Winter-autumn air pollution control plan in North China modified the PM2.5 compositions and sources in Central China

The additional impact of emission-reduction measures in North China (NC) during autumn and winter on the air quality of downwind regions is an interesting but less addressed topic. The mass concentrations of routine air pollutants, the chemical compositions, and sources of fine particles (PM2.5) for January 2018, 2019, and 2020 at a megacity of Central China were identified, and meteorology-isolated by a machine-learning technique. Their variations were classified according to air mass direction. An unexpectedly sharp increase in emission-related PM2.5 by 22.7% (18.0 mug m-3) and 25.7% (19.4 mug m-3) for air masses from local and NC in 2019 was observed compared to those of 2018. Organic materials exhibited the highest increase in PM2.5 compositions by 6.90 mug m-3 and 6.23 mug m-3 for the air masses from local and NC. PM2.5 source contributions related to emission showed an upsurge from 1.39 mug m-3 (biomass burning) to 24.9 mug m-3 (secondary inorganic aerosol) in 2019 except for industrial processes, while all reduced in 2020. From 2018 to 2020, the emission-related contribution of coal combustion to PM2.5 increased from 10.0% to 19.0% for air masses from the local area. To support the priority natural gas quotas in northern China, additional coal in cities of southern China was consumed, raising related emissions from transportation activities and road dust in urban regions, as well as additional biofuel consumption in suburban or rural regions. All these activities could explain the increased primary PM2.5 and related precursor NO2. This study gave substantial evidence of air pollution control measures impacting the downwind regions and promote the necessity of air pollution joint control across the administration.Copyright © 2023 Elsevier Ltd

Air quality changes in Shijiazhuang during COVID-19 outbreak

[Background] The coronavirus disease 2019 (COVID-19) was first detected in December 2019. To combat the disease, a series of strict measures were adopted across the country, which led of improved air quality. This provides an opportunity to discuss the impact of human activities on air quality. [Objective] This study investigates the air quality changes in Shijiazhuang, and analyzes the impacts of epidemic prevention and control measures on air quality, so as to provide reference and ideas for further improving air quality and prevention and control measures. [Methods] The air quality data were collected online from https://www.zq12369.com/ and https://aqicn.org/city/shijiazhuang/cn/. Comparisons in air quality index (AQI) and the concentrations of air pollutants (PM2.5, PM10, SO2, CO, NO2, and O3) were made between the period from December 2019 to June 2020 (reference) and the same period from 2016 to 2019 by t-test and chi-square test. [Results] The daily average AQI dropped by 25.38% in Shijiazhuang during the COVID-19 prevention and control compared with the some period from 2016 to 2019 (t=6.28, P < 0.05). The proportions of pollution days during the COVID-19 outbreak in Shijiazhuang were PM2.5 (44.56%), O3 (31.09%), PM10 (23.83%), and NO2 (2.59%) successively, the pollution days of PM10 decreased significantly (chi2=3.86, P < 0.05) compared with 2016-2019, but during traffic lockdown the numbers of pollution days of PM2.5 and in the mid stage of prevention the number of pollution days of O3 increased (P < 0.05). Compared with the control period, the concentrations of the six air pollutants decreased to varying degrees (P < 0.05), especially SO2 dropped by 55.36%. [Conclusion] The measures taken for COVID-19 control and prevention have reduced the pollution sources and emissions, which resulted in better general air quality of Shijiazhuang City, but have aggravated the pollution of O3 and other pollutants. It is necessary to further explore the causes for the aggravation of O3 pollution in order to formulate reasonable air quality control strategies.Copyright © 2021, Shanghai Municipal Center for Disease Control and Prevention. All rights reserved.

