Browsing by Subject "aerosol"

The COVID-19 pandemic has brought into discussion the role of airborne transmission in infectious diseases. Many studies on enveloped viruses such as influenza suggest that respiratory viruses can be transmitted with large or small droplets formed when the patients talk, breathe, sneeze or cough. This comes under the category of direct contact. These droplets may also be transmitted indirectly as fomites through contact with contaminated surfaces. It has been difficult to prove that aerosols' transmission as the methods to capture virus in the air are not very sensitive. SARS-CoV-2 is a novel coronavirus affecting millions of people since 2019, and it has been challenging to contain the spread of this virus. Hence it is of vital importance to understand the transmission of the virus through aerosol and droplets. In this study, aerosol samples were collected from patients in the Surgical Hospital in Helsinki and patients at home in quarantine using various bioaerosols sampling devices like Biospot, Dekati, Button, and Andersen samplers, and passive sampling techniques to capture aerosols and droplets in the air. Such samples were subjected to cell culture on TMPRSS2 expressing Vero E6 cells to check for infectious viruses and RT-PCR using the N-gene targeting method to detect the presence of SARS-CoV-2 RNA in the samples. Out of the 32 saliva samples collected, 19 samples were tested positive by RT-PCR, but cell culture was not always positive. Bioaerosol samples collected using Dekati, Button, and Biospot samplers were negative by PCR. However, Andersen samplers showed positive results along with various passive aerosol samples collected on MEM, indicating aerosols' production of small sizes that can be transmitted air in the air to far distances and settling due to gravity. A relation between saliva samples and symptom days indicates the decrease in saliva viruses' infectivity with the prolonged infection as seen from the RT-PCR. From these findings, it can be concluded that SARS-CoV-2 can be spread by airborne and fomite transmission, and more so by patients with symptoms day 2-7 who are proven to be more infectious. Additionally, it was inferred that the Six Stage Andersen impactor would be the most efficient for aerosol sampling. Further studies are still needed to understand the characteristics of the spread and extent of infection caused by the variants of SARS-CoV-2.

Cloud condensation nuclei (CCN) participate in controlling the climate, and a better understading of their number concentrations is needed to constrain the current uncertainties in Earth’s energy budget. However, estimating the global CCN concentrations is difficult using only localised in-situ measurements. To overcome this, different proxies and parametrisations for CCN have been developed. In this thesis, accumulation mode particles were used as a substitute for CCN, and continental proxy for number concentration of N100 was developed with CO and temperature as tracers for anthropogenic and biogenic emissions. The data utilised in the analysis contained N100 measurements from 22 sites from 5 different continents as well as CO and temperature from CAMS reanalysis dataset. The thesis aimed to construct a global continental proxy. In addition to this, individual proxies for each site (the site proxy) and proxies trained with other sites’ data (the site excluded proxy) were developed. The performance of these proxies was evaluated using a modified version of K-fold cross-validation, which allowed estimating the effect of dataset selection on the results. Additionally, time series, seasonal variation, and parameter distributions for developed proxies were analysed and findings compared against known characteristics of the sites. Global proxy was developed, but no single set of parameters, that would achieve the best performance at all sites, was found. Therefore, two versions of global proxy were selected and their results analysed. For most of the sites, the site proxy performed better than the global proxies. Additionally, based on the analysis from the site excluded proxy, extrapolating the global proxy to new locations produced results with varying accuracy. Best results came from sites with low concentrations and occasional anthropogenic transport episodes. Additionally, some European rural sites performed well, whereas in mountainous sites the proxy struggled. Comparing the proxy to literature, it performed generally less well or similarly as proxies from other studies. Longer datasets and additional measurement sites could improve the proxy performance.