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.

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.

Assessing capabilities of conducted ambient air pollution health effects studies in 22 Eastern Mediterranean countries to adopt air quality standards: a review.

Purpose: The Eastern Mediterranean Region (EMR) countries suffer from exposure to high levels of ambient air pollutants due to dust storms and have unique climatic as well as topographic and socio-economic conditions which lead to adverse health effects on humans. The purpose of the review was to evaluate the quantity and quality of published articles on air pollution and health-based studies in 22 EMR countries to determine if they can be applied to adopting air quality standards. Methods: We designed a review based on a broad search of the literature in the Scopus, PubMed, and web of science (WOS) databases published from January 1, 2000, to January 2, 2022, using combinations of the following relevant terms: air pollution, health, and EMR countries. The generic eligibility criteria for this review were based on the population, exposure, comparator, outcome, and study design (PECOS) statement. Results: The search results showed that following the PRISMA approach, of 2947 identified articles, 353 studies were included in this review. The analysis of the types of studies showed that about 70% of the studies conducted in EMR countries were Health Burden Estimation studies (31%), Ecological and time trend ecological studies (23%), and cross-sectional studies (16%). Also, researchers from Iran participated in the most published relevant studies in the region 255 (~ 63%) and just 10 published documents met all the PECOS criteria. Conclusion: The lack of sufficient studies which can meet the PECOS appraising criteria and the lack of professionals in this field are some of the issues that make it impossible to use as potential documents in the WHO future studies and adopt air quality standards. Supplementary Information: The online version contains supplementary material available at 10.1007/s40201-023-00862-1.

Physicochemical characterization of porcine respiratory aerosol and considerations for future aerovirology.

Understanding the mechanisms which inactivate airborne viruses is a current challenge. The composition of human respiratory aerosol is poorly understood and needs to be adequately investigated for use in aerovirology studies. Here, the physicochemical properties of porcine respiratory fluid (PRF) from the trachea and lungs were investigated both in bulk solutions and in aerosols. The mass ratio of Na:K in PRF compared with cell culture media (Dulbecco's Modified Eagle Medium, DMEM), which is frequently used in aerovirology studies, was significantly lower (∼2:1 vs ∼16:1). PRF contained significantly more potassium and protein than DMEM. PRF aerosols of all samples were similarly hygroscopic to human respiratory aerosol. PRF particles could nucleate with spatially separated crystals, indicating that the protein matrix was sufficiently viscous to prevent the complete coalescence of aqueous salts prior to efflorescence. The effects of these differences in compositions on the viability of viruses are currently not well understood. The virus suspensions in aerovirology studies need to be reconsidered to adequately reflect a real-world expiration scenario.

Ambient Air Quality Standards and Policies in Eastern Mediterranean Countries: A Review.

Objectives: National ambient air quality standards (NAAQS) are critical tools for controlling air pollution and protecting public health. We designed this study to 1) gather the NAAQS for six classical air pollutants: PM2.5, PM10, O3, NO2, SO2, and CO in the Eastern Mediterranean Region (EMR) countries, 2) compare those with the updated World Health Organizations Air Quality Guidelines (WHO AQGs 2021), 3) estimate the potential health benefits of achieving annual PM2.5 NAAQS and WHO AQGs per country, and 4) gather the information on air quality policies and action plans in the EMR countries. Methods: To gather information on the NAAQS, we searched several bibliographic databases, hand-searched the relevant papers and reports, and analysed unpublished data on NAAQS in the EMR countries reported from these countries to the WHO/Regional office of the Eastern Mediterranean/Climate Change, Health and Environment Unit (WHO/EMR/CHE). To estimate the potential health benefits of reaching the NAAQS and AQG levels for PM2.5, we used the average of ambient PM2.5 exposures in the 22 EMR countries in 2019 from the Global Burden of Disease (GBD) dataset and AirQ+ software. Results: Almost all of the EMR countries have national ambient air quality standards for the critical air pollutants except Djibouti, Somalia, and Yemen. However, the current standards for PM2.5 are up to 10 times higher than the current health-based WHO AQGs. The standards for other considered pollutants exceed AQGs as well. We estimated that the reduction of annual mean PM2.5 exposure level to the AQG level (5 µg m-3) would be associated with a decrease of all natural-cause mortality in adults (age 30+) by 16.9%-42.1% in various EMR countries. All countries would even benefit from the achievement of the Interim Target-2 (25 µg m-3) for annual mean PM2.5: it would reduce all-cause mortality by 3%-37.5%. Less than half of the countries in the Region reported having policies relevant to air quality management, in particular addressing pollution related to sand and desert storms (SDS) such as enhancing the implementation of sustainable land management practices, taking measures to prevent and control the main factors of SDS, and developing early warning systems as tools to combat SDS. Few countries conduct studies on the health effects of air pollution or on a contribution of SDS to pollution levels. Information from air quality monitoring is available for 13 out of the 22 EMR countries. Conclusion: Improvement of air quality management, including international collaboration and prioritization of SDS, supported by an update (or establishment) of NAAQSs and enhanced air quality monitoring are essential elements for reduction of air pollution and its health effects in the EMR.

