Applied Sciences

Research

17 pages, 4788 KiB

Open AccessArticle

Particle Number Measurements Directly from the Tailpipe for Type Approval of Heavy-Duty Engines

by Barouch Giechaskiel, Tero Lähde, Matthias Schwelberger, Timo Kleinbach, Helge Roske, Enrico Teti, Tim van den Bos, Patrick Neils, Christophe Delacroix, Tobias Jakobsson and Hua Lu Karlsson

Appl. Sci. 2019, 9(20), 4418; https://doi.org/10.3390/app9204418 - 18 Oct 2019

Cited by 25 | Viewed by 3073

Abstract

The type approval of heavy-duty engines requires measurement of particulates downstream of a proportional to the exhaust flow partial flow dilution system. However, for particle number systems, which measure in real time, this is not necessary and a fixed dilution could be used. [...] Read more.

The type approval of heavy-duty engines requires measurement of particulates downstream of a proportional to the exhaust flow partial flow dilution system. However, for particle number systems, which measure in real time, this is not necessary and a fixed dilution could be used. In order to assess this dilution possibility, an inter-laboratory exercise was conducted, where a “Golden” system measuring directly from the tailpipe with “hot” (150 °C) fixed dilution was compared with the laboratory regulated systems. Additional “Golden” counters were measuring from 10 nm, below the current cut-off size of 23 nm defined in the regulation, in order to collect data below 23 nm and to confirm that the direct sampling is also possible for smaller sizes. Seven diesel engines and two CNG (compressed naturals gas) engines were used in six laboratories. The results of the “Golden” instruments were within 25% in most cases, reaching 40% in two laboratories for both >23 nm and >10 nm. The repeatability of the measurements (10% to 40%) remained the same for both systems with both cut-off sizes. One test with regeneration showed clear difference between the 10 nm systems, indicating that the thermal pre-treatment only with evaporation tube might not be adequate. Another system measuring from the tailpipe with a fixed “cold” (at ambient temperature) dilution gave differences of up to 50% in most cases (on average +26%). Dedicated tests with this system showed that the differences were the same with fixed or proportional dilution, indicating that it is not the concept that resulted in the overestimation, but the calibration of the system. The main conclusion of this study is that direct sampling with fixed dilution from the tailpipe can be introduced in the future regulation. Full article

(This article belongs to the Special Issue Air Pollution)

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9 pages, 2961 KiB

Open AccessArticle

Air Quality Index and Air Pollutant Concentration Prediction Based on Machine Learning Algorithms

by Huixiang Liu, Qing Li, Dongbing Yu and Yu Gu

Appl. Sci. 2019, 9(19), 4069; https://doi.org/10.3390/app9194069 - 29 Sep 2019

Cited by 119 | Viewed by 11777

Abstract

Air pollution has become an important environmental issue in recent decades. Forecasts of air quality play an important role in warning people about and controlling air pollution. We used support vector regression (SVR) and random forest regression (RFR) to build regression models for [...] Read more.

Air pollution has become an important environmental issue in recent decades. Forecasts of air quality play an important role in warning people about and controlling air pollution. We used support vector regression (SVR) and random forest regression (RFR) to build regression models for predicting the Air Quality Index (AQI) in Beijing and the nitrogen oxides (NO_X) concentration in an Italian city, based on two publicly available datasets. The root-mean-square error (RMSE), correlation coefficient (r), and coefficient of determination (R²) were used to evaluate the performance of the regression models. Experimental results showed that the SVR-based model performed better in the prediction of the AQI (RMSE = 7.666, R² = 0.9776, and r = 0.9887), and the RFR-based model performed better in the prediction of the NO_X concentration (RMSE = 83.6716, R² = 0.8401, and r = 0.9180). This work also illustrates that combining machine learning with air quality prediction is an efficient and convenient way to solve some related environment problems. Full article

(This article belongs to the Special Issue Air Pollution)

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13 pages, 1002 KiB

Open AccessArticle

Modeling of Atmospheric Pollution in Urban and Rural Sites Using a Probabilistic and Objective Approach

by Francisco J. Moral, Francisco J. Rebollo, Pablo Valiente and Fernando López

Appl. Sci. 2019, 9(19), 4009; https://doi.org/10.3390/app9194009 - 25 Sep 2019

Cited by 7 | Viewed by 2026

Abstract

Atmospheric pollution is affected by different individual pollutants (IP) and climatic factors (CF). In this work, the formulation of the Rasch model is proposed to get representative measures of atmospheric pollution in two urban locations, Badajoz and Cáceres, and one rural site, the [...] Read more.