Changes of atmospheric metal(loid) deposition from 2017 to 2021 at Mount Emei under China's air pollution control strategy

Acid deposition and particulate matter (PM) pollution have declined considerably in China. Although metal(loid) and acid deposition and PM have many common sources, the changes of metal(loid) deposition in China in the recent decade have not been well explored by using long-term monitoring. Therefore, we analyzed the dry and wet deposition of eleven metal(loid)s (including Al, As, Ba, Cd, Cu, Cr, Fe, Mn, Pb, Sr, and Zn) from 2017 to 2021 at Mount Emei, which is adjacent to the most economic-developed region in western China (Sichuan Basin (SCB)). Anthropogenic emissions contributed to over 80% of the annual wet deposition fluxes of metal(loid)s and acids (SO4 2-, NO3 -, and NH4 +) at Mount Emei, and the major source regions were the SCB, the Yunnan-Guizhou Plateau, and Gansu Province. Metal(loid) and acid deposition had similar seasonal variations with higher wet deposition fluxes in summer but higher wet deposition concentrations and dry fluxes in winter. The seasonal variations were partially associated with higher precipitation but lower pH in summer (968 mm and 5.52, respectively) than in winter (47 mm and 4.73, respectively). From 2017 to 2021, metal(loid) deposition did not decline as substantially as acid deposition (5.6%-30.4%). Both the annual total deposition fluxes and concentrations of Cr, Cu, Sr, Ba, and Pb were even higher in 2020-2021 than in 2017-2018. The inter-annual and seasonal changes implied the responses of metal(loid) deposition to anthropogenic emission changes were buffered (e.g., transformation, dilution, and degradation) by precipitation rates, acidity, natural emissions, and chemical reactions in the atmosphere, among others.Copyright © 2023 Elsevier Ltd

LEGAL STRATEGIES TO MINIMIZE SUBWAY AIR POLLUTION IN THE UNITED STATES

Air pollution in U.S. subway systems poses a major threat to public health. People in subway stations breathe in dangerously high levels of dusts, called particulate matter. Current legislation does not effectively address this problem;in fact, the United States does not have a comprehensive indoor air quality law at all. Left unregulated, people regularly exposed to subway air pollution could suffer respiratory and cardiovascular issues and even premature death. To mitigate these health effects, some countries have imposed PM standards in subway systems and underground spaces. Others have standards covering all indoor spaces. In the United States, many subway systems have begun exploring technologies to filter subway air in the wake of the coronavirus pandemic. To support their efforts and innovation, the United States should enact legislation establishing a grant and loan program for subway systems' air-purifying initiatives. Modeled after the successful Diesel Emissions Reduction Act, this law would adopt a carrot-based approach to effectively reduce subway air pollution, allowing each system to tailor initiatives to their unique characteristics. While the United States should explore a mandatory standards-based approach long term, it should prioritize this legislation to protect the public more quickly from this ongoing threat. [ FROM AUTHOR] Copyright of Duke Law Journal is the property of Duke University, School of Law and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full . (Copyright applies to all s.)

Sustainable policies for air pollution reduction after COVID‐19 pandemic: Lessons learnt from the impact of the different lockdown periods on air quality

Due to the COVID‐19 pandemic, governments imposed several mobility restrictions which can be used to evaluate their impact on air quality and generate better‐targeted policies to improve it. Therefore, this study aimed to define sustainable mitigation measures to reduce air pollution based on quantifying the impacts of the restrictions imposed during the COVID‐19 pandemic on air quality in Portugal. Thus, hourly concentrations of PM10, PM2.5, NO2, O3, CO and SO2 were obtained from the Portuguese Air Quality Monitoring Network. Data was then divided into six periods (2020–2021) and compared with the corresponding historical periods (2015–2019). Furthermore, the satellite data of NO2, CO, and absorbing aerosol index (AAI) from the sentinel‐5P TROPOMI was collected to complement the analysis conducted for the monitoring data. Overall, air quality improved in all study periods and areas, except in industrial sites. The satellite data corroborated the results herein achieved and thus validated the real effect of the measures adopted in the country during the pandemic on air quality. Sustainable policies to improve air quality could include remote (or hybrid) work whenever possible as a long‐term measure and prohibition of travelling between municipalities when an extraordinary event of high air pollution is predicted or occurs. Other policies should be adopted for industrial areas. Given this, and as the restrictive mobility measures had a strong effect on reducing air pollution, the post‐COVID era represents an opportunity for society to rethink future mobility and other emerging policies, that should favour softer and cleaner means of transportation.

