Expiratory Aerosol pH: The Overlooked Driver of Airborne Virus Inactivation

Respiratory viruses, including influenza virus and SARS-CoV-2, are transmitted by the airborne route. Air filtration and ventilation mechanically reduce the concentration of airborne viruses and are necessary tools for disease mitigation. However, they ignore the potential impact of the chemical environment surrounding aerosolized viruses, which determines the aerosol pH. Atmospheric aerosol gravitates toward acidic pH, and enveloped viruses are prone to inactivation at strong acidity levels. Yet, the acidity of expiratory aerosol particles and its effect on airborne virus persistence have not been examined. Here, we combine pH-dependent inactivation rates of influenza A virus (IAV) and SARS-CoV-2 with microphysical properties of respiratory fluids using a biophysical aerosol model. We find that particles exhaled into indoor air (with relative humidity ≥ 50%) become mildly acidic (pH ∼ 4), rapidly inactivating IAV within minutes, whereas SARS-CoV-2 requires days. If indoor air is enriched with nonhazardous levels of nitric acid, aerosol pH drops by up to 2 units, decreasing 99%-inactivation times for both viruses in small aerosol particles to below 30 s. Conversely, unintentional removal of volatile acids from indoor air may elevate pH and prolong airborne virus persistence. The overlooked role of aerosol acidity has profound implications for virus transmission and mitigation strategies

Inactivation mechanisms of influenza A virus under pH conditions encountered in aerosol particles as revealed by whole-virus HDX-MS

Multiple respiratory viruses, including influenza A virus (IAV), can be transmitted via expiratory aerosol particles, and aerosol pH was recently identified as a major factor influencing airborne virus infectivity. Indoors, small exhaled aerosols undergo rapid acidification to pH ~4. IAV is known to be sensitive to mildly acidic conditions encountered within host endosomes; however, it is unknown whether the same mechanisms could mediate viral inactivation within the more acidic aerosol micro-environment. Here, we identified that transient exposure to pH 4 caused IAV inactivation by a two-stage process, with an initial sharp decline in infectious titers mainly attributed to premature attainment of the post-fusion conformation of viral protein haemagglutinin (HA). Protein changes were observed by hydrogen-deuterium exchange coupled to mass spectrometry (HDX-MS) as early as 10 s post-exposure to acidic conditions. Our HDX-MS data are in agreement with other more labor-intensive structural analysis techniques, such as X-ray crystallography, highlighting the ease and usefulness of whole-virus HDX-MS for multiplexed protein analyses, even within enveloped viruses such as IAV. Additionally, virion integrity was partially but irreversibly affected by acidic conditions, with a progressive unfolding of the internal matrix protein 1 (M1) that aligned with a more gradual decline in viral infectivity with time. In contrast, no acid-mediated changes to the genome or lipid envelope were detected. Improved understanding of respiratory virus fate within exhaled aerosols constitutes a global public health priority, and information gained here could aid the development of novel strategies to control the airborne persistence of seasonal and/or pandemic influenza in the future. IMPORTANCE: It is well established that COVID-19, influenza, and many other respiratory diseases can be transmitted by the inhalation of aerosolized viruses. Many studies have shown that the survival time of these airborne viruses is limited, but it remains an open question as to what drives their infectivity loss. Here, we address this question for influenza A virus by investigating structural protein changes incurred by the virus under conditions relevant to respiratory aerosol particles. From prior work, we know that expelled aerosols can become highly acidic due to equilibration with indoor room air, and our results indicate that two viral proteins are affected by these acidic conditions at multiple sites, leading to virus inactivation. Our findings suggest that the development of air treatments to quicken the speed of aerosol acidification would be a major strategy to control infectious bioburdens in the air

A MSFD complementary approach for the assessment of pressures, knowledge and data gaps in Southern European Seas : the PERSEUS experience

PERSEUS project aims to identify the most relevant pressures exerted on the ecosystems of the Southern European Seas (SES), highlighting knowledge and data gaps that endanger the achievement of SES Good Environmental Status (GES) as mandated by the Marine Strategy Framework Directive (MSFD). A complementary approach has been adopted, by a meta-analysis of existing literature on pressure/impact/knowledge gaps summarized in tables related to the MSFD descriptors, discriminating open waters from coastal areas. A comparative assessment of the Initial Assessments (IAs) for five SES countries has been also independently performed. The comparison between meta-analysis results and IAs shows similarities for coastal areas only. Major knowledge gaps have been detected for the biodiversity, marine food web, marine litter and underwater noise descriptors. The meta-analysis also allowed the identification of additional research themes targeting research topics that are requested to the achievement of GES. 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.peer-reviewe

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

Real-Time, Online Automated System for Measurement of Water-Soluble Reactive Phosphate Ions in Atmospheric Particles

We present a novel automated system for real-time measurements of water-soluble reactive phosphate (SRP) ions in atmospheric particles. Detection of SRP is based on molybdenum blue chemistry with Sn(II) chloride dihydrate reduction. The instrumentation consists of one particle-into-liquid sampler (PILS) coupled with a 250 cm path length liquid waveguide capillary cell (LWCC) and miniature fiber optic spectrometer, with detection wavelength set at 690 nm. The detection limit was 0.4 nM P, equivalent to 0.03 nmol P m-3 in atmospheric particles. Comparison of SRP in collocate PM2.5 aerosol filter sampling with the PILS-LWCC on line system were in good agreement (n = 49, slope = 0.84, R2 = 0.78). This novel technique offers at least an order of magnitude enhancement in sensitivity over existing approaches allowing for SRP measurements of unprecedented frequency (8 min), which will lead to greater understanding of the sources and impacts of SRP in atmospheric chemistry. © 2016 American Chemical Society

