1 5th International Congress of Croatian Society of Mechanics September, 21-23, 2006 Trogir/Split, Croatia REGIONAL AIR POLLUTION MODELLING M. Čavrak, Z. Mrša and G. Štimac Keywords: air pollution, atmospheric modelling, emission sources 1. Introduction The greatest world concern nowadays is how to optimally design emission reduction strate- gies in order to reduce air pollution levels below regulatory thresholds. According to epidemiologi- cal studies high concentration of air infiltrated and air born pollutants, particularly ozone, have di- rect link with many health problems especially cardiovascular. Based on that knowledge ground level measurements of the most hazardous pollutants defined by Geneva and Kyoto protocols be- come regulatory based in a vicinity of every urban, industrial or protected area. Continuous moni- toring link with on-line computer database offer possibility for future prognoses of pollution levels throughout certain geographic areas and fast decision-making of control mechanisms and ulti- mately for public notification. Another issue concerning pollution levels is how transboundary or transcontinental pollution is transported due to certain synoptic and regional scale meteorological conditions. To answer that and similar questions relevant measurements have been conducted and information provided about directional influences of certain pollutants leading to reconstruction of direct emission sources or responsible mechanism. However, rise of computational power of today computers offers the use and evaluation of meteorological and air quality modelling tools to assess pollution levels by per- forming numerical simulations. One such simulation have been performed on specific episode (temporal and spatial) in order to achieve up-stated objectives and to gain insight into influence and connection between regional, mesoscale and local pollution levels. 2. Selection of the simulation episode City of Rijeka and Kvarner area have been chosen as a prefered area of study. On one side rea- son for that statement is that Rijeka is an urban and at the same time industrial area offering great variations and almost continuous threshold air pollutant values. On the other side, due to its topog- raphic complexity and multi-scale influence to the air pollution levels, it offers potential case for validation of air quality modelling systems. Analysis of measured and documented pollutant values for 2005. indicates the presence of three weekends of intense heat wave with stable meteorological conditions, [Fig. 1] and high levels of measured concentrations from which the one with the longest duration has been chosen. In order to minimize uncertainty of boundary and initial conditions, ac- cording to [1], the period of the chosen weekend, from 29 th till 31 st of July 2005, was extended for two days, leading to a final simulation episode from 27 th till 31 st of July 2005.