Global population exposure to landscape fire air pollution from 2000 to 2019.

Wildfires are thought to be increasing in severity and frequency as a result of climate change1-5. Air pollution from landscape fires can negatively affect human health4-6, but human exposure to landscape fire-sourced (LFS) air pollution has not been well characterized at the global scale7-23. Here, we estimate global daily LFS outdoor fine particulate matter (PM2.5) and surface ozone concentrations at 0.25° × 0.25° resolution during the period 2000-2019 with the help of machine learning and chemical transport models. We found that overall population-weighted average LFS PM2.5 and ozone concentrations were 2.5 µg m-3 (6.1% of all-source PM2.5) and 3.2 µg m-3 (3.6% of all-source ozone), respectively, in 2010-2019, with a slight increase for PM2.5, but not for ozone, compared with 2000-2009. Central Africa, Southeast Asia, South America and Siberia experienced the highest LFS PM2.5 and ozone concentrations. The concentrations of LFS PM2.5 and ozone were about four times higher in low-income countries than in high-income countries. During the period 2010-2019, 2.18 billion people were exposed to at least 1 day of substantial LFS air pollution per year, with each person in the world having, on average, 9.9 days of exposure per year. These two metrics increased by 6.8% and 2.1%, respectively, compared with 2000-2009. Overall, we find that the global population is increasingly exposed to LFS air pollution, with socioeconomic disparities.

Toward Standardized Aerovirology: A Critical Review of Existing Results and Methodologies.

Understanding the airborne survival of viruses is important for public health and epidemiological modeling and potentially to develop mitigation strategies to minimize the transmission of airborne pathogens. Laboratory experiments typically involve investigating the effects of environmental parameters on the viability or infectivity of a target airborne virus. However, conflicting results among studies are common. Herein, the results of 34 aerovirology studies were compared to identify links between environmental and compositional effects on the viability of airborne viruses. While the specific experimental apparatus was not a factor in variability between reported results, it was determined that the experimental procedure was a major factor that contributed to discrepancies in results. The most significant contributor to variability between studies was poorly defined initial viable virus concentration in the aerosol phase, causing many studies to not measure the rapid inactivation, which occurs quickly after particle generation, leading to conflicting results. Consistently, studies that measured their reference airborne viability minutes after aerosolization reported higher viability at subsequent times, which indicates that there is an initial loss of viability which is not captured in these studies. The composition of the particles which carry the viruses was also found to be important in the viability of airborne viruses; however, the mechanisms for this effect are unknown. Temperature was found to be important for aerosol-phase viability, but there is a lack of experiments that directly compare the effects of temperature in the aerosol phase and the bulk phase. There is a need for repeated measurements between different research groups under identical conditions both to assess the degree of variability between studies and also to attempt to better understand already published data. Lack of experimental standardization has hindered the ability to quantify the differences between studies, for which we provide recommendations for future studies. These recommendations are as follows: measuring the reference airborne viability using the "direct method"; use equipment which maximizes time resolution; quantify all losses appropriately; perform, at least, a 5- and 10-min sample, if possible; report clearly the composition of the virus suspension; measure the composition of the gas throughout the experiment. Implementing these recommendations will address the most significant oversights in the existing literature and produce data which can more easily be quantitatively compared.

Unraveling Cross-Organ Impacts of Airborne Pollutants: A Multiomics Study on Respiratory Exposure and Gastrointestinal Health.

Poor air quality is increasingly linked to gastrointestinal diseases, suggesting a potential correlation with human intestine health. However, this relationship remains largely unexplored due to limited research. This study used a controlled mouse model exposed to cooking oil fumes (COFs) and metagenomics, transcriptomics, and metabolomics to elucidate interactions between intestine microbiota and host metabolism under environmental stress. Our findings reveal that short-term COF inhalation induces pulmonary inflammation within 3 days and leads to gastrointestinal disturbances, elucidating a pathway connecting respiratory exposure to intestinal dysfunction. The exposure intensity significantly correlates with changes in intestinal tissue integrity, microbial composition, and metabolic function. Extended exposure of 7 days disrupts intestine microbiota and alters tryptophan metabolism, with further changes observed after 14 days, highlighting an adaptive response. These results highlight the vulnerability of intestinal health to airborne pollutants and suggest a pathway through which inhaled pollutants may affect distant organ systems.

