Tower-based profiles of wintertime secondary organic aerosols in the urban boundary layer over Guangzhou.

Secondary organic aerosol (SOA) accounts for a large fraction of fine particulate matter (PM2.5), but the lack of vertical observations of SOA in the urban boundary layer (UBL) limits a comprehensive understanding of its sources and formation mechanisms. In this study, PM2.5 samples were simultaneously collected at 3 m, 118 m, and 488 m on the Canton Tower in Guangzhou during winter. Typical SOA tracers, including oxidation products of isoprene (SOAI), monoterpene (SOAM), sesquiterpene (SOAS), and toluene (ASOA), were investigated alongside meteorological parameters and gaseous/particulate pollutants. Total concentrations of SOA tracers showed an increasing trend with height, with daytime levels exceeding nighttime levels. C5-alkene triols and 2-methylglyceric acid displayed a significant increase with height, potentially affected by nighttime chemistry in the residual layer, determining the overall vertical trend of SOAI tracers. Concentrations of later-generation SOAM (SOAM_S) tracers also increased with height, while those of first-generation SOAM (SOAM_F) tracers decreased, indicating relatively aged SOAM in the upper layers. SOAS and ASOA tracers exhibited higher enhancement under polluted conditions, likely impacted by biomass burning and anthropogenic emissions. The yields of SOAI tracers varied with temperature in the vertical profile. The formation of SOAM_F tracers was negatively correlated with relative humidity, liquid water content, and pH, affecting their vertical distributions. The effect of O3 on SOA formation enhanced significantly with height, influenced by air mass transport, and likely contributed to the higher yields of SOA in the upper layer. However, at ground level, SOA formation was primarily driven by high local emissions of both NOx and volatile organic compounds. We also observed the roles of SO2 in SOA generation, particularly at 118 m. This study demonstrates the vertical diurnal characteristics of SOA tracers in the UBL, highlighting the varying effects of meteorological conditions and anthropogenic pollutants on SOA formation at different heights.

An overview for monitoring and prediction of pathogenic microorganisms in the atmosphere.

Corona virus disease 2019 (COVID-19) has exerted a profound adverse impact on human health. Studies have demonstrated that aerosol transmission is one of the major transmission routes of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Pathogenic microorganisms such as SARS-CoV-2 can survive in the air and cause widespread infection among people. Early monitoring of pathogenic microorganism transmission in the atmosphere and accurate epidemic prediction are the frontier guarantee for preventing large-scale epidemic outbreaks. Monitoring of pathogenic microorganisms in the air, especially in densely populated areas, may raise the possibility to detect viruses before people are widely infected and contain the epidemic at an earlier stage. The multi-scale coupled accurate epidemic prediction system can provide support for governments to analyze the epidemic situation, allocate health resources, and formulate epidemic response policies. This review first elaborates on the effects of the atmospheric environment on pathogenic microorganism transmission, which lays a theoretical foundation for the monitoring and prediction of epidemic development. Secondly, the monitoring technique development and the necessity of monitoring pathogenic microorganisms in the atmosphere are summarized and emphasized. Subsequently, this review introduces the major epidemic prediction methods and highlights the significance to realize a multi-scale coupled epidemic prediction system by strengthening the multidisciplinary cooperation of epidemiology, atmospheric sciences, environmental sciences, sociology, demography, etc. By summarizing the achievements and challenges in monitoring and prediction of pathogenic microorganism transmission in the atmosphere, this review proposes suggestions for epidemic response, namely, the establishment of an integrated monitoring and prediction platform for pathogenic microorganism transmission in the atmosphere.

COVID-19 transmission and control in land public transport: A literature review.

