Humidity Response Research Articles

Constructing a novel humidity sensor using acrylic acid/bagasse cellulose porous hydrogel combining graphene oxide and citral for antibacterial and intelligent fruit preservation

A novel hydrogel humidity sensor was developed using acrylic acid/bagasse cellulose (AA/BC) porous hydrogel triggered by cold plasma (CP) combining graphene oxide (GO) and embedding citral for antibacterial and intelligent fruit preservation. Results showed that both GO and citral were loaded in AA/BC and had strong hydrogen bond interaction with hydrogel. Acrylic acid/bagasse cellulose/graphene oxide (AA/BC/GO) showed the highest humidity response when the compound concentration of GO was 1.0 mg/mL and the test frequency was 1 kHz, and exhibited high electrical conductivity (−2.6 mS/cm). In addition, in continuous and cyclic relative humidity (RH) tests, the response time of AA/BC/GO from 33.70 % RH to 75.30 % RH was about 177.4 s and the recovery time was about 150.6 s, with excellent sensitivity and durability. The sensors also revealed remarkable antibacterial properties against Escherichia coli and Staphylococcus aureus, among which acrylic acid/bagasse cellulose/graphene oxide-citral (AA/BC/GO-C) was the most prominent, and could extend the shelf life of mangoes for about 8 days. By intuitively judging the appearances and total color difference (TCD) of the hydrogel sensors, it could play the role of intelligent preservation by connecting their water absorption and the release of citral. Therefore, this work provided innovative strategies for the application of hydrogel sensors in food preservation.

Ethylene signaling modulates air humidity responses in plants.

Air humidity significantly impacts plant physiology. However, the upstream elements that mediate humidity sensing and adaptive responses in plants remain largely unexplored. In this study, we define high humidity-induced cellular features of Arabidopsis plants and take a quantitative phosphoproteomics approach to obtain a high humidity-responsive landscape of membrane proteins, which we reason are likely the early checkpoints of humidity signaling. We found that a brief high humidity exposure (i.e., 0.5 h) is sufficient to trigger extensive changes in membrane protein abundance and phosphorylation. Enrichment analysis of differentially regulated proteins reveals high humidity-sensitive processes such as 'transmembrane transport', 'response to abscisic acid', and 'stomatal movement'. We further performed a targeted screen of mutants, in which high humidity-responsive pathways/proteins are disabled, to uncover genes mediating high humidity sensitivity. Interestingly, ethylene pathway mutants (i.e., ein2 and ein3eil1) display a range of altered responses, including hyponasty, reactive oxygen species level, and responsive gene expression, to high humidity. Furthermore, we observed a rapid induction of ethylene biosynthesis genes and ethylene evolution after high humidity treatment. Our study sheds light on the potential early signaling events in humidity perception, a fundamental but understudied question in plant biology, and reveals ethylene as a key modulator of high humidity responses in plants.

The effects of humidity on the electrical properties and carrier mobility of semiconducting polymers anion-exchange doped with hygroscopic salts

To improve their electrical conductivity for various applications, semiconducting polymer films are often chemically doped to increase their equilibrium charge carrier density. Recently, a novel doping method involving anion exchange has provided control over the identity of the counterions that reside in such films, leading to increased stability under ambient conditions. In this work, however, we show that by ion-exchanging 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane-doped poly(3-hexylthiophene-2,5-diyl) films with hygroscopic salts like bis(trifluoromethane)sulfonimide lithium or LiPF6, the doped film's electrical conductivity drops significantly when exposed to ambient humidity. The change in electrical conductivity depends directly on the degree of hygroscopicity of the counterion and can be over 50% with relatively modest changes in relative humidity (RH), and up to a factor of four between ambient and completely dry conditions. The film's humidity response is entirely reversible when adsorbed water is removed, potentially allowing the doped semiconducting polymer films to function as humidity sensors. Hall effect measurements show that the cause of the drop in conductivity with increasing RH is due to a decrease in carrier mobility and not due to de-doping. Our results emphasize that it is important to control the sample environment when making electrical measurements on anion-exchange doped semiconducting polymer films.