Health burden and economic loss attributable to ambient PM2.5 in Iran based on the ground and satellite data.

We estimated mortality and economic loss attributable to PM2·5 air pollution exposure in 429 counties of Iran in 2018. Ambient PM2.5-related deaths were estimated using the Global Exposure Mortality Model (GEMM). According to the ground-monitored and satellite-based PM2.5 data, the annual mean population-weighted PM2·5 concentrations for Iran were 30.1 and 38.6 µg m-3, respectively. We estimated that long-term exposure to ambient PM2.5 contributed to 49,303 (95% confidence interval (CI) 40,914-57,379) deaths in adults ≥ 25 yr. from all-natural causes based on ground monitored data and 58,873 (95% CI 49,024-68,287) deaths using satellite-based models for PM2.5. The crude death rate and the age-standardized death rate per 100,000 population for age group ≥ 25 year due to ground-monitored PM2.5 data versus satellite-based exposure estimates was 97 (95% CI 81-113) versus 116 (95% CI 97-135) and 125 (95% CI 104-145) versus 149 (95% CI 124-173), respectively. For ground-monitored and satellite-based PM2.5 data, the economic loss attributable to ambient PM2.5-total mortality was approximately 10,713 (95% CI 8890-12,467) and 12,792.1 (95% CI 10,652.0-14,837.6) million USD, equivalent to nearly 3.7% (95% CI 3.06-4.29) and 4.3% (95% CI 3.6-4.5.0) of the total gross domestic product in Iran in 2018.

Source apportionment, identification and characterization, and emission inventory of ambient particulate matter in 22 Eastern Mediterranean Region countries: A systematic review and recommendations for good practice.

Little is known about the main sources of ambient particulate matter (PM) in the 22 Eastern Mediterranean Region (EMR) countries. We designed this study to systematically review all published and unpublished source apportionment (SA), identification and characterization studies as well as emission inventories in the EMR. Of 440 articles identified, 82 (11 emission inventory ones) met our inclusion criteria for final analyses. Of 22 EMR countries, Iran with 30 articles had the highest number of studies on source specific PM followed by Pakistan (n = 15 articles) and Saudi Arabia (n = 8 papers). By contrast, there were no studies in Afghanistan, Bahrain, Djibouti, Libya, Somalia, Sudan, Syria, Tunisia, United Arab Emirates and Yemen. Approximately 72% of studies (51) were published within a span of 2015-2021.48 studies identified the sources of PM2.5 and its constituents. Positive matrix factorization (PMF), principal component analysis (PCA) and chemical mass balance (CMB) were the most common approaches to identify the source contributions of ambient PM. Both secondary aerosols and dust, with 12-51% and 8-80% (33% and 30% for all EMR countries, on average) had the greatest contributions in ambient PM2.5. The remaining sources for ambient PM2.5, including mixed sources (traffic, industry and residential (TIR)), traffic, industries, biomass burning, and sea salt were in the range of approximately 4-69%, 4-49%, 1-53%, 7-25% and 3-29%, respectively. For PM10, the most dominant source was dust with 7-95% (49% for all EMR countries, on average). The limited number of SA studies in the EMR countries (one study per approximately 9.6 million people) in comparison to Europe and North America (1 study per 4.3 and 2.1 million people respectively) can be augmented by future studies that will provide a better understanding of emission sources in the urban environment.

