Air Pollution Abatement Research Articles

Phytoremediation Mechanisms in Air Pollution Control: a Review

Air pollutants originated from natural and anthropogenic sources and able to bio-magnify and bio-accumulate in the trophic levels, thus increase toxicity in the food chain. Various air pollutants (particulate matters (PMs), volatile organic compounds (VOCs), inorganic air pollutants (IAP), persistent organic pollutants (POPs), heavy metals, and black carbon) resulted in adverse effects on environmental and human health after prolonged exposure. These airborne particles can travel in gaseous form for long distance and deteriorate the air quality of downstream areas. Air pollution abatement can be implemented by reducing emissions at source and purifying pollutants with remediation techniques. However, air pollution remained as the dominant issue to cause burden in human and ecosystem well-being. Due to drawbacks like expensive, high maintenance, and likelihood for pollutants’ reemission, existing conventional remediation technologies is insufficient for air pollutants mitigation. Phytoremediation enters the picture of air pollution control as a cost-effective, energy-saving, and environmental-friendly technology in remediating air pollutants. In phytoremediation, plant organs and associating microbes in the phyllosphere and rhizosphere interacted with each other to remediate air pollutants. Phytoremediation of air pollutants involves the rhizosphere of plants as pollutants may deposit in the soil during leaf fall and precipitation. Additionally, the phytoremediation mechanisms involve phytoextraction, phytovolatilization, phytodegradation, phytostabilization, rhizodegradation, and rhizofiltration. A brief overview of phytoremediation mechanisms for each air pollutants is presented. In short, the benefits of phytoremediation and its associated gaps in air pollution control are described.

Multidecadal trend analysis of in situ aerosol radiative properties around the world

Abstract. In order to assess the evolution of aerosol parameters affecting climate change, a long-term trend analysis of aerosol optical properties was performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Ångström exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann–Kendall (MK) statistical test associated with several pre-whitening methods and with Sen's slope was used as the main trend analysis method. Comparisons with general least mean square associated with autoregressive bootstrap (GLS/ARB) and with standard least mean square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficient trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficient time series also exhibit primarily decreasing trends. For single scattering albedo, 52 % of the sites exhibit statistically significant positive trends, mostly in Asia, eastern/northern Europe and the Arctic, 22 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 26 % of sites have trends which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10-year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10-year trends are primarily found for earlier periods (10-year trends ending in 2010–2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10-year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10-year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10-year trends of the scattering coefficient – there is a shift to statistically significant negative trends in 2009–2012 for all stations in the eastern and central USA. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage provides insight into potential aerosol effects on climate changes.

Effect of lockdown due to SARS COVID-19 on aerosol optical depth (AOD) over urban and mining regions in India

The Severe Acute Respiratory Syndrome-COronaVIrus Diseases 2019 (SARS-COVID-19) pandemic has posed a serious threat to human health (death) and substantial economic losses across the globe. It was however presumed that extreme preventive measures of entire lockdown in India might have reduced the air pollution level and therefore decreased the aerosol optical depth (AOD). The Moderate Resolution Imaging Spectroradiometer (MODIS)-based Multi-angle Implementation of Atmospheric Correction (MAIAC) daily AOD product was deployed to investigate the change in AOD level during lockdown phases across the Indian Territory as compared to the long-term mean AOD level (2000–2019) of the same periods. The key findings of the study revealed that AOD level over the Indian Territory is greatly reduced (~45%) during the lockdown periods as compared to the long-term mean AOD level (2000–2019). Furthermore, a noteworthy negative AOD anomaly (~6 to 37%) was observed across the four metropolitan cities in India during the entire lockdown period (25th March to 15th May 2020). However, coal mining regions of the various coalfields in India showed a positive anomaly (~+11 to 40%) during the lockdown periods due to ongoing mining operations. In a nutshell, the study results indicated a huge drop in the AOD level over Indian Territory during lockdown periods. It is expected that the pandemic can influence some policy decisions to propose air pollution control methods. Lockdown events possibly may play a crucial role as a potential solution for air pollution abatement in the future. It may not be uncommon in future when the governments may implement deliberately selective lockdowns at pollution hotspots to control the pollution level.

