Indoor air quality (IAQ) in semi-enclosed subway environments poses critical public health concerns. This study investigates IAQ in the Shanghai subway system through year-round monitoring of PM2.5 and PM10 across representative stations. Concentrations of particulate matter (PM) were markedly higher indoors, peaking during winter weekday morning rush hours, with indoor/outdoor ratios exceeding unity. An interpretable machine learning model was developed to elucidate key factors affecting subway IAQ, identifying platform screen door design and train frequency as dominant influencing factors. By integrating the model with network-wide operational data and passenger boarding records, we quantified city-scale PM levels and commuter exposure. Further analysis incorporating point-of-interest data revealed that stations near residential zones exhibited the highest exposure, while commercial density intensified pollution. These findings provide a system-level assessment of PM exposure within urban rail transit and highlight the need for targeted ventilation and operational strategies to enhance IAQ and safeguard commuter health.

Nitrous acid (HONO) plays a vital role in atmospheric oxidation capacity (AOC) and ozone (O3) formation. Based on 2017-2021 observations at urban Pudong (PD) and suburban Qingpu (QP) in Shanghai, HONO concentrations ranged from 0.74 +/- 0.45 to 1.38 +/- 0.52 ppb in PD and 0.82 +/- 0.50 to 1.19 +/- 0.62 ppb in QP, with higher levels in summer and a typical morning peak at 8-9 a.m. HONO photolysis produced an average of 1.9 ppb h-1 of OH in summer, significantly elevating AOC. Under HONO constraints, summer O3 production rates via HO2 + NO and RO2 + NO increased by 16% and 20%, respectively. These results highlight the key contribution of HONO chemistry to photochemical pollution and provide implications for air quality control in the Yangtze River Delta.

Nitrogen-containing organic compounds (NOCs) are important light-absorbing constituents of atmospheric PM2.5 and can substantially influence aerosol radiative forcing, air quality, and climate. Previous studies have mainly focused on the source apportionment and concentrations levels of NOCs, while the mechanisms governing their formation and particle-phase partitioning remain insufficiently constrained, particularly in tropical regions. Here, we aim to elucidate regional differences in NOCs characteristics in Myanmar, with emphasis on how relative humidity (RH) and precursor species influence their formation pathways. We report the first molecular-level spatio-temporal characterization of NOCs in Myanmar, identifying 1064 organic compounds in ESI- mode, with NOCs contributing 14 %-21 % of molecular formulas and 13 %-35 % of total mass. Organic nitrates (ONs) dominated CHON species across all sites, with higher abundances in Mandalay than in Yangon. Two ubiquitous nitrophenols, nitrocatechol (C6H5NO4) and dimethyl nitrocatechol (C8H9NO4), showed strong covariance but a distinct relationship of their particle-phase C8H9NO4 / C6H5NO4 ratio with RH. CHemistry with Aerosol Microphysics in Python (PyCHAM) box model simulations reveal that increasing RH enhances aerosol water content, to which C8H9NO4 and C6H5NO4 respond differently because of differences in their partitioning thermodynamics. Increased photochemistry in summertime further promotes C6H5NO4 formation. These two processes, in addition to gas-phase precursor concentration, can explain the observed RH relationship and demonstrate that the C8H9NO4 / C6H5NO4 ratio is sensitive, by comparable extents, to: partitioning thermodynamics, photochemistry and precursor supply. These findings provide new constraints on nitrophenol evolution in humid tropical environments and improve interpretation of NOC sources and aging processes, thereby supporting more accurate assessments of their regional and global radiative impacts.

