Author(s)

H. Heida, M.AJ. Coolen, C.A. Bank, and A.L. de Jong

Abstract

Nitrogen oxides are considered to be one of the foremost acidifying constituents of ambient air pollution in the northern hemisphere. In particular, nitrogen dioxide is an acidifying agent. Its ambient air levels, however, have been slowly declining for the last 10 years, which is in contrast to the previous increase in the period 1970-1985. In those years, the annual mean concentrati- ons of nitrogen dioxide increased from 25 ug/nf to more than 50 ug/nf in downtown Amsterdam. The 98^-percentile values of 24-hr average NC^ concentrations reached levels of over 100 ug/nf, which are still well below the primary air quality standard but clearly above the secondary standard or guideline value which is set at 100 ug/nf.

Keywords