Diverse Metabolic Effects of Cooking Oil Fume from Four Edible Oils on Human BEAS-2B Cells: Implications for Health Guidelines.

The 2021 WHO guidelines stress the importance of measuring ultrafine particles using particle number concentration (PNC) for health assessments. However, commonly used particle metrics such as aerodynamic diameter and number concentrations do not fully capture the diverse chemical makeup of complex particles. To address this issue, our study used high-throughput mass spectrometry to analyze the properties of cooking oil fumes (COFs) in real time and evaluate their impact on BEAS-2B cell metabolism. Results showed insignificant differences in COF number size distributions between soybean oil and olive oil (peak concentrations of 5.20 × 105/cm3), as well as between corn oil and peanut oil (peak concentrations of 4.35 × 105/cm3). Despite the similar major chemical components among the four COFs, variations in metabolic damage were observed, indicating that the relatively small amount of chemical components of COFs can also influence particle behavior within the respiratory system, thereby impacting biological responses. Additionally, interactions between accompanying gaseous COFs and particles may alter their chemical composition through various mechanisms, introducing additional chemicals and modifying existing proportions. Hence, the chemical composition and gaseous components of COFs hold equal importance to the particle number concentration (PNC) when assessing their impact on human health. The absence of these considerations in the current guidelines underscores a research gap. It is imperative to acknowledge that for a more comprehensive approach to safeguarding public health, guidelines must be regularly updated to reflect new scientific findings and robust epidemiological evidence.

Long-term exposure to ozone and sleep disorders in children: A multicity study in China.

Evidence regarding the link between long-term ambient ozone (O3) exposure and childhood sleep disorders is little. This study aims to examine the associations between long-term exposure to O3 and sleep disorders in children. We conducted a population-based cross-sectional survey, including 185,428 children aged 6-18 years in 173 schools across 14 Chinese cities during 2012 and 2018. Parents or guardians completed a checklist using Sleep Disturbance Scale for Children, and O3 exposure at residential and school addresses was estimated using a satellite-based spatiotemporal model. We used generalized linear mixed models to test the associations with adjustment for factors including socio-demographic variables, lifestyle, meteorology and multiple pollutants. Mean concentrations of O3, particulate matter with diameters ≤2.5 mm (PM2.5) and nitrogen dioxide (NO2) were 89.0 µg/m3, 42.5 µg/m3 and 34.4 µg/m3, respectively. O3 and NO2 concentrations were similar among provinces, while PM2.5 concentration varied significantly among provinces. Overall, 19.4% of children had at least one sleep disorder. Long-term exposure to O3 was positively associated with odds of sleep disorders for all subtypes. For example, each interquartile increment in home-school O3 concentrations was associated with a higher odds ratio for global sleep disorder, at 1.22 (95% confidence interval: 1.18, 1.26). Similar associations were observed for sleep disorder subtypes. The associations remained similar after adjustment for PM2.5 and NO2. Moreover, these associations were heterogeneous regionally, with more prominent associations among children residing in southeast region than in northeast and northwest regions in China. We concluded that long-term exposure to O3 is positively associated with risks of childhood sleep disorders. These associations varied by geographical region of China.

Global, regional, and national burden of ischemic heart disease attributable to ambient PM2.5 from 1990 to 2019: An analysis for the global burden of disease study 2019.