Atmospheric pollution is affected by different individual pollutants (IP) and climatic factors (CF). In this work, the formulation of the Rasch model is proposed to get representative measures of atmospheric pollution in two urban locations, Badajoz and Cáceres, and one rural site, the Monfragüe Park (Southwest Spain). After applying the Rasch methodology, the ranking of all days was obtained according to their atmospheric pollution level and the influence on the environmental deterioration of each IP and CF (NO₂, NO, SO₂, O₃, CO, benzene, PM₁₀, precipitation, relative humidity, solar radiation, air temperature, and barometric pressure). The most influential items on atmospheric pollution are the O₃ and the CF, mainly the lack of precipitation and those related to ozone generation (air temperature and solar radiation). Other IP exert a lower influence at both urban locations, being irrelevant at the Monfragüe Park. Unexpected behaviors of the CF or IP can be also analyzed. Full article

(This article belongs to the Special Issue Air Pollution)

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31 pages, 7999 KiB

Open AccessArticle

Modelling the Effects of Aerosol on Mei-Yu Frontal Precipitation and Physical Processes

by Yun Zhang, Zuhang Wu, Lifeng Zhang, Yanqiong Xie, Hengchi Lei, Hepeng Zheng and Xiaolin Ma

Appl. Sci. 2019, 9(18), 3802; https://doi.org/10.3390/app9183802 - 11 Sep 2019

Cited by 2 | Viewed by 2749

Abstract

The Mei-Yu front is a significantly important summer precipitation system in eastern Asia. In recent years, anthropogenic air pollution over the Yangtze-Huaihe region of China has been aggravating continuously. A cloud-resolving model coupled with an idealized frontal model is used to investigate the [...] Read more.

The Mei-Yu front is a significantly important summer precipitation system in eastern Asia. In recent years, anthropogenic air pollution over the Yangtze-Huaihe region of China has been aggravating continuously. A cloud-resolving model coupled with an idealized frontal model is used to investigate the response of aerosols on the Mei-Yu frontal precipitation. The results indicate that increasing droplet concentrations lead to significant precipitation enhancement with the current pollution levels in Mei-Yu frontal system. Under the polluted conditions, the enhanced cold-cloud process is of great importance. Moreover, with the “towing” of active cold-cloud process, cold-cloud and warm-cloud processes developed mutually. These account for the complicated and special microphysical mechanism for aerosol impacts on Mei-Yu frontal system. Furthermore, two types of “microphysical-dynamic positive feedback loop” caused by the interactions of various physical processes and effects (direct dynamic effect, frontogenesis effect, and vapor pump effect) can be found in the Mei-Yu precipitation, which in turn reinforce the microphysical processes. The combined effect is to increase Mei-Yu front precipitation. The interaction of microphysical processes and dynamic processes, and the positive feedback loops they create are the main physical mechanisms behind the significant impacts of aerosol on Mei-Yu frontal precipitation. This may also be an important feature of climate change in eastern Asia. Full article

(This article belongs to the Special Issue Air Pollution)

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13 pages, 2064 KiB

Open AccessArticle

A Deep Belief Network Combined with Modified Grey Wolf Optimization Algorithm for PM2.5 Concentration Prediction

by Yin Xing, Jianping Yue, Chuang Chen, Yunfei Xiang, Yang Chen and Manxing Shi

Appl. Sci. 2019, 9(18), 3765; https://doi.org/10.3390/app9183765 - 9 Sep 2019

Cited by 21 | Viewed by 2595

Abstract

Accurate PM2.5 concentration prediction is crucial for protecting public health and improving air quality. As a popular deep learning model, deep belief network (DBN) for PM2.5 concentration prediction has received increasing attention due to its effectiveness. However, the DBN structure parameters that have [...] Read more.