Albeit the declining concentration of PM2.5, health benefits of air pollution mitigation in China remain limitedly evaluated. Oxidation potential (OP) is the capacity of PM2.5 to generate reactive oxygen species (ROS), served as an indicator for PM-induced adverse health effects. Here, acellular (DTT) and cellular OP (in vitro ROS) as well as detailed composition were characterized for PM2.5 collected in Shanghai (2018-2022). Although PM2.5 significantly decreased, the inhalation associated oxidative burden (OPv) remains mostly unchanged due to the enhanced intrinsic OPm in Shanghai. DTTv and ROSv correlated positively with PM2.5 and Ox (O3 + NO2), exhibiting high sensitivity towards source indicating components (i.e., levoglucosan, transition metals, polycyclic aromatic hydrocarbons (PAHs), and secondary organic aerosol (SOA)) in SHAP (SHapley Additive exPlanations) analysis. As illustrated by positive matrix factorization (PMF) integrating with multiple linear regression (MLR), the major contributors to OPv across different years in Shanghai were biomass burning and traffic (48% for DTTv and 59% for ROSv). Further backward trajectory analysis showed that SOA related air mass has become increasingly important for OPv in recent years (26% of DTTv and 35% of ROSv in 2018 compared to 53% of DTTv and 49% of ROSv in 2022). Results from this study indicate the significance of mitigating secondary pollution for future air quality regulation from a public health perspective.

Background While associations between exposure to air pollution and the prevalence of acute ischaemic stroke (AIS) have been investigated, only a few studies have reported the relationship between air pollution and stroke severity. This study aimed to assess the impact of air pollution on AIS severity based on hourly monitoring data and a stroke-specific registry from 2017 to 2021 in Shanghai.Methods Hourly concentrations of particulate matter (PM2.5 and PM10), O3, SO2, CO and NO2 were monitored from 2017 to 2021. A conditional logistic regression model and a Quasi-Poisson model, both coupled with a distributed lag non-linear model and a time-stratified case-crossover design, were used to evaluate a cohort of 106 623 AIS events documented within the Shanghai Stroke Service registry correspondingly. Counterfactual analyses were applied to reveal the potential reducible fractions (PRFs) of air pollution on baseline National Institute of Health Stroke Scale (NIHSS).Results Conditional logistic regression model suggested that PM2.5 (excessive risk (ER) 2.31% (95% CI 1.32% to 3.32%), p<0.001), PM10 (ER 2.60% (95% CI 1.97% to 3.23%), p<0.001) and SO2 (ER 4.53% (95% CI 3.37% to 5.70%), p<0.001) have the most significant effects on increased baseline NIHSS score, which remained robust in the two-pollutant model. Counterfactual analysis based on a conditional logistic regression model revealed PRFs (PM2.5 1.77% (95% CI 0.86% to 2.68%), p<0.001; PM10 1.01% (95% CI 0.28% to 1.73%), p<0.001 and SO2 4.04% (95% CI 3.04% to 5.03%), p<0.001). Quasi-Poisson analysis showed similar results.Conclusions Short-term exposure to ambient air pollution, particularly PM2.5, PM10 and SO2, was shown to increase AIS severity. This finding underscored the need for targeted emission controls and stroke prevention strategies.

To investigate the temporal and spatial variations in smoking activities in Shanghai, atmospheric fine particles (aerodynamic diameter <= 2.5 mu m) were collected at four sites in different functional zones, a central urban site (XJH), an urban site (PD), a suburban site (BS), and a rural site (QP), between 2012 and 2020 with the concentration of nicotine measured by GC-MS. The results showed that smoking activities in Shanghai decreased significantly from 2012 to 2020. The average concentration of nicotine in fine particles at XJH (2012-2013) was 13.86 ng m-3, while it was 3.39 ng m-3 at BS (2017-2018), and 1.13 ng m-3 and 0.58 ng m-3 at PD and QP during 2018-2020. Nicotine concentration in Shanghai showed strong spatial variability but generally followed a seasonal trend of high in winter and low in summer. At XJH and BS, where higher nicotine concentrations were detected, positive correlations between nicotine and organic carbon in fine particles were observed, but not at PD and QP. A negative correlation between nicotine and ozone was found at QP, suggesting the influence of transported nicotine at the rural site. In general, the concentration of nicotine in atmospheric fine particles is primarily governed by local smoking activities, but is also influenced by meteorological conditions.