Nanomechanics and Morphology of Simulated Respiratory Particles.

The impact of respiratory particle composition on the equilibrium morphology and phase is not well understood. Furthermore, the effects of these different phases and morphologies on the viability of viruses embedded within these particles are equally unknown. Physiologically relevant respiratory fluid analogues were constructed, and their hygroscopic behavior was measured using an ensemble technique. A relationship between hygroscopicity and protein concentration was determined, providing additional validation to the high protein content of respiratory aerosol measured in prior works (>90%). It was found that the salt component of the respiratory particles could crystallize as a single crystal, multiple crystals, or would not crystallize at all. It was found that dried protein particles at indoor-relevant climatic conditions could exist separately in a glassy (∼77% of particles) or viscoelastic state (∼23% of particles). The phase state and morphology of respiratory particles may influence the viability of embedded pathogens. We recommend that pathogen research aiming to mimic the native composition of respiratory fluid should use a protein concentration of at least 90% by solute volume to improve the representativity of the pathogen's microenvironment.

BTEX levels in rural households: Heating system, building characteristic impacts and lifetime excess cancer risk assessment.

BTEX (benzene, toluene, ethylbenzene, and xylene) are a group of toxic organic compounds that exposure to them can cause adverse short and long terms health effects. We measured the levels of BTEX in the indoor and outdoor air of rural areas in Ardebil, Iran. We further assessed their health risks and determinants parameters. BTEX were sampled by drawing air through activated charcoal tubes, using low flow SKC pumps. Samples were extracted by adding carbon disulfide and analyzed by subjecting the aromatic fraction to GC-FID. The results indicated that the concentrations of BTEX in the indoor air were significantly higher than those of outdoor (p-value<0.05). The mean indoor concentrations of benzene, toluene, ethylbenzene, and xylene were 41.69 ± 30.70, 96.73 ± 60.75, 38.73 ± 33.59, and 59.42 ± 35.99 µg m-3, while the mean outdoor concentrations of them were 8.94 ± 7.32, 36.93 ± 21.82, 7.66 ± 5.63, and 18.14 ± 10.25 µg m-3, respectively. The concentrations of BTEX in indoor and outdoor of the rural areas that used kerosene fuel for heating systems were significantly higher than those used natural gas. The results indicated that the tobacco smoke is a notable temporary source of indoor BTEX. The mean inhalation lifetime cancer risk (LTCR) value of benzene for residents of rural houses with the natural gas and kerosene heating systems were 28.6 × 10-6 and 97.2 × 10-6, while for ethylbenzene these figures stood out at 29.1 × 10-6 and 95.8 × 10-6, respectively. LTCR value for residents who used kerosene fuel for heating was higher than the World Health Organization (WHO) recommended limit.

Utility of Three Nebulizers in Investigating the Infectivity of Airborne Viruses.

