Bioaerosols in the atmosphere at two sites in Northern Europe in spring 2021: Outline of an experimental campaign.

A coordinated observational and modelling campaign targeting biogenic aerosols in the air was performed during spring 2021 at two locations in Northern Europe: Helsinki (Finland) and Siauliai (Lithuania), approximately 500 km from each other in north-south direction. The campaign started on March 1, 2021 in Siauliai (12 March in Helsinki) and continued till mid-May in Siauliai (end of May in Helsinki), thus recording the transition of the atmospheric biogenic aerosols profile from winter to summer. The observations included a variety of samplers working on different principles. The core of the program was based on 2- and 2.4--hourly sampling in Helsinki and Siauliai, respectively, with sticky slides (Hirst 24-h trap in Helsinki, Rapid-E slides in Siauliai). The slides were subsequently processed extracting the DNA from the collected aerosols, which was further sequenced using the 3-rd generation sequencing technology. The core sampling was accompanied with daily and daytime sampling using standard filter collectors. The hourly aerosol concentrations at the Helsinki monitoring site were obtained with a Poleno flow cytometer, which could recognize some of the aerosol types. The sampling campaign was supported by numerical modelling. For every sample, SILAM model was applied to calculate its footprint and to predict anthropogenic and natural aerosol concentrations, at both observation sites. The first results confirmed the feasibility of the DNA collection by the applied techniques: all but one delivered sufficient amount of DNA for the following analysis, in over 40% of the cases sufficient for direct DNA sequencing without the PCR step. A substantial variability of the DNA yield has been noticed, generally not following the diurnal variations of the total-aerosol concentrations, which themselves showed variability not related to daytime. An expected upward trend of the biological material amount towards summer was observed but the day-to-day variability was large. The campaign DNA analysis produced the first high-resolution dataset of bioaerosol composition in the North-European spring. It also highlighted the deficiency of generic DNA databases in applications to atmospheric biota: about 40% of samples were not identified with standard bioinformatic methods.

Shipping Remains a Globally Significant Source of Anthropogenic PN Emissions Even after 2020 Sulfur Regulation.

Shipping is the main source of anthropogenic particle emissions in large areas of the globe, influencing climate, air quality, and human health in open seas and coast lines. Here, we determined, by laboratory and on-board measurements of ship engine exhaust, fuel-specific particle number (PN) emissions for different fuels and desulfurization applied in shipping. The emission factors were compared to ship exhaust plume observations and, furthermore, exploited in the assessment of global PN emissions from shipping, utilizing the STEAM ship emission model. The results indicate that most particles in the fresh ship engine exhaust are in ultrafine particle size range. Shipping PN emissions are localized, especially close to coastal lines, but significant emissions also exist on open seas and oceans. The global annual PN produced by marine shipping was 1.2 × 1028 (±0.34 × 1028) particles in 2016, thus being of the same magnitude with total anthropogenic PN emissions in continental areas. The reduction potential of PN from shipping strongly depends on the adopted technology mix, and except wide adoption of natural gas or scrubbers, no significant decrease in global PN is expected if heavy fuel oil is mainly replaced by low sulfur residual fuels. The results imply that shipping remains as a significant source of anthropogenic PN emissions that should be considered in future climate and health impact models.

Concentrations and Adsorption Isotherms for Amphiphilic Surfactants in PM1 Aerosols from Different Regions of Europe.

Predicting the activation of submicrometer particles into cloud droplets in the atmosphere remains a challenge. The importance of surface tension, σ (mN m-1), in these processes has been evidenced by several works, but information on the "surfactants" lowering σ in actual atmospheric particles remains scarce. In this work, PM1 aerosols from urban, coastal, and remote regions of Europe (Lyon, France, Rogoznica, Croatia, and Pallas, Finland, respectively) were investigated and found to contain amphiphilic surfactants in concentrations up to 2.8 µg m-3 in the air and 1.3 M in the particle dry volume. In Pallas, correlations with the PM1 chemical composition showed that amphiphilic surfactants were present in the entire range of particle sizes, supporting recent works. This implied that they were present in hundreds to thousands of particles cm-3 and not only in a few large particles, as it has been hypothesized. Their adsorption isotherms and critical micelle concentration (CMC) were also determined. The low CMC obtained (3 × 10-5-9 × 10-3 M) implies that surface tension depression should be significant for all the particles containing these compounds, even at activation (growth factor ∼ 10). Amphiphilic surfactants are thus likely to enhance the CCN ability of submicrometer atmospheric particles.

Snow cover duration in northern Finland and the influence of key variables through a conceptual framework based on observed variations in snow depth.

Seasonal snow cover duration is the net result from many processes acting on snow fallen on the Earth's surface. Several of these processes feed back into the atmosphere-cryosphere system causing non-linear interactions. The timing of snow retreat is of essential importance, but the duration of snow cover has large spatiotemporal variabilities. However, from a large data set of observed snow depth changes in northern Finland, systematic similar evolutions are identified that allow for a considerable simplification and reduction of the complexity in snow depth changes. Here, a novel conceptual framework is designed based on dividing the season into two main periods (dark and bright period, based on solar irradiance), for which snow depth decrease is parameterized based on three variables, average temperature, incoming shortwave radiation, and light-absorbing particles (LAP) in the snow. The processes are simplified into two linear relations, and a new formulation for concentration enhancement of LAP, which is dependent on snow depth decrease, is given. The results show that the seasonal snow cover duration is shifted by about one day for every 10 mm snow water equivalent of precipitation. This effect is comparable in scale to that of doubling of the amount of LAP concentration in snow. We also found that the combined shift in snow cover duration from interannual variability in ambient temperature and shortwave radiation (warm and bright vs. cold and dark season) is large enough to explain the variability of a couple of weeks for a given precipitation amount in Northern Finland.