Land public transport is an important link within and between cities, and how to control the transmission of COVID-19 in land public transport is a critical issue in our daily lives. However, there are still many inconsistent opinions and views about the spread of SARS-CoV-2 in land public transport, which limits our ability to implement effective interventions. The purpose of this review is to overview the literature on transmission characteristics and routes of the epidemic in land public transport, as well as to investigate factors affecting its spread and provide feasible measures to mitigate the infection risk of passengers. We obtained 898 papers by searching the Web of Science, Pubmed, and WHO global COVID database by keywords, and finally selected 45 papers that can address the purpose of this review. Land public transport is a high outbreak area for COVID-19 due to characteristics like crowding, inadequate ventilation, long exposure time, and environmental closure. Different from surface touch transmission and drop spray transmission, aerosol inhalation transmission can occur not only in short distances but also in long distances. Insufficient ventilation is the most important factor influencing long-distance aerosol transmission. Other transmission factors (e.g., interpersonal distance, relative orientation, and ambient conditions) should be noticed as well, which have been summarized in this paper. To address various influencing factors, it is essential to suggest practical and efficient preventive measures. Among these, increased ventilation, particularly the fresh air (i.e., natural ventilation), has proven to effectively reduce indoor infection risk. Many preventive measures are also effective, such as enlarging social distance, avoiding face-to-face orientation, setting up physical partitions, disinfection, avoiding talking, and so on. As research on the epidemic has intensified, people have broken down many perceived barriers, but more comprehensive studies on monitoring systems and prevention measures in land public transport are still needed.

Applicability of evaluation metrics/schemes for human health burden attributable to regional ozone pollution: A case study in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), South China.

This is a study to identify the applicable/preferable short- and long-term metrics/schemes to evaluate the premature mortality attributable to the ozone pollution in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), one of the most representative populous ozone pollution regions in China, by comprehensively accounting the uncertainty sources. The discrepancy between the observation and the CAQRA reanalysis datasets (2013-2019) was investigated in terms of the concentration variation pattern, which determines the exposure metric change. A set of domestic short-term C-R coefficients for the all-age population were integrated using the meta-analysis respectively corresponding to the metrics of MDA1, MDA8, and Daily average. The dataset-based deviations of the short-term attributable factors (AFs) and their corresponding premature mortalities were respectively about 16.9 ± 13.3 % and <5 % based on MDA8, much smaller than other two metrics; and the MDA8-based evaluation results were the most sensitive to the deteriorative ozone pollution, with the maximum upward trends of 0.095-0.129 %/year. Accordingly, MDA8 was recognized as the most applicable short-term metric. For the long-term exposure, the domestic summer metric SMDA8 could not exactly represent the peak-season ozone maximum level in the GBA, with the deviation from 6MMDA8 as much as 30 %. By considering the ability of metric to represent the peak-season ozone, the relatively smaller dataset-based discrepancies of AFs (6MMDA8-WHO2021: 23.3 ± 16.9 %, AMDA8-T2016: 20.7 ± 15.8 %) and the attributable premature mortalities (6MMDA8-WHO2021: 5 %, AMDA8-T2016: 8 %), and the higher sensitivity of the evaluation results to the deteriorative ozone pollution (6MMDA8-WHO2021: 0.13 %;year, p = 0.01; AMDA8-T2016: 0.15 %/year, p = 0.03), the schemes of 6MMDA8-WHO2021 and AMDA8-T2016 were recognized relatively more preferable for the adult (≥25-year) long-term evaluation. Based on the recognized metric/schemes, the central and the eastern PRE areas of higher NO2 level in the GBA were experiencing the highest health burdens from 2013 to 2019.

Water-energy-vegetation nexus explain global geographical variation in surface urban heat island intensity.

Surface urban heat island (SUHI) is a key climate risk associated with urbanization. Previous case studies have suggested that precipitation (water), radiation (energy), and vegetation have important effects on urban warming, but there is a lack of research that combines these factors to explain the global geographic variation in SUHI intensity (SUHII). Here, we utilize remotely sensed and gridded datasets to propose a new water-energy-vegetation nexus concept that explains the global geographic variation of SUHII across four climate zones and seven major regions. We found that SUHII and its frequency increase from arid zones (0.36 ± 0.15 °C) to humid zones (2.28 ± 0.10 °C), but become weaker in the extreme humid zones (2.18 ± 0.15 °C). We revealed that from semi-arid/humid to humid zones, high precipitation is often coupled with high incoming solar radiation. The increased solar radiation can directly enhance the energy in the area, leading to higher SUHII and its frequency. Although solar radiation is high in arid zones (mainly in West, Central, and South Asia), water limitation leads to sparse natural vegetation, suppressing the cooling effect in rural areas and resulting in lower SUHII. In extreme humid regions (mainly in tropical areas), incoming solar radiation tends to flatten out, which, coupled with increased vegetation as hydrothermal conditions become more favorable, leads to more latent heat and reduces the intensity of SUHI. Overall, this study offers empirical evidence that the water-energy-vegetation nexus highly explains the global geographic variation of SUHII. The results can be used by urban planners seeking optimal SUHI mitigation strategies and for climate change modeling work.