Social cost-benefit assessment as a post-optimal analysis for hydrogen supply chain design and deployment: Application to Occitania (France)

A lot of recent studies have concluded that hydrogen could gradually become a much more significant component of the European energy mix for mobility and stationary fuel cell system applications. Yet, the challenge of developing a future commercial hydrogen economy still remains through the deployment of a viable hydrogen supply chain and an increasing fuel cell vehicle market share, which allows to narrow the existing cost difference regarding the conventional fossil fuel vehicle market. In this paper, the market penetration of hydrogen fuel cell vehicles, as substitutes for internal combustion engine vehicles has been evaluated from a social and a subsidy-policy perspective from 2020 to 2050. For this purpose, the best compromise hydrogen supply chain network configuration after the sequential application of an optimization strategy and a multi-criteria decision-making tool has been assessed through a Social Cost-Benefit Analysis (SCBA) to determine whether the hydrogen mobility deployment increases enough the social welfare. The scientific objective of this work is essentially based on the development of a methodological framework to quantify potential societal benefits of hydrogen fuel cell vehicles. The case study of the Occitania Region in France supports the analysis. The externality costs involve the abatement cost of CO2, noise and local pollution as well as platinum depletion. A subsidy policy scenario has also been implemented. For the case study considered, the results obtained that are not intended to be general, show that CO2 abatement dominates the externalities, platinum is the second largest externality, yet reducing the benefits obtained by the CO2 abatement. The positive externalities from air pollution and noise abatement almost reach to compensate for the negative costs caused by platinum depletion. The externalities have a positive effect from 2025. Using a societal cost accounting framework with externalities and subsidies, hydrogen transition timing is reduced by four years for the example considered.

La-doping induced localized excess electrons on (BiO)2CO3 for efficient photocatalytic NO removal and toxic intermediates suppression

Photocatalysis technology has been extensively adopted to abate typical air pollutants. Nevertheless, it is a challenge to develop photocatalysts aiming to simultaneously improve photocatalytic selectivity and efficiency. In this study, to improve the photocatalytic selectivity and the performance of (BiO)2CO3 in the oxidation of NO to target products (NO2− /NO3−), we developed a novel method to construct La-doped (BiO)2CO3 (La-BOC) for forming localized excess electrons (Ex) on (BiO)2CO3 surface. The results indicate that the Ex could effectively accelerate the activation of reactants and promote charge separation and transfer. Under visible light, the gas molecules could capture the Ex and get activated to produce reactive oxygen species (ROS) with high oxidation ability, which enables complete oxidation of NO to target products instead of producing other toxic by-products. Due to the functionality of the Ex, the photocatalytic selectivity and efficiency of La-BOC have been synchronously improved. Combining experimental and theoretical methods, this work unravels the pathway of charge carriers transportation/transformation and elucidates the photocatalytic NO oxidation mechanism. The present work could provide a novel method to improve photocatalytic selectivity and activity for safe air pollutant abatement.

Unraveling effects of coal output cut policy on air pollution abatement in China using a CGE model

Recently frequent hazy weather in China caused by PM2.5 is mainly attributed to irrational energy consumption structure, so the policies cutting coal output and promoting electric power substitution were initiated. Facing some resistance in the policy implementation, what the proper target of cutting coal output is, or whether there is a need to cut electricity prices for electric power substitution, are still unknown or debatable. To exploring this knowledge gap, this paper set the eight action plan policy scenarios, in which the coal output cut is set from −3% to −10% respectively. Further, in order to observe whether the policy of cutting electric price will reduce the negative effects of action plan policy scenarios, the eight enhanced action plan policy scenarios were also set, in which the coal output cut is set from −3% to −10% respectively with the hypothetical electric price cut −3%. By using the developed computable general equilibrium (CGE) model, the policy scenarios are simulated, and the economic and environmental effects are tested. The results showed that: First, in most policy scenarios, the environmental and economic effects were changing synchronously in inverted U shapes, but the policy to cut coal output would lead to positive environmental effects and negative economic effects. Second, cutting electricity price could contribute to promoting electricity substitution, though it couldn’t be conducive to improving the electricity structure. Third, the reduction of electricity price could also help to reduce the resistance in policy implementation. Consequently, for optimal environmental effects and economic resistance, it is recommended to set the policy target of cutting coal output as −6%, while the moderate reduction of electricity price is needed and set as −3%.