Achieving sustainable air quality improvements in rapidly industrializing regions requires a clear understanding of the emission sources that drive the formation of PM2.5 pollution. This study identified the sources of PM2.5 and its organic carbon (OC) in Zibo, a typical industrial city in Northern China Plain, using the Positive Matrix Factorization (PMF) model during five pollution episodes (P1–P5) from 26 November 2022 to 9 February 2023. A high-temporal-resolution online observation of 61 organic molecular tracers was conducted using an Aerodyne TAG stand-alone system combined with a gas chromatograph–mass spectrometer (TAG-GC/MS) system. The results indicate that during pollution episodes, PM2.5 was contributed by 32.4% from coal combustion and 27.1% from inorganic secondary sources. Moreover, fireworks contributed 13.1% of PM2.5, primarily due to the extensive fireworks during the Gregorian and Lunar New Year celebrations. Similarly, coal combustion was the largest contributor to OC, followed by mobile sources and secondary organic aerosol (SOA) sources, accounting for 16.2% and 15.3%, respectively. Although fireworks contributed significantly to PM2.5 concentrations (31.6% in P4 of 20–24 January 2023), their impact on OC was negligible. Overall, a combination of local and regional industrial combustion emissions, mobile sources, extensive residential heating during cold weather, and unfavorable meteorological conditions led to elevated secondary aerosol concentrations and the occurrence of this haze episode. The high-temporal-resolution measurements obtained using the TAG-GC/MS system, which provided more information on source-indicating organic molecules (tracers), significantly enhanced the source apportionment capability of PM2.5 and OC. The findings provide science-based evidence for designing more sustainable emission control strategies, highlighting that the coordinated management of coal combustion, mobile emissions, and wintertime heating is essential for long-term air quality and public health benefits.

Pt/Ce-Mn-Ti-O cordierite honeycomb-supported catalysts were prepared using the sol-gel and impregnation methods for the catalytic oxidation of ethanol. The catalytic efficiency of the catalyst at 280 degrees C was 99.6 % and 81.7 % after 50 h of continuous testing. The catalytic efficiency after poisoning was higher than 50 %. This is attributed to the synergistic effect of Pt and Ce-Mn-Ti-O, which enhances the adsorption and activation of ethanol.

Phenol and methoxyphenols are key semi-volatile compounds released from biomass burning with great potential in forming secondary organic aerosol (SOA), threatening global climate and public health. However, the underlying toxicity mechanisms of SOA from biomass burning (BBSOA) remain poorly understood. A detailed examination of the chemical composition and in vitro exposure were performed to comprehensively understand the oxidative stress effects of BBSOA on human bronchial epithelial (BEAS-2B) cells. Oxidative damage and inflammatory responses of the cells following exposure to SOA from phenol (PSOA), guaiacol (GSOA), and syringol (SSOA) were evaluated. Exposure to BBSOA resulted in a noticeable reduction in cell viability, marked by a significantly increased apoptosis in BEAS-2B cells. Flow cytometry and confocal image analysis revealed significant increases in reactive oxygen species (ROS), indicating mitochondrial stress in vitro. The oxidative stress effect from PSOA was observed to be the most significant among all the three types of BBSOA. Using PSOA as a model system, RT-qPCR and RNA-sequencing confirmed that BBSOA induces the upregulation of typical oxidative stress genes, such as NQO1, HMOX1, and ALDH1A3, resulting in cell death. From acellular oxidative potential to cellular transcriptomic level, this work provided direct evidence on the oxidative stress effects from BBSOA, highlighting the health impacts of secondary biomass burning aerosol during regional transportation.

Efficient low-temperature methanol catalytic combustion was critical for the removal of industrial methanol. Herein, a highly efficient Al-MOF-based Ag/Mn-Ti-O composite catalyst was synthesized via a sol-gel method and anchored onto cordierite honeycomb ceramics. The catalyst achieves complete methanol combustion at a low temperature of 144 degrees C and retains over 98.7 % activity after 80 h of continuous operation. The experimental results and first-principles calculations reveal that Ag enhances methanol adsorption and activation via charge redistribution, while Al-MOF facilitates oxygen diffusion, thereby enhancing low-temperature redox capability of the catalyst. This work provides a new strategy for developing highly efficient methanol combustion catalysts.

