METHODOLOGICAL APPROACHES TO THE AMBIENT AIR IMPACT ASSESSMENT OF THE CROSSROADS OF AUTOMOBILE TRANSPORT ROUTES

The purpose of the paper is to find out the approach to assess the impact of transport ways and crossroads on the air basin of the city of Lviv. The specifics of the distribution of traffic flows, their composition and intensity were studied in the spring-summer period in different districts of the city of Lviv at the crossroads of Lychakivska - Pasichna, Chornovola - Lypinsky, Zelena - Pasichna, and Stryyska - Naukova streets. The total mass emissions of pollutants from motor vehicles were calculated for each crossroads. The shaping of temporary quasi-stationary "formation" of cars with running engines standing in line to cross the crossroads was observed during "rush" hours. The dimensions of this "formation" are determined by the length of the queue on each street adjacent to the crossroads and the width of the carriageway of the streets. Such "formations" have their own unique mode of operation, which is determined by the duration of "rush" hours (an average of 6 hours per day). Taking this into account one can consider such a "formation" as a complex of quasi-stationary sources of emissions of pollutants, the number of which is equal to the number of cars at the crossroads. Therefore, in terms of its impact on the atmosphere, it can be equated to an industrial enterprise, for which the width of the sanitary protection zone is established based on the hazard class. If the queue of cars on each street adjacent to the intersection as a component of the "formation" is considered as a group of approximately identical equidistant point sources that retain their spatial coordinates for a certain time, have the shape of a line and a certain size, then its impact on atmospheric air may be modeled as a stationary line emitting source. In order to assess the impact of transport ways and crossroads on the air basin of the city the environmental hazard levels (EHL) and the hazard category of object are determined for each crossroads and corresponding sizes of sanitary protection zones are proposed on the basis of the calculated values of pollutants mass emissions from motor vehicles, as well as the hazard class of each substance and its ambient air quality standard concentration. The levels and scale of crossroad impact on ambient air are determined by the modelling of the atmospheric dispersion of automobile effluents. In the case of crossroads the sanitary-protective zone delineates a buffer zone from the crossroads to the residential buildings. The sanitary-protective zone size (width) is a field for planning solutions regarding the organization of traffic flows and the building strategy, the space zoning in the vicinity of the crossroads. With the respect to the level of ecological danger all studied crossroads of city of Lviv can be equated to the industrial enterprise of the second category of danger with a sanitary-protective zone of 500 m. The results of computer modelling of the dispersion of vehicle emissions at crossroads at rush hours indicate extremely high values of ground-level concentrations of the main pollutants: nitrogen dioxide, oxide, hydrocarbons at the levels which overcome the ambient air quality standards up to 10 times. The zone of ambient air impact of crossroads may expand from predefined 500 м up to 800 - 2250 m and cover an area about 1-10 km2 depending on the traffic load. In view of this, the proposed approaches to assessing the ambient air impact of crossroads in urban areas on the basis of the determination of environmental hazard level and the prediction of ambient concentrations of pollutants and their distribution distances may introduce significant sanitary restrictions into the planning structure of the city.