Trend analysis of urban NO sub(2) concentrations and the importance of direct NO sub(2) emissions versus ozone/NO sub(x) equilibrium

• Published in: Atmospheric environment (1994) 2009-10, Vol.43 (31), p.4780-4783
• Main Authors: Keuken, M, Roemer, M, van den Elshout, S
• Format: Article
• Language: English
• ISSN: 1352-2310
• DOI: 10.1016/j.atmosenv.2008.07.043

The annual air quality standard of NO sub(2) is often exceeded in urban areas near heavy traffic locations. Despite significant decrease of NO sub(x) emissions in 1986-2005 in the industrial and harbour area near Rotterdam, NO sub(2) concentrations at the urban background remain at the same level since the end of the nineties. Trend analysis of monitoring data revealed that the ozone/NO sub(x) equilibrium is a more important factor than increasing direct NO sub(2) emissions by traffic. The latter has recently been identified as an additional NO sub(2) source due to the introduction of oxy-catalytic converters in diesel vehicles and the growing number of diesel vehicles. However, in Rotterdam over the period 1986-2005 direct NO sub(2) emissions by road traffic only increased 3-4%. Due to the importance of the ozone/NO sub(x) equilibrium, it is concluded that local NO sub(x) emissions in Rotterdam need substantial reduction to achieve lower NO sub(2)urban background levels. This is a relatively costly abatement strategy and, therefore, a ''hotspot'' approach aiming at reducing NO sub(x) emissions by local traffic measures is more effective to meet European air quality standards.