Nitrogen-containing organic compounds (NOCs) are key components of particulate matter (PM), but their compositional evolution and light-absorbing properties during atmospheric aging remain poorly understood. In this study, ultra-high-performance liquid chromatography coupled with Orbitrap mass spectrometry was used to semi-quantitatively analyze 59 PM1 samples collected in Shanghai. NOCs accounted for 31 % and 64 % of the detected species in negative (ESI-) and positive (ESI+) ionization modes, respectively. Atmospheric aging significantly reduced the molecular diversity of polar organics, with both the number and mass concentration percentages of CHON- compounds showing significant negative correlations with aging degree. Van Krevelen analysis demonstrated a decrease in the number of carboxylic-rich alicyclic molecules and their CHON- contributions during the aging process (from 37.7 % in fresh samples to 21.2 % in aged samples). CHN+ compounds, a major NOCs group in ESI+ mode, also decreased with aging. Correlation analyses involving the Bep/(Bep+Bap) ratio, relative humidity, and mass absorption efficiency at 365 nm revealed a decline in light absorption capacity with aging, suggesting aqueous-phase oxidation as a dominant aging mechanism. CHON- and CHN+ compounds were identified as the principal light-absorbing constituents in PM1. This work provides new insights into the aging-induced transformations of NOCs in urban PM1, and their changing role in light absorption, highlighting the need for further investigation of the aging mechanisms of NOCs.

Vertical observations were used to explore the explosive growth (EG) of PM2.5 in Shanghai in 2018 to investigate the rapid evolutionary mechanisms and health effects of a highly severe haze episode. The EG is defined as the net increase in PM2.5 concentration by more than 100 µg/m3 within 6 or 9 h. The average PM2.5 concentration during EG was 118.1 µg/m3, dominated by NO3-, NH4+, SO42- (SNA), and organic matter (OM), with a proportion of 31.1 %, 15.1 %, 14.8 %, and 18.8 %, respectively. In addition to being affected by chemical reactions, regional transport was the main influencing factor for OM, but local emissions were the main factor for SNA. Vertical observation results showed that EG events were influenced commonly by local emission, regional transport, and chemical reactions with a different proportion. Moreover, the heterogeneous reaction could possibly cause more severe pollution. The daily average nonaccidental mortality for EG [13.9 (95 % CI: 5.5, 25.0)] was about 4.0 times higher than that in Clean Days (CDs) [3.5 (1.4, 6.3)], and EG episodes caused a more severe effect on cardiovascular disease compared with respiratory disease. Moreover, local emissions and secondary gas-phase oxidation exhibited crucial factors for human health during EG, but regional transport during CDs. To sum up, ground-level observation could not fully explain the process of atmospheric pollution, but the vertical measurements help to understand the regional transport influence on the EG process. In the future, it is recommended that vertical observation should play a vital role in investigating regional heavy pollution episodes.

The health impacts of aerosols from southwestern China remain poorly understood. To identify the key chemical contributors and sources of PM2.5 toxicity in this region, detailed chemical composition (carbonaceous and inorganic species), different air volume normalized acellular oxidative potential (OP) metrics (OPDTTV and OPEPRV), and cellular oxidative stress (in vitro ROSV) were measured using PM2.5 collected from Chongqing. OPDTTV was measured to be 1.1-5.4 nmol min-1 m-3 with a mean value of 2.8 nmol min-1 m-3, which was higher than the values reported in other coastal cities. In particular, airborne radicals (OPEPRV) were measured to be in the range of 4.1 × 10-3-2.3 × 10-2 nmol m-3 with a mean value of 1.2 × 10-2 nmol m-3. The OPV and in vitro ROSV increased significantly during haze episodes compared with those during clean episodes. OC, Cu, Zn, polycyclic aromatic hydrocarbons (PAHs), and oxygenated PAHs (OPAHs) were observed to be the major contributors to OPDTTV, while nitrated PAHs (NPAHs), EC, Fe, and Cu primarily influenced OPEPRV and in vitro ROSV. Backward trajectory and potential source contribution function (PSCF) analysis indicated that the source of PM2.5 oxidative stress effects was mainly derived from the local and western air masses, indicating the roles of atmospheric aging and industrial emission in the health impacts of PM2.5. Overall, by revealing that transition metals, PAHs, and functionalized PAHs are the most imperative components for both the acellular and cellular health impacts of wintertime PM2.5 of southwestern China, this work sheds light on future mitigation strategies for improving urban air quality from a public health perspective.