Information on the spatio-temporal patterns of the burden of ischemic heart disease (IHD) caused by ambient ambient fine particulate matter (PM2.5) in the global level is needed to prioritize the control of ambient air pollution and prevent the burden of IHD. The Global Burden of Disease Study (GBD) 2019 provides data on IHD attributable to ambient PM2.5. The IHD burden and mortality attributable to ambient PM2.5 were analyzed by year, age, gender, socio-demographic index (SDI) level, geographical region and country. Estimated annual percentage change (EAPC) was calculated to estimate the temporal trends of age-standardized mortality rate (ASMR) and age-standardized disability-adjusted life years rate (ASDR) from 1990 to 2019. Globally, the ASMR and ASDR for ambient PM2.5-related IHD tended to level off generally, with EAPC of -0.03 (95% CI: -0.06, 0.12) and 0.3 (95% CI: 0.22, 0.37), respectively. In the past 30 years, there were obvious differences in the trend of burden change among different regions. A highest increased burden was estimated in low-middle SDI region (EAPC of ASMR: 3.73 [95% CI: 3.56, 3.9], EAPC of ASDR: 3.83 [95% CI: 3.64, 4.02]). In contrast, the burden in high SDI region (EAPC of ASMR: -4.48 [95% CI: -4.6, -4.35], EAPC of ASDR: -3.98 [95% CI: -4.12, -3.85]) has declined most significantly. Moreover, this burden was higher among men and older populations. EAPCs of the ASMR (R = -0.776, p < 0.001) and ASDR (R = -0.781, p < 0.001) of this burden had significant negative correlations with the countries' SDI level. In summary, although trends in the global burden of IHD attributable to ambient PM2.5 are stabilizing, but this burden has shifted from high SDI countries to middle and low SDI countries, especially among men and elderly populations. To reduce this burden, the air pollution management prevention need to be further strengthened, especially among males, older populations, and middle and low SDI countries.

Predicting the effect of confinement on the COVID-19 spread using machine learning enriched with satellite air pollution observations.

The real-time monitoring of reductions of economic activity by containment measures and its effect on the transmission of the coronavirus (COVID-19) is a critical unanswered question. We inferred 5,642 weekly activity anomalies from the meteorology-adjusted differences in spaceborne tropospheric NO2 column concentrations after the 2020 COVID-19 outbreak relative to the baseline from 2016 to 2019. Two satellite observations reveal reincreasing economic activity associated with lifting control measures that comes together with accelerating COVID-19 cases before the winter of 2020/2021. Application of the near-real-time satellite NO2 observations produces a much better prediction of the deceleration of COVID-19 cases than applying the Oxford Government Response Tracker, the Public Health and Social Measures, or human mobility data as alternative predictors. A convergent cross-mapping suggests that economic activity reduction inferred from NO2 is a driver of case deceleration in most of the territories. This effect, however, is not linear, while further activity reductions were associated with weaker deceleration. Over the winter of 2020/2021, nearly 1 million daily COVID-19 cases could have been avoided by optimizing the timing and strength of activity reduction relative to a scenario based on the real distribution. Our study shows how satellite observations can provide surrogate data for activity reduction during the COVID-19 pandemic and monitor the effectiveness of containment to the pandemic before vaccines become widely available.

Coronavirus Disease 2019 and Airborne Transmission: Science Rejected, Lives Lost. Can Society Do Better?

This is an account that should be heard of an important struggle: the struggle of a large group of experts who came together at the beginning of the COVID-19 pandemic to warn the world about the risk of airborne transmission and the consequences of ignoring it. We alerted the World Health Organization about the potential significance of the airborne transmission of SARS-CoV-2 and the urgent need to control it, but our concerns were dismissed. Here we describe how this happened and the consequences. We hope that by reporting this story we can raise awareness of the importance of interdisciplinary collaboration and the need to be open to new evidence, and to prevent it from happening again. Acknowledgement of an issue, and the emergence of new evidence related to it, is the first necessary step towards finding effective mitigation solutions.

Dynamics and Viability of Airborne Respiratory Syncytial Virus under Various Indoor Air Conditions.