Laboratory-generated bioaerosols are widely used in aerobiology studies of viruses; however, few comparisons of alternative nebulizers exist. We compared aerosol production and virus survival for a Collison nebulizer, vibrating mesh nebulizer (VMN), and hydraulic spray atomizer (HSA). We also measured the dry size distribution of the aerosols produced and calculated the droplet sizes before evaporation and the dry size distribution from normal saline solution. Dry count median diameters of 0.11, 0.22, and 0.30 µm were found for normal saline from the Collison nebulizer, VMN, and HSA, respectively. The volume median diameters were 0.323, 1.70, and 1.30 µm, respectively. The effect of nebulization on the viability of two influenza A viruses (IAVs) (H1N1 and H3N2) and human rhinovirus 16 (HRV-16) was assessed by nebulization into an SKC BioSampler. The HSA had the least impact on surviving fractions (SFs) of H1N1 and H3N2 (89% ± 3% and 94% ± 2%, respectively), followed by the Collison nebulizer (83% ± 1% and 82% ± 2%, respectively). The VMN yielded SFs of 78% ± 2% and 76% ± 2%, respectively. Conversely, for HRV-16, the VMN produced higher SFs (87% ± 8%). Our findings indicate that there were no statistical differences between SFs of the viruses nebulized by these nebulizers. However, VMN produced higher aerosol concentrations within the airborne size range, making it more suitable where high aerosol mass production is required. IMPORTANCE Viral respiratory tract infections cause millions of lost days of work and physician visits globally, accounting for significant morbidity and mortality. Respiratory droplets and droplet nuclei from infected hosts are the potential carriers of such viruses within indoor environments. Laboratory-generated bioaerosols are applied in understanding the transmission and infection of viruses, modeling the physiological aspects of bioaerosol generation in a controlled environment. However, little comparative characterization exists for nebulizers used in infectious disease aerobiology, including Collison nebulizer, vibrating mesh nebulizer, and hydraulic spray atomizer. This study characterized the physical features of aerosols generated by laboratory nebulizers and their performance in producing aerosols at a size relevant to airborne transmission used in infectious disease aerobiology. We also determined the impact of nebulization mechanisms of these nebulizers on the viability of human respiratory viruses, including IAV H1N1, IAV H3N2, and HRV-16.

In situ measurements of human cough aerosol hygroscopicity.

The airborne dynamics of respiratory droplets, and the transmission routes of pathogens embedded within them, are governed primarily by the diameter of the particles. These particles are composed of the fluid which lines the respiratory tract, and is primarily mucins and salts, which will interact with the atmosphere and evaporate to reach an equilibrium diameter. Measuring organic volume fraction (OVF) of cough aerosol has proved challenging due to large variability and low material volume produced after coughing. Here, the diametric hygroscopic growth factors (GF) of the cough aerosol produced by healthy participants were measured in situ using a rotating aerosol suspension chamber and a humidification tandem differential mobility analyser. Using hygroscopicity models, it was estimated that the average OVF in the evaporated cough aerosol was 0.88 ± 0.07 and the average GF at 90% relative humidity (RH) was 1.31 ± 0.03. To reach equilibrium in dry air the droplets will reduce in diameter by a factor of approximately 2.8 with an evaporation factor of 0.36 ± 0.05. Hysteresis was observed in cough aerosol at RH = ∼35% and RH = ∼65% for efflorescence and deliquescence, respectively, and may depend on the OVF. The same behaviour and GF were observed in nebulized bovine bronchoalveolar lavage fluid.

The effect of COVID-19 pandemic on human mobility and ambient air quality around the world: A systematic review.

We conducted this systematic review to identify and appraise studies investigating the coronavirus disease 2019 (COVID-19) effect on ambient air pollution status worldwide. The review of studies was conducted using determined search terms via three major electronic databases (PubMed, Web of Science, and Scopus) according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) approach. A total of 26 full-text studies were included in our analysis. The lockdown measures related to COVID-19 pandemic caused significant decreases in the concentrations of PM2.5, NO2, PM10, SO2 and CO globally in the range of 2.9%-76.5%, 18.0%-96.0%, 6.0%-75.0%, 6.8%-49.0% and 6.2%-64.8%, respectively. However, O3 concentration increased in the range of 2.4%-252.3%. The highest decrease of PM2.5 was found in 16 states of Malaysia (76.5%), followed by Zaragoza (Spain) with 58.0% and Delhi (India) with 53.1%. The highest reduction of NO2 was found in Salé city (Morocco) with 96.0%, followed by Mumbai (India) with 75.0%, India with 70.0%, Valencia (Spain) with 69.0%, and São Paulo (Brazil) with 68.0%, respectively. The highest increase of O3 was recorded for Milan (Italy) with 252.3% and 169.9% during the first and third phases of lockdown measures, and for Kolkata (India) with 87% at the second phase of lockdown measures. Owing to the lockdown restrictions in the studied countries and cities, driving and public transit as a proxy of human mobilities and the factors affecting emission sources of ambient air pollution decreased in the ranges of 30-88% and 45-94%, respectively. There was a considerable variation in the reduction of ambient air pollutants in the countries and cities as the degree of lockdown measures had varied there. Our results illustrated that the COVID-19 pandemic had provided lessons and extra motivations for comprehensive implementing policies to reduce air pollution and its health effects in the future.