To better understand the potential adverse health effects of atmospheric fine particles in the Southeast Asian developing countries, PM2.5 samples were collected at two urban sites in Yangon and Mandalay, representing coastal and inland cities in Myanmar, in winter and summer during 2016 and 2017. The concentrations of 21 polycyclic aromatic hydrocarbons (PAHs) in PM2.5 were determined using a gas chromatography-mass spectrometry (GC-MS). The concentrations of PAHs in PM2.5 in Yangon and Mandalay ranged from 7.6 to 180 ng m-3, with an average of 72 ng m-3. The PAHs were significantly higher in winter than in summer, and significantly higher in Mandalay than in Yangon. The health risk analysis of PAHs, based on the toxic equivalent quantity (TEQ) calculation, and the incremental lifetime cancer risk (ILCR) assessment indicated that PM2.5 in Myanmar has significant health risks with higher health risks in Mandalay compared to Yangon. Diagnostic ratios of PAHs, correlation of PAHs with other species in PM2.5 and the positive matrix factorization (PMF) analysis showed that TEQ is strongly affected by biomass burning and vehicular emissions in Myanmar. Additionally, it was found that the aging degree of aerosols and air mass trajectories had great influences on the concentration and composition of PAHs in PM2.5 in Myanmar, thereby affecting the toxicity of PM2.5.

Rapidly increasing urbanization in recent decades has elevated the subway as the primary public transportation mode in metropolitan areas. Indoor air quality (IAQ) inside subways is an important factor that influences the health of commuters and subway workers. This review discusses the subway IAQ in different cities worldwide by comparing the sources and abundance of particulate matter (PM2.5 and PM10) in these environments. Factors that affect PM concentration and chemical composition were found to be associated with the subway internal structure, train frequency, passenger volume, and geographical location. Special attention was paid to air pollutants, such as transition metals, volatile/semi-volatile organic compounds (VOCs and SVOCs), and bioaerosols, due to their potential roles in indoor chemistry and causing adverse health impacts. In addition, given that the IAQ of subway systems is a public health issue worldwide, we calculated the Gini coefficient of urban subway exposure via meta-analysis. A value of 0.56 showed a significant inequity among different cities. Developed regions with higher per capita income tend to have higher exposure. By reviewing the current advances and challenges in subway IAQ with a focus on indoor chemistry and health impacts, future research is proposed toward a sustainable urban transportation systems.

Acute ischemic stroke (AIS) is one of the most predominant causes of mortality and disability in China. Significant uncertainties in stroke diagnosis and time of onset have resulted in inconsistent evidence on the association between ambient air pollution and the risk of AIS. The present study aimed to evaluate the impact of air pollution on AIS onset based on high time-resolution air pollution data and a stroke-specific registry across the past five years. Hourly concentrations of PM2.5, PM10, O3, SO2, CO, NO2 and nitrous acid (HONO) were monitored from 2017 to 2021, with which a distributed lag non-linear model and conditional logistic regression models coupled with a time-stratified case-crossover design were applied to 106,623 AIS cases recorded in the Shanghai Stroke Service (4S) database during the study period. Results from the conditional logistic regression models indicate that acute exposure to PM2.5, PM10, SO2, NO2 and HONO was found to be associated with AIS onset, respectively. The corresponding cumulative excessive risks of AIS onset were 0.8 %, 1 %, 2.4 %, 2.1 % and 1.8 % for each interquartile range increase in the respective concentration. The longest lag-effect (up to 13 h) was observed for reactive nitrogen species (RNS), such as NO2 and HONO, which remained robust in two-pollutant models. Similar important role of RNS in AIS onset were confirmed by the distributed lag non-linear model. By demonstrating the transient effect of ambient air pollution on AIS, especially the relationships between RNS and AIS for the first time, our study provides stringent evidence for future mitigation strategies for pollution emission and public health.

