Impact of absolute values and changes in meteorological and air quality conditions on community-acquired pneumonia in Germany

Community-acquired pneumonia (CAP) is a major global health concern as it is a leading cause of morbidity, mortality and economic burden to the health care systems. In Germany, more than 15,000 people die every year from CAP. Climate change is altering weather patterns, and it may influence the probability and severity of CAP. The increasing frequency and intensity of extreme weather events necessitate the study of their impact on CAP hospitalizations. In this regard, we examine the influence of absolute values and changes in various meteorological and air quality conditions on the frequency of CAP hospitalizations. We matched weather data to the German CAPNETZ-Cohort of 10,660 CAP patients from 22 healthcare facilities between 2003 and 2017. Our findings show that daily fluctuations in meteorological conditions (maximum temperature, 99th percentile precipitation), apart from relative humidity, are likely to result in triggering CAP hospitalizations than absolute conditions. In contrast, the absolute values of air quality (CO, NO2, O3, PM2.5, SO2, and total aerosols) are found to exert a greater influence on CAP hospitalizations than changes in air quality. The study outcomes have implications for public health measures, early warning systems, and public awareness, with the aim of mitigating the risk of CAP.

Review of factors affecting virus inactivation in aerosols and droplets

The inactivation of viruses in aerosol particles (aerosols) and droplets depends on many factors, but the precise mechanisms of inactivation are not known. The system involves complex physical and biochemical interactions. We reviewed the literature to establish current knowledge about these mechanisms and identify knowledge gaps. We identified 168 relevant papers and grouped results by the following factors: virus type and structure, aerosol or droplet size, temperature, relative humidity (RH) and evaporation, chemical composition of the aerosol or droplet, pH and atmospheric composition. These factors influence the dynamic microenvironment surrounding a virion and thus may affect its inactivation. Results indicate that viruses experience biphasic decay as the carrier aerosols or droplets undergo evaporation and equilibrate with the surrounding air, and their final physical state (liquid, semi-solid or solid) depends on RH. Virus stability, RH and temperature are interrelated, but the effects of RH are multifaceted and still not completely understood. Studies on the impact of pH and atmospheric composition on virus stability have raised new questions that require further exploration. The frequent practice of studying virus inactivation in large droplets and culture media may limit our understanding of inactivation mechanisms that are relevant for transmission, so we encourage the use of particles of physiologically relevant size and composition in future research.

Dependence on relative humidity in the formation of reactive oxygen species in water droplets

Water microdroplets (7 to 11 µm average diameter, depending on flow rate) are sprayed in a closed chamber at ambient temperature, whose relative humidity (RH) is controlled. The resulting concentration of ROS (reactive oxygen species) formed in the microdroplets, measured by the amount of hydrogen peroxide (H2O2), is determined by nuclear magnetic resonance (NMR) and by spectrofluorimetric assays after the droplets are collected. The results are found to agree closely with one another. In addition, hydrated hydroxyl radical cations (•OH-H3O+) are recorded from the droplets using mass spectrometry and superoxide radical anions (•O2-) and hydroxyl radicals (•OH) by electron paramagnetic resonance spectroscopy. As the RH varies from 15 to 95%, the concentration of H2O2 shows a marked rise by a factor of about 3.5 in going from 15 to 50%, then levels off. By replacing the H2O of the sprayed water with deuterium oxide (D2O) but keeping the gas surrounding droplets with H2O, mass spectrometric analysis of the hydrated hydroxyl radical cations demonstrates that the water in the air plays a dominant role in producing H2O2 and other ROS, which accounts for the variation with RH. As RH increases, the droplet evaporation rate decreases. These two facts help us understand why viruses in droplets both survive better at low RH values, as found in indoor air in the wintertime, and are disinfected more effectively at higher RH values, as found in indoor air in the summertime, thus explaining the recognized seasonality of airborne viral infections.

Indoor air humidity revisited: Impact on acute symptoms, work productivity, and risk of influenza and COVID-19 infection

Recent epidemiological and experimental findings reconfirm that low indoor air humidity (dry air) increases the prevalence of acute eye and airway symptoms in offices, result in lower mucociliary clearance in the airways, less efficient immune defense, and deteriorate the work productivity. New epidemiological and experimental research also support that the environmental conditions for the risk of infection of influenza and COVID-19 virus is lowest in the Goldilocks zone of 40-60% relative humidity (RH) by decrease of the airways' susceptibility, which can be elevated by particle exposure. Furthermore, low RH increases the generation of infectious virus laden aerosols exhaled from infected people. In general, elevation of the indoor air humidity from dry air increases the health of the airways concomitantly with lower viability of infectious virus. Thus, the negative effects of ventilation with dry outdoor air (low absolute air humidity) should be assessed according to 1) weakened health and functionality of the airways, 2) increased viability and possible increased transmissibility of infectious virus, and 3) evaporation of virus containing droplets to dry out to droplet nuclei (also possible at high room temperature), which increases their floating time in the indoor air. The removal of acid-containing ambient aerosols from the indoor air by filtration increases pH, viability of infectious viruses, and the risk of infection, which synergistically may further increase by particle exposure. Thus, the dilution of indoor air pollutants and virus aerosols by dry outdoor air ventilation should be assessed and compared with the beneficial health effects by control of the center zone of 40-60% RH, an essential factor for optimal functionality of the airways, and with the additional positive impact on acute symptoms, work productivity, and reduced risk of infection.

Water-solid contact electrification causes hydrogen peroxide production from hydroxyl radical recombination in sprayed microdroplets

Contact electrification between water and a solid surface is crucial for physicochemical processes at water-solid interfaces. However, the nature of the involved processes remains poorly understood, especially in the initial stage of the interface formation. Here we report that H2O2 is spontaneously produced from the hydroxyl groups on the solid surface when contact occurred. The density of hydroxyl groups affects the H2O2 yield. The participation of hydroxyl groups in H2O2 generation is confirmed by mass spectrometric detection of 18O in the product of the reaction between 4-carboxyphenylboronic acid and 18O-labeled H2O2 resulting from 18O2 plasma treatment of the surface. We propose a model for H2O2 generation based on recombination of the hydroxyl radicals produced from the surface hydroxyl groups in the water-solid contact process. Our observations show that the spontaneous generation of H2O2 is universal on the surfaces of soil and atmospheric fine particles in a humid environment.

Sprayed Water Microdroplets Are Able to Generate Hydrogen Peroxide Spontaneously

Ultrapure N₂ gas was bubbled through water, and the humidified output containing undetectable concentrations of ozone filled a closed chamber in which 18 MΩ-cm water was sprayed through a silica capillary to form microdroplets. Analysis of the collected microdroplets by NMR spectroscopy showed the presence of hydrogen peroxide at a concentration level ranging from 0.3 to 1.5 μM depending on the flow conditions. This was confirmed using a spectrofluorometric assay. We suggest that this finding establishes that when sprayed to form microdroplets, water has the ability to produce hydrogen peroxide by itself. When the N₂ gas is replaced by compressed air or O₂ gas, the concentration of hydrogen peroxide is found to increase, indicating that gas-surface interactions with O₂ in aqueous microdroplets promote the formation of hydrogen peroxide.