The factors governing the viability of airborne viruses embedded within respiratory particles are not well understood. This study aimed to investigate the relative humidity (RH)-dependent viability of airborne respiratory syncytial virus (RSV) in simulated respiratory particles suspended in various indoor air conditions. We tested airborne RSV viability in three static indoor air conditions, including sub-hysteresis (RH < 39%), hysteresis (39% < RH < 65%), and super-hysteresis (RH > 65%) air as well as in three dynamic indoor air conditions, including the transitions between the static conditions. The dynamic conditions were hysteresis → super-hysteresis → hysteresis, sub-hysteresis → hysteresis, and super-hysteresis → hysteresis. We found that after 45 min of particle aging in static conditions, the viability of RSV in sub-hysteresis, hysteresis, and super-hysteresis air was 0.72% ± 0.06%, 0.03% ± 0.006%, and 0.27% ± 0.008%, respectively. After 45 min of aging in dynamic conditions, the RSV viability decreased for particles that remained in a liquid (deliquesced) state during aging when compared with particles in a solid (effloresced) state. The decreased viability of airborne RSV for deliquesced particles is consistent with prolonged exposure to elevated aqueous solutes. These results represent the first measurements of the survival of airborne RSV over particle aging time, with equal viability in low, intermediate, and high RHs at 5 and 15 min and a V-shaped curve after 45 min.

Characterization of Biodiesel and Diesel Combustion Particles: Chemical Composition, Lipid Metabolism, and Implications for Health and Environment.

Biodiesel, derived from alkyl esters of vegetable oils or animal fats, has gained prominence as a greener alternative to diesel due to its reduced particle mass. However, it remains debatable whether biodiesel exposure has more severe health issues than diesel. This study performed high-resolution mass spectrometry to examine the detailed particle chemical compositions and lipidomics analysis of human lung epithelial cells treated with emissions from biodiesel and diesel fuels. Results show the presence of the peak substances of CHO compounds in biodiesel combustion that contain a phthalate ester (PAEs) structure (e.g., n-amyl isoamyl phthalate and diisobutyl phthalate). PAEs have emerged as persistent organic pollutants across various environmental media and are known to possess endocrine-disrupting properties in the environment. We further observed that biodiesel prevents triglyceride storage compared to diesel and inhibits triglycerides from becoming phospholipids, particularly with increased phosphatidylglycerols (PGs) and phosphatidylethanolamines (PEs), which potentially could lead to a higher probability of cancer metastasis.

Influence of Polycyclic Aromatic Compounds and Oxidation States of Soot Organics on the Metabolome of Human-Lung Cells (A549): Implications for Vehicle Fuel Selection.

Decades of research have established the toxicity of soot particles resulting from incomplete combustion. However, the unique chemical compounds responsible for adverse health effects have remained uncertain. This study utilized mass spectrometry to analyze the chemical composition of extracted soot organics at three oxidation states, aiming to establish quantitative relationships between potentially toxic chemicals and their impact on human alveolar basal epithelial cells (A549) through metabolomics-based evaluations. Targeted analysis using MS/MS indicated that particles with a medium oxidation state contained the highest total abundance of compounds, particularly oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) composed of fused benzene rings and unsaturated carbonyls, which may cause oxidative stress, characterized by the upregulation of three specific metabolites. Further investigation focused on three specific OPAH standards: 1,4-naphthoquinone, 9-fluorenone, and anthranone. Pathway analysis indicated that exposure to these compounds affected transcriptional functions, the tricarboxylic acid cycle, cell proliferation, and the oxidative stress response. Biodiesel combustion emissions had higher concentrations of PAHs, OPAHs, and nitrogen-containing PAHs (NPAHs) compared with other fuels. Quinones and 9,10-anthraquinone were identified as the dominant compounds within the OPAH category. This knowledge enhances our understanding of the compounds contributing to adverse health effects observed in epidemiological studies and highlights the role of aerosol composition in toxicity.

The quest for improved air quality may push China to continue its CO2 reduction beyond the Paris Commitment.