Traffic characteristics and pollutant emission from road transport in urban area

In this work, the traffic characteristics and emissions of air pollutants were predicted for two vehicle classifications (passenger cars and trucks) at the national highway in Kyoto City, Japan. Traffic characteristic information (traffic volume, travel speed, and degree of congestion) was estimated based on the digitised data collected by the Ministry of Land, Infrastructure, Transport, and Tourism (MLIT) of Japan. A vehicle emission model, known as the computer program to calculate emissions from road transport (COPERT), was utilised to compute the emission factors (EFs) and total emissions of air pollutants in terms of exhaust particulate matter (PMExh), benzene (C6H6), carbon monoxide (CO), and nitrogen oxide (NOx). Input variables, such as fuel data, activity data, driving conditions, and meteorological conditions, are needed. The findings revealed that the pollutant emissions reached the higher values over the slower travel speed phase. Road no. 1 with the most congested road segment has intensified vehicle numbers, and the slowest traffic flow movement exposed a greater magnitude of pollutant emissions. C6H6 and CO emissions are obviously more emitted from the passenger cars whereas the trucks are responsible for the greater emission of NOx and PMExh. The EFs of pollutants were compared with the Japanese Emission Standards through JE05 and JC08 chassis dynamometer test cycles. The estimated EFs showed inconsistency with the EFs derived from the test cycles. These results may be deployed as the input in air quality dispersion modelling in urban areas for designing the air pollution abatement strategy.

Impact of mobile source emission inventory adjustment on air pollution photochemical model performance

Coupled weather forecasting and chemical transport models are useful tools to evaluate air pollution episodes in big cities for the purpose of forecasting and air pollution abatement measures' evaluation. However, large set of accurate data of various sources and modeling calibrations are needed for such complex modeling system to be reliable. The problem becomes more obvious when the model is operated over a domain in which there is a general lack of accurate input data such as emission inventory data. The current study investigates the possibility of model tuning for more accurate prediction of air pollutant concentrations in the city of Tehran in an air pollution episode as a case study. In the last several years, Tehran has frequently experienced long episodes of air pollution, often resulted in forced holidays in the city. WRF/CAMx modeling system were used to simulate the spatial distribution of pollutants concentrations over the city of Tehran in a highly polluted episode during December 2017. In order to improve model performance, a methodology was developed and used to adjust the emission inventory of the system. Due to lack of national emission inventory and background data, effects of introducing a top-down national emission inventory to the modeling system was investigated. This emission inventory can also be used to prepare more accurate boundary concentrations for countries located near Iran. In addition, emission rates of the most dominant emission sources of the city of Tehran – mobile sources – were adjusted using the results from chassis dynamometer tests. Also, the hourly variations of emission were improved using measured ambient NO2 concentrations. Comparison of modeled and measured concentrations at air quality monitoring stations for various pollutant showed that emission adjustment was the most effective method which resulted in considerable model performance improvement over Tehran. Results showed that due to better and more realistic emission factors used in the model, bias error for CO, NO2, O3 and PM2.5 reduced by 0.36 ppm, 3.4 ppb, 0.19 ppb and 2.14 μg/m3, respectively and correlation coefficient for CO, O3 and PM2.5 increased by 0.13, 0.02 and 0.6. This proves the possibility of using such method to improve model performance when there is a general lack of accurate input data.

