Lessons learned and questions raised during and post-COVID-19 anthropopause period in relation to the environment and climate.

In the first part, this work reports that during the global "anthropopause" period, that was imposed in March and April 2020 for limiting the spread of COVID-19, the concentrations of basic air pollutants over Europe were reduced by up to 70%. During May and June, the gradual lift of the stringent measures resulted in the recovery of these reductions with pollution concentrations approaching the levels before the lockdown by the end of June 2020. In the second part, this work examines the alleged correlations between the reported cases of COVID-19 and temperature, humidity and particulate matter for March and April 2020 in Europe. It was found that decreasing temperatures and relative humidity with increasing concentrations of particulate matter are correlated with an increase in the number of reported cases during these 2 months. However, when these calculations were repeated for May and June, we found a remarkable drop in the significance of the correlations which leads us to question the generally accepted inverse relation between pandemics and air temperature at least during the warmer months. Such a relationship could not be supported in our study for SARS-CoV-2 virus and the question remains open. In the third and last part of this work, we examine the question referring to the origin of pandemics. In this context we have examined the hypothesis that the observed climate warming in Siberia and the Arctic and the thawing of permafrost could result to the release of trapped in the permafrost pathogens in the atmosphere. We find that although such relations cannot be directly justified, they present a possible horrifying mechanism for the origin of viruses in the future during the developing global warming of our planet in the decades to come. Overall the findings of our study indicate that: (1) the reduction of anthropogenic emissions in Europe during the "anthropopause" period of March and April 2020 was significant, but when the lockdown measures were raised the concentrations of atmospheric pollutants quickly recovered to pre-pandemic levels and therefore any possible climatic feedbacks were negligible; (2) no robust relationship between atmospheric parameters and the spread of COVID-19 cases can be justified in the warmer part of the year and (3) more research needs to be done regarding the possible links between climate change and the release of new pathogens from thawing of permafrost areas.

Human thermal sensation over a mountainous area, revealed by the application of ANNs: the case of Ainos Mt., Kefalonia Island, Greece.

Mt. Ainos in Kefalonia Island, Greece, hosts a large variety of plant species, some of them endemic to the region. Because of its rich biodiversity, a large portion of the mountain area is designated as National Park and is protected from human activities such as hunting or logging. Therefore, the area presents a lot of opportunities for ecotourist activities, such as trekking, birdwatching, and mountain climbing. In order to estimate its touristic activities potential, it is essential to assess the mountain's biometeorological conditions. To achieve that, the human thermal index PET (physiologically equivalent temperature) was used, which is based on a human energy balance model. However, it is difficult to get the specific meteorological data over mountainous areas (air temperature, humidity, wind speed, and global solar radiation), appropriate as input variables for PET modeling. In order to overcome this limitation, artificial neural networks (ANNs) were developed for the estimation of PET index in ten sites within the Ainos National Park. In the process, the spatiotemporal distributions of the PET thermal index were illustrated, taking into consideration the ANN modeling. The findings of the performed analysis shed light that Mt. Ainos offers the greatest touristic opportunities from May to September, when thermal comfort conditions appear. The study also proves that the highest frequency of thermal comfort appears within the aforementioned time period over the highest altitudes, while on the contrary, slightly warm class appears as the altitude decreases on both sides of the mountain.

Modeling and in situ measurements of biometeorological conditions in microenvironments within the Athens University Campus, Greece.

The objective of this research is to assess and analyze the biometeorological perception in complex microenvironments in the Athens University Campus (AUC) using urban micromodels, such as RayMan. The human thermal sensation in such a place was considered of great significance due to the great gathering of student body and staff of the University. The quantification of the biometeorological conditions was succeeded by the estimation of the physiologically equivalent temperature (PET), which is a biometeorological index based on the human energy balance. We carried out, on one hand, field measurements of air temperature, relative humidity, wind speed, and global solar irradiance for different sites (building atrium, open area, and green atrium) of the examined microurban environment in order to calculate PET during January-July 2013. Additionally, on the other hand, PET modeling was performed using different sky-view factors and was compared to a reference site (meteorological station of Laboratory of Climatology and Atmospheric Environment, University of Athens). The global radiation was transferred to the examined sites with the RayMan model, which considers the sky-view factors for the adaptation of the radiation fluxes to simple and complex environments. The results of this study reveal the crucial importance of the existence of trees and green cover in a complex environment, as a factor that could be the solution to the efforts of stake holders in order to mitigate strong heat stress and improve people's living quality in urban areas.