Influence of natural ventilation design on the dispersion of pathogen-laden droplets in a coach bus.

Natural ventilation is an energy-efficient design approach to reduce infection risk (IR), but its optimized design in a coach bus environment is less studied. Based on a COVID-19 outbreak in a bus in Hunan, China, the indoor-outdoor coupled CFD modeling approach is adopted to comprehensively explore how optimized bus natural ventilation (e.g., opening/closing status of front/middle/rear windows (FW/MW/RW)) and ceiling wind catcher (WCH) affect the dispersion of pathogen-laden droplets (tracer gas, 5 µm, 50 µm) and IR. Other key influential factors including bus speed, infector's location, and ambient temperature (Tref) are also considered. Buses have unique natural ventilation airflow patterns: from bus rear to front, and air change rate per hour (ACH) increases linearly with bus speed. When driving at 60 km/h, ACH is only 6.14 h-1 and intake fractions of tracer gas (IFg) and 5 µm droplets (IFd) are up to 3372 ppm and 1394 ppm with ventilation through leakages on skylights and no windows open. When FW and RW are both open, ACH increases by 43.5 times to 267.50 h-1, and IFg and IFd drop rapidly by 1-2 orders of magnitude compared to when no windows are open. Utilizing a wind catcher and opening front windows significantly increases ACH (up to 8.8 times) and reduces IF (5-30 times) compared to only opening front windows. When the infector locates at the bus front with FW open, IFg and IFd of all passengers are <10 ppm. More droplets suspend and further spread in a higher Tref environment. It is recommended to open two pairs of windows or open front windows and utilize the wind catcher to reduce IR in coach buses.

A portable acetylcholinesterase-based electrochemical sensor for field detection of organophosphorus.

A portable acetylcholinesterase (AChE)-based electrochemical sensor based on a screen-printed carbon electrode (SPCE) and a miniature potentiostat was constructed for the rapid field detection of organophosphorus pesticides (OPs). Graphene (GR) and gold nanoparticles (AuNPs) were successively introduced onto SPCE for surface modification. Due to the synergistic effect of the two nanomaterials, the signal of the sensor has a significant enhancement. Take isocarbophos (ICP) as a model for chemical warfare agents (CAWs) and Ops; the SPCE/GR/AuNPs/AChE/Nafion sensor shows a wider linear range (0.1-2000 µg L-1), and a lower limit of detection (0.012 µg L-1) than SPCE/AChE/Nafion and SPCE/GR/AChE/Nafion sensors. Tests in actual fruit and tap water samples also yielded satisfactory results. Therefore, the proposed method can be used as a simple and cost-effective strategy for construction of portable electrochemical sensors for OP field detection.

Particle Deposition in Large-Scale Human Tracheobronchial Airways Predicted by Single-Path Modelling.

The health effects of particles are directly related to their deposition patterns (deposition site and amount) in human airways. However, estimating the particle trajectory in a large-scale human lung airway model is still a challenge. In this work, a truncated single-path, large-scale human airway model (G3-G10) with a stochastically coupled boundary method were employed to investigate the particle trajectory and the roles of their deposition mechanisms. The deposition patterns of particles with diameters (dp) of 1-10 µm are investigated under various inlet Reynolds numbers (Re = 100-2000). Inertial impaction, gravitational sedimentation, and combined mechanism were considered. With the increasing airway generations, the deposition of smaller particles (dp < 4 µm) increased due to gravitational sedimentation, while that of larger particles decreased due to inertial impaction. The obtained formulas of Stokes number and Re can predict the deposition efficiency due to the combined mechanism in the present model, and the prediction can be used to assess the dose-effect of atmospheric aerosols on the human body. Diseases in deeper generations are mainly attributed to the deposition of smaller particles under lower inhalation rates, while diseases at the proximal generations mainly result from the deposition of larger particles under higher inhalation rates.

Predominance of inhalation route in short-range transmission of respiratory viruses: Investigation based on computational fluid dynamics.