Modulation of electronic and ionic conduction in mixed polymer conductors via additive engineering: Towards targeted applications under varying humidity

Polymer solids with mixed ion and electron transport hold great promise for next-generation organic electronics, and rational regulation of ionic/electronic contribution within these materials can enable a broadened spectrum of practical applications. However, a fundamental understanding of the conduction mechanisms and their correlations with morphological characteristics remains limited, especially under varying environmental humidity conditions. In the present work, simple additive engineering enables the effective regulation of electronic and ionic contribution in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) based conductors, giving rising to ion- and/or electron-dominant conductions. As a demonstration, PEDOT:PSS films with different electrical characteristics are successfully applied for thermal energy harvesting, healthcare monitoring and human motion detection upon humidity exposure. Combining operando alternating current (AC) impedance spectroscopy and grazing incidence small-angle X-ray scattering at low and high humidity levels, additive-dependent charge transport mechanisms are elucidated, and correlations between morphological alterations and conductivity evolutions are revealed. This work achieves highly tailorable PEDOT:PSS conduction utilizing Zonyl, dimethyl sulfoxide (DMSO) and carbon nanotubes (CNTs) as additives with distinct humidity responses and gains an in-depth comprehension of underlying mechanisms, which are expected to pave the way for next-generation organic electronics.

Wearable Fiber SPR Respiration Sensor Based on a LiBr-Doped Silk Fibroin Film.

Respiration is essential for supporting human body functions. However, a biocompatible fiber respiration sensor has rarely been discussed. In this study, we propose a wearable fiber surface plasmon resonance (SPR) respiration sensor using a LiBr-doped silk fibroin (SF) film. The SPR sensor monitors respiration by responding to airway humidity variation during inhalation and exhalation. We fabricated the SPR respiration sensor by depositing the core of a plastic-clad optical fiber with a gold film and an SF-LiBr composite film. The SF-LiBr composite film can absorb water through the interaction between water molecules and hydrogen bonds linking fibroin chains. Thus, humidity variation can change the SF-LiBr composite film's refractive index (RI), altering the phase-matching condition of the surface plasmon polaritons and shifting the SPR spectral dip. In experiments, we test the effect of the LiBr doping ratio on humidity response and confirm that the SF-22.1 wt % LiBr sensor has balanced performances. The SF-22.1 wt % LiBr sensor has a broad sensing range of 35-99% relative humidity (RH), a reasonable overall sensitivity of -6.5 nm/% RH, a fast response time of 135 ms, a quick recovery time of 150 ms, good reversibility, and good repeatability, which is capable of tracking different respiration states and patterns. Finally, we encapsulate this sensor in a conventional nasal oxygen cannula for wearable respiration monitoring, proving that the sensor is suitable for high-sensitivity, real-time, and accurate respiration monitoring.

Characterization of an Impedance-Type Humidity Sensor Based on Porous SnO2/TiO2 Composite Ceramics Modified with Molybdenum and Zinc.

In this study, we report on the room-temperature characteristics of an impedance-type humidity sensor based on porous tin oxide/titanium oxide (SnO2/TiO2) composite ceramics modified with Mo and Zn. The SnO2/TiO2-based composites synthesized in the solid-state processing technique have been structurally characterized using X-ray diffraction, scanning electron microscopy, energy dispersive, and Raman spectroscopy. Structural analysis indicated the desired porous nature of the synthesized ceramics for sensing applications, with an average crystallite size in the nano range and a density of about 80%. The humidity-sensing properties were evaluated within a wide relative humidity range from 15% to 85% at room temperature, and the results showed that a better humidity response had a sample with Mo. This humidity-sensing material exhibits a linear impedance change of about two orders of magnitude at the optimal operating frequency of 10 kHz. Furthermore, fast response (18 s) and recovery (27 s), relatively small hysteresis (2.8%), repeatability, and good long-term stability were also obtained. Finally, the possible humidity-sensing mechanism was discussed in detail using the results of complex impedance analysis.

