftertreatments. The appropriate characterization of Tier 4 engine emissions in consideration of aftertreatment operation is important for projecting emissions and developing mitigation strategies. The current method of aggregating emissions over an entire duty cycle and averaging them by engine load has a limitation in developing emission profiles over various duty cycles of Tier 4 engines, especially at low-load operations, where aftertreatment control for NOx may not be effective. In this study, an engine power binning method was developed to characterize emissions for Tier 4 construction equipment with aftertreatment systems, especially at low-power operating conditions. This binning method was applied to real-time emissions and activity data for four different types of Tier 4 construction equipment. Results show that low-power operations (<20% engine power) are responsible for 38–60% NOx and 11–51% of PM_2.5 emissions depending on the equipment types. These results underscore the need for controlling NOx emissions during low-power operations. PM_2.5 EFs for non-DPF backhoes were one to two orders of magnitude greater than all the other equipment due to the lack of a DPF, despite being certified to the same PM_2.5 standard. This shows the benefits of DPFs on construction equipment and that they are substantial in reducing PM_2.5 emissions. Estimated emission differences between using the binning and the averaging methods were 49–86% and 16–82% for NOx and PM_2.5, respectively. These differences may change once the binning method is applied to larger emission datasets obtained from real-world vocational activities. Full article

(This article belongs to the Special Issue Air Quality Impacts of Vehicle Emissions)

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19 pages, 5933 KiB

Open AccessArticle

Ozone Trends and the Ability of Models to Reproduce the 2020 Ozone Concentrations in the South Coast Air Basin in Southern California under the COVID-19 Restrictions

by Lynsey Karen Parker, Jeremiah Johnson, John Grant, Pradeepa Vennam, Rajashi Parikh, Chao-Jung Chien and Ralph Morris

Atmosphere 2022, 13(4), 528; https://doi.org/10.3390/atmos13040528 - 26 Mar 2022

Cited by 3 | Viewed by 1930

Abstract

The current U.S. emission control requirements for on-road motor vehicles are driven by the ozone problem in the South Coast Air Basin (SoCAB) in southern California. Based on ozone modeling performed for Air Quality Management Plans (AQMPs), the SoCAB ozone attainment plan requires [...] Read more.

The current U.S. emission control requirements for on-road motor vehicles are driven by the ozone problem in the South Coast Air Basin (SoCAB) in southern California. Based on ozone modeling performed for Air Quality Management Plans (AQMPs), the SoCAB ozone attainment plan requires large (>80%) amounts of emission reductions in oxides of nitrogen (NOx) from current levels with more modest (~40%) controls on Volatile Organic Compounds (VOC). The shelter in place orders in response to the 2020 COVID-19 pandemic resulted in an immediate reduction in emissions, but instead of ozone being reduced, in 2020 the SoCAB saw some of the highest observed ozone levels in decades. We used the abrupt emissions reductions from 2019 to 2020 caused by COVID-19 to conduct a dynamic model evaluation of the Community Multiscale Air Quality (CMAQ) model to evaluate whether the models used to develop ozone control plans can correctly simulate the ozone response to the emissions reductions. Ozone modeling was conducted for three scenarios: 2019 Base, 2020 business-as-usual (i.e., without COVID reductions), and 2020 COVID. We found that modeled ozone changes between 2019 and 2020 were generally consistent with the observed ozone changes. We determined that meteorology played the major role in the increases in ozone between 2019 and 2020; however, the reduction in NO_X emissions also caused ozone increases in Los Angeles County and into western San Bernardino County, with more widespread ozone decreases further to the east. Full article

(This article belongs to the Special Issue Air Quality Impacts of Vehicle Emissions)

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22 pages, 3297 KiB

Open AccessArticle

Undiluted Measurement of the Particle Size Distribution of Different Oxygenated Biofuels in a Gasoline-Optimised DISI Engine

by Tara Larsson, Ulf Olofsson and Anders Christiansen Erlandsson

Atmosphere 2021, 12(11), 1493; https://doi.org/10.3390/atmos12111493 - 11 Nov 2021

Cited by 4 | Viewed by 1586

Abstract

The utilisation of internal combustion engines is one of the main causes of particle emissions in urban areas. As the interest for the utilisation of biofuels increases, it is important to understand their effect on particle number emissions. In this paper, the particle [...] Read more.