During the Coronavirus disease 2019 pandemic, short-range virus transmission has been observed to have a higher risk of causing infection than long-range virus transmission. However, the roles played by the inhalation and large droplet routes cannot be distinguished in practice. A recent analytical study revealed the predominance of short-range inhalation over the large droplet spray route as causes of respiratory infections. In the current study, short-range exposure was analyzed via computational fluid dynamics (CFD) simulations using a discrete phase model. Detailed facial membranes, including eyes, nostrils, and a mouth, were considered. In CFD simulations, there is no need for a spherical approximation of the human head for estimating deposition nor the "anisokinetic aerosol sampling" approximation for estimating inhalation in the analytical model. We considered two scenarios (with two spheres [Scenario 1] and two human manikins [Scenario 2]), source-target distances of 0.2 to 2 m, and droplet diameters of 3 to 1,500 µm. The overall CFD exposure results agree well with data previously obtained from a simple analytical model. The CFD results confirm the predominance of the short-range inhalation route beyond 0.2 m for expiratory droplets smaller than 50 µm during talking and coughing. A critical droplet size of 87.5 µm was found to differentiate droplet behaviors. The number of droplets deposited on the target head exceeded those exposed to facial membranes, which implies a risk of exposure through the immediate surface route over a short range. Electronic Supplementary Material ESM: the Supplementary Materials are available in the online version of this article at 10.1007/s12273-022-0968-y.

Conversational head movement decreases close-contact exposure to expired respiratory droplets.

People constantly move their heads during conversation, as such movement is an important non-verbal mode of communication. Head movement alters the direction of people's expired air flow, therefore affecting their conversational partners' level of exposure. Nevertheless, there is a lack of understanding of the mechanism whereby head movement affects people's exposure. In this study, a dynamic meshing method in computational fluid dynamics was used to simulate the head movement of a human-shaped thermal manikin. Droplets were released during the oral expiration periods of the source manikin, during which it was either motionless, was shaking its head or was nodding its head, while the head of a face-to-face target manikin remained motionless. The results indicate that the target manikin had a high level of exposure to respiratory droplets when the source manikin was motionless, whereas the target manikin's level of exposure was significantly reduced when the source manikin was shaking or nodding its head. The source manikin had the highest level of self-exposure when it was nodding its head and the lowest level of self-exposure when its head was motionless. People's level of exposure during close contact is highly variable, highlighting the need for further investigations in more realistic conversational scenarios.

Aqueous-phase chemistry of atmospheric phenolic compounds: A critical review of laboratory studies.

Phenolic compounds (PhCs) are crucial atmospheric pollutants typically emitted by biomass burning and receive particular concerns considering their toxicity, light-absorbing properties, and involvement in secondary organic aerosol (SOA) formation. A comprehensive understanding of the transformation mechanisms on chemical reactions in atmospheric waters (i.e., cloud/fog droplets and aerosol liquid water) is essential to predict more precisely the atmospheric fate and environmental impacts of PhCs. Laboratory studies play a core role in providing the fundamental knowledge of aqueous-phase chemical transformations in the atmosphere. This article critically reviews recent laboratory advances in SOA formation from the aqueous-phase reactions of PhCs. It focuses primarily on the aqueous oxidation of PhCs driven by two atmospheric reactive species: OH radicals and triplet excited state organics, including the important chemical kinetics and mechanisms. The effects of inorganic components (i.e., nitrate and nitrite) and transition metal ions (i.e., soluble iron) are highlighted on the aqueous-phase transformation of PhCs and on the properties and formation mechanisms of SOA. The review is concluded with the current knowledge gaps and future perspectives for a better understanding of the atmospheric transformation and SOA formation potential of PhCs.

Thermal perception and lung function: a panel study in young adults with exercise under high outdoor temperature.

It has been observed that high temperature exposure is associated with a reduction in lung function and some possible biological mechanisms have been suggested. However, it is unclear if thermal perception plays a role in the association. From September 3rd to 15th, 2018, in Guangzhou, China, we repeatedly measured daily thermal perception and lung function among 126 participants with outdoor military training. We performed a linear mixed model and stratified analyses by the origin of students, gender, and the training period to evaluate the effects of thermal perception on lung function. A total of 399 measurements were collected. Per vote increase in thermal sensation vote towards the "hot" direction was associated with a - 0.04 L (95% CI: - 0.08 to - 0.01) decrease in forced vital capacity (FVC), and - 0.04 L (95% CI: - 0.08 to - 0.01) decrease in forced expiratory volume in 1 s (FEV1). Per grade increase towards the "very uncomfortable" direction for thermal comfort vote was associated with an increased percentage of forced expiratory volume in 1 s (FEV1%) by 1.52% (95% CI: 0.18 to 2.86). For thermal preference, with preferred cooler vote increased by one level, FVC and FEV1 decreased by - 0.05 L/s (95% CI: - 0.08 to - 0.02) and - 0.05L/s (95% CI: - 0.08 to - 0.02), respectively. The effects of thermal perception on lung function were stronger among non-local and in the first week of training. Our study suggests that in the same high-temperature environment, thermal perception is associated with lung function, even in healthy adults.