High-volume evacuation mitigates viral aerosol spread in dental procedures.

Dental healthcare personnel (DHCP) are subjected to microbe-containing aerosols and splatters in their everyday work. Safer work conditions must be developed to ensure the functioning of the healthcare system. By simulating dental procedures, we aimed to compare the virus-containing aerosol generation of four common dental instruments, and high-volume evacuation (HVE) in their mitigation. Moreover, we combined the detection of infectious viruses with RT-qPCR to form a fuller view of virus-containing aerosol spread in dental procedures. The air-water syringe produced the highest number of aerosols. HVE greatly reduced aerosol concentrations during procedures. The air-water syringe spread infectious virus-containing aerosols throughout the room, while other instruments only did so to close proximity. Additionally, infectious viruses were detected on the face shields of DHCP. Virus genomes were detected throughout the room with all instruments, indicating that more resilient viruses might remain infectious and pose a health hazard. HVE reduced the spread of both infectious viruses and viral genomes, however, it did not fully prevent them. We recommend meticulous use of HVE, a well-fitting mask and face shields in dental procedures. We advise particular caution when operating with the air-water syringe. Due to limited repetitions, this study should be considered a proof-of-concept report.

Driver and passenger exposure to aerosol particles in buses and trams in Helsinki, Finland.

This study investigates commuter and driver exposure to aerosol particles in buses and trams in Helsinki, Finland. Particle number and PM(2.5) concentrations were determined in the cabin and the driver's compartment. In addition, the <2.5 microm black carbon concentration was measured in the driver's compartment and PM(2.5) was collected for elemental analysis in the cabin. The measurements were repeated on two generations of buses and trams including two measurement days in each vehicle type. Fine particle number and mass concentrations in the driver's compartments were only slightly increased compared to Helsinki background air. Daily average ratios of number and mass to the background varied in range 0.8-4.3 and 1.0-2.9, respectively, both being the highest in the older bus type. However, the drivers were exposed to elevated levels of black carbon, which some studies have addressed to be strongly correlated with adverse health effects. The daily average ratio of black carbon to the background varied between 2.4 and 11.4. Additionally, the black carbon concentration had spatial variation. The drivers were exposed to higher peak concentrations of black carbon in downtown area. Particle concentrations were smaller in the driver's compartment than in the cabin. The newer technology in the newer model of the tram and bus seemed to decrease driver exposure to aerosol particles.

Characteristics of particle emissions and their atmospheric dilution during co-combustion of coal and wood pellets in a large combined heat and power plant.

Coal combustion is one of the most significant anthropogenic CO2 and air pollution sources globally. This paper studies the atmospheric emissions of a power plant fuelled with a mixture of industrial pellets (10.5%) and coal (89.5%). Based on the stack measurements, the solid particle number emission, which was dominated by sub-200 nm particles, was 3.4×1011 MJ-1 for the fuel mixture when electrostatic precipitator (ESP) was cleaning the flue gas. The emission factor was 50 mg MJ-1 for particulate mass and 11 740 ng MJ-1 for the black carbon with the ESP. In the normal operation situation of the power plant, i.e., including the flue-gas desulphurisation and fabric filters (FGD and FF), the particle number emission factor was 1.7×108 MJ-1, particulate mass emission factor 2 mg MJ-1 and black carbon emission factor 14 ng MJ-1. Transmission electron microscopy (TEM) analysis supported the particle number size distribution measurement in terms of particle size and the black carbon concentration. The TEM images of the particles showed variability of the particle sizes, morphologies and chemical compositions. The atmospheric measurements, conducted in the flue-gas plume, showed that the flue-gas dilutes closed to background concentrations in 200 sec. However, an increase in particle number concentration was observed when the flue gas aged. This increase in particle number concentration was interpret as formation of new particles in the atmosphere. In general, the study highlights the importance of detailed particle measurements when utilizing new fuels in existing power plants. Implications: CO2 emissions of energy production decrease when substituting coal with biofuels. The effects of fuels changes on particle emission characteristics have not been studied comprehensively. In this study conducted for a real-scale power plant, co-combustion of wood pellets and coal caused elevated black carbon emissions. However, it was beneficial from the total particle number and particulate mass emission point of view. Flue-gas cleaning can significantly decrease the pollutant concentrations but also changes the characteristics of emitted particles. Atmospheric measurements implicated that the new particle formation in the atmospheric flue-gas plume should be taken into account when evaluating all effects of fuel changes." Are implication statements part of the manuscript?

Photochemical degradation affects the light absorption of water-soluble brown carbon in the South Asian outflow.

Light-absorbing organic aerosols, known as brown carbon (BrC), counteract the overall cooling effect of aerosols on Earth's climate. The spatial and temporal dynamics of their light-absorbing properties are poorly constrained and unaccounted for in climate models, because of limited ambient observations. We combine carbon isotope forensics (δ13C) with measurements of light absorption in a conceptual aging model to constrain the loss of light absorptivity (i.e., bleaching) of water-soluble BrC (WS-BrC) aerosols in one of the world's largest BrC emission regions-South Asia. On this regional scale, we find that atmospheric photochemical oxidation reduces the light absorption of WS-BrC by ~84% during transport over 6000 km in the Indo-Gangetic Plain, with an ambient first-order bleaching rate of 0.20 ± 0.05 day-1 during over-ocean transit across Bay of Bengal to an Indian Ocean receptor site. This study facilitates dynamic parameterization of WS-BrC absorption properties, thereby constraining BrC climate impact over South Asia.