Compliance with the annual NO2 air quality standard in Athens. Required NOx levels and expected health implications

Recent risk assessment studies have shown that high outdoor NO2 levels observed in residential areas contribute to increased respiratory and cardiovascular diseases and mortality. Detailed information on present NO2 levels as well as predictions of NO2 concentrations corresponding to reduced NOx levels in urban areas are very useful to decision and policy makers in order to protect the public health. In the present paper, monitoring stations of the Athens network are initially classified into two main groups, traffic affected and urban background, using effectively a criterion based on the ratio of annual mean NO:NO2 concentrations. Two empirical methodologies are then considered and compared for assessing the effect of different NOx levels on the attainment of the annual NO2 air quality standard at urban-background locations in the Athens area. An interesting finding is that these two methodologies, one more general and one both year and site dependent, give similar results for the specific study area and can be applied alternatively based on the length of available concentration time series. The results show that in order to meet the EU annual mean NO2 objective at all the urban-background locations of the Athens area, annual NOx concentrations should be reduced to approximately 60 μg m−3, requiring NOx emission reductions of up to 30%. An analysis of the health implications of the currently observed NO2 levels is conducted, based on a dose–response relationship, and is coupled with available health-related data for the Athens area. This analysis suggests that if NO2 concentrations were reduced to the levels of the annual EU air quality standard, then a decrease of hospital admissions of up to 2.6% would be observed, depending on the levels of NO2 measured at different monitoring sites of the Athens conurbation.