Accurate PM2.5 concentration prediction is crucial for protecting public health and improving air quality. As a popular deep learning model, deep belief network (DBN) for PM2.5 concentration prediction has received increasing attention due to its effectiveness. However, the DBN structure parameters that have a significant impact on prediction accuracy and computation time are hard to be determined. To address this issue, a modified grey wolf optimization (MGWO) algorithm is proposed to optimize the DBN structure parameters containing number of hidden nodes, learning rate, and momentum coefficient. The methodology modifies the basic grey wolf optimization (GWO) algorithm using the nonlinear convergence and position update strategies, and then utilizes the training error of the DBN to calculate the fitness function of the MGWO algorithm. Through the multiple iterations, the optimal structure parameters are obtained, and a suitable predictor is finally generated. The proposed prediction model is validated on a real application case. Compared with the other prediction models, experimental results show that the proposed model has a simpler structure but higher prediction accuracy. Full article

(This article belongs to the Special Issue Air Pollution)

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11 pages, 2021 KiB

Open AccessArticle

Experimental Study on the Removal of Real Exhaust Pollutants from a Diesel Engine by Activated Carbon

by Zongyu Wang, Hailang Kuang, Jifeng Zhang, Lilin Chu and Yulong Ji

Appl. Sci. 2019, 9(15), 3175; https://doi.org/10.3390/app9153175 - 5 Aug 2019

Cited by 6 | Viewed by 3054

Abstract

So far, most of the experimental researchers studying the removal of diesel exhaust pollutants have done so with simulated exhaust gas, which cannot demonstrate the ability of catalysts accurately. Because activated carbon (AC) has low price, no secondary pollution, good adsorption performance, and [...] Read more.

So far, most of the experimental researchers studying the removal of diesel exhaust pollutants have done so with simulated exhaust gas, which cannot demonstrate the ability of catalysts accurately. Because activated carbon (AC) has low price, no secondary pollution, good adsorption performance, and certain catalytic activity, it has good application prospects in the field of marine exhaust pollutant removal. In this paper, the removal of particulate matter (PM), carbon monoxide (CO), and NO_x from real exhaust gas by AC was studied. The results show that PM removal efficiency reached up to 77%, while the pressure drop increased with running time. AC may degenerate to some extent with the increase of temperature, resulting in a negative removal efficiency of CO. The denitration efficiency of AC was up to 34.5% without urea, and further increased to 44.8% after spraying urea, still a distance from industrial applications. In the future, it may be necessary to install a fan to compensate the reactor or to backwash the reactor to avoid excessive pressure drop. The thermal stability of the AC also needs to be improved. To increase the denitration performance, it may be helpful to modify the AC or impregnate other metal oxides. Full article

(This article belongs to the Special Issue Air Pollution)

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16 pages, 1646 KiB

Open AccessArticle

Distribution of PM_2.5 Air Pollution in Mexico City: Spatial Analysis with Land-Use Regression Model

by Israel Hinojosa-Baliño, Oscar Infante-Vázquez and Maite Vallejo

Appl. Sci. 2019, 9(14), 2936; https://doi.org/10.3390/app9142936 - 23 Jul 2019

Cited by 22 | Viewed by 6674

Abstract

In this study, the spatial distribution of PM_2.5 air pollution in Mexico City from 37 personal exposures was modeled. Meteorological, demographic, geographic, and social data were also included. Geographic information systems (GIS), spatial analysis, and Land-Use Regression (LUR) were used to generate [...] Read more.

In this study, the spatial distribution of PM_2.5 air pollution in Mexico City from 37 personal exposures was modeled. Meteorological, demographic, geographic, and social data were also included. Geographic information systems (GIS), spatial analysis, and Land-Use Regression (LUR) were used to generate the final predictive model and the spatial distribution map which revealed two areas with very high concentrations (up to 109.3 µg/m³) and two more with lower concentrations (between 72 to 86.5 µg/m³) (p < 0.05). These results illustrate an overview trend of PM_2.5 in relation to human activity during the studied periods in Mexico City and show a general approach to understanding the spatial variability of PM_2.5. Full article

(This article belongs to the Special Issue Air Pollution)

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12 pages, 2532 KiB

Open AccessArticle

NO Removal by Plasma-Enhanced NH₃-SCR Using Methane as an Assistant Reduction Agent at Low Temperature

by Weixuan Zhao, Yanghaichao Liu, Heng Wei, Renxi Zhang, Gang Luo, Huiqi Hou, Shanping Chen and Ruina Zhang

Appl. Sci. 2019, 9(13), 2751; https://doi.org/10.3390/app9132751 - 8 Jul 2019

Cited by 9 | Viewed by 3529

Abstract

The effects of using CH₄ as an assistant reduction agent in plasma-assisted NH₃–SCR were investigated. The new hybrid reaction system performed better than DBD–NH₃–SCR when the O₂ concentration varied from 2% to 12%. Compared with DBD–NH₃ [...] Read more.