China is challenged with the simultaneous goals of improving air quality and mitigating climate change. The "Beautiful China" strategy, launched by the Chinese government in 2020, requires that all cities in China attain 35 µg/m3 or below for annual mean concentration of PM2.5 (particulate matter with aerodynamic diameter less than 2.5 µm) by 2035. Meanwhile, China adopts a portfolio of low-carbon policies to meet its Nationally Determined Contribution (NDC) pledged in the Paris Agreement. Previous studies demonstrated the cobenefits to air pollution reduction from implementing low-carbon energy policies. Pathways for China to achieve dual targets of both air quality and CO2 mitigation, however, have not been comprehensively explored. Here, we couple an integrated assessment model and an air quality model to evaluate air quality in China through 2035 under the NDC scenario and an alternative scenario (Co-Benefit Energy [CBE]) with enhanced low-carbon policies. Results indicate that some Chinese cities cannot meet the PM2.5 target under the NDC scenario by 2035, even with the strictest end-of-pipe controls. Achieving the air quality target would require further reduction in emissions of multiple air pollutants by 6 to 32%, driving additional 22% reduction in CO2 emissions relative to the NDC scenario. Results show that the incremental health benefit from improved air quality of CBE exceeds 8 times the additional costs of CO2 mitigation, attributed particularly to the cost-effective reduction in household PM2.5 exposure. The additional low-carbon energy polices required for China's air quality targets would lay an important foundation for its deep decarbonization aligned with the 2 °C global temperature target.

Stringent Emission Controls Are Needed to Reach Clean Air Targets for Cities in China under a Warming Climate.

Quantifying the threat that climate change poses to fine particle (PM2.5) pollution is hampered by large uncertainties in the relationship between PM2.5 and meteorology. To constrain the impact of climate change on PM2.5, statistical models are often employed in a different manner than physical-chemical models to reduce the requirement of input data. A majority of statistical models predict PM2.5 concentration (often log-transformed) as a simple function of meteorology, which could be biased due to the conversion of precursor gases to PM2.5. We reduced this bias by developing a unique statistic model where the sum of PM2.5 and the weighted precursor gases, rather than the PM2.5 alone, was predicted as a function of meteorology and a proxy of primary emissions, where the input data of PM10, CO, O3, NOx, and SO2 were obtained from routine measurements. This modification, without losing the simplicity of statistical models, reduced the mean-square error from 27 to 17% and increased the coefficient of determination from 47 to 67% in the model cross-validation using daily PM2.5 observations during 2013-2018 for 74 cities over China. We found a previously unrecognized mechanism that synoptic climate change in the past half-century might have increased low quantiles of PM2.5 more strenuously than the upper quantiles in large cities over China. Climate change during 1971-2018 was projected to increase the annual mean concentration of PM2.5 at a degree that could be comparable with the toughest-ever clean air policy during 2013-2018 had counteracted it, as inferred from the decline in the daily concentration of carbon monoxide as an inert gas. Our estimate of the impact of climate change on PM2.5 is higher than previous statistical models, suggesting that aerosol chemistry might play a more important role than previously thought in the interaction between climate change and air pollution. Our result indicated that air quality might degrade if the future synoptic climate change could continue interacting with aerosol chemistry as it had occurred in the past half-century.

Ultrafine particle exposure and biomarkers of effect on small airways in children.