Dielectric and Humidity Sensing Properties in Iron Nanoparticle Substituted Polyaniline Composite

The existence of graphene-based Polyaniline nanocomposite has been demonstrated to be exceptional host matrices for entrapping nano-sized particles, and its composites are widely used in a variety of applications such as transducers, sensors, electrodes, microwave absorption, and thermoelectric applications. The purpose of this study is to investigate the dielectric properties and humidity sensing response of a Fe doped PANI/Graphene (PAFG) composite synthesized in-situ polymerization using adhathoda vasica plant extract. The FT-IR, XRD, and SEM-EDX techniques were used to characterize the sample. The dielectric measurements were performed at 298K over a wide frequency range 5x101 to 5x106 Hz. Humidity response studies were performed at room temperature. Iron nanoparticles distributed homogeneously in the PANI matrix were ascertained from IR spectral data. At room temperature, the dielectric properties of the synthesized DS-4 powder outperform those of the synthesized pristine PANI and Fe nanoparticles, with superior dielectric constant and high dielectric loss. When the synthesized iron decorated composite was exposed between 10% and 97% RH, the electrical resistance decreased, which is attributed to the polarization process affecting electrical conductivity within these materials. The PAFG-40% composite exhibited high sensitivity at low humidity levels ranging from 30% to 70% RH.

Research on mapping relationship between environmental load and vibration response of bridge structure based on structural health monitoring data

AbstractWith the increasing lifespan of bridges, various forms of deterioration will inevitably occur. The bridge health monitoring system enables direct monitoring of the loads (such as wind, temperature, and vehicles) experienced by the bridge during operation, as well as the corresponding vibration response of the bridge structure (including main beam deformation, tower top displacement, cable acceleration, etc.). These data provide valuable insights into the safety and durability of the bridge during its operational lifetime. However, the challenge lies in extracting meaningful information from the vast amount of collected data. This article focuses on the Fuyu Bridge as a research case and analyzes the variations in environmental factors, such as temperature, humidity, wind load, and structural vibration responses (main beam and cable), obtained from the Fuyu Bridge's structural health monitoring system. It also conducts a structural safety assessment during the operational period of the bridge. Furthermore, the research explores the relationship between environmental factors, load effects, and structural response to establish a foundation for future structural safety assessments of the Fuyu Bridge during its operational period. For instance, changes in environmental factors or load effects can be used to predict structural responses. Additionally, this study provides access to the structural health monitoring data of the Fuyu Bridge, facilitating data‐driven research for other scholars in the field.

Humidity-sensitive and fluorescent bio-based polyhydroxylamides toward sustainable adhesives

Bio-based polyhydroxyamides (PHAs) are promising functional materials that have the potential to be utilized in various fields. However, the complex steps required for synthesizing high-performance PHAs limit their large-scale manufacture and further applications. To address this challenge, a novel and simple strategy was proposed for preparing strong PHAs with tunable adhesion, sensitive humidity response, and unique fluorescence properties by using bio-based monomers via melt polycondensation. These PHAs are thermally stable and possess tunable mechanical properties. The multiple hydrogen bonds endow PHAs with excellent adhesive properties. The overlapping shear strength was 24.6 MPa when using stainless steel plates. The humidity response of PHAs can be controlled by adjusting the water absorption content, and the hygroscopic-induced crystallization endows PHAs with excellent shape re-editing and shape memory properties. The presence of abundant amide bonds in PHAs promotes the formation of amide cluster-induced luminescence in these PHAs. The combination of sustainable raw materials and high-performance PHAs presents various opportunities for the development of new functional polyamides toward strong sustainable adhesives.

PEDOT:PSS/Natural Rubber Latex Inks for Screen‐Printing Multifunctional Wearable Strain–Humidity Sensors

Wearable strain–humidity sensors are increasingly recognized for their role in healthcare and detecting human motion signals. However, many strain–humidity sensors require complex manufacturing processes and have limited applicability. In this study, based on the good miscibility between natural rubber latex (NRL) and poly (3,4‐ethylenedioxythiophene):poly (4‐styrenesulfonate) (PEDOT:PSS), PEDOT:PSS/NRL composite conductors are transferred onto fabric substrate through screen printing and prepared high‐performance strain–humidity sensor. The PEDOT:PSS/NRL blends strain–humidity sensor exhibited good stability and durability (500 cycles) at 10% strain, achieves a gauge factor (GF) of 123.8 with excellent linearity, making it operational in detecting various human motions, such as finger bending, elbow bending, wrist bending, and so on. In addition, the PEDOT:PSS and water molecules interaction results in a humidity response time as low as 0.72 s and recovery time as low as 0.85 s for the PEDOT:PSS/NRL composite strain–humidity sensor, and a wide relative humidity detection range (6–83%), allowing it to be utilized for precise detection of human breathing. Furthermore, it can monitor the use's joint movement, facial muscle movement, and respiratory rate, which show its potential application prospect in health monitoring.