The utilisation of internal combustion engines is one of the main causes of particle emissions in urban areas. As the interest for the utilisation of biofuels increases, it is important to understand their effect on particle number emissions. In this paper, the particle size distribution and the particle number emissions from a gasoline-optimised direct-injected spark-ignited (DISI) engine are investigated. The effects of five different biofuel alternatives on these emissions were evaluated and compared to gasoline. The utilisation of the high-resolution, high-temperature ELPI+ enabled undiluted measurements of the particle size distribution down to 6 nm, without extensive cooling of the engine exhaust. Contrary to other studies, the results show that the particle number emissions for the three measured cut-off sizes (23, 10 and 7 nm) increased with the utilisation of oxygenated biofuels. The results indicate that the decreased volatility and energy density of the alcohols has a more significant impact on the particle formation in a DISI engine than the increased oxygen content of these fuels. Full article

(This article belongs to the Special Issue Air Quality Impacts of Vehicle Emissions)

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19 pages, 5142 KiB

Open AccessArticle

Regional Emissions Analysis of Light-Duty Battery Electric Vehicles

by Andrew Burnham, Zifeng Lu, Michael Wang and Amgad Elgowainy

Atmosphere 2021, 12(11), 1482; https://doi.org/10.3390/atmos12111482 - 9 Nov 2021

Cited by 8 | Viewed by 6895

Abstract

Light-duty battery electric vehicles (BEVs) can reduce both greenhouse gas (GHG) and criteria air pollutant (CAPs) emissions, when compared to gasoline vehicles. However, research has found that while today’s BEVs typically reduce GHGs, they can increase certain CAPs, though with significant regional variability [...] Read more.

Light-duty battery electric vehicles (BEVs) can reduce both greenhouse gas (GHG) and criteria air pollutant (CAPs) emissions, when compared to gasoline vehicles. However, research has found that while today’s BEVs typically reduce GHGs, they can increase certain CAPs, though with significant regional variability based on the electric grid mix. In addition, the environmental performance of electric and gasoline vehicles is not static, as key factors driving emissions have undergone significant changes recently and are expected to continue to evolve. In this study, we perform a cradle-to-grave life cycle analysis using state-level generation mix and vehicle operation emission data. We generated state-level emission factors using a projection from 2020 to 2050 for three light-duty vehicle types. We found that BEVs currently provide GHG benefits in nearly every state, with the median state’s benefit being between approximately 50% to 60% lower than gasoline counterparts. However, gasoline vehicles currently have lower total NOx, urban NOx, total PM_2.5, and urban PM_2.5 in 33%; 15%; 70%; and 10% of states, respectively. BEV emissions will decrease in 2050 due to a cleaner grid, but the relative benefits when compared to gasoline vehicles do not change significantly, as gasoline vehicles are also improving over this time. Full article

(This article belongs to the Special Issue Air Quality Impacts of Vehicle Emissions)

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16 pages, 28612 KiB

Open AccessArticle

Comparison of Top-Down and Bottom-Up Road Transport Emissions through High-Resolution Air Quality Modeling in a City of Complex Orography

by Felipe Cifuentes, Carlos M. González, Erika M. Trejos, Luis D. López, Francisco J. Sandoval, Oscar A. Cuellar, Sonia C. Mangones, Néstor Y. Rojas and Beatriz H. Aristizábal

Atmosphere 2021, 12(11), 1372; https://doi.org/10.3390/atmos12111372 - 20 Oct 2021

Cited by 14 | Viewed by 3315

Abstract

Vehicular emissions are a predominant source of pollution in urban environments. However, inherent complexities of vehicular behavior are sources of uncertainties in emission inventories (EIs). We compare bottom-up and top-down approaches for estimating road transport EIs in Manizales, Colombia. The EIs were estimated [...] Read more.

Vehicular emissions are a predominant source of pollution in urban environments. However, inherent complexities of vehicular behavior are sources of uncertainties in emission inventories (EIs). We compare bottom-up and top-down approaches for estimating road transport EIs in Manizales, Colombia. The EIs were estimated using a COPERT model, and results from both approaches were also compared with the official top-down EI (estimated from IVE methodology). The transportation model PTV-VISUM was used for obtaining specific activity information (traffic volumes, vehicular speed) in bottom-up estimation. Results from COPERT showed lower emissions from the top-down approach than from the bottom-up approach, mainly for NMVOC (−28%), PM₁₀ (−26%), and CO (−23%). Comparisons showed that COPERT estimated lower emissions than IVE, with higher differences than 40% for species such as PM₁₀, NO_X, and CH₄. Furthermore, the WRF–Chem model was used to test the sensitivity of CO, O₃, PM₁₀, and PM_2.5 predictions to the different EIs evaluated. All studied pollutants exhibited a strong sensitivity to the emission factors implemented in EIs. The COPERT/top-down was the EI that produced more significant errors. This work shows the importance of performing bottom-up EI to reduce the uncertainty regarding top-down activity data. Full article

(This article belongs to the Special Issue Air Quality Impacts of Vehicle Emissions)

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16 pages, 3990 KiB

Open AccessArticle

Particle Number Emissions of Gasoline, Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG) Fueled Vehicles at Different Ambient Temperatures

by Tero Lähde and Barouch Giechaskiel

Atmosphere 2021, 12(7), 893; https://doi.org/10.3390/atmos12070893 - 9 Jul 2021

Cited by 17 | Viewed by 3675

Abstract

Compressed natural gas (CNG) and liquefied petroleum gas (LPG) are included in the group of promoted transport fuel alternatives for traditional fossil fuels in Europe. Both CNG and LPG fueled vehicles are believed to have low particle number and mass emissions. Here, we [...] Read more.