The small size and large surface area of ultrafine particles (UFP) enhance their ability to deposit in the lung periphery and their reactivity. The Ultrafine Particles from Traffic Emissions and Children's Health (UPTECH) cross-sectional study was conducted in 8-11-year-old schoolchildren attending 25 primary (elementary) schools, randomly selected from the Brisbane Metropolitan Area, Queensland, Australia. Main study findings outlined indirect evidence of distal airway deposition (raised C reactive protein) but as yet, there is no direct evidence in the literature of effects of UFP exposure on peripheral airway function. We present further UPTECH study data from two sensitive peripheral airway function tests, Oscillometry and Multiple Breath Nitrogen Washout (MBNW), performed in 577 and 627 children (88% and 96% of UPTECH study cohort) respectively: mean(SD) age 10.1(0.9) years, 46% male, with 50% atopy and 14% current asthma. Bayesian generalised linear mixed effects regression models were used to estimate the effect of UFP particle number count (PNC) exposure on key oscillometry (airway resistance, (Rrs), and reactance, (Xrs)) and MBNW (lung clearance index, (LCI) and functional residual capacity, (FRC)) indices. We adjusted for age, sex, and height, and potential confounders including socio-economic disadvantage, PM2.5 and NO2 exposure. All models contained an interaction term between UFP PNC exposure and atopy, allowing estimation of the effect of exposure on non-atopic and atopic students. Increasing UFP PNC was associated with greater lung stiffness as evidenced by a decrease in Xrs [mean (95% credible interval) -1.63 (-3.36 to -0.05)%] per 1000#.cm-3]. It was also associated with greater lung stiffness (decrease in Xrs) in atopic subjects across all models [mean change ranging from -2.06 to -2.40% per 1000#.cm-3]. A paradoxical positive effect was observed for Rrs across all models [mean change ranging from -1.55 to -1.70% per 1000#.cm-3] (decreases in Rrs indicating an increase in airway calibre), which was present for both atopic and non-atopic subjects. No effects on MBNW indices were observed. In conclusion, a modest detrimental effect of UFP on peripheral airway function among atopic subjects, as assessed by respiratory system reactance, was observed extending the main UPTECH study findings which reported a positive association with a biomarker for systemic inflammation, C-reactive protein (CRP). Further studies are warranted to explore the pathophysiological mechanisms underlying increased respiratory stiffness, and whether it persists through to adolescence and adulthood.

Improved morbidity-based air quality health index development using Bayesian multi-pollutant weighted model.

BACKGROUND: The widely used Air Quality Index (AQI) has been criticized due to its inaccuracy, leading to the development of the air quality health index (AQHI), an improvement on the AQI. However, there is currently no consensus on the most appropriate construction strategy for the AQHI. OBJECTIVES: In this study, we aimed to evaluate the utility of AQHIs constructed by different models and health outcomes, and determine a better strategy. METHODS: Based on the daily time-series outpatient visits and hospital admissions from 299 hospitals (January 2016-December 2018), and mortality (January 2017-December 2019) in Guangzhou, China, we utilized cumulative risk index (CRI) method, Bayesian multi-pollutant weighted (BMW) model and standard method to construct AQHIs for different health outcomes. The effectiveness of AQHIs constructed by different strategies was evaluated by a two-stage validation analysis and examined their exposure-response relationships with the cause-specific morbidity and mortality. RESULTS: Validation by different models showed that AQHI constructed with the BMW model (BMW-AQHI) had the strongest association with the health outcome either in the total population or subpopulation among air quality indexes, followed by AQHI constructed with the CRI method (CRI-AQHI), then common AQHI and AQI. Further validation by different health outcomes showed that AQHI constructed with the risk of outpatient visits generally exhibited the highest utility in presenting mortality and morbidity, followed by AQHI constructed with the risk of hospitalizations, then mortality-based AQHI and AQI. The contributions of NO2 and O3 to the final AQHI were prominent, while the contribution of SO2 and PM2.5 were relatively small. CONCLUSIONS: The BMW model is likely to be more effective for AQHI construction than CRI and standard methods. Based on the BMW model, the AQHI constructed with the outpatient data may be more effective in presenting short-term health risks associated with the co-exposure to air pollutants than the mortality-based AQHI and existing AQIs.

Targeted reduction of airborne viral transmission risk in long-term residential aged care.

COVID-19 has demonstrated the devastating consequences of the rapid spread of an airborne virus in residential aged care. We report the use of CO2-based ventilation assessment to empirically identify potential 'super-spreader' zones within an aged care facility, and determine the efficacy of rapidly implemented, inexpensive, risk reduction measures.

Risk of SARS-CoV-2 in a car cabin assessed through 3D CFD simulations.

