Abstract:
The article reveals temporal and spatial trends in greenhouse gases and aerosols in the atmosphere over Bulgaria. The period of study is from 09.2002 to 12.2015, and it is determined by the available database, which is based mainly on satellite measurements. Carbon dioxide and methane are measured by the instrument AIRS (Atmospheric Infrared Sounder) on board of NASA‘s satellite Aqua. The total amount of aerosols over Bulgaria expressed by aerosol optical depth at a wavelength of 0.55 microns is measured by the instrument MODIS (Moderate Resolution Imaging Spectroradiometer) on board of NASA‘s satellite Terra. Data for specific humidity at levels 1000 hPa and 700 hPa for the territory of Bulgaria are obtained from The European Centre for Medium-Range Weather Forecasts (ECMWF) ERAInterim reanalysis. Statistical and cartographic methods were used in this research. Intra-annual and inter-annual course of specific humidity of the troposphere over Bulgaria are determined by the corresponding course of air temperature in direct proportion, and spatial distribution is determined mainly by three factors – atmospheric circulation, relief and the presence of large water bodies. Intra-annual course and spatial distribution of CO2 in the troposphere are determined mainly by the life cycle of plants and their total amount in a particular territory or aquatory. Vegetation and, light and temperature-humidity conditions largely determine intra-annual course and spatial distribution of concentration of CH4 in the atmosphere over Bulgaria. Aerosol optical depth depends on both natural and anthropogenic factors. Intra-annual course is determined mainly by natural factors, the most important being vertical motions in atmosphere and presence or absence of snow cover. Inter-annual tendencies in the amount of aerosols are determined by the above mentioned natural factors but also by anthropogenic factors. Spatial distribution of aerosol optical depth depends mainly on the anthropogenic factor in summer and on natural factors in winter. All three studied greenhouse gases have a statistically significant positive trend in the beginning of the 21st century, which means enhanced greenhouse effect and a corresponding increase in air temperature. Results of this study show that the increase in carbon dioxide and methane is an order of magnitude greater than that of water vapor, but on the other hand water vapor has a much stronger greenhouse effect. The decrease in aerosols, which is statistically significant, also leads to an increase in near surface air temperature, which increase is mainly driven by shortwave radiation fluxes, unlike greenhouse gases, which affect mainly longwave radiation fluxes. The trend in aerosols is comparable to that in the specific humidity. The main conclusion is that in the early 21st century the trends in all studied atmospheric constituents lead to an increase in air temperature of near surface layer.