Characteristics and source attribution of PM2.5 during 2016 G20 Summit in Hangzhou: Efficacy of radical measures to reduce source emissions

Net effect of air pollution controls on health risk in the Beijing-Tianjin-Hebei region during the 2022 winter Olympics and Paralympics

Due to the non-linearity in ozone (O3) formation, reducing the emission of nitrogen oxides (NOx) may increase O3 concentration. Given the counteractive O3 response to NOx reduction, overall impact of air pollution controls can be ambiguous when the assessments focus on the changes in pollutant concentrations. In this study, a risk-based method was used to gauge the net effect of air pollution controls on mortality risk in the Beijing-Tianjin-Hebei (BTH) region during the 2022 Winter Olympics and Paralympics (WOP). This mega-event presents a unique opportunity to investigate the efficacy of deep cuts in pollutant emissions. Results show that O3 concentrations greatly increased as nitrogen dioxide (NO2) concentrations decreased in the BTH. Due to the active photochemical formations, O3 became the dominant pollutant that affected human health during the WOP. Despite the substantial O3 increases, the health benefits of NO2 reductions overwhelmed the adverse health effects of O3 increases in most regions of the BTH (at 81 out of 112 stations). After considering the impacts of particulate matter, the integrated health risk of air pollution mixtures declined almost everywhere in the BTH. Our results underscore the great necessity of changing the assessment paradigm of pollution control from using concentration-based methods to using risk-based methods. Together with the carbon neutrality policy, stringent control of NOx emission from combustion sources is a promising way to achieve synergistic control solutions for air pollution and climate change.

Size distribution and lung-deposition of ambient particulate matter oxidative potential: A contrast between dithiothreitol and ascorbic acid assays

Particulate matter (PM) inhaled into human lungs causes oxidative stress and adverse health effects through antioxidant depletion (oxidative potential, OP). However, there is limited knowledge regarding the association between the lung-deposited dose (LDD) of PM and OP in extrathoracic (ET), tracheobronchial (TB), and pulmonary (P) regions of human lungs. Dithiothreitol (DTT) and ascorbic acid (AA) assays were employed to measure the OP of PM size fractions to investigate OP distribution in human lungs and identify the chemical drivers. Quasi-ultrafine particles (quasi-UFP, ≤0.49 μm) exhibited high OP deposition in the TB and P regions, while coarse particles (CP, ≥3.0 μm) dominated in the ET region. A plot of extrinsic (per air volume) and intrinsic (per PM mass) OP versus LDD revealed that the OP for fine and coarse particles was greatest in the ET region, whereas the OP of quasi-UFP was greatest in alveoli. The study also demonstrated that extrinsic OP and PM doses are not strongly related. The decline in OP with increasing PM dose reveals the need for further investigation of the antagonistic effects of the chemical compositions. Overall, the results presented herein help address the gap in knowledge regarding the association between the OP and LDD of ambient particles in specific regions of human lungs.

Study on characteristics and microscopic mechanism of composite environment-friendly dust suppressant for urban construction site soil fugitive dust based on response surface methodology optimization

Soil fugitive dust pollution caused by urban construction sites is a significant problem. To improve the dust suppression efficiency on the urban construction sites, hydroxypropyl guar (HPG), dodecyl dimethyl amine oxide (OB-2), and hydroxypropyl methylcellulose (HPMC) were selected as individual components of the composite dust suppressant using a single-factor test. The response surface methodology (RSM) was used to determine the optimal mixing proportions. After preparation, the characteristics of the composite dust suppressant were tested. Fourier-transform infrared spectroscopy and scanning electron microscopy (SEM) were used to characterize the composite dust suppressant and explore its mechanism. The results showed that 0.327% HPG, 0.6% OB-2, and 0.5% HPMC were the best compound concentrations. Under optimum conditions, the viscosity of the composite dust suppressant was 151.1 [Formula: see text], penetration time was 61.4 s, and water retention rate was 30.67%. Compared with traditional dust control by spraying water, it showed better resistance to evaporation at high temperatures and better wind erosion resistance. The antievaporation rate was 39.42% at 60 °C. After 11 d of continuous wind erosion at level 7, the wind erosion resistance rate was as high as 98.24%. The reason for the excellent dust suppression effect of the composite dust suppressant is that the methyl and hydroxyl groups in the solution diffuse to the surface of the soil fugitive dust particles using Brownian motion and gradually approach the corresponding groups in the soil fugitive dust particles. When the distance between the two reaches 10 [Formula: see text], adsorption occurs, causing small dust particles to stick together. Because of the stability of the covalent bonds in the methyl and hydroxyl groups, a stable solidified layer is formed on the soil fugitive dust surface after the evaporation of the composite dust inhibitor solution, thereby avoiding secondary dust. In addition, the composite dust suppressant is noncorrosive and friendly to the construction site environment. Therefore, the composite dust suppressant can effectively reduce soil fugitive dust, alleviate environmental pollution, and provide a reference for preventing and controlling soil fugitive dust on urban construction sites and preparing composite environment-friendly dust suppressants.