Transcutaneous auricular vagus nerve stimulation in poststroke cognitive impairment: protocol for a randomised controlled trial.

BACKGROUND: As one of the most common stroke sequelae, poststroke cognitive impairment significantly impacts 17.6%-83% of survivors, affecting their rehabilitation, daily living and quality of life. Improving cognitive abilities among patients in stroke recovery is therefore critical and urgent. Transcutaneous auricular vagus nerve stimulation (TAVNS) is a non-invasive, safe, cost-effective treatment with great potential for improving the cognitive function of poststroke patients. This clinical research will evaluate the effectiveness, and help elucidate the possible underlying mechanisms, of TAVNS for improving poststroke cognitive function. METHODS AND ANALYSIS: A single-centre, parallel-group, allocation concealment, assessor-blinded randomised controlled clinical trial. We will allocate 88 recruited participants to the TAVNS or sham group for an intervention that will run for 8 weeks, 5 days per week with twice daily sessions lasting 30 min each. Blood tests will be performed and questionnaires issued at baseline and 8-week and 12 week follow-ups. Primary outcomes will be changes in cognitive function scores. Secondary outcomes will be changes in activities of daily living, quality of life and serum oxidative stress indicators. ETHICS AND DISSEMINATION: The Ethics Committee of the First Affiliated Hospital of Hunan University of Chinese Medicine has approved the protocol (No. HN-LL-YJSLW-2022200). Findings will be published in peer-reviewed academic journals and presented at scientific conferences. TRIAL REGISTRATION NUMBER: ChiCTR2200057808.

Role of pathogen-laden expiratory droplet dispersion and natural ventilation explaining a COVID-19 outbreak in a coach bus.

The influencing mechanism of droplet transmissions inside crowded and poorly ventilated buses on infection risks of respiratory diseases is still unclear. Based on experiments of one-infecting-seven COVID-19 outbreak with an index patient at bus rear, we conducted CFD simulations to investigate integrated effects of initial droplet diameters(tracer gas, 5 µm, 50 µm and 100 µm), natural air change rates per hour(ACH = 0.62, 2.27 and 5.66 h-1 related to bus speeds) and relative humidity(RH = 35% and 95%) on pathogen-laden droplet dispersion and infection risks. Outdoor pressure difference around bus surfaces introduces natural ventilation airflow entering from bus-rear skylight and leaving from the front one. When ACH = 0.62 h-1(idling state), the 30-min-exposure infection risk(TIR) of tracer gas is 15.3%(bus rear) - 11.1%(bus front), and decreases to 3.1%(bus rear)-1.3%(bus front) under ACH = 5.66 h-1(high bus speed).The TIR of large droplets(i.e., 100 µm/50 µm) is almost independent of ACH, with a peak value(∼3.1%) near the index patient, because over 99.5%/97.0% of droplets deposit locally due to gravity. Moreover, 5 µm droplets can disperse further with the increasing ventilation. However, TIR for 5 µm droplets at ACH = 5.66 h-1 stays relatively small for rear passengers(maximum 0.4%), and is even smaller in the bus middle and front(<0.1%). This study verifies that differing from general rooms, most 5 µm droplets deposit on the route through the long-and-narrow bus space with large-area surfaces(L∼11.4 m). Therefore, tracer gas can only simulate fine droplet with little deposition but cannot replace 5-100 µm droplet dispersion in coach buses.

Influence of urban spatial and socioeconomic parameters on PM2.5 at subdistrict level: A land use regression study in Shenzhen, China.