Tracing China's inter-regional cost transfer of air pollution through domestic supply chains

Abstract: Provinces that provide emission-intensive products now are facing huge financial pressure to control regional air pollutant emissions. Assessing the actual regional air emission abatement costs of each province from the consumer perspective can help to clarify regional pollution abatement responsibilities and formulate sound monetary compensation policies between consumers and producers in China. In this study, we employ a multiregional input-output model to estimate the total air pollution abatement costs and economic benefits caused by interregional trade for each region in 2012. The results indicate that regions with higher GDP per capita, such as the Beijing-Tianjin, East Coast, and South Coast regions, outsourced total pollution abatement costs (TPAC) for air emissions to undeveloped central and western regions via interregional trade within China. Based on a comparison of the cost-benefit index among regions, wealthy regions left nearly 80% of their consumption-based value added locally but outsourced more than 50% of their consumption-based TPAC to other regions, especially to northwestern and central regions with lower GDP per capita. Such a mismatch necessitates in-depth cross-boundary collaboration for control of air pollutant emissions in regions suffering terrible haze problems, such as the North China Plain.

Evaluating the potential of nature-based solutions to reduce ozone, nitrogen dioxide, and carbon dioxide through a multi-type green infrastructure study in Ontario, Canada

The application of green infrastructure presents an opportunity to improve air quality using a multi-faceted ecosystems-based approach. A controlled field study evaluates the impact of multiple green infrastructure applications on air pollution and carbon dioxide concentrations across different urban, suburban and peri-urban morphologies. This study demonstrates that multiple types of green infrastructure applications are beneficial in air pollution abatement, specifically the reduction of ozone and nitrogen dioxide. This study also shows that multiple types of green infrastructure applications are beneficial in reducing carbon dioxide concentrations and are not limited to specific treatments regardless of location, geography, or land use type.

Photocatalysts for Air Pollution Control and Abatement

Titanium dioxide (TiO2) has been largely studied in the past decades for its photocatalytic properties [1]. The material is a n-type of superconductor whose photocatalytic property is due to the absorption of photons (hv) with energy higher than the energy of the valence band. The electrons in the valence band use such energy to jump into the conduction band. This process, originally studied for the photolysis of water [2], has revealed itself of great use for the efficient removal of hazardous molecules and micro-organisms in water and in the air [3]. The high energy required by the electrons in the valence band to jump in the conduction band, which is 3.2eV for anatase TiO2, has limited the use of the material to the very narrow wavelength bandwidth of the ultraviolet (UV) radiation. In order to make use of the material under a much larger spectrum of light frequencies, especially under visible light, modifications of the TiO2 lattice by adding extra elements have been made and they still represent today a challenge for the research community. The change of the lattice can be done by doping TiO2 with different elements, this includes non-metal elements like carbon and nitrogen [4]. The importance of these studies stands on the fact that the resulting material, simply exposed to sun light or LED light, is able to sterilize the air from harmful bacteria and neutralize other well-known indoor volatile organic pollutants such as formaldehyde. This work presents some experimental observations on visible light photocatalytic carbon doped titanium dioxide, C-TiO2, obtained by a sol gel method. The study focuses on the crystal structure of the synthesized material. The aim is to evaluate the consistency of the method in reproducing the desired crystal structure and therefore the desired photo-catalytic properties of this material.

Local fractions – a method for the calculation of local source contributions to air pollution, illustrated by examples using the EMEP MSC-W model (rv4_33)

Abstract. We present a computationally inexpensive method for individually quantifying the contributions from different sources to local air pollution. It can explicitly distinguish between regional–background and local–urban air pollution, allowing for fully consistent downscaling schemes. The method can be implemented in existing Eulerian chemical transport models and can be used to distinguish the contribution of a large number of emission sources to air pollution in every receptor grid cell within one single model simulation and thus to provide detailed maps of the origin of the pollutants. Hence, it can be used for time-critical operational services by providing scientific information as input for local policy decisions on air pollution abatement. The main limitation in its current version is that nonlinear chemical processes are not accounted for and only primary pollutants can be addressed. In this paper we provide a technical description of the method and discuss various applications for scientific and policy purposes.