Air quality changes in Taiwan over the past decades and during the COVID-19 crisis

Over the past decades, Taiwan has achieved remarkable goals in air pollution reduction with the concentrations of several common air pollutants such as CO, NOx, PM10, PM2.5, and SO2 going down. In contrast to these achievements, the mitigation of O3 remains extremely tough due to the complexity of its formation process involving synergistic effects of precursor reductions and meteorological influences. During the local COVID-19 crises in Taiwan and the Level 3 alert in 2021, air pollutants directly emitted from the traffic such as CO and NOx present clear relationships with the drop of the recorded freeway traffic volume due to the alert, while PM10 and PM2.5 which are also relevant to the traffic do not show indications of being greatly influenced by the decrease of the traffic flow. Although road traffic is not regarded as a main source of SO2 by current understanding, the unusual SO2 variation patterns found in this study suggest a prolonged impact for months from the changes of travel behavior during the epidemic. In contrast, the epidemic did not exert influences on industrial SO2 concentration which accounts for a large portion of total SO2 in Taiwan, and a similar scenario is also seen in each type of O3 monitoring. Although some results discussed in this study are not in line with current consensuses and understandings in terms of the nation of certain air pollutants, these findings may disclose new perspectives which could be a potential benefit to air quality improvement projects in the future.

Impacts of Omicron associated restrictions on vertical distributions of air pollution at a suburb site in Shanghai

To prevent the Omicron transmission, Shanghai government implemented varying degrees of restraint measures. This study provided a new insight into the responses of air pollution altitude dependence to restraint measures by conducting vertical observations at a suburb site in Shanghai. Based on the difference-in-differences (DiD) models that compare the results in 2021 (normal scenario) and 2022 (Omicron-based restriction), we evaluated the casual effects of restrictions on (i) nitrogen dioxide (NO 2), (ii) aerosol (presented by aerosol extinction coefficient (AEC)), formaldehyde (HCHO) and glyoxal (CHOCHO) and (iii) ozone (O 3), which are generally treaded as primary, multi-sources and secondary pollutants, respectively. The estimated results from 0.0 to 2.0 km show that the drop/rise induced by restrictions is greater below 1.0 km than that above 1.0 km. Averaged on vertical distributions, AEC, NO 2 , HCHO and CHOCHO during restrictions felled by 15.1% (0.12 km−1), 40.3% (1.65 ppbv), 10.0% (0.26 ppbv) and 28.6% (21.79 pptv), respectively, while O 3 increased by 21.3% (18.12 μg/m3). It indicates that restrictions induce significant drops in primary pollutants and enhancements in secondary pollutants. For multi-sources pollutants, the decline from primary sources can be partly offset by enhanced secondary productions, and the ratio of increased secondary sources to decreased primary sources can be elevated with height. The discrepancies of responses to restrictions are reflected in vertical distribution and types of air pollution, emphasizing the significance of vertical observations for diversified pollution. These finding can also be meaningful in the strategy development for prevention and control of air pollution. [Display omitted] • This study provided a new insight into the responses of air pollution altitude dependence to restraint measures by employing vertical observations. • The difference-in differences model was applied to evaluate the casual effects of restrictions on different types of pollution. • The decline of multi-sources pollutants from primary sources can be partly offset by enhanced secondary productions. [ FROM AUTHOR]

Lockdown as an Empirical Strategy to Curb Air Pollution: Evidence from a Quasi‐Natural Experiment

In this study, three approaches namely parallel, sequential, and multiple linear regression are applied to analyze the local air quality improvements during the COVID‐19 lockdowns. In the present work, the authors have analyzed the monitoring data of the following primary air pollutants: particulate matter (PM10 and PM2.5), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO). During the lockdown period, the first phase has most noticeable impact on airquality evidenced by the parallel approach, and it has reflected a significant reduction in concentration levels of PM10 (27%), PM2.5 (19%), NO2 (74%), SO2 (36%), and CO (47%), respectively. In the sequential approach, a reduction in pollution levels is also observed for different pollutants, however, these results are biased due to rainfall in that period. In the multiple linear regression approach, the concentrations of primary air pollutants are selected, and set as target variables to predict their expected values during the city's lockdown period.The obtained results suggest that if a 21‐days lockdown is implemented, then a reduction of 42 µg m−3 in PM10, 23 µg m−3 in PM2.5, 14 µg m−3 in NO2, 2 µg m−3 in SO2, and 0.7 mg m−3 in CO can be achieved.