Susceptibility of an Airborne Common Cold Virus to Relative Humidity.

The viability of airborne respiratory viruses varies with ambient relative humidity (RH). Numerous contrasting reports spanning several viruses have failed to identify the mechanism underlying this dependence. We hypothesized that an "efflorescence/deliquescence divergent infectivity" (EDDI) model accurately predicts the RH-dependent survival of airborne human rhinovirus-16 (HRV-16). We measured the efflorescence and deliquescence RH (RHE and RHD, respectively) of aerosols nebulized from a protein-enriched saline carrier fluid simulating the human respiratory fluid and found the RH range of the aerosols' hygroscopic hysteresis zone (RHE-D) to be 38-68%, which encompasses the preferred RH for indoor air (40-60%). The carrier fluid containing HRV-16 was nebulized into the sub-hysteresis zone (RHD) air, to set the aerosols to the effloresced/solid or deliquesced/liquid state before transitioning the RH into the intermediate hysteresis zone. The surviving fractions (SFs) of the virus were then measured 15 min post nebulization. SFs were also measured for aerosols introduced directly into the RHD zones without transition. SFs for transitioned aerosols in the hysteresis zone were higher for effloresced (0.17 ± 0.02) than for deliquesced (0.005 ± 0.005) aerosols. SFs for nontransitioned aerosols in the RHD zones were 0.18 ± 0.06, 0.05 ± 0.02, and 0.20 ± 0.05, respectively, revealing a V-shaped SF/RH dependence. The EDDI model's prediction of enhanced survival in the hysteresis zone for effloresced carrier aerosols was confirmed.

The role of respiratory droplet physicochemistry in limiting and promoting the airborne transmission of human coronaviruses: A critical review.

Whether virulent human pathogenic coronaviruses (SARS-CoV, MERS-CoV, SARS-CoV-2) are effectively transmitted by aerosols remains contentious. Transmission modes of the novel coronavirus have become a hot topic of research with the importance of airborne transmission controversial due to the many factors that can influence virus transmission. Airborne transmission is an accepted potential route for the spread of some viral infections (measles, chickenpox); however, aerosol features and infectious inoculum vary from one respiratory virus to another. Infectious virus-laden aerosols can be produced by natural human respiratory activities, and their features are vital determinants for virus carriage and transmission. Physicochemical characteristics of infectious respiratory aerosols can influence the efficiency of virus transmission by droplets. This critical review identifies studies reporting instances of infected patients producing airborne human pathogenic coronaviruses, and evidence for the role of physical/chemical characteristics of human-generated droplets in altering embedded viruses' viability. We also review studies evaluating these viruses in the air, field studies and available evidence about seasonality patterns. Ultimately the literature suggests that a proportion of virulent human coronaviruses can plausibly be transmitted via the air, even though this might vary in different conditions. Evidence exists for respirable-sized airborne droplet nuclei containing viral RNA, although this does not necessarily imply that the virus is transmittable, capable of replicating in a recipient host, or that inoculum is sufficient to initiate infection. However, evidence suggests that coronaviruses can survive in simulated droplet nuclei for a significant time (>24 h). Nevertheless, laboratory nebulized virus-laden aerosols might not accurately model the complexity of human carrier aerosols in studying airborne viral transport. In summary, there is disagreement on whether wild coronaviruses can be transmitted via an airborne path and display seasonal patterns. Further studies are therefore required to provide supporting evidence for the role of airborne transmission and assumed mechanisms underlying seasonality.