Enhanced performance on simultaneous removal of NOx-SO2-CO2 using a high-gravity rotating packed bed and alkaline wastes towards green process intensification

In order to intensify the gas-liquid absorption processes in the field of energy and environment, high-gravity rotating packed bed (HiGee RPB) has been successfully applied in the multiple air pollutants abatement and CO2 capture by mineralization. Since the mass transfer and chemical reaction through gas-liquid absorption were found to be the key factors affecting acid gas removal, a mass transfer model based on the two-film theory for simultaneous removal of NOx-SO2-CO2 in an RPB was developed in this study. The mass transfer parameters including overall gas-phase mass transfer coefficient (KGa), height of a transfer unit (HTU), liquid mass transfer rate (kL) and enhancement factor (E) were theoretically determined from the experimental data. The effect of key dimensionless operating factors such as high gravity factor (β), gas-to-liquid ratio (GLR), and liquid-to-solid ratio (LSR) on mass transfer parameters were evaluated. Based on the results obtained in this study, the enhancement of high gravity filed on mass transfer and removal efficiencies of NOx and CO2 were significantly higher than that of SO2. It was inferred that the carbonation reaction could compensate the removal efficiency of acid gaseous pollutants at the lower mass transfer rate. The relationship between mass transfer rate and energy consumption for the multiple air pollutant control via a HiGee process was established. The favorable operating factors for NOx-SO2-CO2 simultaneous removal in an RPB were suggested as β of 233.8, GLR of 69.5 and LSR of 40.

An in-depth analysis of the evolution of the policy mix for the sustainable energy transition in China from 1981 to 2020

Global warming and the acute domestic air pollution in China have necessitated transition to a sustainable energy system away from coal-dominated energy production. Through a systematic review of the national policy documents, this study investigates the policy mix adopted by the Chinese government to facilitate its energy transition and how that policy mix has evolved between 1981 and 2020. The chronological analysis emphasizes two dimensions of temporal changes in the policy mix: (1) changes in the policy intensity and density, and (2) the shift in policy instrument combinations. The policy mix has evolved from a few authority-based instruments to the current response that has a large density of instruments with a good diversity of instrument types. The Chinese government imposes an increasing policy intensity on air pollution abatement and a decreasing policy intensity on renewable energy support, and experiments with innovative policy instruments to reduce carbon dioxide emissions. The evolutionary trajectory features layering new policy instruments, calibrating existing ones and some degree of policy replacement and sequencing. Overall, the study shows that the Chinese government has adopted a complex mix of policy instruments to abate emissions (e.g. carbon dioxide and sulphur dioxide) in the coal-based energy system and to support renewable energy technologies. The study provides an in-depth understanding of Chinese policy design in the environment and energy fields and contributes to the public policy literature by filling a research gap – the comparative lack of empirical analyses on the temporal changes in the policy mixes.

Federally Mandated but Locally Administered: Political Differences in Air Pollution Abatement Under the Clean Air Act

In the US, federal statute delegates much of the authority to administer the Clean Air Act (CAA) to individual states. States are responsible primarily for the administration of the National Ambient Air Quality Standards (NAAQS), which impose technological and other requirements on stationary emission sources located in areas in “nonattainment” with the standards. In this paper, we examine the differential state level implementation of the CAA’s abatement technology requirements across political regimes. We use a regression discontinuity design to estimate the effect of each state’s political leadership on the expenditures and types of new air pollution abatement technology at electric utilities. We find that the political affiliation of a state’s governor has no effect on either outcome in areas that meet the NAAQS. However, in nonattainment areas, Republican gubernatorial control decreases electric utilities’ new air pollution abatement capital expenditures and their probability of installing the most effective nitrogen oxide abatement technology, relative to electric utilities in states with a Democratic governor. In a supplementary multidimensional regression dis-continuity analysis of the legislative branch, we find that Republican majority control of the lower state house has qualitatively similar, but weaker differential impacts on air pollution abatement capital outcomes in nonattainment areas. These results are consistent with the structure of the regulatory environment, where the executive branch has direct control of the NAAQS implementation and enforcement process, but the legislative branch wields indirect influence. Finally, we present evidence that the additional costs of air pollution abatement technology adoption at electric utilities in nonattainment areas with a Democratic governor may exceed the additional health benefits of decreased NOx emissions in these areas, especially in the short term.