Evaluation of an Air Cleaning Device Equipped with Filtration and UV: Comparison of Removal Efficiency on Particulate Matter and Viable Airborne Bacteria in the Inlet and Treated Air.

Since the COVID-19 pandemic, improving indoor air quality (IAQ) has become vital for the public as COVID-19 and other infectious diseases can transmit via inhalable aerosols. Air cleaning devices with filtration and targeted pollutant treatment capabilities can help improve IAQ. However, only a few filtration/UV devices have been formally tested for their effectiveness, and little data is publicly available and UV doses comparable. In this research, we upgraded a particulate matter (PM) air filtration prototype by adding UV-C (germicidal) light. We developed realistic UV dose metrics for fast-moving air and selected performance scenarios to quantify the mitigation effect on viable airborne bacteria and PM. The targeted PM included total suspended particulate (TSP) and a coarse-to-fine range sized at PM10, PM4, PM2.5, and PM1. The PM and viable airborne bacteria concentrations were compared between the inlet and outlet of the prototype at 0.5 and 1.0 m3/s (low and high) air flow modes. The upgraded prototype inactivated nearly 100% of viable airborne bacteria and removed up to 97% of TSP, 91% of PM10, 87% of PM4, 87% of PM2.5, and 88% of PM1. The performance in the low flow rate mode was generally better than in the high flow rate mode. The combination of filtration and UV-C treatment provided 'double-barrier' assurance for air purification and lowered the risk of spreading infectious micro-organisms.

Assessment and Impacts of Air Pollution from Brick Kilns on Public Health in Northern Pakistan

Brick kilns add enormous quantities of organic pollutants to the air that can cause serious health issues, especially in developing countries;poor air quality is associated with community health problems, yet receives no attention in Northern Pakistan. The present study, therefore, assessed the chemical composition and investigated the impacts of air pollution from brick kilns on public health. A field-based investigation of air pollutants, i.e., PM1, PM2.5 and PM10, CO2, CO, NO, NO2, H2S, and NH3 using mobile scientific instruments was conducted in selected study area locations. Social surveys were conducted to investigate the impacts of air pollution on community health. The results reveal the highest concentrations of PM1, PM2.5, and PM10, i.e., 3377, 2305, and 3567.67 µg/m3, respectively, in specific locations. Particulate matter concentrations in sampling points exceeded the permissible limits of the Pakistan National Environmental Quality Standard and, therefore, may risk the local population’s health. The highest mean value of CO2 was 529 mg/L, and other parameters, such as CO, NO, NO2, H2S, and NH3 were within the normal range. The social survey’s findings reveal that particulate matter was directly associated with respiratory diseases such as asthma, which was reported in all age groups selected for sampling. The study concluded by implementing air pollution reduction measures in brick kiln industries to protect the environment and community health. In addition, the region’s environmental protection agency needs to play an active role in proper checking and integrated management to improve air quality and protect the community from air hazards.

Variations in Sulfur and Nitrogen Oxidation Rates in Summer Aerosols from 2014 to 2020 in Wuhan, China

To date, research regarding the changes of the sulfur and nitrogen rates in Wuhan during the summer is limited. In this study, we analyzed the air quality in Wuhan, China, using water-soluble ion, gaseous precursor, and weather data. A Spearman correlation analysis was then performed to investigate the temporal changes in air quality characteristics and their driving factors to provide a reference for air pollution control in Wuhan. The results indicate that SO2 in the atmosphere at Wuhan undergoes secondary conversion and photo-oxidation, and the conversion degree of SO2 is higher than that of NO2. During the summers of 2016 and 2017, secondary inorganic atmospheric pollution was more severe than during other years. The fewest oxidation days occurred in summer 2020 (11 days), followed by the summers of 2017 and 2014 (25 and 27 days, respectively). During the study period, ion neutralization was the strongest in summer 2015 and the weakest in August 2020. The aerosols in Wuhan were mostly acidic and NH4+ was an important neutralizing component. The neutralization factors of all cations showed little change in 2015. K+, Mg2+, and Ca2+ level changes were the highest in 2017 and 2020. At low temperature, high humidity, and low wind speed conditions, SO2 and NO2 were more easily converted into SO42− and NO3−.

