Abstract—Pollution of the Tbilisi atmospheric air with PM2.5 and PM10 in usual and pandemic situations by using the data of 5 stationary observation points is investigated. The values of the statistical characteristic parameters of PM in the atmosphere of Tbilisi are analyzed and trend graphs are constructed. By means of analysis of pollution levels in the quarantine and usual periods the proportion of vehicle traffic in pollution of city is estimated. Experimental measurements of PM2.5, PM10 in the atmosphere have been carried out in different districts of the city and map of the distribution of their concentrations were constructed. It is shown that maximum pollution values are recorded in the city center and along major motorways. It is shown that the average monthly concentrations vary in the range of 0.6-1.6 Maximum Permissible Concentration (MPC). Average daily values of concentration vary at 2-4 days intervals. The distribution of PM10 generated as a result of traffic is numerical modeled. The modeling results are compared with the observation data. Keywords—Air pollution, numerical modeling, PM2.5, PM10. I. INTRODUCTION BILISI is one of the biggest administrative centers of the South Caucasus and, respectively, its highways are overloaded with motor transport, that is encouraged by the fact that Georgia is a transit country between the Near East and Europe. It is known that the motor transport is one of the main sources of atmosphere pollution with PM. PM 2.5 and PM 10 are so small-size particles that they easily penetrate the human organism through breathing ways and cause different kinds of diseases dangerous to health [1], [2]. II. STATEMENT OF THE PROBLEM PM concentrations in the atmospheric air of Tbilisi city are measured at 5 fixed surveillance points in a continuous mode 24 hours a day (Fig. 1). Natia Gigauri is with the Institute of Hydrometeorology, Georgian Technical University, Tbilisi, Georgia (corresponding author, phone: +995 598 83-18-83; e-mail: natiagigauri18@yahoo.com). Vepkhia Kukhalashvili is with the M. Nodia Institute of Geophysics, Iv. Javakhishvili Tbilisi State University, Tbilisi, Georgia (e-mail: vepkhia.kukhalashvili@tsu.ge). Valida Sesadze is with Georgian Technical University, Tbilisi, Georgia (e- mail: valida_sesadze@yahoo.com). Aleksandre Surmava and Liana Intskirveli are with Institute of Hydrometeorology, Georgian Technical University, Tbilisi, Georgia (e-mail: aasurmava@yahoo.com, intskirvelebi2@yahoo.com). In the present work, on the basis of the National Environment Agency data [3], there is analyzed a change in PM concentrations in both the routine rhythm of city life (2019) and during emergency situation caused by COVID-19 pandemic (2020). Maximum, minimum and average values of the monthly concentrations are estimated. Hourly and daily change trends of PM 2.5 and PM 10 concentrations are considered. Numerical modeling of PM 10 propagation in the atmospheric air of Tbilisi city is carried out in Georgia during western light air using the regional model of atmosphere pollution research [4]. III. RESEARCH RESULTS The graphs for maximum, minimum and average monthly values of PM 2.5 and PM 10 concentrations throughout 2020 are shown in Fig. 2. It is seen from Fig. 2 that maximum values of PM concentrations exceed MPC in winter period, while in spring and summer their concentrations are within normal limits. It should be noted that concentrations registered in March sharply drop in April (e.g., from 183 to 61 µg/m 3 for PM 10 ). Interesting pattern was obtained, when comparing the average monthly concentrations of 2019 and 2020. In the first three months of 2020, including March, PM 2.5 and PM 10 concentrations are relatively higher compared with the last year and their values approach MPC magnitudes (Fig. 3). As for the April data, we have a different picture. Concentrations registered in 2020 are roughly twice lesser than in 2019 and 2,5-times smaller than MPC (Fig. 4). This circumstance can be explained by the fact that the emergency situation was declared in April on a national scale in Georgia and motor transport traffic was limited. In Fig. 5 daily concentrations in April 2020 are shown, it is seen that the highest concentrations of PM 2.5 and PM 10 throughout a month were registered as 18 and 35 µg/m 3 , respectively. On April 17, concentrations were even more dropped, as far as the Georgian government has declared the state of emergency namely that day motor transport traffic was limited. On April 27-28, inter-city borders were open, transport has started to operate and heavy increase of PM concentrations were registered, though their values in none of the cases exceed MPC. N. Gigauri, V. Kukhalashvili, V. Sesadze, A. Surmava, L. Intskirveli Investigation of Tbilisi City Atmospheric Air Pollution with PM in Usual and Emergency Situations Using the Observational and Numerical Modeling Data T World Academy of Science, Engineering and Technology International Journal of Environmental and Ecological Engineering Vol:15, No:8, 2021 183 International Scholarly and Scientific Research & Innovation 15(8) 2021 ISNI:0000000091950263 Open Science Index, Environmental and Ecological Engineering Vol:15, No:8, 2021 publications.waset.org/10012141/pdf