The intraurban distribution of PM2.5 concentration is influenced by various spatial, socioeconomic, and meteorological parameters. This study investigated the influence of 37 parameters on monthly average PM2.5 concentration at the subdistrict level with Pearson correlation analysis and land-use regression (LUR) using data from a subdistrict-level air pollution monitoring network in Shenzhen, China. Performance of LUR models is evaluated with leave-one-out-cross-validation (LOOCV) and holdout cross-validation (holdout CV). Pearson correlation analysis revealed that Normalized Difference Built-up Index, artificial land fraction, land surface temperature, and point-of-interest (POI) numbers of factories and industrial parks are significantly positively correlated with monthly average PM2.5 concentrations, while Normalized Difference Vegetation Index and Green View Factor show significant negative correlations. For the sparse national stations, robust LUR modelling may rely on a priori assumptions in direction of influence during the predictor selection process. The month-by-month spatial regression shows that RF models for both national stations and all stations show significantly inflated mean values of R2 compared with cross-validation results. For MLR models, inflation of both R2 and R2CV was detected when using only national stations and may indicate the restricted ability to predict spatial distribution of PM2.5 levels. Inflated within-sample R2 also exist in the spatiotemporal LUR models developed with only national stations, although not as significant as spatial LUR models. Our results suggest that a denser subdistrict level air pollutant monitoring network may improve the accuracy and robustness in intraurban spatial/spatiotemporal prediction of PM2.5 concentrations.

Numerical Investigations of Urban Pollutant Dispersion and Building Intake Fraction with Various 3D Building Configurations and Tree Plantings.

Rapid urbanisation and rising vehicular emissions aggravate urban air pollution. Outdoor pollutants could diffuse indoors through infiltration or ventilation, leading to residents' exposure. This study performed CFD simulations with a standard k-ε model to investigate the impacts of building configurations and tree planting on airflows, pollutant (CO) dispersion, and personal exposure in 3D urban micro-environments (aspect ratio = H/W = 30 m, building packing density λp = λf = 0.25) under neutral atmospheric conditions. The numerical models are well validated by wind tunnel data. The impacts of open space, central high-rise building and tree planting (leaf area density LAD= 1 m2/m3) with four approaching wind directions (parallel 0° and non-parallel 15°, 30°, 45°) are explored. Building intake fraction is adopted for exposure assessment. The change rates of demonstrate the impacts of different urban layouts on the traffic exhaust exposure on residents. The results show that open space increases the spatially-averaged velocity ratio (VR) for the whole area by 0.40−2.27%. Central high-rise building (2H) can increase wind speed by 4.73−23.36% and decrease the CO concentration by 4.39−23.00%. Central open space and high-rise building decrease under all four wind directions, by 6.56−16.08% and 9.59−24.70%, respectively. Tree planting reduces wind speed in all cases, raising by 14.89−50.19%. This work could provide helpful scientific references for public health and sustainable urban planning.

Predominant airborne transmission and insignificant fomite transmission of SARS-CoV-2 in a two-bus COVID-19 outbreak originating from the same pre-symptomatic index case.

The number of people infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to increase worldwide, but despite extensive research, there remains significant uncertainty about the predominant routes of SARS-CoV-2 transmission. We conducted a mechanistic modeling and calculated the exposure dose and infection risk of each passenger in a two-bus COVID-19 outbreak in Hunan province, China. This outbreak originated from a single pre-symptomatic index case. Some human behavioral data related to exposure including boarding and alighting time of some passengers and seating position and mask wearing of all passengers were obtained from the available closed-circuit television images/clips and/or questionnaire survey. Least-squares fitting was performed to explore the effect of effective viral load on transmission risk, and the most likely quanta generation rate was also estimated. This study reveals the leading role of airborne SARS-CoV-2 transmission and negligible role of fomite transmission in a poorly ventilated indoor environment, highlighting the need for more targeted interventions in such environments. The quanta generation rate of the index case differed by a factor of 1.8 on the two buses and transmission occurred in the afternoon of the same day, indicating a time-varying effective viral load within a short period of five hours.

Insufficient ventilation led to a probable long-range airborne transmission of SARS-CoV-2 on two buses.

Uncertainty remains on the threshold of ventilation rate in airborne transmission of SARS-CoV-2. We analyzed a COVID-19 outbreak in January 2020 in Hunan Province, China, involving an infected 24-year-old man, Mr. X, taking two subsequent buses, B1 and B2, in the same afternoon. We investigated the possibility of airborne transmission and the ventilation conditions for its occurrence. The ventilation rates on the buses were measured using a tracer-concentration decay method with the original driver on the original route. We measured and calculated the spread of the exhaled virus-laden droplet tracer from the suspected index case. Ten additional passengers were found to be infected, with seven of them (including one asymptomatic) on B1 and two on B2 when Mr. X was present, and one passenger infected on the subsequent B1 trip. B1 and B2 had time-averaged ventilation rates of approximately 1.7 and 3.2 L/s per person, respectively. The difference in ventilation rates and exposure time could explain why B1 had a higher attack rate than B2. Airborne transmission due to poor ventilation below 3.2 L/s played a role in this two-bus outbreak of COVID-19.