Atmospheric Deposition of Macronutrients (Dissolved Inorganic Nitrogen and Phosphorous) onto the Black Sea and Implications on Marine Productivity*

Two-sized aerosol samples were obtained from a rural site located close to Sinop on the south coastline of the Black Sea. In addition, bulk deposition samples were collected at Varna, located on the west coastline of the Black Sea. Both aerosol and deposition samples were analyzed for the main macronutrients, NO3-, NH4+, and PO43-. The mean aerosol nitrate and ammonium concentrations were 7.1 +/- 5.5 and 22.8 +/- 17.8 nmol m(-3), respectively. The mean aerosol phosphate concentration was 0.69 +/- 0.31 nmol m(-3), ranging from 0.21 to 2.36 nmol m(-3). Interestingly, phosphate concentration over Sinop was substantially higher than those of most Mediterranean sites. Comparison of the atmospheric and riverine inputs for the Black Sea revealed that atmospheric dissolved inorganic nitrogen (DIN) only ranged between 4% and 13%, while the atmospheric dissolved inorganic phosphorus (DIP) fluxes had significantly higher contributions with values ranging from 12% to 37%. The molar N:P ratios in atmospheric deposition for Sinop and Varna were 13 and 14, respectively, both of which were lower than the Redfield ratio (16). The atmospheric molar N:P ratios over the Black Sea were considerably lower than those reported for riverine fluxes (41) and the Mediterranean region (more than 200). The atmospheric P flux can sustain 0.5%-5.2% of the primary production, whereas the N flux can sustain 0.4%-4.8% of the primary production. The contribution of the atmospheric flux may enhance by 2.6 when the new production is considered

Influence of Atmospheric Processes on the Solubility and Composition of Iron in Saharan Dust

Aerosol iron was examined in Saharan dust plumes using a combination of iron near-edge X-ray absorption spectroscopy and wet-chemical techniques. Aerosol samples were collected at three sites located in the Mediterranean, the Atlantic, and Bermuda to characterize iron at different atmospheric transport lengths and time scales. Iron(III) oxides were a component of aerosols at all sampling sites and dominated the aerosol iron in Mediterranean samples. In Atlantic samples, iron(II and III) sulfate, iron(III) phosphate, and iron(II) silicates were also contributors to aerosol composition. With increased atmospheric transport time, iron(II) sulfates are found to become more abundant, aerosol iron oxidation state became more reduced, and aerosol acidity increased. Atmospheric processing including acidic reactions and photoreduction likely influence the form of iron minerals and oxidation state in Saharan dust aerosols and contribute to increases in aerosol-iron solubility. © 2016 American Chemical Society

Sugars in atmospheric aerosols over the Eastern Mediterranean

International audienceAerosol samples (PM10) were collected at Finokalia monitoring station in a remote area of Crete in the Eastern Mediterranean over a two-year period. They were analyzed for total organic carbon (OC), water-soluble organic carbon (WSOC), and the molecular distribution of sugars. WSOC comprised 45% of OC while the contribution of sugars to the OC and WSOC content in the PM10 particles averaged 3 ± 2% (n = 218) and 11 ± 6% (n = 132), respectively. The total concentration of sugars ranged between 6 and 334 ng m−3 with the two most abundant sugars over the two-year period being glucose and levoglucosan, contributing about 25% each to the total carbohydrate pool. Primary saccharides (glucose, fructose, and sucrose) peaked at the beginning of spring (21, 17, and 15 ng m−3, respectively), indicating significant contributions of bioaerosols to the total organic aerosol mass. On the other hand, higher concentrations of anhydrosugars (biomass burning tracers levoglucosan, mannosan, galactosan) were recorded in winter (19, 1.4, and 0.2 ng m−3 respectively) than in summer (9.1, 1.1, and 0.5 ng m−3 respectively). Levoglucosan was the dominant monosaccharide in winter (37% of total sugars) while the low concentration measured in summer (19% of total sugars) was probably due to the enhanced photochemical oxidation by hydroxyl (OH) radicals which impact anhydrosugars. Based on levoglucosan observations, biomass burning was estimated to contribute up to 13% to the annual average OC measured at Finokalia. Annual OC, WSOC, and carbohydrate dry deposition fluxes for the two-year sampling period were estimated at 414, 175, and 9 mg C m−2 y−1, respectively. Glucose and levoglucosan accounted for 34% and 2% of the total sugar fluxes. According to our estimations, atmospheric OC and WSOC inputs account for 0.70% and 0.71%, respectively of the carbon in the annual primary production in the Cretan Sea. Considering the entire Mediterranean, dry deposition of OC can provide at least 3 times more C than riverine inputs of Rhone. Carbohydrate dry deposition flux represents a small fraction of total carbon flux up to 0.04% of the C used for the primary production in the Cretan Sea, while this value is <0.01% for the entire Mediterranean. OC and WSOC contributions are in the order of 0.33% and 0.14% for the whole Mediterranean basin and further underline a minor contribution of the atmosphere in the carbon cycle of the Mediterranean Sea