In this study, the risk of infection from SARS-CoV-2 Delta variant of passengers sharing a car cabin with an infected subject for a 30-min journey is estimated through an integrated approach combining a recently developed predictive emission-to-risk approach and a validated CFD numerical model numerically solved using the open-source OpenFOAM software. Different scenarios were investigated to evaluate the effect of the infected subject position within the car cabin, the airflow rate of the HVAC system, the HVAC ventilation mode, and the expiratory activity (breathing vs. speaking). The numerical simulations here performed reveal that the risk of infection is strongly influenced by several key parameters: As an example, under the same ventilation mode and emitting scenario, the risk of infection ranges from zero to roughly 50% as a function of the HVAC flow rate. The results obtained also demonstrate that (i) simplified zero-dimensional approaches limit proper evaluation of the risk in such confined spaces, conversely, (ii) CFD approaches are needed to investigate the complex fluid dynamics in similar indoor environments, and, thus, (iii) the risk of infection in indoor environments characterized by fixed seats can be in principle controlled by properly designing the flow patterns of the environment.

What were the historical reasons for the resistance to recognizing airborne transmission during the COVID-19 pandemic?

The question of whether SARS-CoV-2 is mainly transmitted by droplets or aerosols has been highly controversial. We sought to explain this controversy through a historical analysis of transmission research in other diseases. For most of human history, the dominant paradigm was that many diseases were carried by the air, often over long distances and in a phantasmagorical way. This miasmatic paradigm was challenged in the mid to late 19th century with the rise of germ theory, and as diseases such as cholera, puerperal fever, and malaria were found to actually transmit in other ways. Motivated by his views on the importance of contact/droplet infection, and the resistance he encountered from the remaining influence of miasma theory, prominent public health official Charles Chapin in 1910 helped initiate a successful paradigm shift, deeming airborne transmission most unlikely. This new paradigm became dominant. However, the lack of understanding of aerosols led to systematic errors in the interpretation of research evidence on transmission pathways. For the next five decades, airborne transmission was considered of negligible or minor importance for all major respiratory diseases, until a demonstration of airborne transmission of tuberculosis (which had been mistakenly thought to be transmitted by droplets) in 1962. The contact/droplet paradigm remained dominant, and only a few diseases were widely accepted as airborne before COVID-19: those that were clearly transmitted to people not in the same room. The acceleration of interdisciplinary research inspired by the COVID-19 pandemic has shown that airborne transmission is a major mode of transmission for this disease, and is likely to be significant for many respiratory infectious diseases.

Coronavirus Disease 2019 Patients in Earlier Stages Exhaled Millions of Severe Acute Respiratory Syndrome Coronavirus 2 Per Hour.

Coronavirus disease 2019 (COVID-19) patients exhaled millions of severe acute respiratory syndrome coronavirus 2 RNA copies per hour, which plays an important role in COVID-19 transmission. Exhaled breath had a higher positive rate (26.9%, n = 52) than surface (5.4%, n = 242) and air (3.8%, n = 26) samples.

Associations of Particulate Matter Sizes and Chemical Constituents with Blood Lipids: A Panel Study in Guangzhou, China.

Existing evidence is scarce concerning the various effects of different PM sizes and chemical constituents on blood lipids. A panel study that involved 88 healthy college students with five repeated measurements (440 blood samples in total) was performed. We measured mass concentrations of particulate matter with diameters ≤ 2.5 µm (PM2.5), ≤1.0 µm (PM1.0), and ≤0.5 µm (PM0.5) as well as number concentrations of particulate matter with diameters ≤ 0.2 µm (PN0.2) and ≤0.1 µm (PN0.1). We applied linear mixed-effect models to assess the associations between short-term exposure to different PM size fractions and PM2.5 constituents and seven lipid metrics. We found significant associations of greater concentrations of PM in different size fractions within 5 days before blood collection with lower high-density lipoprotein cholesterol (HDL-C) and apolipoprotein A (ApoA1) levels, higher apolipoprotein B (ApoB) levels, and lower ApoA1/ApoB ratios. Among the PM2.5 constituents, we observed that higher concentrations of tin and lead were significantly associated with decreased HDL-C levels, and higher concentrations of nickel were associated with higher HDL-C levels. Our results suggest that short-term exposure to PM in different sizes was deleteriously associated with blood lipids. Some constituents, especially metals, might be the major contributors to the detrimental effects.