The effects of using CH₄ as an assistant reduction agent in plasma-assisted NH₃–SCR were investigated. The new hybrid reaction system performed better than DBD–NH₃–SCR when the O₂ concentration varied from 2% to 12%. Compared with DBD–NH₃–SCR, DBD–NH₃–CH₄–SCR (NH₃:CH₄ = 1:1) showed a more significant promotion effect on the performance and N₂ selectivity for NO_X abatement. When the O₂ concentration was 6% and the SIE was 512 J/L, the NO removal efficiency of the new hybrid system reached 84.5%. The outlet gas components were observed via FTIR to reveal the decomposition process and its mechanism. This work indicated that CH₄, as an assistant agent, enhances DBD–NH₃–SCR in excess oxygen to achieve a new process with significantly higher activity at a low temperature (≤348 K) for NO_X removal. Full article

(This article belongs to the Special Issue Air Pollution)

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15 pages, 3929 KiB

Open AccessFeature PaperArticle

Exhaust Gas Condensation during Engine Cold Start and Application of the Dry-Wet Correction Factor

by Barouch Giechaskiel, Alessandro A. Zardini and Michael Clairotte

Appl. Sci. 2019, 9(11), 2263; https://doi.org/10.3390/app9112263 - 31 May 2019

Cited by 28 | Viewed by 5970

Abstract

Gas components, like carbon monoxide (CO) and dioxide (CO₂), can be measured on a wet- or dry-basis depending on whether the water is left or removed from the sample before analysis. The dry concentrations of gaseous components in the exhaust from [...] Read more.

Gas components, like carbon monoxide (CO) and dioxide (CO₂), can be measured on a wet- or dry-basis depending on whether the water is left or removed from the sample before analysis. The dry concentrations of gaseous components in the exhaust from internal combustion engines are converted to wet concentrations with conversion factors based on the combustion products and the fuel properties. Recent CO₂ measurements with portable emissions measurement systems (PEMS) compared to laboratory grade equipment showed differences during the first minutes after engine start. In this study we compared instruments measuring on a dry- and wet-basis using different measuring principles (non-dispersive infrared detection (NDIR) and Fourier-transform infrared spectroscopy (FTIR)) at the exhaust of gasoline, compressed natural gas (CNG), and diesel light-duty and L-category vehicles. The results showed an underestimation of the CO₂ and CO mass emissions up to 13% at cold start when the conversion factor is applied and not direct “wet” measurements are taken, raising concerns about reported CO₂ and CO cold start emissions in some cases. The underestimation was negligible (<1%) for CO₂ when the whole test (20–30 min) was considered, but not for CO (1%–10% underestimation) because the majority of emissions takes place at cold start. Exhaust gas temperature, H₂O measurements and different expressions of the dry-wet corrections confirmed that the differences are due to condensation at the exhaust pipes and aftertreatment devices when the surface temperatures are lower than the dew point of the exhaust gases. The results of this study help to interpret differences when comparing instruments with different principles of operation at the same location, instruments sampling at different locations, or the same instrument measuring different driving test cycles or at different ambient temperatures (e.g., −7 °C). Full article

(This article belongs to the Special Issue Air Pollution)

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13 pages, 1824 KiB

Open AccessArticle

Nitrogen Oxide Removal by Coal-Based Activated Carbon for a Marine Diesel Engine

by Zongyu Wang, Hailang Kuang, Jifeng Zhang, Lilin Chu and Yulong Ji

Appl. Sci. 2019, 9(8), 1656; https://doi.org/10.3390/app9081656 - 22 Apr 2019

Cited by 10 | Viewed by 3686

Abstract

Vanadium-based catalysts are mainly used for marine diesel exhaust denitration. However, their poor catalytic ability at low temperature and poor sulfur tolerance, as well as high toxicity and cost, are big turnoffs. AC (Activated carbon) exhibits good adsorption capacity and catalytic ability in [...] Read more.