Application of Gaseous ClO2 on Disinfection and Air Pollution Control: A Mini Review

ABSTRACT During the sever pandemic of coronavirus, the development and deployment of efficient disinfection technology have attracted hospitals’ attention. Chlorine dioxide (ClO2) gas has been validated as an efficient disinfector and air pollution control due its high oxidation ability. This article reviewed the principles and application of ClO2 gas on disinfection, sterilization and air pollutants abatement. The principles of ClO2 gas production, chemistry and related generator issues were discussed. We also review some case studies of the application of ClO2 gas in the medical field and food industry as a sterilizer. Oxidation of nitrogen oxide (NOx), sulfur oxide (SOx), mercury (Hg), and volatile organic compounds (VOCs) using ClO2 gas has been investigated. The process chemistry and demonstration of applying ClO2 gas for air pollutants oxidation and absorption have also been provided. In conclusion, we suggest the future priority research direction of ClO2 gas application are included the development of smart and robust ClO2 gas release system, the integration of an innovative robotic technology in ClO2 sterilization for epidemic prevention, and the evaluation of ClO2 emissions impact on indoor air quality in hospitals.

Photothermocatalysis for efficient abatement of CO and VOCs

Nanostructured metal oxides and their nanocomposites exhibit highly efficient catalytic activity and excellent durability for photothermocatalytic abatement of air pollutants.

Environmental Degradation and Public Opinion: The Case of Air Pollution in Vietnam

Air pollution is a pressing problem of public health for developing countries, but governments have few incentives to abate air pollution without public awareness of the issue. Focusing on the case of Vietnam, we examine the determinants of public awareness of air pollution. Using representative survey data for the entire country from 2017, we find that local exposure to air pollution increases public awareness and reduces satisfaction with governments but does not provoke opposition to coal-fired power generation. In contrast, education leads people to oppose coal-fired power plants. These results suggest that while local air pollution contributes to awareness and dissatisfaction with the government, support for effective policy measures depends on education levels.

Stack emissions and health risk integrated (SEHRI) model: a tool for stack emissions and health risk modeling

The quantitative assessment of health burden of coal power stack emissions is a vital step to frame effective policy measures to achieve emission reductions and corresponding health benefits. A plant-specific stack emission, dispersion, and health risk integrated (SEHRI) model has been proposed to estimate coal power stack emissions, resulting ambient air concentrations and associated health risks in the vicinity of a coal power plant. In this study, we have estimated the health benefits due to closure of Badarpur Thermal Power Station (BTPS), New Delhi. The SEHRI model has been applied to estimate decreased health risks due to particulates (PM2.5) and gaseous (SO2, NOx) stack emissions released from the plant. More than 1050 premature deaths are avoided and 526 life years are saved resulting from reduction in particulate and gaseous stack emissions, respectively, due to closure of the plant. It is expected that environmental engineers, scientists, and air quality managers would find the SEHRI model as a useful tool to study emissions and health impacts related to coal-based power plants and guide an effective control policy for air pollution abatement.

Assessing the environmental benefits of multi-purpose water uses of hydropower reservoirs on the Han River in South Korea

The South Korean Government is trying to implement multi-purpose water uses of six hydropower reservoirs on the Han River to strengthen the linkage between water and energy. The expected environmental improvements are an improvement in flood control, an increase in the water supply for environmental improvement, an increase in the water supply for the instream flow requirement, and the abatement of air pollutants and greenhouse gas emissions. This article aims to value the four improvements by applying a choice experiment. For the purpose of reflecting the preference heterogeneity, by investigating the choice experiment data gathered from a survey of 1000 people, a Bayesian estimation of a mixed logit model is employed. The environmental benefits of a 1% improvement in flood control, a 1% increase in the water supply for environmental improvement, a 1% increase in the water supply for the instream flow requirement, and a 1% abatement of air pollutants and greenhouse gas emissions are estimated to be KRW 71 (USD 0.06), 51 (0.05), 28 (0.03), and 77 (0.07), respectively, per household per year. The expected improvements for the four attributes are 25.2%, 17.7%, 17.7%, and 1.0%, respectively. Thus, the expected environmental benefits are worth KRW 3265 (USD 2.96) per household per year and the national value amounts to KRW 63.74 billion (USD 57.77 million).