Compressed natural gas (CNG) and liquefied petroleum gas (LPG) are included in the group of promoted transport fuel alternatives for traditional fossil fuels in Europe. Both CNG and LPG fueled vehicles are believed to have low particle number and mass emissions. Here, we studied the solid particle number (SPN) emissions >4 nm, >10 nm and >23 nm of bi-fuel vehicles applying CNG, LPG and gasoline fuels in laboratory at 23 °C and sub-zero (−7 °C) ambient temperature conditions. The SPN23 emissions in CNG or LPG operation modality at 23 °C were below the regulated SPN23 limit of diesel and gasoline direct injection vehicles

6 \times 10^{11}

1/km. Nevertheless, the limit was exceeded at sub-zero temperatures, when sub-23 nm particles were included, or when gasoline was used as a fuel. The key message of this study is that gas-fueled vehicles produced particles mainly <23 nm and the current methodology might not be appropriate. However, only in a few cases absolute SPN >10 nm emission levels exceeded

6 \times 10^{11}

1/km when >23 nm levels were below

6 \times 10^{11}

1/km. Setting a limit of

1 \times 10^{11}

1/km for >10 nm particles would also limit most of the >4 nm SPN levels below

6 \times 10^{11}

1/km. Full article

(This article belongs to the Special Issue Air Quality Impacts of Vehicle Emissions)

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Review

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19 pages, 1595 KiB

Open AccessReview

Vehicle Emissions and Urban Air Quality: 60 Years of Progress

by Timothy J. Wallington, James E. Anderson, Rachael H. Dolan and Sandra L. Winkler

Atmosphere 2022, 13(5), 650; https://doi.org/10.3390/atmos13050650 - 20 Apr 2022

Cited by 23 | Viewed by 5956

Abstract

The past 60 years have seen large reductions in vehicle emissions of particulate matter (PM), nitrogen oxides (NO_x), carbon monoxide (CO), hydrocarbons (HCs), sulfur dioxide (SO₂), and lead (Pb). Advanced emission after-treatment technologies have been developed for gasoline and [...] Read more.

The past 60 years have seen large reductions in vehicle emissions of particulate matter (PM), nitrogen oxides (NO_x), carbon monoxide (CO), hydrocarbons (HCs), sulfur dioxide (SO₂), and lead (Pb). Advanced emission after-treatment technologies have been developed for gasoline and diesel vehicles to meet increasingly stringent regulations, yielding absolute emission reductions from the on-road fleet despite increased vehicle miles traveled. As a result of reduced emissions from vehicles and other sources, the air quality in cities across the U.S. and Europe has improved greatly. Turn-over of the on-road fleet, increasingly stringent emission regulations (such as Tier 3 in the U.S., LEV III in California, Euro 6 in Europe, and upcoming rules in these same regions), and the large-scale introduction of electric vehicles will lead to even lower vehicle emissions and further improvements in air quality. We review historical vehicle emissions and air quality trends and discuss the future outlook. Full article

(This article belongs to the Special Issue Air Quality Impacts of Vehicle Emissions)

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30 pages, 5910 KiB

Open AccessReview

Vehicle Emissions and Air Quality: The Early Years (1940s–1950s)

by S. Kent Hoekman and J. Steve Welstand

Atmosphere 2021, 12(10), 1354; https://doi.org/10.3390/atmos12101354 - 16 Oct 2021

Cited by 3 | Viewed by 5777

Abstract

During the 1940s, an unusual form of air pollution was experienced in the Los Angeles (LA) area of Southern California. Referred to as LA smog, this pollution differed from previously known air pollution with respect to its temporal patterns (daytime formation and nighttime [...] Read more.

During the 1940s, an unusual form of air pollution was experienced in the Los Angeles (LA) area of Southern California. Referred to as LA smog, this pollution differed from previously known air pollution with respect to its temporal patterns (daytime formation and nighttime dissipation), eye irritation, high oxidant levels, and plant damage. Early laboratory and field experimentation discovered the photochemical origins of LA smog. Though mechanistic understanding was incomplete, it was determined that hydrocarbon (HC) compounds in the atmosphere participate in smog formation, enabling build-up of higher ozone concentrations than would otherwise occur. It being a significant source, there was great interest in characterizing and controlling HC emissions from motor vehicles. Considerable work was done in the 1940s and 1950s to understand how emissions varied with vehicle operating conditions and deterioration of engine components. During this time, procedures were developed (and improved) to sample and quantify vehicle emissions. Besides exhaust, HC emissions from crankcase blowby, carburetor evaporation, and fuel tank losses were measured and characterized. Initial versions of both catalytic and non-catalytic exhaust after-treatment systems were developed. The knowledge gained from this pre-1960 work laid the foundation for many advancements that reduced vehicle emissions and improved air quality during subsequent decades. Full article

(This article belongs to the Special Issue Air Quality Impacts of Vehicle Emissions)

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