Vanadium-based catalysts are mainly used for marine diesel exhaust denitration. However, their poor catalytic ability at low temperature and poor sulfur tolerance, as well as high toxicity and cost, are big turnoffs. AC (Activated carbon) exhibits good adsorption capacity and catalytic ability in denitration because of its high specific surface area and chemical activity. In this paper, coal-based AC was used for simulating diesel exhaust denitration in different conditions. The results show that the NO removal ability of AC is poor in an NO/N₂ system. The NO₂ removal ability is excellent in an NO₂/N₂ system, where NO is desorbed. The NOx removal efficiency is 95% when the temperature is higher than 200 °C in an NO₂/NH₃/N₂ system. When the temperature is lower than 100 °C, AC can catalytically oxidize NO to NO₂ in an NO₂/O₂/N₂ system. The near-stable catalytic efficiencies of AC for a slow SCR (Selective Catalytic Reduction) reaction, a standard SCR reaction, and a fast SCR reaction at 300 °C are 12.1%, 31.6%, and 70.8%, respectively. When ships use a high-sulfur fuel, AC can be used after wet scrubber desulfurization to catalytically oxidize NO to NO₂ at a low temperature. When ships use a low-sulfur fuel, AC can be used as a denitration catalyst at high temperatures. Full article

(This article belongs to the Special Issue Air Pollution)

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11 pages, 2121 KiB

Open AccessFeature PaperArticle

Characterization of Emission Factors Concerning Gasoline, LPG, and Diesel Vehicles via Transient Chassis-Dynamometer Tests

by Gyutae Park, Sunhee Mun, Heekyoung Hong, Taekho Chung, Sungwoon Jung, Sunmoon Kim, Seokjun Seo, Jounghwa Kim, Jongtae Lee, Kyunghoon Kim, Taehyun Park, Seokwon Kang, Jihee Ban, Dong-Gil Yu, Jung-Hun Woo and Taehyoung Lee

Appl. Sci. 2019, 9(8), 1573; https://doi.org/10.3390/app9081573 - 16 Apr 2019

Cited by 33 | Viewed by 5378

Abstract

Gaseous emissions from vehicles contribute substantially to air pollution and climate change. Vehicular emissions also contain secondary pollutants produced via chemical reactions that occur between the emitted gases and atmospheric air. This study aims at understanding patterns concerning emission of regulated, greenhouse, and [...] Read more.

Gaseous emissions from vehicles contribute substantially to air pollution and climate change. Vehicular emissions also contain secondary pollutants produced via chemical reactions that occur between the emitted gases and atmospheric air. This study aims at understanding patterns concerning emission of regulated, greenhouse, and precursor gases, which demonstrate potential for secondary aerosol (SA) formation, from vehicles incorporating different engine technologies—multi-point injection (MPI) and gasoline direct injection (GDI)—and using different fuels—gasoline, liquefied petroleum gas (LPG), and diesel. Drive cycles from the National Institute of Environmental Research (NIER) were used in this study. Results obtained from drive cycle tests demonstrate a decline in aggregate gas emissions corresponding to an increase in average vehicle speed. CO₂ accounts for more than 99% of aggregate gaseous emissions. In terms of concentration, CO and NH₃ form predominantly non-CO₂ emissions from gasoline and LPG vehicles, whereas nitrogen oxides (NOx) and non-methane hydrocarbons (NMHC) dominate diesel-vehicle emissions. A higher percentage of SO₂ is emitted from diesel vehicles compared to their gasoline- and LPG-powered counterparts. EURO-5- and EURO-6-compliant vehicles equipped with diesel particulate filters (DPFs) tend to emit higher amounts of NO₂ compared to EURO-3-compliant vehicles, which are not equipped with DPFs. Vehicles incorporating GDI tend to emit less CO₂ compared to those incorporating MPI, albeit at the expense of increased CO emissions. The authors believe that results reported in this paper concerning regulated and unregulated pollutant-emission monitoring can contribute towards an accurate evaluation of both primary and secondary air-pollution scenarios in Korea. Full article

(This article belongs to the Special Issue Air Pollution)

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15 pages, 4582 KiB

Open AccessArticle

Estimation of Source-Based Aerosol Optical Properties for Polydisperse Aerosols from Receptor Models

by Chang Hoon Jung, Ji Yi Lee, Junshik Um, Seoung Soo Lee, Young Jun Yoon and Yong Pyo Kim

Appl. Sci. 2019, 9(7), 1443; https://doi.org/10.3390/app9071443 - 6 Apr 2019

Cited by 11 | Viewed by 3571

Abstract

We estimated source-based aerosol optical properties for polydisperse aerosols according to a chemical-species-resolved mass contribution method based on source apportionment. We investigated the sensitivity of aerosol optical properties based on PM2.5 (particulate matter that have a diameter of less than 2.5 micrometers) monitoring [...] Read more.

