Use of a passive sampling network for the determination of urban NO2 spatiotemporal variations

Nitrogen dioxide levels were systematically measured by means of passive samplers at 79 sites in the city of Elche (southeastern Spain) with the aim of investigating the factors affecting NO2 spatiotemporal variations and quantitatively assessing the impact of traffic on urban NO2 concentrations. One-week sampling campaigns were performed approximately once a month during 2007 and 2008. The average NO2 concentration during the two-year period was 32 ± 12 μg m−3, with minima in summer and maxima from fall to early spring. Temporal variations of nitrogen dioxide concentrations were mainly affected by meteorological factors. On the other hand, the relative spatial distribution of NO2 levels, which remained fairly constant during the study period, was controlled by both traffic flow allocation and urban street layout. Using cluster analysis, the sampling sites were grouped into four representative classes of urban NO2 pollution, indicating that a considerable reduction in the number of measurement points for monitoring the spatial and temporal variability of nitrogen dioxide levels is feasible. By means of regression analysis, we estimated a weekly average concentration decrease of ∼1 μg NO2 m−3 if a reduction of 4000 vehicles per week occurred in city centre streets. These results can be useful for improving urban air quality management and control efficiency.

► Temporal trends in NO2 concentrations mostly controlled by ambient conditions.
► Spatial NO2 distribution dependent on urban structure and traffic flow allocation.
► Seventy-nine sites divided into 4 groups with similar NO2 levels by cluster analysis.
► Dependence of NO2 levels on traffic flows determined by correlation analyses.
► A reduction of 20,000 vehicles per week would cause a decrease of 4–6 μg NO2 m−3.