Air quality measurements in urban green areas – a case study

The influence of traffic-induced pollutants (e.g. CO, NO, NO2 and O3) on the air quality of urban areas was investigated in the city of Essen, North Rhine-Westphalia (NRW), Germany. Twelve air hygiene profile measuring trips were made to analyse the trace gas distribution in the urban area with high spatial resolution and to compare the air hygiene situation of urban green areas with the overall situation of urban pollution. Seventeen measurements were made to determine the diurnal concentration courses within urban parks (summer conditions: 13 measurements, 530 30 min mean values, winter conditions: 4 measurements, 128 30 min mean values). The measurements were carried out during mainly calm wind and cloudless conditions between February 1995 and March 1996. It was possible to establish highly differentiated spatial concentration patterns within the urban area. These patterns were correlated with five general types of land use (motorway, main road, secondary road, residential area, green area) which were influenced to varying degrees by traffic emissions. Urban parks downwind from the main emission sources show the following typical temporal concentration courses: In summer rush-hour-dependent CO, NO and NO2 maxima only occurred in the morning. A high NO2/NO ratio was established during weather conditions with high global radiation intensities (K>800 W m−2), which may result in a high O3 formation potential. Some of the values measured found in one of the parks investigated (Gruga Park, Essen, area: 0.7 km2), which were as high as 275 μg m−3 O3 (30-min mean value) were significantly higher than the German air quality standard of 120 μg m−3 (30-min mean value, VDI Guideline 2310, 1996) which currently applies in Germany and about 20% above the maximum values measured on the same day by the network of the North Rhine–Westphalian State Environment Agency. In winter high CO and NO concentrations occur in the morning and during the afternoon rush-hour. The highest concentrations (CO=4.3 mg m−3, NO=368 μg m−3, 30-min mean values) coincide with the increase in the evening inversion. The maximum measured values for CO, NO and NO2 do not, however, exceed the German air quality standards in winter and summer.