Impact of short-term control measures on air quality: A case study during the 7th Military World Games in central China

The 7th Military World Games held in Wuhan (WH) in Oct 2019 provided an opportunity to clarify the impact of short-term control measures on air quality. Fine particulate matters (PM_2.5) were collected in WH, Huangshi (HS), and Huanggang (HG) during the control (Oct 13-28, 2019) and non-control periods (Oct 29- Nov 5, 2019). The results showed that air quality was good during the control period, with the concentrations of PM_2.5 and gaseous pollutants being below the Grade Ⅱ of China Ambient Air Quality Standard. Concentrations of PM_2.5 and its major chemical components in the control period were significantly lower than those in the non-control period, with reductions ranging from 17% (trace elements) to 46% (elemental carbon). However, higher contributions of secondary components such as SO₄^2-, NO₃^-, NH₄⁺ and secondary organic carbon (SOC) to PM_2.5 were observed during the control period, suggesting the important role of secondary transformation. Potential source contribution function (PSCF) of PM_2.5 showed that the main source regions were potentially located in surrounding cities Hubei Province, but regional transport can't be ignored. Six sources were identified by positive matrix factorization (PMF) for both control and non-control period. The contributions of combustion emissions and vehicle emissions were amplified in the control period, while the contribution of construction dust increased significantly when the control measures ended. Emission reductions contributed more to PM_2.5 concentration decrease in WH (55%) than that in HS (51%) and HG (49%), which was consistent with the stricter control measures implemented in WH. These results indicated that short-term controls were effective at lowering PM_2.5 concentration. However, the elevated contributions of secondary aerosols and the influence of regional transport on the study areas also need to be paid attention for air quality improvement in the future.

The use of generalized synthetic control method to evaluate air pollution control measures of G20 Hangzhou Summit

The traditional campaign-style enforcement in environmental governance has been debated whether its rebound effect is likely to eat away the short-term environmental benefits and subsequently bring about severer pollution. There are methodological challenges in assessing the effect of temporary environmental intervention. By applying the generalized synthetic control method (GSCM), we quantified and characterized the effectiveness of environmental regulations implemented for the G20 Hangzhou Summit held on 4-5 September, 2016. The summit was successful in reducing Air Quality Composite Index by 17.40% (95% CI: 9.53%, 24.60%), 13.30% (95% CI: 4.23%, 21.50%), and 10.09% (95% CI: 2.01%, 17.51%) in the core, strictly-regulated and regulated areas respectively, comparing with the index expected under a "No-G20" scenario during the preparatory period and the summit period (July-September 2016), and the reduction of the levels in specific pollutants (PM₁₀, PM_2.5, NO₂, and CO) was also observed. Besides, the environmental benefits lasted for at least 3 months after the summit. This study demonstrates that the pollution control measures during the G20 Hangzhou Summit improved air quality immediately and continuously, and the GSCM provides a useful tool for evaluating the intervention effects of environmental regulations.

Potency of the pandemic on air quality: An urban resilience perspective

Since the outbreak of COVID-19 pandemic, the lockdown policy across the globe has brought improved air quality while fighting against the coronavirus. After the closure, urban air quality was subject to emission reduction of air pollutants and rebounded to the previous level after the potency period of recession. Different response patterns exhibit divergent sensitivities of urban resilience in regard to air pollution. In this paper, we investigate the post-lockdown AQI values of 314 major cities in China to analyse their differential effects on the influence factors of urban resilience. The major findings of this paper include: 1) Cities exhibit considerable range of resilience with their AQI values which are dropped by 21.1% per day, took 3.97 days on average to reach the significantly decreased trough point, and reduced by 49.3% after the lockdown initiatives. 2) Mega cities and cities that locate as the focal points of transportation for nearby provinces, together with those with high AQI values, were more struggling to maintain a good air quality with high rebounds. 3) Urban resilience shows divergent spatial sensitivities to air pollution controls. Failing to consider multi-dimensional factors besides from geomorphological and economical activities could lead to uneven results of environmental policies. The results unveil key drivers of urban air pollution mitigation, and provide valuable insights for prediction of air quality in response to anthropogenic interference events under different macro-economic contexts. Research findings in this paper can be adopted for prevention and management of public health risks from the perspective of urban resilience and environmental management in face of disruptive outbreak events in future.