Preparation of graphene oxide composited zinc oxide films by electrostatic spray deposition for humidity sensors

This work aimed to study the preparation of graphene oxide (GO) and zinc oxide (ZnO) composited films by electrostatic spray deposition for use in fabricated humidity sensors. The physical properties of prepared films were examined with X-ray diffraction, Raman spectroscopy, and scanning electron microscope. Subsequently, a humidity sensor was fabricated using a low-cost interdigitated electrode pattern with the print circuit board. The humidity sensing behaviors were assessed with fixed humidity levels in a saturated aqueous salt solution in the humidity range of 11 – 93%RH. The impedance value of the device was obtained with a precision LCR meter. It was found that the composited film of 0.50 %wt. GO demonstrated the highest humidity response with optimized humidity sensitivity, hysteresis error, and response/recovery times of 2.68 ´ 103, 4.89%, and 228/19 s, respectively. Moreover, the equivalent circuits for the prepared device at various humidity levels were acquired with impedance spectroscopy to propose the mechanism for the humidity sensing of the device.

Biodegradable ion-conductive polyvinyl alcohol/okra polysaccharide composite films for fast-response respiratory monitoring sensors

Polyvinyl alcohol (PVA) and okra polysaccharide (OP) are biodegradable polymers with high hydrophilicity and good biocompatibility with potential for use as flexible humidity-sensitive materials. Herein, biodegradable flexible composite films (named POP films) were prepared from PVA, OP, and phytic acid using a solution-casting method based on. POP films exhibited excellent mechanical strength, flexibility, flame retardancy, water resistance, humidity response, and humidity-sensing characteristics. Notably, the POP humidity sensors exhibited a hysteresis value of 1.88 % relative humidity for the adsorption and desorption processes and good sensitivity over a wide humidity range of 35–95 %. In addition, the humidity sensor distinguished the frequency of nose breathing, and its response and recovery times were 0.9 and 1.98 s, respectively. The excellent performance of POP sensors in monitoring humidity and human respiratory rates demonstrates the sensor's potential for wearable smart devices.

LiCl-assisted polysiloxane electrolyte complexes for highly sensitive humidity sensing

Polyelectrolytes with hydrophilic and hydrophobic structures are widely employed in humidity sensors, but their response properties necessitate improvement. This paper introduces the development of crosslinked polysiloxane electrolytes via Zr4+ coordination and LiCl assistance for humidity sensing applications. The composition, microstructure, thermal stability, and humidity response of polymer complexes based on ZrOCl2 were thoroughly investigated. The resulting complexes exhibited porous structures and demonstrated excellent thermal stability. The ionic conductivity displayed an exponential change of 106 - 107 within the relative humidity (RH) range of 43–95 %. The polymer complexes with 5 mol% ZrOCl2 exhibited the most favorable humidity sensing properties, including a response time of 90 s and a recovery time of 7 s. The addition of LiCl as an assistant further enhanced the humidity sensing properties of the polymer complexes. The optimal sensor exhibited high sensitivity, reaching 1175 throughout the entire RH range from 11 % to 95 %. It demonstrated good linearity, minimal humidity hysteresis (2.3 % RH), and rapid response/recovery time of 16/9 s. The development of LiCl-assisted polysiloxane polyelectrolyte-Zr complexes has provided a strategy for the creation of high-performance humidity sensors.

Fabrication of Micro-Cantilever Sensor Based on Clay Minerals for Humidity Detection.

In this paper, novel humidity sensors based on montmorillonite, kaolinite, and composite films coated on micro-cantilevers were prepared to measure the relative humidity (RH) values by the deflection of a micro-cantilever (MC) at room temperature. The humidity-sensing properties, such as response and recovery, sensitivity, repeatability, humidity hysteresis, and long-term stability, were investigated in the range of working humidity (10-80% RH). The humidity response in the close humidity range of 10% RH to 80% RH revealed a linear increase in water absorption of montmorillonite, kaolinite, and montmorillonite/kaolinite mixed dispersant (1:1) as a function of RH with linear correlation factors between the humidity change and deflection estimated to be 0.994, 0.991, and 0.946, respectively. Montmorillonite's sensitivity was better than kaolinite's, with the mixed-clay mineral film's response falling somewhere in between. This research provides a feasible and effective approach to constructing high-performance MC humidity sensors that can be operated at room temperature based on clay minerals.