How climate change can affect cholera incidence and prevalence? A systematic review.

Although the number of cholera infection decreased universally, climate change can potentially affect both incidence and prevalence rates of disease in endemic regions. There is considerable consistent evidence, explaining the associations between cholera and climatic variables. However, it is essentially required to compare and interpret these relationships globally. The aim of the present study was to carry out a systematic review in order to identify and appraise the literature concerning the relationship between nonanthropogenic climatic variabilities such as extreme weather- and ocean-related variables and cholera infection rates. The systematic literature review of studies was conducted by using determined search terms via four major electronic databases (PubMed, Web of Science, Embase, and Scopus) according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) approach. This search focused on published articles in English-language up to December 31, 2018. A total of 43 full-text studies that met our criteria have been identified and included in our analysis. The reviewed studies demonstrated that cholera incidence is highly attributed to climatic variables, especially rainfall, temperature, sea surface temperature (SST) and El Niño Southern Oscillation (ENSO). The association between cholera incidence and climatic variables has been investigated by a variety of data analysis methodologies, most commonly time series analysis, generalized linear model (GLM), regression analysis, and spatial/GIS. The results of this study assist the policy-makers who provide the efforts for planning and prevention actions in the face of changing global climatic variables.

A field indoor air measurement of SARS-CoV-2 in the patient rooms of the largest hospital in Iran.

The coronavirus disease 2019 (COVID-19) emerged in Wuhan city, China, in late 2019 and has rapidly spread throughout the world. The major route of transmission of SARS-CoV-2 is in contention, with the airborne route a likely transmission pathway for carrying the virus within indoor environments. Until now, there has been no evidence for detection of airborne severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and this may have implication for the potential spread of the COVID-19. We investigated the air of patient rooms with confirmed COVID-19 in the largest hospital in Iran, on March 17, 2020. To collect the SARS-CoV-2 particles, ten air samples were collected into the sterile standard midget impingers containing 20 mL DMEM with 100 µg/mL streptomycin, 100 U/mL penicillin and 1% antifoam reagent for 1 h. Besides, indoor particle number concentrations, CO2, relative humidity and temperature were recorded throughout the sampling duration. Viral RNA was extracted from samples taken from the impingers and Reverse-Transcription PCR (RT-PCR) was applied to confirm the positivity of collected samples based on the virus genome sequence. Fortunately, in this study all air samples which were collected 2 to 5 m from the patients' beds with confirmed COVID-19 were negative. Despite we indicated that all air samples were negative, however, we suggest further in vivo experiments should be conducted using actual patient cough, sneeze and breath aerosols in order to show the possibility of generation of the airborne size carrier aerosols and the viability fraction of the embedded virus in those carrier aerosols.

Spatial homogeneity and heterogeneity of ambient air pollutants in Tehran.

To investigate spatial inequality of ambient air pollutants and comparison of their heterogeneity and homogeneity across Tehran, the following quantitative indicators were utilized: coefficient of divergence (COD), the 90th percentile of the absolute differences between ambient air pollutant concentrations and coefficient of variation (CV). Real-time hourly concentrations of particulate matter (PM) and gaseous air pollutants (GAPs) of twenty-two air quality monitoring stations (AQMSs) were obtained from Tehran Air Quality Control Company (TAQCC) in 2017. Annual mean concentrations of PM2.5, PM10-2.5, and PM10 (PMX) ranged from 21.7 to 40.5, 37.3 to 75.0 and 58.0 to 110.4 µg m-3, respectively. Annual mean PM2.5 and PM10 concentrations were higher than the World Health Organization air quality guideline (WHO AQG) and national standard levels. NO2, O3, SO2 and CO annual mean concentrations ranged from 27.0 to 76.8, 15.5 to 25.1, 4.6 to 12.2 ppb, and 1.9 to 3.8 ppm over AQMSs, respectively. Our generated spatial maps exhibited that ambient PMX concentrations increased from the north into south and south-western areas as the hotspots of ambient PMX in Tehran. O3 hotspots were observed in the north and south-west, while NO2 hotspots were in the west and south. COD values of PMX demonstrated more results lower than the 0.2 cut off compared to GAPs; indicating high to moderate spatial homogeneity for PMX and moderate to high spatial heterogeneity for GAPs. Regarding CV approach, the spatial variabilities of air pollutants followed in the order of O3 (87.3%) > SO2 (65.2%) > CO (61.8%) > PM10-2.5 (52.5%) > PM2.5 (48.9%) > NO2 (48.1%) > PM10 (42.9%), which were mainly in agreement with COD results, except for NO2. COD values observed a statistically (P < 0.05) positive correlation with the values of the 90th percentile across AQMSs. Our study, for the first time, highlights spatial inequality of ambient PMX and GAPs in Tehran in detail to better facilitate establishing new intra-urban control policies.