Spatialized Analysis of Air Pollution Complaints in Beijing Using the BERT+CRF Model

(1) Background: To better carry out air pollution control and to assist in accurate investigations of air pollution, in this study, we fully explore the spatial distribution characteristics of air pollution complaint results and provide guidance for air pollution control by combining regional air monitoring data. (2) Methods: By selecting the air pollution complaint information in Beijing from 2019 to 2020, in this study, we extract the names and addresses of complaint points, as well as the complaint times and types by adopting the BERT (bidirectional encoder representations from transformers) + CRF (conditional random field) model deep learning method. Moreover, through further filtering and processing of the complaint points’ address information, we achieve address matching and spatial positioning of the complaint points, and realize the regional spatial representation of air pollution complaints in Beijing in the form of a heat map. (3) Results: The experimental results are compared and analyzed with the ranking data of total suspended particulate (TSP) concentration of townships (streets) in Beijing during the same period, indicating that the key areas of air pollution complaints have a high correlation with the key polluted township (street) areas. The distribution of complaints and the types of complaints in each township (street) differ according to the population density in each township (street), the level of education, and economic activity. (4) Conclusions: The results of this study show that the public, as the intuitive perceiver of air pollution, is sensitive to the air pollution situation at a smaller spatial scale;furthermore, complaints can provide guidance and reference for the direction of air pollution control and law enforcement investigations when coupled with geographical features and economic status.

Efficiency of Emission Reduction Technologies for Residential Biomass Combustion Appliances: Electrostatic Precipitator and Catalyst

Residential biomass combustion has been pointed out as one of the largest sources of atmospheric pollutants. Rising awareness of the environmental effects of residential biomass combustion emissions boosted the development of different emission reduction devices that are currently available on the market for small-scale appliances. However, detailed studies on the efficiency of these devices in different combustion systems available in Southern European countries are lacking. In this study, two pollution control devices (catalytic converter and electrostatic precipitator) were tested in two different combustion systems (batch mode operated woodstove and automatically fed pellet stove) in order to assess the emission reduction potential of the devices. Pine firewood was used to fuel the woodstove. One commercial brand of pellets and an agricultural fuel (olive pit) were taken for the experiments in the pellet stove. While the efficiency of the electrostatic precipitator in reducing PM10 was only recorded for woodstove emissions (29%), the effect of the catalyst in decreasing gaseous emissions was only visible when applied to the pellet stove flue gas. For wood pellet combustion, reductions of CO and TOC emissions were in the range of 60–62% and 74–77%, respectively. For olive pit combustion, a lower decrease of 59–60% and 64% in CO and TOC emissions, respectively, was recorded.

Forecasting and Seasonal Analysis of Air Quality Index using Machine Learning Models during COVID-19 Pandemic

In many cities, air pollution prevention and control have become a necessity. Industries and excessive automotive traffic in cities pollute the air to unacceptable levels, which have a harmful impact on human health. To defend individuals from health risks, forecasting, predicting and regulating air pollution are critical. There has been substantial research into predicting when inadequate air quality would occur. However, most studies are constrained by a lack of panel data, hence making it impossible to account for the factors, including seasonal behaviour. This paper presents methods of predicting air quality using machine learning techniques and forecasting the air pollution levels to take precautionary measures to minimise air pollution. This paper analyses concentrations of major pollutants in metropolitan areas (PM2.5, PM10, NO2, BTX, O3, CO, SO2, and NH3), contributing to air pollution. This paper also analysed the effect of lockdown due to the pandemic COVID-19 on the AQI at different places at Jaipur. It includes three locations of Jaipur from where the data are gathered;then, the paper will suggest the solutions that can be implemented to achieve the most desirable results, which will lead to lower levels of pollution at a lower cost. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Use of Low-Cost Sensors to Characterize Occupational Exposure to PM2.5 Concentrations Inside an Industrial Facility in Santa Ana, CA: Results from a Worker- and Community-Led Pilot Study