Fabrication and Characterization of Humidity Sensors Based on PEDOT:PSS Doped with Gold and Silver Nanoparticles by Laser Ablation

This paper presents a simple, fast, and inexpensive method for the large-scale fabrication of polymer-based humidity sensors on glass substrates. The nanoparticles were synthesized using laser ablation, this is an environmentally friendly method for fabricating metal nanoparticles and provides a unique tool for nanofabrication. In this work, humidity sensing material, poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) along with different kinds of nanoparticles, Au and Ag, are employed to enhance the stability and sensitivity to humidity sensing. Based on the experimental results, the TEM images show the crystallinity of the nanoparticles, indicating alloying of the nanoparticles. Based on XRD, this result indicates that the amorphous structure of PEDOT:PSS is only slightly affected by mixing with nanoparticles. According to FE-SEM analysis, the formation of interconnected crystallites facilitates the charge transport mechanism in the polymer chains due to improved conduction paths. Has been Characterization of humidity sensors Using (LCR), study the effect of humidity on capacitance at different frequencies (100[Formula: see text]Hz, 1[Formula: see text]kHz, 10[Formula: see text]kHz, and 100[Formula: see text]kHz), and the response and recovery time characteristics. The results show excellent linear and active behavior of the capacitive humidity response. Ag, PEDOT, and Au NPs have a synergistic effect, exhibiting a more extended sensing range and better stability. This work shows a high-sensitivity and low-cost sensing material for different humidity sensor applications.

FP Interferometric Optic Fiber Humidity Sensor Based on Acrylate AB Adhesive Film

In this paper, an optical fiber humidity sensor based on acrylate AB adhesive film is studied, and two methods—a bubbling method and a dual pressure assisted method—for preparing thin films are proposed. The forms will make the thin film lighter and make the sensor more sensitive. Using a glass tube to connect the acrylate AB adhesive film to the single mode optical fiber, the humidity sensor is obtained. Through humidity response experiments, the sensor’s sensitivity reaches 167.5 pm/% RH, and the response time reaches 4.8 s/% RH. At the same time, the experiments show that the sensor has good repeatability and stability. Finally, the influence of temperature on the working process is analyzed, and we provide a method for improvement through FBG.

In-situ hydrothermally derived highly responsive MgO doped mesoporous KIT-6 based novel humidity sensor

ABSTRACT Herein in this work, the synthesis as well as study of Magnesium-oxide loaded mesoporous silica KIT-6 (a 3D material, first synthesised by Ryoo’s research group in 2003 material, in Korean Institute of Technology) for sensing at room temperature was done by employing KIT-6 as a hard template. The unique arrangement mesoporous KIT-6 having Ia3d symmetry along with a three-dimensional cubic arrangement of pore provides more tunnels for transportation of charge carriers. Water molecules are more effectively adsorbable due to KIT-6’s extremely porous structure, and the mesoporous framework’s broad, uniform pore channels make it simple for charged ions to flow freely. Despite these qualities, undoped KIT-6 does not exhibit a superior relative humidity (RH) sensitivity in humid environments hence metallic nanoparticles (MgO/KIT-6) have been used to improve the sensing capabilities of RH sensors. In the current work, we offer a straightforward, easy-to-follow hydrothermal synthesis method for producing effective humidity sensing materials made of MgO-loaded KIT-6. Different MgO concentrations (1, 5 and 10 wt%) were added to KIT-6 in order to employ it as a humidity sensor material to effectively monitor and regulate humidity levels. Here at MgO/KIT-6 presents swift humidity response and recovery time along with it change in ≥3 orders of magnitude in resistance were observed over as compared to pure KIT-6 in the 11%–98% RH range at room temperature. The structural insights were examined using X-ray diffraction (XRD), Fourier transform infrared, High-resolution transmission electron microscopy , Field emission scanning electron microscopy with energy dispersive x-ray (EDX) microanalysis and textural properties of the synthesised mesoporous KIT-6 silica and MgO/KIT-6 (X) nanocomposites were examined in depth with the N2 adsorption-desorption isotherm from which it was analysed that as the amount of MgO is incremented, the surface area gets decreased. Among all the tested samples of different weight%, optimal results obtained for 5 weight% MgO-loaded KIT-6 [abbreviated as MgO/KIT-6(5)] exhibits impressive humidity sensing responsiveness, little hysteresis, short response as well as recovery time (31 s/35 s), consistent linearity, extremely high accuracy over a varied working temperature range, repeatability and great stability in the 11–98% RH range. The investigation of humidity sensing properties of MgO/KIT-6 hybrid nanocomposite justifies that this material is good candidates to be used as a innovative high performance humidity sensor.