Effects of tree plantings and aspect ratios on pedestrian visual and thermal comfort using scaled outdoor experiments.

Urban trees ameliorate heat stress for urban dwellers. However, it is difficult to quantitatively assess the integrated impacts of tree planting and street layouts on visual and thermal comfort in simulations and urban field experiments. We conducted scaled outdoor experiments in Guangzhou to investigate the influence of tree plantings on pedestrian visual and thermal comfort in street canyons with various aspect ratios (H/W = 1, 2, 3; H = 1.2 m). We considered the effects of tree crown covers (big and small crown) and tree planting densities (ρ = 1, 0.5) on pedestrian illuminance level and two thermal comfort indices (Physiological Equivalent Temperature: PET and Index of Thermal Stress: ITS). When ρ = 1, trees in most cases reduce pedestrian illuminance (maximum 140.0klux) and improve visual comfort. Decreasing ρ from 1 to 0.5 increases the illuminance (maximum 179.5klux) in the streets with big crown trees (H/W = 1, 2) and in the street with small crown trees (H/W = 2). When ρ = 1 (H/W = 1, 2), big crown trees decrease the peak daytime PET (by about 4.0 °C) and ITS (by about 285 W). Small crown trees (ρ = 1, H/W = 1, 2) produce a warming effect on peak daytime PET (2.0-3.0 °C), but a reduction in ITS is observed when H/W = 2, 3. After reducing ρ from 1 to 0.5, big crown trees increase peak daytime thermal stress according to both indices when H/W = 1, 2. Small crown trees exhibit a similar PET cycle between ρ = 0.5 and ρ = 1 across various H/W, but their daytime reduction of ITS is less effective when ρ = 0.5 (H/W = 2). The discrepancies between PET and ITS are attributed to their different approaches to modelling radiation fluxes. The narrower the street, the lower the illuminance, PET, and ITS, while their increases caused by reduced ρ are limited in narrow streets. Our study informs some potential urban tree planting strategies and produces high-quality validation data for numerical simulations and theoretical models.

Regional modeling of secondary organic aerosol formation over eastern China: The impact of uptake coefficients of dicarbonyls and semivolatile process of primary organic aerosol.

Capturing the secondary organic aerosol (SOA) concentration using the chemical transport model is difficult due to a large knowledge gap of its formation mechanism. Previous studies demonstrated the uptake of dicarbonyls and semivolatile process of primary organic aerosol (POA) emissions are the significant sources of SOA. However, the uptake coefficients of dicarbonyls have large uncertainties and the SOA from the semivolatile process of POA emission remains unclear. We applied the revised reactive uptake parameterization, with "salting effects" for dicarbonyls, and updated approaches for POA to the Community Multiscale Air Quality Modeling System (CMAQ) simulations for October 2014 to study their impacts on modeling the SOA formation over eastern China. We introduce a method of quantifying crystalized or deliquescent aerosols to further improve the parameterization. The revised glyoxal uptake coefficients results in higher glyoxal SOA in the Beijing-Tianjin-Hebei region, where is typically under low relative humidity (RH) and high aerosol pH conditions. It gives lower glyoxal SOA in the Pearl River Delta region, where is typically under high RH and low pH conditions. The updated parameterization gives negligible methylglyoxal SOA due to the low uptake coefficients. The implementation of semivolatile process of POA and the approach for potential SOA from combustion sources will largely decrease the predicted POA and increase the modeled SOA concentrations over eastern China. The increased SOA from POA emissions could improve the model performance for organic carbon and SOA. It slightly improves the performance in PM2.5 modeling by compensating the reduction of modeled POA. This study indicates the mixed impact of a parameterization considering "salting effects" on modeling the dicarbonyls SOA in key regions of eastern China. It also demonstrates the improved performance by implementing the POA approaches in aerosol modeling using CMAQ. Meanwhile, the uncertainty in the revised reactive uptake parameterization and POA approaches is discussed.