Effectiveness of Green Corridor in Reducing the Level of Tropospheric Ozone Concentration in Legnica (Lower Silesia, SW Poland)

Introducing vegetation into towns and cities, for example through establishing green corridors which ensure a continuous character of urban green areas is a way to counteract negative effects of urban climate. The aim of the study was to assess the role of a green corridor and the contribution of vegetation to regulating the level of hourly tropospheric ozone concentrations in Legnica. Hourly values of tropospheric ozone concentrations (O3, μg m-3) and wind directions (D, °) collected between 2011 and 2014 from an urban background station for air quality monitoring of the Provincial Inspectorate for Environmental Protection were used in the study. To prepare a land cover map, data from the Database of Topographic Objects provided by the Geodesy and Cartography Department of the Marshal’s Office of the Lower Silesian Voivodship were used. The estimations of frequency of hourly O3 concentrations for given seasons of the year and the analysis of land cover within 2 km from the measuring point were made based on an 8-wind compass rose. In summer, the frequency of hourly O3 concentrations was assessed for every direction and for every hour of the day. A Pearson correlation matrix was generated to illustrate the relationship between land cover type and the frequency of pollution coming from each direction, Between 21:00 and 6:00, increased frequency of hourly O3 concentrations in the 0–40 μg m-3 range coming from the southwest was recorded, which accounted for 70–90% of all concentration ranges. Correlation analyses showed a statistically significant relationship between increased high vegetation coverage and decreased frequency of hourly O3 concentrations in the 41–80 μg m-3 range. It was demonstrated that between 2011 and 2014, during summers, hourly O3 concentrations <40 μg m-3 came most frequently from the direction characterised by the highest total share of vegetation-covered land. On the other hand, pollutants with concentrations in the 41–80 μg m-3 range came more frequently at night time from the directions characterised by compact and dense development. The obtained results demonstrated that in summer, the urban park, the Kaczawa River and the green areas along the river play an important role as a green ventilation corridor.