CFD investigation of a fast-response humidifier for high-power PEMFC test stations

Unlike operating PEMFC systems with internal humidification from hydrogen recirculation, fuel cell stack test stations mainly rely on external humidification. Response time in the order of 10s and power over 100 kW are crucial requirements for test stations for vehicle fuel cell stacks. In the present study, a 3D computational fluid dynamics (CFD) model of a swirl spray humidifier is developed to simulate the conjugated heat and mass transfer in such a humidifier. In the model, hot, dry air enters from the bottom portion of the humidifier tangentially and mixes with liquid droplets from a nozzle placed near the middle. A discrete phase model (DPM) is employed to model the atomized droplets. Time variations of the flow structure and humidity distribution are studied. A parametric study with the nozzle parameters on humidifier performance is carried out, showing that optimal humidifier performance can be obtained with a single nozzle and spray temperature at 300 K. The humidity response at the humidifier exit subject to a load change is investigated. The simulation results show that the humidifier's dynamic response time for the baseline case is about 32s, with a steady relative humidity of 95.25% and an evaporation rate of 98.4% at the exit. The present model can guide the future design of fast-response, high-power humidifiers for fuel cell stack test stations.

Super-Deformed Asymmetric Actuators: Balance of Photothermal and Humidity Response Effects through Structural Regulation

Super-Deformed Asymmetric Actuators: Balance of Photothermal and Humidity Response Effects through Structural Regulation

Prediction of daily PM2.5 and ozone based on high-density weather stations in China: Nonlinear effects of meteorology, human and ecosystem health risks

In recent decade, despite the implementation of strict emission reductions, PM2.5 and surface ozone (O3) in China are still at high pollution level. In this study, based on observations at air quality stations (∼1500 mainly in urban region), daily PM2.5 and MDA8 (the daily maximum 8 h average) O3 concentrations in high-density and uniform meteorological sites (∼2000) over China during 2017–2019 were retrieved using generalized additive models (GAMs) for different regions on a seasonal scale, in order to establish 0.1° gridded datasets and investigate their spatiotemporal characteristics, nonlinear effects of meteorology, and ambient air pollution-attributable health risks on a regional scale. This model can provide high accuracy in the estimation of daily PM2.5 (O3) in 2018 with overall cross-validation R2 and RMSE of 0.81 (0.80) and 12.73 (17.63) μg/m3 and predictive capability in 2017 and 2019 with R2 of 0.67 (0.70) for PM2.5 (O3). Temperature, relative humidity and visibility are three main meteorological factors driving PM2.5 (O3) response. PM2.5 generally exhibits an exponential decrease with increasing visibility and an increase with increasing relative humidity, while is suppressed at the thresholds of 60% and 70%. For O3, in northern China, positive response of temperature is more important and O3 suppression exists at 36 °C ∼ 41.5 °C, whereas negative response of relative humidity is dominating in southern China. Overall, annual averaged PM2.5 (O3) values across China reduced (increased) by 18.7% (11.2%) between 2017 and 2019, with the highest concentrations and variation in North China. These variations contributed to a 14.9% reduction in PM2.5 attributed premature deaths, but a 10.4% increase in O3 exposure related deaths. Generally, central-eastern China still exists greater health risk with per capita premature mortality ranging from 0.80‰ to 1.19‰ for PM2.5 and 1.91‰ to 2.60‰ for O3. Additionally, O3 vegetation damages demonstrate a decline (increase) by 1.3% (21.7%) in North China with higher O3 pollution (southern China with slight pollution) between 2017 and 2019. These findings highlight the essentiality for the synergistic control of PM2.5 and O3 based on regional differences in China.