We estimated source-based aerosol optical properties for polydisperse aerosols according to a chemical-species-resolved mass contribution method based on source apportionment. We investigated the sensitivity of aerosol optical properties based on PM2.5 (particulate matter that have a diameter of less than 2.5 micrometers) monitoring results. These aerosols were composed of ions, metals, elemental carbon, and water-soluble organic carbon which includes humic-like carbon substances and water-soluble organic carbon. We calculated aerosols’ extinction coefficients based on the PM2.5 composition data and the results of a multivariate receptor model (Solver for Mixture Problem model, SMP). Based on the mass concentration of chemical composition and nine sources calculated with the SMP receptor model, we estimated the size-resolved mass extinction efficiencies for each aerosol source using a multilinear regression model. Consequently, this study quantitatively determined the size resolved sources contributing to the apportionment-based aerosol optical properties and calculated their respective contributions. The results show that source-resolved mass concentrations and extinction coefficients had varying contributions. This discrepancy between the source-based mass concentration and extinction coefficient was mainly due to differences between the source-dependent aerosol size distribution and the aerosol optical properties from different sources. Full article

(This article belongs to the Special Issue Air Pollution)

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13 pages, 1111 KiB

Open AccessArticle

Identifying Key Sources of City Air Quality: A Hybrid MCDM Model and Improvement Strategies

by Kou-Hsiung Chen, Jui-Mei Yien, Cheng-Hsin Chiang, Pei-Chun Tsai and Fu-Sheng Tsai

Appl. Sci. 2019, 9(7), 1414; https://doi.org/10.3390/app9071414 - 4 Apr 2019

Cited by 18 | Viewed by 3292

Abstract

Improvements for air quality were prioritized according to gaps between criteria. Existing improvement strategies for air quality often focus on a single criterion, without considering associations among criteria. Moreover, solutions are often temporary, failing to provide long-term improvement. Therefore, this study employed a [...] Read more.

Improvements for air quality were prioritized according to gaps between criteria. Existing improvement strategies for air quality often focus on a single criterion, without considering associations among criteria. Moreover, solutions are often temporary, failing to provide long-term improvement. Therefore, this study employed a multiple-criteria decision-making model and a substitution method based on causal relationships to analyze potential improvement strategies for air quality in Kaohsiung, Taiwan. Results revealed that coal-fired power plants and factory emissions are the major sources of pollution in Kaohsiung. This study suggests that environmental authorities in Kaohsiung should facilitate plants to improve energy efficiency with anti-pollution facilities. Full article

(This article belongs to the Special Issue Air Pollution)

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17 pages, 3586 KiB

Open AccessArticle

Experimental Assessment of an Electrofilter and a Tandem Positive-Negative Corona Charger for the Measurement of Charged Nanoparticles formed in Selective Catalytic Reduction Systems

by Matthias Schwelberger, Athanasios Mamakos, Martin Fierz and Barouch Giechaskiel

Appl. Sci. 2019, 9(6), 1051; https://doi.org/10.3390/app9061051 - 13 Mar 2019

Cited by 15 | Viewed by 3476

Abstract

Onboard measurement of non-volatile particle number (PN) emissions with portable emissions measurement systems (PEMS) was introduced for the type-approval of passenger cars in Europe since 2017 and is foreseen for heavy-duty (HD) vehicles in 2021. First studies on the performance of PN-PEMS with [...] Read more.