PM2.5 is an air contaminant that has been widely associated with adverse respiratory and cardiovascular health, leading to increased hospital admissions and mortality. Following concerns reported by workers at an industrial facility located in Santa Ana, California, workers and community leaders collaborated with experts in the development of an air monitoring pilot study to measure PM2.5 concentrations to which employees and local residents are exposed during factory operating hours. To detect PM2.5, participants wore government-validated AtmoTube Pro personal air monitoring devices during three separate workdays (5 AM–1:30 PM) in August 2021. Results demonstrated a mean PM2.5 level inside the facility of 112.3 µg/m3, nearly seven-times greater than outdoors (17.3 µg/m3). Of the eight workers who wore personal indoor sampling devices, five showed measurements over 100 μg/m3. Welding-related activity inside the facility resulted in the greatest PM2.5 concentrations. This study demonstrates the utility of using low-cost air quality sensors combined with employee knowledge and participation for the investigation of workplace air pollution exposure as well as facilitation of greater health-related awareness, education, and empowerment among workers and community members. Results also underscore the need for basic measures of indoor air pollution control paired with ongoing air monitoring within the Santa Ana facility, and the importance of future air monitoring studies aimed at industrial facilities.

Air pollution control for indoor environments using nanofiber filters: a brief review and post-pandemic perspectives

Air pollution control has been a recurrent challenge, given the several harmful effects on human health and the environment. Indoor air quality is an issue that needs attention due to the long-time people spend in indoor environments and the various industrial processes that require clean air in these places. In recent years, there has been an increase in innovative technologies capable of retaining fine particles, including microorganisms, such as the new coronavirus-2019. This brief review presents the development, use, and perspectives regarding electrospun nanofibers as air filter media, considering the unbelievable impacts arising from COVID-19. We remark that nanofiber filters produced by electrospinning are an efficient alternative for controlling nanometric bioaerosols and other hazardous pollutants in indoor environments since it is possible to combine desirable characteristics to control them. Finally, we recommend a better collaboration between academia and industry to accelerate the technology transfer processes.

Air quality status before, during and after the pandemic COVID-19 Movement Control Order (MCO) at urban and suburban areas in Malaysia

A severe acute respiratory syndrome, COVID-19 outbreak started in December 2019 reported in the city of Wuhan, China has spread rapidly in other countries around the world. Declared as a pandemic, the lockdowns, industrial shutdowns, closing international borders and overall reduced mobility of the population either for tourism or work commutes have led to air pollution reduction. The lockdown implemented worldwide including Malaysia has come as a respite to the environment, especially in air pollutant levels. Utilizing the Air Pollutant Index (API) data recorded on an hourly basis throughout different series of national lockdown phases, this study is undertaken to evaluate the air quality status before, during and after the implementation of MCO by comparing the selected urban and suburban areas in Malaysia. Six (6) locations including Bandaraya Melaka, Cheras and Alor Setar (urban) and Seri Manjung, Kangar and Kuantan (suburban) were chosen in this study. The result revealed that the air quality has shown improvements after a further extension of lockdown days at both urban (API 36.3-61.5%) and suburban areas (API 46.5-48.6%). It has indirectly changed the air quality status from ‘moderate’ to ‘good’ in all 6 urban and suburban areas. The air quality trends, however, gradually deteriorate and has increased as more restrictions were eased at a later stage. The implementation of lockdown measures not only restricted the spread of infection rate but has reduced ambient air pollutants levels that lead to enhanced air quality. The results obtained in this study can be a useful insight for the regulatory agencies in controlling air pollution and restore the environment quality.

Rethinking of the adverse effects of NOx-control on the reduction of methane and tropospheric ozone – Challenges toward a denitrified society