Molecular markers in organic aerosol (OA) provide specific source information on PM2.5, and the contribution of cooking organic aerosols to OA is significant, especially in urban environments. However, the low time resolution of offline measurements limits the effectiveness when interpreting the tracer data, the diurnal variation in cooking emissions and the oxidation process. In this study, we used online thermal desorption aerosol gas chromatography and mass spectrometry (TAG) to measure organic molecular markers in fine particulate matter (PM2.5) at an urban site in Changzhou, China. The concentrations of saturated fatty acids (sFAs), unsaturated fatty acids (uFAs) and oxidative decomposition products (ODPs) of unsaturated fatty acids were measured every 2 h to investigate the temporal variations and the oxidative decomposition characteristics of uFAs in urban environments. The average concentration of total fatty acids (TFAs, sum of sFAs and uFAs) was measured to be 105.70 +/- 230.28 ng m(-3). The average concentration of TFAs in the polluted period (PM2.5 >= 35 mu g m(-3)) was 147.06 ng m(-3), which was 4.2 times higher than that in the clean period (PM2.5 < 35 mu g m-3) and higher than the enhancement of PM2.5 (2.2 times) and organic carbon (OC) (2.0 times) concentrations when comparing the polluted period to the clean period. The mean concentration of cooking aerosol in the polluted period (4.0 mu g m(-3)) was about 5.3 times higher than that in the clean period (0.75 mu g m(-3)), which was similar to the trend of fatty acids. Fatty acids showed a clear diurnal variation. Linoleic acid / stearic acid and oleic acid / stearic acid ratios were significantly higher at dinnertime and closer to the cooking source profile. By performing backward trajectory clustering analysis, under the influence of short-distance air masses from surrounding areas, the concentrations of TFAs and PM2.5 were relatively high, while under the influence of air masses from easterly coastal areas, the oxidation degree of uFAs emitted from local culinary sources was higher. The effective rate constants (k(O)) for the oxidative degradation of oleic acid were estimated to be 0.08-0.57 h(-1), which were lower than kL (the estimated effective rate constants of linoleic acid, 0.16-0.80 h(-1)). Both k(O) and k(L) showed a significant positive correlation with O-3, indicating that O-3 was the main nighttime oxidant for uFAs in the city of Changzhou. Using fatty acids as tracers, cooking was estimated to contribute an average of 4.6 % to PM2.5 concentrations, increasing to 7.8 % at 20:00 UTC+8 h. Cooking was an important source of OC, contributing 8.1 %, higher than the contribution of PM2.5. This study investigates the variation in the concentrations and oxidative degradation of fatty acids and corresponding oxidation products in ambient air, which can be a guide for the refinement of aerosol source apportionment and provide scientific support for the development of cooking source control policies.

Nitrous acid (HONO) plays a significant role in radical cycling and atmospheric oxidative chemistry. While the source and evolution of HONO in the Yangtze River Delta (YRD) region of China after 2018 remains largely unknown, this work monitored HONO and other air pollutants throughout 2019 at an urban site (Pudong, PD) and a suburban site (Qingpu, QP) in Shanghai. Episodes with high HONO mixing ratios but different PM2.5 levels, namely haze and clean episodes, were chosen for HONO budget analysis. Using an observation-based photochemical box model, relative importance of different sources and sinks of HONO were evaluated. Gas-phase reaction of NO with OH was found to be one of the most important daytime HONO formation sources, especially during the QPhaze period (accounting for 40.3 % of daytime HONO formation). In particular, heterogeneous conversion of NO2 on ground and aerosol surface was found to be the dominant source for nocturnal HONO. Photo-enhanced NO2 conversion on ground surface plays an important role in daytime HONO production (19.4 % in PDhaze vs. 27.6 % in PDclean, and 19.8 % in QPhaze vs. 25.9 % in QPclean). In addition, photo-enhanced NO2 conversion at the aerosol surface during haze episodes made more significant contributions to HONO formation compared to the clean periods (20.9 % in PDhaze vs. 17.1 % in PDclean, and 19.7 % in QPhaze vs. 11.2 % in QPclean). The role of multiphase reactions was found to be increasingly important in HONO generation with enhanced relative humidity (RH) during daytime. Significant unknown HONO source was further analyzed and found to be positively related with photolytic as well as multiphase pathways. Overall, our study sheds light on the budget of HONO in one of the biggest megacities in east China, which would help developing future mitigation strategies for urban HONO and atmospheric oxidation capacity.