Onboard measurement of non-volatile particle number (PN) emissions with portable emissions measurement systems (PEMS) was introduced for the type-approval of passenger cars in Europe since 2017 and is foreseen for heavy-duty (HD) vehicles in 2021. First studies on the performance of PN-PEMS with HD engine exhaust revealed larger differences between established PN-PEMS techniques than what was observed for passenger cars. Particles forming in selective catalytic reduction (SCR) systems for NO_x of late technology HD engines have recently been identified as a potential reason for the observed differences. The formed particles have a size distribution peaking below the regulatory limit of 23 nm and most importantly acquire high (more than one) positive charges at the elevated exhaust temperatures. Precise measurement of such highly charged nanosized particles with PN-PEMS instrumentation utilizing diffusion charger (DC) based counters requires proper conditioning of these charges. Two approaches were investigated in this study: (a) an electrofilter (EF) to completely remove charged particles below the regulated size and (b) a tandem negative-positive corona (TC) charger to directly condition pre-charged particles. The two technical solutions were tested alongside the unmodified DC-based PN-PEMS, a PN-PEMS utilizing a condensation particle counter (CPC) and a reference stationary PN system using exhaust of two SCR-equipped HD engines. The results confirmed that the particles forming in such SCR systems are responsible for the observed inconsistencies and that both technical solutions efficiently address the interferences of these pre-charged nanoparticles. Full article

(This article belongs to the Special Issue Air Pollution)

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13 pages, 1199 KiB

Open AccessArticle

Assessing Concentration Changes of Odorant Compounds in the Thermal-Mechanical Drying Phase of Sediment-Like Wastes from Olive Oil Extraction

by Diógenes Hernández, Héctor Quinteros-Lama, Claudio Tenreiro and David Gabriel

Appl. Sci. 2019, 9(3), 519; https://doi.org/10.3390/app9030519 - 3 Feb 2019

Cited by 12 | Viewed by 4652

Abstract

In the industrial production of olive oil, both solid wastes and those produced from their incineration are a serious environmental problem since only 20% w/w of the fruit becomes oil and the rest is waste, mainly orujo and alperujo. A key [...] Read more.

In the industrial production of olive oil, both solid wastes and those produced from their incineration are a serious environmental problem since only 20% w/w of the fruit becomes oil and the rest is waste, mainly orujo and alperujo. A key aspect to transforming these wastes into an important source of energy such as pellets is to recognize the most appropriate time of the year for waste drying, with the objective of minimizing the environmental impact of the volatile compounds contained in the waste. In this work, the emissions produced during thermal-mechanical drying were studied throughout a period of six months of waste storage in which alperujo and orujo were stored in open containers under uncontrolled environmental conditions. The studied emissions were produced when both wastes were dried in a pilot rotary drying trommel at 450 °C to reduce their initial humidity of around 70–80% w/w to 10–15% w/w. Results indicated that when the storage time of the wastes in the uncontrolled environments increased, the emission of odorant compounds during drying also increased as a consequence of the biological and chemical processes occurring in the containers. The main odorant VOCs were quantified monthly for six months at the outlet of the drying trommel. It was determined that the drying of this type of waste could be carried out properly until the third month of storage. Afterwards, the concentration of most VOCs produced widely exceeded the odor thresholds of selected compounds. Full article

(This article belongs to the Special Issue Air Pollution)

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20 pages, 2197 KiB

Open AccessArticle

Simulation of Turbulent Mixing Effects on Essential NO_x–O₃–Hydrocarbon Photochemistry in Convective Boundary Layer

by Mi-Sug Kim

Appl. Sci. 2019, 9(2), 357; https://doi.org/10.3390/app9020357 - 21 Jan 2019

Cited by 1 | Viewed by 3439

Abstract

The turbulence kinetics model (TKM) describes an overall reaction rate for microscopic mass transfer phenomenon expressed as separation intensity, I_s, in a turbulent reacting flow. This study examines the effects of turbulent mixing in the convective boundary layer (CBL) on essential [...] Read more.

