C-2-C-5 hydrocarbon measurements in the Netherlands 1981-1991

Measurements of C-2-C-5 hydrocarbons on an hourly basis at the TNO site in Delft from 1982 to 1984 and at Moerdijk over the period 1981-1991 are prese nted. In combination with meteorological data (wind direction and wind spee d) the Delft and Moerdijk series are evaluated to identify source categorie s, annual variations, background concentrations and trends. The C-2-C-5 hyd rocarbon concentrations at Delft and Moerdijk are determined mainly by emis sion characteristics and meteorological dispersion the dominant sources are relatively nearby and atmospheric degradation is not of much importance. U nder conditions of high wind speed the concentrations measured at Moerdijk in the marine sector are close to the Atlantic background concentrations in winter and somewhat above this in summer. The continental background conce ntrations are higher than the marine background concentrations by a factor of almost two. The annual variation of acetylene is more pronounced than th at of the other hydrocarbons, most likely due to a different seasonal varia tion in acetylene emissions. The annual variation of propene is smoother, i ndicating stronger sources in summer than in winter. This feature of propen e is observed in continental as well as in marine sectors. The observations show that at Moerdijk C-2-C-4 concentrations measured in Rjjnmond sector h ave decreased considerably since the early 1980s, corresponding with change s in emissions in that area. Averaged over all wind directions the trend of all species is downward, but for acetylene the trend is significant at a 9 5% confidence interval. The acetylene concentrations show an annual downwar d trend of 3% during the 1980s, supporting other estimates of decreasing hy drocarbon emissions from traffic over this period at the same rate. (C) 199 9 Published by Elsevier Science Ltd. All rights reserved.