Nitrogen oxides (NOx = NO + NO2) are key precursors of tropospheric ozone (O3) together with volatile organic compounds (VOC) and carbon monoxide (CO). Since O3 has positive radiative forcing and is harmful to human health, the reduction of anthropogenic emissions of NOx is thought to be beneficial from the perspectives of climate change and air pollution in principle. However, there have been discussions contending that the reduction of NOx emissions is not necessarily beneficial for the mitigation of climate change and improvement of air quality, since 1) it decreases the atmospheric mixing ratio of hydroxyl radicals (OH), which increases the atmospheric lifetime of methane (CH4), and 2) O3 formation is VOC-limited in urban areas and the decrease of NOx emission would increases urban O3 by facilitating the NO titration effect. In order to scrutinize such discussion, literature review have been made on the temporal variations of the increasing rate of tropospheric CH4 in the last 30 years, and on urban/rural O3 issues related to the NOx-limited/VOC-limited regime. Based on the review, it may be concluded that the variation of emissions of CH4 itself paly a dominant role, and the variation of consumption rate by OH play a minor role for the recent variation of CH4. It has been suggested that NOx and NMVOC should be reduced simultaneously in order to avoid the adverse effect on climate change mitigation. From the review on policy-related discussion of NOx-limited and VOC-limited O3 formation, the increase of O3 by the decrease in NOx emissions has generally been seen in winter and nighttime when photochemical production is minimal, and the higher percentile or diurnal maximum mixing ratios of O3 in summer tends to decrease with the decrease in NOx emissions. We suggested that the NOx-limited/VOC-limited approach is not appropriate as a long-term policy guideline for ozone control, since it is unreasonable that NOx reduction is not recommended when ambient NOx levels are high, while further NOx reduction is recommended only when the VOC/NOx ratio gets high after NOx control has been achieved based on other policy principle. Simultaneous reduction of NOx and NMVOC would be beneficial for reducing global, regional, and urban O3 to alleviate climate change and human health impacts. The ultimate reduction of anthropogenic emissions of NOx can be envisioned toward a denitrified (de-NOx) society along with a decarbonized (de-CO2) society.

Disparate air pollution reductions during California’s COVID-19 economic shutdown

Minority communities in the United States often experience higher-than-average exposures to air pollution. However, the relative contribution of institutional biases to these disparities can be difficult to disentangle from other factors. Here, we use the economic shutdown associated with the 2020 COVID-19 shelter-in-place orders to causally estimate pollution exposure disparities caused by the in-person economy in California. Using public and citizen-science ground-based monitor networks for respirable particulate matter, along with satellite records of nitrogen dioxide, we show that sheltering in place produced disproportionate air pollution reductions for non-White (especially Hispanic and Asian) and low-income communities. We demonstrate that these racial and ethnic effects cannot be explained by weather patterns, geography, income or local economic activity as measured by local changes in mobility. They are instead driven by regional economic activity, which produces local harms for diffuse economic benefits. This study thus provides indirect, yet substantial, evidence of systemic racial and ethnic bias in the generation and control of pollution from the portion of the economy most impacted in the early pandemic period. © 2022, The Author(s), under exclusive licence to Springer Nature Limited.

Temporal variation analysis, impact of COVID-19 on air pollutant concentrations, and forecasting of air pollutants over the cities of Bangalore and Delhi in India

Indian cities are highly vulnerable to atmospheric pollution in recent years, due to exponential growth in urbanisation and industrialisation, and the increased pollution has been made to focus on the temporal variation analysis and forecasting of air pollutants over major Indian cities like Delhi and Bangalore. PM2.5 concentrations are nearly 60.5% less than the annual average value during monsoon season while 76.3% more during the winter months. Ozone concentrations increase during the summer months (~ 46.3% more than the annual average) in Delhi, whereas in Bangalore, ozone concentrations are more (~ 75% more than the annual average) during the winter months. Variations of carbon monoxide and nitrogen oxides are significantly less comparatively. COVID-19 lockdown has a substantial positive impact on air pollution. Air pollutant concentrations are reduced during phase I and phase II of the lockdown. Pollutants, especially NOx and PM2.5 concentrations, are drastically reduced compared to the previous years. NOx concentrations are reduced by ~ 20% in Bangalore, whereas ~ 50% in Delhi. PM2.5 concentrations are reduced by ~ 41% in Delhi and ~ 55% in Bangalore. Forecasting of pollutants will be helpful in providing the valuable information for the optimal air pollution control strategies. It has been observed that linear model gives better results compared to ARIMA and Exponential Smoothening models. By forecasting, the concentration of NO2 is 115.288 µg/m3, the ozone is 30.636 µg/m3, SO2 is 11.798 µg/m3, and CO is 2.758 mg/m3 over Delhi in 2021. All the pollutants during forecasting showed a rising trend except sulphur dioxide.