The turbulence kinetics model (TKM) describes an overall reaction rate for microscopic mass transfer phenomenon expressed as separation intensity, I_s, in a turbulent reacting flow. This study examines the effects of turbulent mixing in the convective boundary layer (CBL) on essential NOx–O₃–Hydrocarbon photochemistry containing sources of NO and a surrogate reactive hydrocarbon. The modeling approach applies for all species except OH with an assumption of a photostationary steady state. The TKM results reveal principal findings as follows: (1) effects of turbulence on reaction rates lead to significant segregations throughout most of the CBL in reaction pairs NO + O₃, RH + OH and NO + HO₂; (2) segregations permit significantly higher concentrations of NO and RH to build up and endure in the CBL than would occur for a non-turbulent atmosphere; (3) turbulent segregation influences limit and shift the ranges of NO and O₃ concentrations compared to the non-turbulent case; (4) while there are differences between the TKM results and those for a published Large Eddy simulation (LES) of the same chemical system, there are also strong similarities. Therefore, a future study remains to compare model results to observations if and when appropriately time-resolved measurements of reacting species are obtained. Full article

(This article belongs to the Special Issue Air Pollution)

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Review

Jump to: Research, Other

27 pages, 2505 KiB

Open AccessReview

Chemical Characteristics of Fine Particulate Matter in Poland in Relation with Data from Selected Rural and Urban Background Stations in Europe

by Barbara Błaszczak, Kamila Widziewicz-Rzońca, Natalia Zioła, Krzysztof Klejnowski and Katarzyna Juda-Rezler

Appl. Sci. 2019, 9(1), 98; https://doi.org/10.3390/app9010098 - 28 Dec 2018

Cited by 17 | Viewed by 4119

Abstract

Air pollution by particulate matter (PM) is recognized as a one of the most important environmental issue. A particular attention is being paid to fine PM fraction (PM_2.5, PM_1.0) due to its detrimental impact on human health and long-term [...] Read more.

Air pollution by particulate matter (PM) is recognized as a one of the most important environmental issue. A particular attention is being paid to fine PM fraction (PM_2.5, PM_1.0) due to its detrimental impact on human health and long-term persistence in the air. Presented work is an in-depth bibliometric study on the concentrations and chemical composition of PM_2.5 among 27 rural and 38 urban/urban background stations dispersed across the Europe. Obtained results indicate that the chemical composition of PM_2.5, in terms of mass concentrations and percentage contribution of main chemical constituents, is relatively different in various parts of Europe. Urban and urban background stations are typically characterized by higher share of total carbon (TC) in PM_2.5, compared to rural background sites, mostly pronounced during the heating periods. The share of the secondary inorganic aerosol (SIA) is typically higher at rural background stations, especially in North-Western Europe. In general, the relative contribution of SIA in PM_2.5 mass, both at rural and urban background stations, showed more or less pronounced seasonal variation, opposite to Polish measurement sites. Moreover, Poland stands out from the majority of the European stations by strong dominance of total carbon over secondary inorganic aerosol. Full article

(This article belongs to the Special Issue Air Pollution)

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14 pages, 3841 KiB

Open AccessFeature PaperTechnical Note

Performance Test of MicroAeth^® AE51 at Concentrations Lower than 2 μg/m³ in Indoor Laboratory

by Jeonghoon Lee

Appl. Sci. 2019, 9(13), 2766; https://doi.org/10.3390/app9132766 - 9 Jul 2019

Cited by 16 | Viewed by 4574

Abstract

It is difficult to find information about how the microAeth^® AE51 performs, in spite of its versatility for about a decade in various research fields such as black carbon measurements and personal exposure studies. Stimulated by this, we conducted real-time tests for [...] Read more.

It is difficult to find information about how the microAeth^® AE51 performs, in spite of its versatility for about a decade in various research fields such as black carbon measurements and personal exposure studies. Stimulated by this, we conducted real-time tests for indoor aerosol in order to provide performance characteristics toward proper usage. We calculated the attenuation (ATN) using the reference signal together with the sensing signal to compare it with the ATN recorded in a microAeth^® AE51. Performance was evaluated under extremely low concentration through the zero test, using filtered clean air. Ten-day-long continuous measurements were done for both indoor aerosol and filtered particle free air to examine the feasibility of microAeth^® AE51 in an indoor use. Generally, MicroAeth^® AE51 exhibited excellent performance, though it showed relatively low performance under some conditions. Noise was intensified while it was directly connected to a power adaptor. Another issue includes the occurrence of negative concentrations for extremely clean air. The noise amplification turned out to be related to a power source independent on the internal battery, and it was able to be removed by post-processing. Uncertainty analysis was carried out to better understand the origin of unwanted noise. Technical perspective of a proper usage will be addressed with regard to what will play a role for a long-term monitoring. Full article

(This article belongs to the Special Issue Air Pollution)

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