Air pollutants associated with smoking in indoor/outdoor of waterpipe cafés in Tehran, Iran: Concentrations, affecting factors and health risk assessment.

Despite increasingly growth in waterpipe smoking in Tehran, so far no study has been conducted on the air quality of the waterpipe and cigarette cafés. Thirty-six cafés were selected and the concentration of three pollutants including formaldehyde, carbon monoxide and nicotine were measured in both indoor and outdoor air of cafés two times (week-day and weekend's session). Air sampling was performed for 180 min for each pollutant. It was observed that the concentration of pollutants inside the cafés was higher during weekend session (with a higher number of "active waterpipe heads") compared with findings during the week-day sessions. Furthermore, the concentration of pollutants in the indoor air of the cafés was significantly higher than that of the outdoors (p < 0.05). According to path analysis, the number of "active waterpipe heads" had the maximum impact on generation of pollutants inside the cafés, followed by the type of tobacco as the second influential factor. The average of lifetime cancer risk (LTCR) resulted by formaldehyde exposure through inhalation in waterpipe (WS), cigarette (CS), waterpipe and cigarette (WCS) and none-smoking (NS) cafés in week-day and weekend sessions were estimated to be 111 × 10-5 and 61.2 × 10-5, 33.7 × 10-5 and 39.4 × 10-5, 271 × 10-5 and 322 × 10-5, and 4.80 × 10-5 and 5.90 × 10-5, respectively, which exceed the limit value by the U.S.EPA and WHO. The concentration of pollutants in the indoor air of smoking cafés in Tehran is significantly high, such that it can pose serious risks for the health of both personnel and customers. Therefore, decision makers are expected to enact applicable and strict policies so as to abate this public health risk.

Exposure to ambient air pollution and risk of childhood cancers: A population-based study in Tehran, Iran.

The relationship between air pollution and childhood cancer is inconclusive. We investigated the associations between exposure to ambient air pollution and childhood cancers in Tehran, Iran. This project included children between 1 and 15 years-of-age with a cancer diagnosis by the Center for the Control of Non Communicable Disease (n = 161) during 2007 to 2009. Controls were selected randomly within the city using a Geographic Information System (GIS) (n = 761). The cases were geocoded based on exact home addresses. Air pollution exposure of cases and random controls were estimated by a previously developed Land Use Regression (LUR) model for the 2010 calendar year. The annual mean concentrations of Particulate Matter ≤ 10 µm (PM10), nitrogen dioxide (NO2) and sulfur dioxide (SO2) in the locations of cancer cases were 101.97 µg/m3, 49.42 ppb and 38.92 ppb respectively, while in the random control group, respective mean exposures were 98.63 µg/m3, 45.98 ppb and 38.95 ppb. A logistic regression model was used to find the probability of childhood cancer per unit increase in PM10, NO2 and SO2. We observed a positive association between exposures to PM10 with childhood cancers. We did, however, observe a positive, but not statistically significant association between NO2 exposure and childhood cancer. Our study is the first to highlight an association between air pollution exposure and childhood cancer risk in Iran, however these findings require replication through future studies.